To Snow Or Not To Snow

That is the question as we head into December. Right now, we are dealing with a strong La Nina. So, are we going to get cold and is it going to snow?

The NAO is expected to go negative. Some of the Ensemble guidance takes the NAO down to around -3, -4, which is pretty strong. However, the NAO is east based. The NAO needs to retrograde westward, and bring the highest height anomalies over Eastern Canada. With the-NAO west based, the blocking would hold in troughs over the Eastern US. The AO is expected to go negative as well. 

Problem then becomes what becomes of the Pacific. The Pacific is going to be quite unfavorable over the next couple of weeks. Why? The PNA is expected to be negative. Because of the Pacific Jet crashing into the Pacific Northwest (NW Flow aloft)  any of those s/w's will knock down the Western Ridge or +PNA. The Pac Jet is a staple of La Nina however. Typically, you'd want troughing in the NE Pacific as that would help to build up the +PNA ridge. 

The s/w's that do come onshore will not be able to dig south enough. What happens is that the energy amplifies and phases west of the Mississippi River Valley due to the -PNA. So, those storms head into the Lakes, and brings SW flow aloft over the East which floods the East with warmth.

However, because of the -NAO, it leads to more of a zonal flow over the east. The SE ridge is very evident in La Nina years, and each time a storm moves out, the ridge builds again. Sometimes, those G/L Cutters run into strong blocking, and secondary off the coast. Typically, they redevelop too far north, and don't undergo bombogenesis until off the NE Coast. We call these storms Miller B's. 

If the NAO was positive, we'd be dealing with a blow torch and a lot of warmth. 

If the PNA was positive, those s/w's will be able to dig further south and east, and be able to phase east of the Mississippi. You won't have phased energy heading into the Lakes, but rather a Miller A which can run up the east coast.

What do we want to look for?

The Ensemble guidance as of today do have the PNA index rising which can correlate to big East Coast snowstorms. The AO and NAO are expected to remain negative for the time being, and we'd like to see the -NAO block retrograde into Eastern Canada. The NAO allows for troughing to stay over the east, as well as blocking to keep storms from being progressive, quick movers. It can also hold in surface high pressure to the NW to allow for low level cold air to bleed in. 

Summery Pattern to prevail for next week!!

Hi guys, sorry for the absence, there just hasn't been much to write home about. It looks like we're going into a much more summery pattern. Why? Simple. Let's look at the upper level pattern. Right now, a trough is centered along the west coast. At the same, a ULL can be found over the northern part of Hudson Bay. The Polar Jet, which recently has dipped into New England will be shunted north of the Great Lakes into Canada. An ULL can be found over Iceland. This correlates to a +AO. At the same, the -NAO pattern from the winter remains, but it's now focused over rhe northern latitudes and is east based. The cooler airmass is now centered over Northern New England. An impressive ridge will build from the SE states, westward into the Plains. Relatively fast, zonal flow will rule the rest of the country, with the ridge to the south, and the trougb over the western states. A surface high will set up shop off the SE coast, which means a southwesterly flow becomes established not only in the low levels, but in the mid levels as well. A hot and humid airmass will become established over the Northern Mid Atlantic, except for mesoscale features, such as thunderstorms or sea breezes. From time to time, weak mid level disturbances will invade from the G/L. Most of the period should be dry however. Some "relief" might be found with a cold frontal passage later next week. But get ready for 80's and 90's with high dewpoints. Summer is here folks!!!

Forecast Discussion for May 20, 2010

As you can see on the WV imagery, the lead s/w trough that brought us the rainy weather is now heading out, NEward as it treks through New England. Another one is dropping southward over the area this morning. This has kept the low clouds in the picture for most of the overnight, and into the early morning hours. Regional observations show a few showers, relatively weak and scattered about, so it clip the western portions of the forecast area. Latest surface analysis shows weak low pressure moving out over Maine, and a surface ridge over the OH Valley. Both these features are very weak, so there is no pressure gradient between the two. A cold front front is movig down from Canada as well.

We'll begin to lose the clouds throughout the morning, as the s/w trough treks out. I'll go for mostly sunny skies by the early afternoon. The cold front will continue to trek southward, and a pre-frontal trough will develop out ahead of it. They'll be a few showers/thunderstorms, as indicated on a few short-range models such as the WRF. These showers should die out with the loss of daytime heating as they head southward with the front. So pops around 20% will be put into the grids.

As the s/w trough moves out with its associated cool pool aloft, temps at 850mb will begin to rise. We'll see temps between 10 and 12'C, which correlates to temperatures around 80 degrees or so. Afternoon seabreezes will be had at the coast, with an onshore flow ahead of the cold front, so temps there will be cooler.

Any showers or isolated thunderstorms will die out with the loss of heating. The cold front will run into the surface high that is building to our west, and should wash out with time. Temps will fall into the mid 60's in the urban corridor, Winds decouple over the interior, with decent radiational cooling conditions expected, with lows in the 50's as the airmas behind the washing out front is not all that cooler.

Forecast Discussion for May 16, 2010

Hi guys. Gonna do a forecast discussion for the next several days, let's get started.

A weak shortwave trough pushed through the area today, but that did not deter the beautiful weather we've had since yesterday. Scattered clouds can be found across the area, but that will lead to clearing skies this evening, before mid and level high clouds move in overnight. I am expecting party cloudy conditions across the metro tonight. The southwest-west winds should begin to diminish and a NW wind should become established aloft and a pretty decent radiational cooling night can be expected, especially away from the coast. I expect upper 30's to low 40's in the interior, and upper 40's along the coastline. Looking at the MOS guidance, I cut a few degrees off. But it has a pretty good handle on this.

The upper level ridge axis (576dm) will pass south of the area on Monday morning. This means the beautiful weather we've experienced will begin to go downhill. A cut off upper level low (cut off from the northern stream) will develop over the Tennessee Valley and slowly trek northeastward towards the NYC metro area. At the same time, a surface low will develop in the OH Valley. Then that low will secondary to another surface low pressure system off the Mid-Atlantic coast. Strong PVA is forecast to develop, that will help to allow the secondary low to intensify a little bit as the ULL closes off.

I'll increase clouds tomorrow afternoon, but not go to high chance pops until tomorrow night. Why? precip may initally be slow to develop before the coastal storm forms, plus there is not a lot of model support with regards to a stronger LLJ and insentropic ascent. Hoever, with the presence of a developing h85 theta ridge moving towards the area, the forcing for ascent will begin to increase. I will increase pops to likely on Tuesday

The NAM was an initial outlier, before the other models trended more northwest with the surface low. Better agreement regarding the NAM with the ECMWF/GGEM/GFS models. Because of this, we might not see such a tight gradient (northwest to southeast) in regards to the precip shield located with the surface low. The 12Z GGEM gets the low down into the upper 990's, while the ECMWF/GFS/NAM is weaker. With the strong PVA, I'll take the middle of the approach between the stronger GGEM and the weaker GFS/ECMWF/NAM. Undercut temperatures by a lot as the GFS/NAM were too warm. Mid to upper 50's will be the norm under a east-northeast wind in the low levels and moderate to heavy rain under a thick cloud deck. The H5 trough will be slow to move out, as it meanders eastward. Showers will linger into Wednesday evening before the H5 trough is kicked out by approaching high pressure at the surface and a mid level ridge. Temps a little warmer on Wednesday. Temperatures moderate rapidly under a building southwest flow aloft. Very well could see 80 degree temperatures next Friday. Latest ECMWF/GFS guidance show another upper level cut-off for next weekend, with another development of a coastal storm. Stay tuned!

Evening Update for Severe Wx

Hi guys. Going to do a evening update here.

Looked at the afternoon mesoscale analysis from the SPC and looked at surface observations, I noted broken clusters of thunderstorms, a few of them strong to severe treking eastward from the Apps into the Mid-Atlantic states. These storms will be capable of producing damaging winds and large hail, especially as they continue to transverse eastward into a swath of greater instability values. Noting 35-50 knots of 0-6km of bulk shear and MULCAPE values around 1500 J/KG and higher.

Destablization has been slow today.....mainly because of warmer mid level temperatures and some subsidence after the morning showers treked through the area. I've noted this across New Jersey, Eastern PA and SE NY. But in those same areas, the latest mesoscale models show an increase in instability, which has occured, with some storms turning severe in Central and Eastern PA. Bulk Shear increases a bit as well, and this helps to convection becoming better organized. Threat still includes large hail and damaging wind gusts, especially in Western NJ. In areas closer to the east, instability is not as prevalent, but there is higher levels of low level shear closer to the warm front, which could also lead to damaging wind gusts, even as instability levels are not as high. The front should be offshore after midnight, with drier air gradually working in on NW winds later on tonight.

Severe Storms This Afternoon?

That is the question being asked this morning. Gonna put the entire CWA area in a slight risk for severe thunderstorms, except for Suffolk County in Eastern LI, as they will be under a general risk for thunderstorms. That area may not see much in the way of destablization as they continue to sit in the marine layer.  As of 12Z, the surface warm has not yet cleared the area and the surface low, at 1015mb is located in Western New York with the surface cold front driving through NW Ohio. Instability will increase after the passage of the cold front, as models show about 45 knots of 0-6km bulk shear, and forcing increases for ascent. This leads to an enviornment for updrafts, mainly after 18Z or 3PM this afternoon. Favorable wind fields and the presence of some low level shear could make for damaging wind gusts mainly for areas southwestern areas of the forecast area, including SW Jersey. I am still iffy on areas further to the north, including Long Island. It will depend on how much destablization occurs after the warm frontal passage. I think Long Island will stay in an onshore flow, which will limit the amount of destablization present, due to a southerly low level flow over the cooler waters. Here, they will stay in the marine layer, but western sections of Long Island were kept in the slight risk. NYC and points west will warm into the upper 70's-lower 80's, while Long Island stays in the upper 60's-lower 70's with the onshore flow.

Dewpoints should continue to rise into the mid 60's. If everthing goes as according to plan, the presence of a cold front..forcing..50kts of 0-6km bulk shear..and at least 1000j/kg of MLCAPE suggests the potential for at least isolated damaging wind gusts by 18-21z.

Forecast Discussion for Thursday, May 13, 2010

Hi guys. Today was a raw, wet, cool, disgusting day. Will tomorrow be better? Looking at surface obs and short term model soundings, there is plenty of low level moisture in place, thanks to low level easterly flow. That means areas of drizzle and the potential for patchy fog in a few spots.

Low pressure is currently passing southeastward of Long Island and will continue to trek into the Atlantic tonight. Then high pressure will build in from the north, and a weak upper level ridge will build in. The nicer weather will be short-lived. This is what happens in a progressive pattern like this. Once the high moves offshore, the next frontal boundary from the Mid-West will move through. The GFS model continues to be too quick with bringing in precipitation tomorrow night. Even with the progressive upper level flow in place, it's still too quick with shortwaves moving through the flow. But there could be some showers later tomorrow night as a warm front approaches from the southwest. So I included pops for the NYC metro area as the warm front surges northward, as the area becomes warm sectored on Friday. As mentioned, the GFS becomes too aggressive with precipitation, while the NAM is further north with the precip. The SREF model becomes the reasonable middle alternative between the GFS/NAM and wll be used.

Ugly. raw and disgusting: Is this May?

That's the question being asked today. With reports of light snow in PA, and a WAA out for Ulster County, NY calling for up to 5 inches, I am beginning to wonder what happened to the warm weather.

We're going to be stuck in this weather up until the weekend. Reason for this: the surface warm front. The ULL, which affected us with the unseasonably cold airmass of this past weekend is now a 50/50 low and for now, is not going anywhere. This can be blamed to the west based -NAO which again has set up in the North Atlantic. So the pattern up there is somewhat blocky. The west based -NAO does now allow the surface warm front to move northward over the NYC metro area. Instead, the warm front will stall to the south of New Jersey.

Let's put up the 12Z NAM as an example.

What's fascinating about this? Looks at the temperature gradient. The 10M winds show a strong onshore flow (southeasterly low level winds) north of the warm front, while places SW of the warm front are in a southwesterly low level wind flow. This is as the surface low is still transferring east-southeast of Long Island and there is a lower level circulation just off the Jersey coastline.

The surface warm front is still well back in the OH Valley, but the 700mb and 850mb warm front has surged north of the surface warm front. Very dry, stable air is sitting north of the surface warm front in the cool sector, with dewpoints in the 20's and 30's. This is due to presence of high pressure nestled over New Jersey. But over Central PA where rain has fallen, temperatures have actually fell, into the upper 30's. So if the surface warm is still back over West Virginia, what is causing the rain to fall? Temperature difference in the mid levels to the surface. This is creating pretty decent instentropic lifting. There's your rain.

Clouds did increase, due to the presence of a weakening shortwave, being sheared by a PV in Eastern Canada, and a ridge in the southern states. This shortwave is treking NE in fast upper level, relatively zonal flow. The SE ridge heights were a little bit over-forecasted by the models, and because of this, the s/w is treking further southward as the height field bent southward a bit. At the surface, low pressure is slowly weakening as it treks eastward through the OH Valley, and will transfer to a weak area of low pressure off the Long Island coast. The surface warm front will attempt to approach overnight, and this combined with insentropic lift and ascent (southerly to southeasterly moist inflow) will provide for a period of light to moderate overrunning rainfall. Not expecting much in the way of QPF, about .50 inches or so. Easterly onshore flow should continue tomorrow with temperatures hovering in the upper 40's or so. The surface low pulls out tomorrow evening, with clearing skies. Should be somewhat of a temperature gradient with cool, moist marine air to the north of the warm front, as it rides along the nose of the 500mb ridge axis, and a more pronounced southerly flow to the south of the warm front.

Weather for May 10, 2010; Less windy tomorrow?

It appears that the strong winds will begin to diminish by tomorrow morning as the pressure gradient between high pressure building eastward and low pressure slowly lifting through the Canadian Maritimes begins to relax. The flow tomorrows turns anti-cyclonic. However, it will still be breezy but under mostly sunny skies as there will be some low level mixing. Temperatures will struggle into the lower 60's, so it will be another cool, but dry May day.

A colder regime is setting up into early next week

That's right folks, a colder regime is setting up and will presist into early next week. A potent ULL is currently tracking eastward from out of the Plains states, as its associated surface low, at 997mb at 00Z and its cold front is treking eastward into the OH Valley.

The 12Z GFS/NAM have trended drier with the frontal passage. Why? The upper level forcing will be north of the NYC area. A warm front, clearly shown on the WV imagery at 850mb in the mid levels is trying to trek to the NE at this hour. That will bring an increase in clouds in SW low level flow. A couple of things play against the warm front clearing the NYC area to the north: the surface low is still well to the west, chilly ocean waters, and a developing LLJ at 850mb not overspreading the region until morning. The front should clear southern portions of the NYC area. However, the best lifting and convergence is to the north.

However, there is a chance for thunderstorms. First, theta e ridge will advect in to create marginal to moderate levels of instability, however elevated in nature because the warm front should not make much progress northward and those north of the front will be stuck in a stable, cool airmass. Remember, the airmass is not all that humid and moist. Shear is impressive in the low levels as well as deep layer shear is impressive. Could see some convection fire by daybreak in the vincinity of the warm front. Then the warm front tries to lift through by 12Z.

Looking for an afternoon frontal passage after blending the ECMWF/GFS/NAM. Should see plenty of cloud cover, and that will inhibit destablization of the atmosphere. However, if skies clear faster, then watch for a line of low topped thunderstorms moving W to E with the cold front with strong mid level forcing, strong deep layer shear, and enough of a mid level wind profile. Damaging winds will be the main threat if those low topped thunderstorms develop.

After the frontal passage, strong CAA will commence, and winds will increase as the stacked low intensifies in the Gulf of Maine and Candian Maritimes and High Pressure builds out of Central Canada eastward to the Mid-Atlantic. Winds could advisory level criteria tomorrow evening on Long Island. Temps will rapidly drop into the 40's most areas tomorrow night. Sunday will be a cool day with cyclonic flow aloft. Temperatures will struggle to get to 60 degrees. The high continues to build overhead on Monday, and the low turns more anti-cyclonic. Still, temperatures will struggle into the lower 60's. Tuesday and Wednesday, a warm front tries to approach from the southwest, bringing a chance of showers, with moderating temperatues to near normal levels.

Thunderstorms today?

Currently, we have a shortwave approaching from the G/L treking eastward with an associated cold front. Most of the convection so far has been confined to PA and western NJ this afternoon. As this convection heads east, it will encounter very dry air in the low levels, as dewpoints are in the 40's and 50's. That will help to inhibit the convection as well as the intensity of the convection. Soundings indicate that the storms could produce microburst wind  gusts and hail. Shear looks great, with about 60 knots of bulk shear, but very little instability due to the dry air and low moisture content. So straight line winds can be expected with the strongest storms as the front marches eastward.

Severe Wx tomorrow?

The pressing question for tomorrow besides the heat is going to be whether we see severe wx or not. So, let's get to it.

Let's put up the WV imagery first:

The cold front is well off to the west of the area, as it slowly crawls eastward through the MW states. The upper level ridge is clearly in place in the east, and by later on tonight and tomorrow, the ridge axis will move off the coast. For most of the day, the axis was over New Jersey. SW flow aloft is clearly in place, and more moist humid air will advect in tomorrow from the Eastern G/L states. High cirrus clouds will move in the ridge, a "dirty ridge" to be exact for tomorrow as convective debris attempts to move in from the Tenessee Valley.

For tommorow to start the day, we will be dealing with some mid level and high level clouds as a shortwave trough tranverses the region to the NE. There could be some advection fog and stratus clouds across Long Island and SE CT, which will burn off during the morning under low level SW flow over still colder Atlantic waters. Then partly sunny conditions will be found and surface heating will commence over interior areas allowing for temperatures to once again get up into the 80's and lower 90's, even as 850mb temperatures are a tad bit higher tomorrow than today. Strong SW flow in the lower levels will allow for seabreezes at the coast, making for cooler conditions there. However, amny areas on Long Island did hit 80 degrees earlier on before the seabreezes kicked in. It will be more humid tomorrow, as dewpoints climb into the 60's.

So, severe wx tomorrow? I'd think so. The ingredients will be there for afternoon convection. First trigger is the approaching cold front. The cold front will approach very slowly eastward as it alligns with the SW upper flow, running paraellel to the front. Problem here is there is not a ton of upper level support to kick the front through so the front will weaken with time. MLCAPES will top off around 1,000 K/KG, more low level moisture as we see a rise in dewpoints. So the front will run into a moderately unstable airmass. We were capped for most of the day today, but that won't be the case tomorrow as a mid level shortwave treks through, and it will provide lift, so little to no capping. Another trigger will be the pre-frontal trough that will develop to the west of the NYC area. Soundings show pretty decent low level shear and deep layer shear and a 50 knot SW LLJ will develop at 850mb, that will be a huge key as well. Strong mid level winds, strong deep layer and low level shear will be conducive for supercells and bowing segments to form, as well as a isolated tornado or two. Large hail and damaging winds can also be found. Further east, the marine layer will inhibit surface instability, thus convection as well. Upper jet support won't arrive until later at night for those areas, but loss of heating will prevent any severe wx, but weaker convective activity can still be found. Showers will continue tomorrow night as the front slowly sinks southward. Models show some elevated marginal instability, and with enough forcing from the front, thunder is possible.

Not a pretty day expected tomorrow.

Weather for Friday, April 30, 2010; Warm weather on the way!

Tomorrow is going to be the start of a beautiful stretch of weather coming up. Tomorrow is going to be a beautiful day. West-southwest flow will develop in the lower levels, while west flow dominates in the upper levels. What does this mean? Increasing heights aloft and much warmer weather. Looking at the WV imagery, there is strong WAA going on to the west of the area as a mid-level ridge builds from the G/L down into the southern states. In the NE/MA, a strong 300mb jet roared in at 120 knots, which brought the strong winds earlier as deep mixing occured. The ULL, which has plagued us over the last several days has finally moved out. Temperatures in the 70's can be found in most areas tomorrow. Dry conditions will be found tomorrow, aside from some clouds as moisture content increases a little bit.

Pattern Change On The Way; Warmer And More Humid By The Weekend!!

A pattern change is on the way folks and a welcome one at that! The ULL, currently spinning through New York State, is treking to the east today. The surface low, well off  the coast, is treking to the northeast as a kicker upper level disturbance is shunting the low off to the NE. It's also dragging a cold front through as winds have switched over the northwest, ushering in much cooler and drier air. Dewpoints have since dropped into the 30's and 40's. Tomorrow will be a rather cool day however, as the pressure gradient tightens as the upper disturbance over the Tennessee Valley phases with the surface low offshore and the upper cold pool moves over the area.

Once that pesky ULL moves out, there will be a rapid moderation in temperatures as a ridge begins to build in from the west. The computer models are having a difficult time with the possible break-down of the blocky regime we've had over North America.

Let's throw up the 12Z GFS 500mb pattern for a second.

See that ULL to the east of Maine. That ULL has been associated with a -NAO. However, the models want to breakdown the blocky regime. That ULL will begin to shift to the northeast. You can clearly see the ridge over the Eastern US. That is called the SE ridge. We've seen over the past several weeks, average to below average temperatures, marine airmasses, and slow moving low pressure systems. That is due to that ULL and the -NAO. That ULL will shift north of the Canadian Maritimes, and the ridge axis can build up into Southeastern Canada, leading to a SW flow aloft and at the surface. What does that mean? Warm, dry and humid conditions through the weekend. By early next week, a backdoor cold front will try to move south from Ontario. Each day will feature scattered showers and thunderstorms as impulses move up and over the ridge. Temps in the 70's and 80's can be expected each day. Summer is here now folks!!!!!!!!!

Outlook for Monday, April 26, 2010; Rainy, raw day on tap

Tomorrow is not looking like a very nice day. The ULL will be treking east over the area by tomorrow night. The warm front should stay south of the NYC/LI area, thus keeping the area cool sectored and in persistent easterly to northeasterly flow. The sreadiest rain should let up in intensity by tomorrow afternoon, but one last wave of low pressure will trek along the warm front and east off the Jersey coast, resulting in one rounbd of steadier rainfall. Temperatures will hover in the 50's north of the front. All in all, a wet, cold day.

Afternoon Discussion for April 25, 2010; Rainy weather continues

Hello folks. As you can see, it's a miserable day outside. Many areas picked up over an inch of rain this morning, however moist easterly flow continues to keep in the clouds, drizzle, and cool temperatures. Let's look at the WV imagery for a second.

The troublemaker responisble for this dreary weaather is currently spinning in the MW. The ULL is tracking eastward through Indiana ATM. Moisture continues to be transported up the coasr in SW flow aloft, while easterly flow continues in the lower levels, with high pressure anchored off the NE coast.

Now let's look at the current surface analysis from TWC.

The warm front is still south of Long Island, as of 4:38 PM. The warm front shouldn't make much more progress either northward or southward due to the upper flow running parallel to the front. A potent shortwave trough is dropping southeastward out of Eastern Canada into New England, and that is helping to keep those northern areas drier as it shunts the deeper moisture and associated lifting southward.

The light rain/drizzle should transition into stratiform rain again later tonight as a shortwave rotating around the ULL moves eastward along the warm front. Moisture should deepen again and instentropic lift should increase. Another 0.50 to 0.75 inches of rain should fall into tomorrow afternoon.Models advertise a third and final shortwave treking eastward along the front, but most of the rainfall should stay off the coast. On Tuesday, the ULL moves through into New England, and we could see some showers in cyclonic flow aloft s the ULL's associated cold pool aloft works on through. Winds should shift to the North Northwest by Tuesday, ushering in cooler, drier air and conditions should slowly improve on Wednesday.

Discussion for April 25th-27th RainStorm

Okay, I have a lot to get through in this discussion, so let's get to it. First up is the WV imagery, so I can show you what's going on currently.

So, what are we looking at? Currently, the ULL is closed and spinning in the MW states. There is a sub-tropical jet feed right out of the Gulf of Mexico. A potent shortwave is tracking southeastward out of Central Canada, and another ULL is dropping south from Labrador. The MW ULL will slowly weaken and open as it slowly treks to the east, through the OH Valley and then eastward into New England. On the WV imagery, there is a clear -NAO pattern in place over the Northern Atlantic, which is important because it helps to slow the pattern down. However, the 12Z ECMWF is a little more progressive than the 12Z GFS in lifting everything out earlier.


Now, let's look at the current surface analysis.

This is from Intellicast, at 8PM Saturday. The warm front is slowly lifting through the OH Valley, there is a ripple of low pressure that developed on the warm front over Southwestern Virginia, and the ULL is back over the border of Iowa and Missouri. High pressure has since shifted offshore, but the ridge axis has yet to move off the coast.


There will be a persistent easterly to northeasterly fetch over the next several days. This is due to upper level confluence over Northern New England. This is important because it helps to maintain high pressure and CAD, or cold air damming to the east and northeast. The parent ULL is still well to the west. The ULL helps to lift the warm front northward overnight into Sunday morning. However, the warm front should stay south of Long Island, keeping the NYC Metro Area cool sectored. Climatology at this time of year also suggests the warm front won't move north of Long Island. An onshore moist marine flow can be expected into Tuesday, before the low level flow turns more north and northwesterly by Tuesday afternoon and evening.


Rain will enter the picture later on tonight. There could be a few hours of virga because the rain is entering a cool, dry airmass and the dry sub cloud layer. Insentropic lift is when warm, moist air overruns cool, dry air and the moisture becomes enhanced as the two air masses clash. It becomes apparent near the warm front. Omega increases at 700mb across the area. Also apparent is convergence in the 1000mb-500mb layer also near the approaching warm front. The warm front helps the lifting as moisture from the GOM overruns the warm front, resulting in a stratiform rain.


A round of rain will occur later on tonight into Sunday afternoon, before there is a break in the action. However, moist easterly flow will continue to keep in clouds, fog, and drizzle. The MW ULL could be far enough east at this point, so it provides its own lift. A second surface low, indicated by the NAM/GFS/GGEM will track from the Mid Atlantic coast eastward out to sea on Monday, resulting in another round of rain. The cold front, associated with the ULL will move through on Tuesday, bringing another round of showers as its asslociated anomalous cold pool (temperatures around -25c-30C) moves through as well.


One last thing to worry about in southern areas of the CWA is the potential for thunderstorms, in which a few could become severe. The warm front will help to destablize the atmosphere. However, positive LI indexes and very little CAPE values will help to hinder the threat. Not sure on how much sunshine we will see to help fire off convection. A few storms could become severe due to steep lapse rates and being near the warm front. Can't rule this out as dynamics should be pretty potent.


Now onto QPF values.


HPC Guidance

12Z GFS Guidance

12Z GGEM Guidance

12Z NAM Guidance

I don't foresee any flooding concerns. Some places could see over 2 inches of rainfall, but this will be spread out over the course of a few days. But expect a raw, rainy ugly couple of days!!

Weather for April 24, 2010: Nice day before the weather goes downhill!

Friday was just a gorgeous day. Plenty of sunshine, low humidity, a refreshing NW breeze, and temperatures in the 60's. This was due to high pressure building in from the west.


Tomorrow should feature more of the same. High pressure will move to the south of the NYC area, and because of that, an afternoon sea breeze will develop at the coast, leading to cooler conditions. Tomorrow should be sunny, I don't see any rain during the day as the upper level ridge in place holds on a little longer. Temperatures inland should be in the 60's, if not a few degrees higher than Friday's. Once the ridge axis moves off the coast tomorrow night, a warm front will attempt to push in due to a ULL spinning in the western states. So the best chances for rain will  be during the overnight hours. The 12Z ECMWF may be too quick to move out the ridge axis, and the best chances for rain may come much later at night.

Weather for Friday, April 23, 2010. Much Better Day On Tap!!

The weather tomorrow looks much better. The cold front should have cleared the NYC Metro Area by later on tonight and the winds will switch over to the northwest. Behind the front, a drier and slightly cooler airmass will take hold for both tomorrow and into Saturday. High Pressure should build in from the west throughout the day, and that will lead to a pleasant late April day. Temperatures should be at comfortable levels, with 60's to be had. Again, there could be a few 70 degree readings scattered about the region. Frost may be an issue tomorrow night in the interior, as conditions could be favorable.

Afternoon Update for April 22, 2010

Just going to throw up the WV, so I can show you guys a few things.

As of 12Z, the surface cold front was located back into NW PA and Upstate NY. Another interesting thing, clearly seen on the WV imagery, is the presence of a potent shortwave trough, clearly shown treking eastward through NY State. The trough will do two things: 1) help to steer the cold front eastward, and 2) to initiate convection.


Now, will we see showers and possible thunderstorms? That will be determined by how much surface based instability there is to work with. Less instability to work with, less thunderstorm activity to work with. Looking at dewpoints this morning, there not all that high, because the airmass in front of the cold front is not all that warm and steamy. Yes, there is drier air behind the front, but the airmass is not all that cold. So we're not going to see the classic clashes of airmasses. Dewpoints are only hovering in the 40's right now, not all that high. Like yesterday, there is a mid level cold pool aloft, as temperatures at 500mb range around -25C. So because of that, mid level lapse rates are fairly steep. So, we could see some surface cape develop out of and just along the cold front. This is from New Jersey into interior portions of CT. So with the developing surface cape and the approach of the shortwave trough, this may be enough to fire off some convection out ahead of the front. For the coastal areas, convection will fire west of the coast, because an afternoon seabreeze would have an stablizing effect on the atmosphere and convection should weaken once hitting the marine layer in place.


So a few thunderstorms could contain some hail, some gusty winds, and heavy rains. The front should clear the coast later on this evening, bringing with it, drier and slightly cooler air. Temperatures today will be in the 60's most places, with a few 70 degree readings to the SW.

Weather for Thursday, April 22, 2010; Better day?

Currently, a very potent s/w/vort max is moving eastward through Southern NJ, while its associated surface low, 1006mb is currently in NW Virginia. What has caused some showers and a few thunderstorms to break out is the combination of some lift, some instability, and cold air aloft in the mid levels, from 500mb to 700mb. As these showers translate eastward, they will weaken as they encounter the marine layer to the east.


Onto to tomorrow. There could be some breaks of sunshine early in the day, but that will be short-lived as a cold front crosses the area, bringing an increase in clouds. Not expecting much precip with the front, as there isn't a lot of moisture to work with. Cooler, drier air will follow behind the frontal passage tomorrow night with NW flow. Temperatures look to be in the 60's most areas, with a few 70 degree readings scattered about to the southwest.

Weather for Wednesday, April 21, 2010

Gonna throw up the WV Imagery from WeatherTap, as this will have implications on the weather for tomorrow.

What are we looking at? Currently, there is a rather potent s/w treking through theTennessee Valley. The HPC surface analysis shows a 1016mb surface high off Hatteras, and a 1015mb surface high over Chicago with a surface cold front centered off the Northern G/L. A surface trough can be found along the spine of the Apps. What does this all mean?

Well first, the infrared satelite image shows high clouds streaming in from the southwest, now overtaking Eastern PA, NJ, LI, and into Eastern CT. Clouds will increase tomorrow as the front continues to near and the s/w translates eastward. There is a risk for some showers during the afternoon, but any lifting mechanism will be quite weak, even though there is some frontogenesis, and the showers will be scattered in nature. Some instability can be found in southern areas in southern NJ, southern PA for example. I can't rule out a few rumbles of thunder as well. Highest temperatures to the NE, lowerst temperatures to the SW. Temperatures in the 60's can be found for most areas tomorrow.