Doug Simonian

Long Range Update: Cold Intensifies, Active Pattern to Follow

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Good evening! As has been heavily advertised for a while, a pattern change to cold is now imminent, and should be able to sustain itself for a couple of weeks thanks to retrograding and deepening troughing near the Aleutians. This leads to continued downstream impressive responses near the West Coast, with plenty of latent heat release and poleward ridging. This will dislodge a couple of shots of Arctic air into the Eastern two thirds of the US — into a lot of the major markets.

While the first shot of colder air later this week and weekend will be impressive in some spots, it is the second shot of colder air around the middle of next week that should be much more impressive, as it will truly have an Arctic source region, thanks to the poleward ridging. There will be a nearly direct pipeline due north to south from the Arctic for this cold air to plunge towards the US.

The above video explains this progression and highlights the significance of this cold. We also discuss the potential for moderation late in the month, and how the Pacific Jet extension that may cause this moderation could lead to a major winter storm somewhere in the East as we get closer to the Holidays. Additionally, we discuss the potential for other winter storms in the more near future, though their significance may be limited by a lack of good wave spacing.

 

Miguel Pierre

Mild & Rainy Tuesday, Cold & Active Pattern Arrives Late Week

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Happy Monday! Fair and chilly weather will continue for the rest of today, as high pressure remains in control. Some clouds will increase this afternoon, ahead of an approaching frontal system. But high temperatures will be in the upper 40s over the Interior to the lower 50s near the coast, which is near or slightly above normal for this time of year. But as we’ve been discussing before, some big pattern changes are coming for the rest this week, that will support more wintry weather for the mid-December — this pattern will be ushered in by the aforementioned cold front.

First, a strong cold front associated with a large upper-level trough will be approaching from the west tomorrow. Tonight will be mostly cloudy with temperatures not falling too much, with southerly flow and clouds increasing ahead of the front. Then the front will cause some showers to spread east during the day. Later in the afternoon and evening, dynamics will increase from a strong southerly jet, tight thermal gradient, and a moisture fetch from the Gulf of Mexico. Thus, rainfall may become heavy at times tomorrow night. There’s even a slight chance for isolated thunderstorms as some elevated instability increases.

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Steven Copertino

Big Changes Next Week, Cold and Potentially Active Pattern Shaping Up

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Good Afternoon! 

Welcome to December folks! Today was a relatively cool and calm day as another area of high pressure has edged its way into the Northeast after a cold front passed through the region last night and brought some light rain to most locations. This area of high pressure has ushered in some cooler temperatures aloft and at the surface, in addition to some drier air that allow temperatures today to drop to near-normal levels, with most of the Northeast staying in the middle to upper 40’s, with locations closer to the coast getting into the 50’s. Despite the near-normal temperatures, the air did have some bite to it this afternoon as winds gusted up to 20 mph in some locations, which certainly made conditions feel a little cooler than they actually were. Regardless, this was a rather beautiful start to December with mainly clear skies area-wide. With high pressure still in control as we head into the evening hours, conditions will be quite favorable for radiational cooling to take place across the entire northeast. There may be come high clouds from some weak remnant upper level energy passing by, but we expect temperatures to drop into the low 30’s and upper 20’s for the immediate New York suburbs, with middle to lower 20’s possible for locations to the north and west of the area.

A look at the RTMA this evening showing cooling and clear conditions over the entire Northeast. Lows tonight are expected to fall sharply into the 20's and 30's across much of the area (Courtesy of Simuawips)

A look at the RTMA this evening showing cooling and clear conditions over the entire Northeast. Lows tonight are expected to fall sharply into the 20’s and 30’s across much of the area (Courtesy of Simuawips)

This Weekend 

Saturday should start off quite clear and cool in the morning hours, as the area of high pressure begins to move up and out of the Northeast. As the high gradually shifts east during the day, surface winds should begin to respond and shift to a more southerly/southeasterly component. This should allow slightly warmer temperatures to move in tomorrow for the southern portions of New England and the Mid Atlantic states where highs in the upper 40’s to lower 50’s will be possible closer to the coast. Highs in the northern and western locations of the Northeast should stay in the low to middle 40’s as more stubborn cold air holds its ground. Tomorrow looks rather pleasant as the entire nation is stuck in this progressive west to east flow that has dominated the pattern of the past few weeks. A weak shortwave trough will be embedded in this fast west to east flow tomorrow, and should pass over the Northeast by the early afternoon hours. This shortwave trough will be highly sheared and moisture starved, so only some high clouds are expected from this system. Calm and clear conditions will extend into the evening and overnight hours as the aforementioned shortwave rockets off the east coast. With light winds, dry mid levels, and cool mid level temperatures, conditions will once again be supportive of efficient radiational cooling to take place. Expect lows to once again drop down into the low  20’s for locations well removed from the coast, with upper 20’s and lower 30’s as you get closer to the New York City metro area.

Sunday also looks to be another nice and quiet day across much of the Northeast. Previously, there was a chance at some light rain showers from a weak disturbance moving through Canada, but since Wednesday model guidance has been trending weaker and drier with that system, so at best this system may be able to increase clouds throughout the afternoon hours. With the zonal flow still in place and no real airmass change in site, we expect temperatures to remain generally right around average for this time of year, with highs in the lower to upper 40’s across much of the area. some locations closer to the coast may once again be able to nudge into the lower 50’s if sunnier conditions and offshore winds persist. High clouds may last into the evening and overnight hours on Sunday, but this should have relatively little impact on the overall sensible weather. Expect lows to drop into the low to middle 20’s north and west, with upper 20’s to low 30’s likely across the New York Metro area. Overall, this weekend looks to be a quiet one with seasonable temperatures, so if you’re planning to get the holiday decorations up, this weekend would be an excellent time to do so!

This afternoons ECMWF model showing the zonal flow pattern that the CONUS has been stuck in for a while now. The west to east flow does not allow for systems to slow down and strengthen, leading to relatively dry and quiet conditions across s the country

This afternoons ECMWF model showing the zonal flow pattern that the CONUS has been stuck in for a while now. The west to east flow does not allow for systems to slow down and strengthen, leading to relatively dry and quiet conditions across s the country

Big Changes In the Pattern Moving Up In Time

We are still on track for a substantial and total change in the overall synoptic pattern across the Northern Hemisphere starting as early as next Wednesday. By this time, a massive area of mid level ridging will balloon over the west coast and up into the Yukon territories of Canada. As this ridge goes up, we’ll also see another area of anomalous riding go up near Greenland. As these features build and establish themselves during the middle of next week, we should see the atmosphere respond in a rather big way. A large storm system should take shape in the central part of the country, and then move north into Canada. Large storm systems that cut up the central part of the country are usually tell-tale signs that change is coming to the pattern. As the low pressure area quickly heads up into Canada, Arctic air will rush down on the western side of the low thanks to the aforementioned area of ridging that will be established over the west coast. This blast of colder air will move quickly behind a strong cold front associated with the decaying low pressure that will move well into the northern portions of Canada by the end of next week. This cold front may have some significant precipitation associated with it as the mid level trough accompanying it is able to dive all the way down into the Gulf of Mexico.

This afternoons EPS showing the difference between the zonal flow we have been stuck in compared to the much more amplified pattern we're heading into

This afternoons EPS showing the difference between the zonal flow we have been stuck in compared to the much more amplified pattern we’re heading into

After the initial cold shot by the end of the week, we should begin to see a near-constant feed of Arctic air into the central and eastern portions of the country, with the possibility of numerous northern stream disturbances diving down from Canada. Since we should have an established block by this period, we may have to watch as these systems will have the chance to slow down, and strengthen close to the east coast. This is an idea that is supported by this afternoons latest model guidance and fits the pattern of years past as well. Regardless, we are going to be moving into a much more winter-like pattern by the end of next week, with the initial setup taking place by the middle of next week. This cold and potentially active pattern should last at least into the middle of December, with the potential for the pattern to reload and strengthen throughout the rest of the month. We will have more updates early next week on this pattern!

This afternoons GFS model showing the initial cutter that kicks off the pattern change and brings in much colder air into the CONUS with a potentially active storm track across the country over the next few weeks

This afternoons GFS model showing the initial cutter that kicks off the pattern change and brings in much colder air into the CONUS with a potentially active storm track across the country over the next few weeks

For more information and posts like this one, make sure you sign up for Premium Forecasts — where multiple detailed articles, videos, and interactives are posted each day. Also, come interact with our staff and many other weather enthusiasts at 33andrain.com!

Have a great night!

Steve Copertino 

 

Steven Copertino

Dry and Seasonable Pattern Holding On, Substantial Changes Looking More Likely Next Week!

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Good Evening! 

Today was the warmest in a series of mild days across the entire Northeast. Dry air in the mid levels of the atmosphere was quite abundant this afternoon, and this dry air helped to mix the warmer mid level temperatures down to the surface with stout northwesterly/westerly flow. Mostly sunny skies and light winds helped much of the region see highs rise into the well-above normal values this afternoon, with many stations across the Northeast breaking the 60 degree mark. In fact, some stations across portions of Long Island and southern New Jersey saw readings in the middle 60’s, which is a good 10-15 degrees above normal for this time of year! As the day progressed, we had a weak cold front with extremely limited moisture push through the Northeast. This front was weak enough that surface temperature did not/have not immediately responded as the main cold air pool is located well behind the surface front. High pressure is gradually building into the Northeast this evening, with the onset of cooler temperatures finally reaching northern portions of New York and New England where temperatures have since fell off into the low to middle 30’s.

The rest of this evening should be quiet, with winds shifting to more northerly/northwesterly. As this happens, conditions will be rather good for efficient radiational cooling to take place across much of the Northeast. This should allow for lows to drop into the middle to lower 30’s across much of the area, with middle to upper 20’s possible further north and west.

This evenings Real Time Mesoanalysis showing surface temperatures and surface observations across the Northeast. Temperatures are gradually becoming cooler from north to south across the region as a cooler airmass works in (Courtesy of Simuawips)

This evenings Real Time Mesoanalysis showing surface temperatures and surface observations across the Northeast. Temperatures are gradually becoming cooler from north to south across the region as a cooler airmass works in (Courtesy of Simuawips)

Thursday and the Weekend

Thursday should start off a good deal cooler than Wednesday did, but as the area of high pressure currently located over Canada quickly moves offshore, we should see offshore flow overspread much of the Northeast, leading to increased temperatures and available moisture. As this high quickly rockets east, a shortwave trough will also be quickly heading east, embedded in the fast west to east zonal flow over the country. This disturbance should be located over the Great Lakes region by tomorrow afternoon, with a cold front extending southward. Unlike the past few fronts, this one may be able to tap into some moisture lingering over the Gulf of Mexico, which should allow the front to be a bit more active with showers likely along the front. As we head into tomorrow afternoon, southwesterly flow should be rather stout at the surface as well as the mid levels, ushering warmer mid level temperatures as well. With the increased low level moisture from the offshore flow, there may be more clouds than sun across portions of the Northeast, but we still expect temperatures to still reach into the upper 40’s to lower 50’s. This should be right around normal for this time of year, but some locations to the south of the NYC area may see readings into the middle 50’s.

By tomorrow evening, the cold front should begin to move through the Northeast with light to occasionally moderate rain likely. The rain along this front should be limited due to the overall dry mid to upper level conditions and quick movement of the upper level system. With clear conditions behind the front expect temperatures to generally fall into the lower to middle 30’s across much of the area, with colder readings to the north and west.

This evenings RPM model showing the progression of the weak cold front moving over the Northeast tomorrow evening. Only light rain accumulations are expected (Courtesy of WSI)

This evenings RPM model showing the progression of the weak cold front moving over the Northeast tomorrow evening. Only light rain accumulations are expected (Courtesy of WSI)

Another high pressure will build into the Northeast by Friday morning, bringing in renewed northwesterly flow and slightly cooler temperatures in the mid levels. The vast majority of the day should be dry, but a couple of spotty showers may be possible around Long Island and Connecticut as some residual energy behind the aforementioned cold front moves over the area. Highs will likely stay around normal for this time of year, with readings in the middle to upper 40’s-with a couple of locations reaching 50 possible. Friday night looks to be a calm and clear evening with radiational cooling likely, so we expect lows to drop down into the upper 20’s and lower 30’s across the immediate NYC metro area. Areas farther north and west could see lows drop into the middle 20’s if conditions allow strong enough cooling to take place.

Saturday and Sunday look rather quiet and seasonable, with highs likely staying in the upper 40’s to lower 50’s range. The only real chance of precipitation may come on Sunday night when a sloppy mid level piece of energy moves quickly eastward from Canada. This system looks to be rather moisture-starved, so it does not appear to be of major concern at this time.

This afternoons ECMWF model showing above normal temperatures persisting across much of the country this weekend as a mid level ridge builds in.

This afternoons ECMWF model showing above normal temperatures persisting across much of the country this weekend as a mid level ridge builds in.

Substantial Changes Likely Next Week! 

We have been watching the pattern for the upcoming week very closely for the past seven days or so, and it seems like with every successive model run, things continue to look more and more interesting for a major pattern change to take place in this time period. By the middle of next week, we should begin to see the development of a major ridge over the west coast of the United States, which should extend deep into Canada. This ridge is whats referred to as a “PNA ridge”, and when coupled with the right ingredients, can lead to a very cold and potentially stormy pattern across the United States. As this ridge gets stronger as time goes on next week, it will begin to send Arctic air from the far northern regions of Canada and even Russia into a building trough which will likely be located over the central part of the country.

This afternoons ECMWF model showing a very impressive area of mid level ridging going up over the west coast and deep into Canada. This pattern is highly supportive of colder weather in the east.

This afternoons ECMWF model showing a very impressive area of mid level ridging going up over the west coast and deep into Canada. This pattern is highly supportive of colder weather in the east.

Another key ingredient of this pattern change will be increased high pressure/ridging over Greenland (a negative NAO), which will help to slow down the trough in the central/eastern US. This is very important as it will allow the Arctic air to pour in and build as it moves east. Model guidance has been very consistent on these ingredients taking shape, and have even been strengthening them to a degree as we get closer in time which is extremely important for this pattern to actually come to fruition. With the ridging in the west and in the east, the pattern becomes “blocked up”, meaning that systems have a chance to slow down and amplify, which is the exact opposite of the pattern we are currently in! This means that there will be an increasing storm threat for the eastern half of the country starting late next week and into the middle portion of December. At this point in time, it seems that below-normal temperatures are very likely in the 8-14 day period across the central and eastern parts of the country, and possibly extending deep into the month. In summary, it appears that starting next week we will see major changes taking place across the hemisphere that could gradually push us into a classic winter pattern for the month of December! We’ll have more on this pattern as new details arise!

University of Wisconsin CIPS analogs based on the GEFS showing extremely high probabilities for below normal temperatures starting as soon as next week!

University of Wisconsin CIPS analogs based on the GEFS showing extremely high probabilities for below normal temperatures starting as soon as next week!

For more information and posts like this one, make sure you sign up for Premium Forecasts — where multiple detailed articles, videos, and interactives are posted each day. Also, come interact with our staff and many other weather enthusiasts at 33andrain.com!

Have a great night!

Steve Copertino