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Mild and Calm Conditions Take Hold, Watching a Potential Coastal Storm for Friday

Good evening! 

After the cool and dreary conditions over the past couple of days, today was a slight improvement for much of the Northeast as a cold front gradually passed through the region, signaling a change to the sensible weather pattern. This front was luckily rather tame in nature, as the energy associated with the front was strung-out and not well-organized. This allowed for only moderate changes to gradually take place during the course of the day, with a rather cloudy and cool start to the day. As the day continued on, we saw high to mid level clouds lessen with time, eventually giving way to some peaks of sun. Winds shifted to the northwest behind the front, with more dry and cool air filtering into the Northeast. Modest cloud cover and a renewed airmass from Canada kept temperatures in check, with highs ranging from the lower to upper 40’s, with some locations reaching the 50 degree mark. Dry air from the north and west should continue to mix out any residual low level moisture over the next 6-12 hours, leading to mostly clear skies this evening. Additionally, an area of high pressure will be building in over the Mid Atlantic and Northeast tonight, so expect any winds to gradually diminish over time. These conditions will be quite favorable for radiational cooling to take place overnight, with temperatures likely dropping quite a bit into the lower to middle 30’s over much of the area. Some locations off to the north and west will likely drop into the middle 20’s this evening, causing any residual moisture on roadways to freeze, so please watch out for slick patches if you’re driving tonight.

This evenings latest high resolution water vapor imagery, surface observations, and surface winds, showing a more calm temporarily setting up.

This evenings latest high resolution water vapor imagery, surface observations, and surface winds, showing a more calm temporarily setting up.

Tuesday through Thursday 

Tuesday will likely start off quite chilly, but clear as the area of high pressure continues to build and move eastward with time tomorrow morning. Conditions will be quite dry throughout the majority of the atmosphere, so skies will likely remain mostly sunny for the majority of the day, with a few upper level cirrus clouds passing through. The fresh Canadian airmass in place in combination with the high pressure will work in tandem to keep conditions cool, but not too cool over the entire Northeast. Highs tomorrow afternoon should remain in the middle to upper 40’s, with some inland locations likely hitting the 50 degree mark again. All in all, tomorrow should be a rather nice day, but will likely still require a light jacket to stay comfortable. Tomorrow night looks to be calm and cool as well, but not quite as cool as tonight. Lows will likely dip down into the middle to upper 30’s for the majority of the Northeast, with some locations possibly just getting below freezing.

Wednesday looks to be one of the more mild days of the week as the area of high pressure that has been dominating the east begins to move off the Mid Atlantic coast. This should create more southerly flow in the mid to low levels of the atmosphere, bringing in slightly warmer highs for the afternoon hours. Moisture looks to also increase with the southerly flow as a shortwave trough digs into the desert southwest, sending some residual energy into the east. This energy out ahead of the main system should allow for some clouds and even a few isolated showers to develop in the late afternoon hours, but not significant rain is expected. Highs will likely be able to rise into the lower to middle 50’s across the vast majority of the Northeast. Cloudy conditions will likely continue throughout the overnight hours, with the threat of a couple of showers lasting into the early morning hours. Cloud cover and southerly winds should keep lows from dipping too much, with readings likely staying in the middle to upper 30’s-with some locations seeing lows in the lower 40’s.

Things begin to get a little more interesting on Thursday, as the system that was in the southwest begins to move into the Plains and interacts with another shortwave coming down from Canada. As these systems interact and attempt to phase, a primary surface low pressure system should form over the Great Lakes region, with a large area of rain expected over much of the Southeast. As this low moves closer to the Northeast, cloudiness will likely increase in addition to the threat of some showers as we head into the late afternoon hours. Later in the evening, this area of low pressure should continue to intensify, as the mid level system becomes much more organized. This process should continue into the overnight hours, as a stationary front likely sets up over the Mid Atlantic, which may become the focus for a secondary low pressure system to form. Temperatures on Thursday will likely remain mild, with highs in the lower to middle 50’s over the entire Northeast.

This evenings NAM model showing the development of a potentially impactful system for the Northeast

This evenings NAM model showing the development of a potentially impactful system for the Northeast

Potentially Impactful Coastal System Shaping up for Friday 

This afternoons model guidance continues to show the potential for the primary low pressure system that travels over the Ohio Valley to redevelop just off the Mid Atlantic coast early Friday morning, but there are still a large amount of uncertainties with this forecast. Regardless, what we do know is that an area of blocking will be located over Greenland, which will act to slow down the mid level system and allow it to strengthen as it nears the coast. This should lead to the development of a strong low pressure system adjacent to the Mid Atlantic coast during the day on Friday, likely leading to a wide range of impacts. Almost all of the model guidance shows an impressive swath of winds just above the surface with this system due to a tight pressure gradient. Additionally, this system will be capable of tapping moist air from the south, so it will likely have a good amount of moisture to work with, leading to the development of widespread moderate to heavy precipitation. Lastly, winds out over the ocean will likely be directed towards the coast, which will create at least a moderate threat of coastal flooding as we enter a full-moon phase. One of the main things we do not know at this time is exactly when and how much phasing will occur with the two original disturbances over the Ohio Valley. A quicker phase would lead to a stronger coastal low tucked right along the coast, while less/delayed phasing will likely lead to a weaker and more elongated system.

There is also the question of precipitation type, which is something that seems to be highly sensitive at this time. While a stronger system would be able to create enough dynamic cooling for some snow to fall, this solution would also mean that the primary low in the Great Lakes sticks around longer, which creates more warm air for the coastal plain. At this time it does not seem like a widespread significant snowfall is likely from this system, but there could be some locally heavy snow in the higher terrains of the Northeast if conditions line up correctly. We will be keeping a very close eye on this system this week and will continue to provide updates as they become available!

This afternoons European ensemble individual members showing a wide variety of solutions for Friday's system

This afternoons European ensemble individual members showing a wide variety of solutions for Friday’s system

Have a great night! 

Steve Copertino

Changes Blowing Through the East, Active Pattern Looming Next Week

Good Evening! 

Well, we have been talking about the pattern change for around two weeks now, and things have transpired according to plan across much of the Northern Hemisphere. We have a massive area of ridging set up over the West Coast that has caused record high temperatures as well as wildfires across California. Our second area of ridging has taken shape over Greenland and both of these features have led to a deep trough digging into the central US and east, which we’ll discuss in further detail in just a bit. Today was a cooler and calmer day across the entire Northeast after the passage of a rather large cold front that moved through yesterday evening. While the immediate temperature change didn’t occur for hours, the front did bring in a new Arctic source region for our airmass for the duration of the week. This new Arctic airmass has been modified somewhat was leftover Pacific air, but partly cloud skies and cooler temperatures aloft allowed highs to only get into the upper 30’s and lower 40’s this afternoon, with some slightly warmer readings closer to the coast. The main story behind this front was the dramatically decreasing dewpoints across the entire Northeast, signalling the arrival of a dry continental polar airmass. Additionally, winds were a bit gusty this afternoon, on the order of 15-20 miles per hour, which certainly added to the winter chill in the air. Calm conditions should continue throughout the evening, with light winds from the southwest taking over. Despite the southwesterly winds, cold air advection is expected over much of the area, with decent conditions for radiational cooling to take place. Overall, expect a rather chilly night with lows in the upper 20’s and lower 30’s near the New York City metro, and lower to middle 20’s further to the north and west.

Last light GOES13 visible satellite imagery, regional radar mosaic, and surface observations, showing calmer and cooler conditions taking over the Northeast. Some high to mid level clouds are possible later this evening (Credit Simuawips)

Last light GOES13 visible satellite imagery, regional radar mosaic, and surface observations, showing calmer and cooler conditions taking over the Northeast. Some high to mid level clouds are possible later this evening (Credit Simuawips)

Thursday and a Close-Call On Friday 

The large area of trofiness will continue to dig into the central and eastern portions of the US tomorrow morning, allowing a massive and intense upper level jet streak to work in over the Northeast. This jet streak may provide some high level clouds tomorrow, but the majority of the active weather will likely stay over portions of the deep south and Gulf of Mexico throughout the day. Conditions should be mostly sunny tomorrow with light subsiding winds, so expect near-normal temperatures across the area, with highs likely reaching into the upper 30’s and lower 40’s. This should be right around normal for this time of year. These calm conditions will likely remain throughout the day as a secondary jet streak to our north creates large-scale sinking air over the Northeast. Temperatures Thursday night should be able to fall a little steeper this time around, with lows likely dipping into the middle to lower 20’s across much of the Northeast, with locations farther north and west likely seeing upper teens and lower 20’s for lows, which will be a good bit below-average.

As mentioned, things become a bit more interesting on Friday as the same upper level jet-streak begins to intensify as energy from the deep-south begins to quickly head north as the trough over the eastern third of the country begins to tilt. This tilting will cause the jet streak over the east coast to retrograde , or head westward throughout the day on Friday. Some more high level cirrus clouds are expected during the day, with another shot of cold air in the lower levels also likely. This should allow highs over the region to remain in the middle to upper 30’s, with locations closer to the coast likely hitting the 40-degree mark. The aforementioned strong upper level jet streak will work with copious amounts of energy just off the east coast to produce widespread precipitation along a frontal boundary.

This evenings NAM model showing a very impressive and intense jet streak over the Northeast, promoting the development of precipitation near the east coast (Credit: Tomer Burg)

This evenings NAM model showing a very impressive and intense jet streak over the Northeast, promoting the development of precipitation near the east coast (Credit: Tomer Burg)

This frontal boundary could have a wave of low pressure develop along it that may allow precipitation to affect portions of the coast, and possibly into the NYC area. Model guidance has been going back and forth with this frontal system, showing light to moderate precipitation over the area on one run, just to show virtually of the precip off the coast on the next. At this time, we think that there is a decent chance that far eastern locations near the coast (especially Long Island) may see some light snow out of this frontal system. Depending on how things transpire over the next day or so, there is a rather low risk of accumulating snowfall west of central Long Island, but I wouldn’t be surprised to see some snow falling across the lower Hudson valley on Friday night, as many of these weak frontal systems with strong jet-stream energy tend to tick north and west in the last 24 hours. We will certainly be monitoring this system over the next two days and will provide updates when necessary!

NAM simulated radar imagery showing the potential evolution of the system on Friday/Saturday

NAM simulated radar imagery showing the potential evolution of the system on Friday/Saturday

Potentially Active Period Next Week

With the massive ridging over the west, deep trough in the central/eastern US, and limited blocking over Greenland, we could be looking at the potential for a few light snow events over the next week. The first would be possible on Sunday as the upper level low from the storm system on Friday begins to rotate over the region. Only snow showers would be possible with this system, but we should lake effect snow increase quite substantially from this system as cold low level air moves over the still-warm lakes. The next chance for something of substance would be on Tuesday as a large amount of energy dives down from Canada and into the base of the trough over the east. The models have been extremely inconsistent with the handling of this piece of energy, but it seems that this system may try to phase with a very strong upper level low over the Great Lakes region, which would promote a storm developing just to our south or over our region. At this time, there is no support for a sizable storm, but with a setup like this and a good deal of energy involved, its always good to watch these systems as they come down from Canada. Lastly, we look at late next week and into the weekend when more energy begins to dive down from Canada. This energy may have a better shot at successfully phasing with that same strong upper level low over the Great Lakes, but it will be a couple of days before this potential system comes into the reliable range of the computer model guidance. With an active period shaping up for the rest of December, remember to check back for updates as they come out!

This afternoons European model showing a good amount of energy diving into the base of the trough located over the east. This setup needs to be watched for a late-developing storm near our area next week

This afternoons European model showing a good amount of energy diving into the base of the trough located over the east. This setup needs to be watched for a late-developing storm near our area next week

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Have a great evening!

-Steve Copertino 

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

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!

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Have a great night!

Steve Copertino 

Public Analysis: Calm and Cool Conditions Gives Way to Hot and Stormy By Friday

Good Evening! 

We had a rather wild Saturday morning this past weekend as the remnants of Tropical Storm Cindy stormed through the area along with a rather strong cold front. All of the deep tropical moisture and forcing from Cindy and the cold front allowed a rather impressive line of torrential rain and embedded thunderstorms to move through the area early on Saturday morning. This area of heavy rain did bring some flooding to locations as rainfall rates increased to over one inch per hour, but also brought some extensive wind damage, along with two confirmed tornadoes in Monmouth county, New Jersey! After the cold front moved through, we saw a much direr air mass take over yesterday, which has persisted through the day today, and should last another 48 hours. Afterwards, it appears that a large area of high pressure will form just off the East Coast and looks to bring above normal temperatures back to the region, with the addition of another muggy air-mass and the threat of some strong thunderstorms towards the end of the week.

———-

This Evening Into Tomorrow

As mentioned, today was a very pleasant day with mostly sunny skies, light winds, and cooler temperatures thanks to a rather moderate and dry air mass in place over the region. High temperatures were able to stick into the mid to upper 70’s, which is slightly-below, or just around seasonable for this time of year. Some locations saw temperatures drop off a bit during the afternoon hours as sea-breezes made their way inland over portions of Long Island and Connecticut. There was some threat of isolated showers and thunderstorms this afternoon, but the lack of a strong trigger and very dry mid levels of the atmosphere seem to point that nothing more than a few cumulus clouds should be expected for the remainder of the day and into the evening.

As we continue into the evening hours, a very unusually strong mid level trough for this time of year will continue to pivot eastward, and drags another cold front with it. While this afternoons models were hinting at some rain later this evening associated with this cold front, it seems that the aforementioned dry air should put a kibosh on any precipitation. As the front approached the area, falling heights out ahead of the upper level trough should allow for clouds to increase, but with light winds and a very cool vertical temperature profile in place, overnight lows should drop to below-normal levels, with low to mid 60’s likely for most of the area, and 50’s possible for areas further away from the coast.

This evenings latest regional radar mosaic, HRES visible satellite imagery, and surface observations showing relatively calm conditions, with some showers and thunderstorms to the north and west (Courtesy of College of DuPage)

This evenings latest regional radar mosaic, HRES visible satellite imagery, and surface observations showing relatively calm conditions, with some showers and thunderstorms to the north and west (Courtesy of College of DuPage)

Tuesday morning should feature mostly sunny skies to start the day as a cold front begins to move through the region. By the late morning to early afternoon hours, the anomalously strong trough centered to our north and west will continue to move east and be overtop the area, with very cool mid level temperatures. These cold mid level temperatures will become important tomorrow afternoon as the surface temperatures begin to rapidly warm up, causing a very healthy amount of rising motion in the atmosphere. Combined with very marginal instability, we could see one or two showers or even an isolated thunderstorm pop tomorrow afternoon, but due to continued dry mid levels of the atmosphere and the overall lack of a trigger, the most likely outcome is that clouds should begin to increase, with cumulus clouds becoming quite numerous by the late afternoon. With the cooler mid level temperatures in place and light southerly/southwesterly winds expected to be in place, high temperatures should be able to reach into the mid to upper 70’s, with some areas possibly even hitting the 80 degree mark with prolonged sun.

Otherwise, skies should begin to clear and winds should become calm as an area of high pressure begins to build in behind the cold front to our west. This high pressure system will usher in another cool and dry airmass for the region, which should allow quite favorable conditions for radiational cooling to take place during the evening hours tomorrow. This should allow temperatures to drop into the lower 60’s and even the 50’s once again!

This afternoons high resolution North American model showing a very pleasant day on Tuesday afternoon just before a cold front works its way on in from the west, bringing yet another mild and dry airmass (Courtesy of Tomer Burg)

This afternoons high resolution North American model showing a very pleasant day on Tuesday afternoon just before a cold front works its way on in from the west, bringing yet another mild and dry airmass (Courtesy of Tomer Burg)

Wednesday and Beyond

Wednesday will likely start off rather calm as an area of mid level ridging begins to build and move eastward during the day, with high pressure mainly in control. This should allow for mostly sunny skies and light winds from the south/southwest to take over during the day, which will likely bring temperatures in the upper 70’s to the lower 80’s for some of the more southern locations. All in all, Wednesday should be a rather beautiful day, with slightly below-normal highs and building clouds later in the day and approaching the evenings hours as a warm front begins to advance east.

By Thursday, the riding should become stationary over area and make little if any forward progress during the day, so expect winds to become a bit steadier from the southwest. Temperatures aloft will also begin to warm quite a bit, so temperatures will likely be able to climb into the low to middle 80’s during the day Thursday with mostly sunny conditions expected.

As we get towards the end of the week on Friday, its looking likely that precipitation chances will be on the increase as the area of high pressure along the east coast shifts eastward and allows rich tropical moisture to bleed northward once again. Temperatures will also be on the increase, with highs likely getting into the middle to upper 80’s, with some locations likely hitting that 90-degree mark as well. Friday appears to have more organized instability, better shear, and a more coherent trigger than any day this week, so we do feel that there is an increased risk of strong to possibly severe thunderstorms during the day on Friday, but we will have to revisit this later in the week. Otherwise, this pattern looks to continue through the weekend before another high pressure system moves through and brings a more mild airmass in time for the beginning of next week.

This afternoons European Ensembles showing an increased potential for above normal temperatures by the end of this week and into this weekend (Courtesy of TropicalTidbits)

This afternoons European Ensembles showing an increased potential for above normal temperatures by the end of this week and into this weekend (Courtesy of TropicalTidbits)

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 evening!

Steve Copertino