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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

Stay tuned for public updates later this week. Sign up for our Enterprise Forecasts for more frequent or tailored updates, technical analysis, videos and long range discussion. Also join us at 33andrain forums for free discussion on everything weather-related.

Have a great evening!

-Steve Copertino 

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Attention Turns to Jose, Two More Systems Active Over the Open Atlantic

Good Afternoon! 

The tropics have begun to really ramp up yet again, with Jose still meandering north of the southern Bahamas, newly formed Tropical Depression 14, and a vigorous tropical wave that has been designated Invest 96L.

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Tropical storm Jose has been on the upswing over the past 18 hours or so, as the strong wind shear that has been blasting it ever since Irma made landfall has finally abated to some degree. The storm developed very cold convection right over the center last evening, and this likely worked to help reorganize the storms core a bit, since earlier microwave passes showed that the system had become severely tilted to the point that the mid level and low level centers were no longer aligned. At this post is being written, the hurricane hunters are currently investigating the system, and have found winds just around the threshold for a Category 1 hurricane along the southeast portion of the circulation. Typically the strongest winds are found in the northeast quadrant, so I would no be surprised if this mission found winds of around 80 mph, but I will wait for the NHC to make that official decision of reclassifying it as a hurricane. As stated, shear has begun to weaken, and Jose will be over very warm sea surface temperatures of around 29-30C for the next 36 hours, along with relatively moist mid level atmospheric conditions. This should allow the system to strengthen back to a high-end Category 1 Hurricane, or even a low-end Category 2 before shear really begins to increase to high levels in about 48-60 hours.

Current hi-res visible satellite imagery of Tropical Storm Jose over the open Atlantic with 70mph winds.

Current hi-res visible satellite imagery of Tropical Storm Jose over the open Atlantic with 70 mph winds.

The track of Jose is what remains the hot-ticket item. Over the past few days, there has been a noticeable shift westward, with some global models even showing Jose making landfall along the east coast. Once Jose is positioned between Bermuda and North Carolina on Monday, steering currents will begin to break down and the storm should begin to slow a bit while moving to the north. As the storm slows down, the consensus from the reliable models seems to show that more mid level ridging will build over and around Jose to slow it down even more once we get to the Tuesday afternoon period. By this time, a the storm will likely be encountering very strong wind shear and much cooler waters, which should force it to become a large extra-tropical system near the 40/70 ‘benchmark’ by Wednesday. While direct impacts are unlikely from this system outside of some gusty winds and possible rainfall along with coasts, strong wave action and life-threatening rip currents are likely to last well into next week as the storm slowly moves eastward over time. There will also be an enhanced threat for beach erosion, especially if the storm slows down as it nears the area. We will have a special update this weekend if conditions change, and direct impacts from Jose seem to be on the increase.

This afternoons ECMWF model showing Jose south of New England and heading towards the east

This afternoons ECMWF model showing Jose south of New England and heading towards the east

Invest 96L East of the Lesser Antilles 

A strong tropical wave with a healthy amount of spin is currently located about 1000 miles east of the Lesser Antilles, and has become much better organized over the past day and a half. This system was a par of a large eastern Atlantic monsoon trough, which split into two halves, with the right side of the trough organizing into TD14. During the day today, the system has been able to sustain moderate to heavy amounts of convection over its presumed center of circulation. Visible satellite imagery shows that this system may have a weak surface reflection, with banding beginning to show up on the southern periphery of the invest. However, we have not had a reliable scatterometer pass of this system that is able to show whether or not a system has a closed surface circulation. Regardless, the system is currently within a very favorable area of windshear which lies around the 5-10 knot range. Additionally, the system is over warm waters of 28-29C, and remains embedded within a very moist pouch that surrounds the system. The environment looks very favorable for continued development of this system over the next day or so, and I would not be surprised to see the system become a tropical depression or storm as early as Saturday evening.

Invest 96L this afternoon showing the system gradually becoming better organized

Invest 96L this afternoon showing the system gradually becoming better organized

Over the next few days 96L should continue heading west/west northwest towards the Lesser Antilles, possibly reaching the islands as soon as Tuesday. With favorable environmental conditions, it appears likely that the system will at least be a mid-grade tropical storm at that point, with some of the other model guidance showing a hurricane nearing the islands. Due to the fact that we do not even know whether or not the system has a closed circulation, it is very heard to gauge exactly how strong this will be once it nears the islands, but the Islands should very closely monitor the progress of this system over the next five days, especially the island of Antigua, which is currently housing the population of Barbuda, which was completely destroyed by Irma when it was a 185 mph hurricane. The track of this system beyond the islands will be heavily reliant on the future of Jose, so make sure to check back over the next few days when these details become clearer.

This afternoons GFS model showing 96L becoming a strong tropical storm/hurricane just before reaching the Lesser Antilles

This afternoons GFS model showing 96L becoming a strong tropical storm/hurricane just before reaching the Lesser Antilles

Tropical Depression 14-No Threat To Land

TD14 formed over the far eastern Atlantic from a strong tropical wave, and was designated by the NHC yesterday evening. The system seems to be experiencing some moderate amounts of mid level shear this afternoon, which has displaced the heaviest convection from the low level center. Despite this, the system will be over warm waters and within a moist environment over the next 72 hours, and is expected to become a tropical storm over the next few days as it gradually heads WNW. TD 14 is thousands of miles away from land, and most models show the storm eventually dissipating as it encounters very strong shear and dry air from an upper level trough over the central Atlantic. Depending on what 96L does over the next 48 hours, the next two names on the list of Lee and Maria.

We will have a full update on Monday!

Afternoon visible shot of Tropical Depression 14 over the far Eastern Atlantic

Afternoon visible shot of Tropical Depression 14 over the far Eastern Atlantic

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Have a great weekend!

Steve Copertino

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Premium Long Range: Cooler, Active Pattern Next Week…More Changes Late Month?

Good morning! More summer-like weather with more heat and humidity will continue for the rest of the week,with some scattered showers and thunderstorms possible each afternoon or evening. But it appears the Western Hemispheric pattern will undergo another more significant changes to support some cooler weather again for next week.

First changes, will start occurring over North Pacific as usual this week. An upper-level low will be near the Aleutian Islands or Southwest Alaska. This will cause a high-amplitude ridge to build over the West Coast by early next week. This will result in a larger trough digging and encompassing much of the Central and Eastern US over for next week.  Then cooler airmasses from Canada will be invading the CONUS, with temperatures well below over the much of the Northern and Central Plains and into parts of Great Lakes and Ohio Valley.

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Public Analysis: Potentially Active Week Ahead With Multiple Thunderstorm Threats

Good Evening! 

This morning we saw rather pleasant conditions set up over the area as an area of weak high pressure off the Mid Atlantic coast continues to back towards the east, which has been feeding in southerly/easterly winds from off the ocean. With relatively modest humidity and low level moisture, we saw partly cloudy skies with some more sustained periods of sunshine persist for locations well-removed from the coast. This partly cloudy environment, with a few more clear locations allowed high temperatures to rise into the low to middle 80’s across much of the area. Locations around Long Island and Connecticut saw slightly lower highs due to a more persistent southerly wind, bringing in more a maritime airmass.

For much of the afternoon this maritime airmass has kept a pretty stout lid on the atmosphere, not allowing any shower activity to develop, but as we can see from the loop below, the dew points (in green) have begun to rise quite a bit due to a weak surface warm front ahead of a mid level shortwave currently located over the Ohio Valley. This surface warm front has some very meager lift associated with it, and with the increased moisture advecting north, it seems likely that some showers and even a brief thunderstorms may develop this evening. Nothing too extreme is expected to develop outside of a locally heavy rain threat as the atmosphere remains in a minimally supportive environment for shower development.

After sunset, the complex located in the Ohio Valley that currently has numerous severe thunderstorm and tornado warnings will continue to move eastward in the aforementioned stable airmass. This will cause complex to weaken significantly, and there has already been a noticeable decrease in lightning activity noted on the regional mosaic. It appears that this afternoons model guidance has been rather poor with its overall performance in handling the shortwave responsible for generating these storms, but it appears that at the very least that an increase in clouds is expected for the Tuesday AM hours.

This afternoon/evenings latest high resolution visible satellite, regional radar mosaic, and surface observations showing some weak showers breaking out over New Jersey, with more showers and thunderstorms moving in from the Ohio Valley (Courtesy of Simuawips.com)

Tuesday Into Tuesday Evening

Tuesday morning looks to start off with partly sunny skies, with some heavier areas of cloudiness likely near the coast as moisture continues to increase in the mid to lower levels in the atmosphere through the early morning hours. This moisture will be coming in from the south and west as another shortwave trough and its associated mid level energy quickly moved east during the late morning hours and into the early afternoon. Earlier model guidance had this initial shortwave arriving later in the day on Tuesday, but as I mentioned earlier, these shortwave disturbances in the general flow over the country have not been modeled well, with all the disturbances actually progressing much quicker than originally thought.

So what does this mean for tomorrow? Well, with the first disturbance likely coming through around 11am-2pm, this will mean the area has much less time than originally thought to destabilize through daytime heating. Additionally, it will mean that any shower and thunderstorms that do form will also be able to use up any marginal parameter space that may be present by that time. After this initial passage of showers and thunderstorms, it will be crucial to see whether or not we can lose any left over cloud cover. With winds out of the south/southwest, conditions could be favorable for instability to once again rebound over the area, but this will be very highly dependent on how the initial morning shortwave behaves.

If the area does indeed destabilize to what the NAM and other computer model guidance shows, then forecast soundings from across NJ/NY/CT suggest that showers and thunderstorms could develop off to our west and then begin to gradually move east during the mid to late afternoon hours. As these storms move into a potentially more unstable airmass with modest levels of unidirectional shear, they could grow into mutil-cell clusters, as well as pulse-type cells. The main threat with these storms will be locally damaging winds, very heavy downpours, and even some small hail in the more intense updrafts. While not explicity likely, there may be just enough low-level turning in the atmosphere to support some more robust mesocyclones, but high cloud bases may preclude any outright tornado threat tomorrow. We will likely have to revisit this threat tomorrow morning and afternoon just to get a sense of what the overall threat will be after the initial shortwave passage.

This afternoons NAM model showing the area destabilizing quite nicely after an initial round of showers and storms moving through the area. The situation will have to be monitored closely tomorrow afternoon to gauge the overall threat

This afternoons NAM model showing the area destabilizing quite nicely after an initial round of showers and storms moving through the area. The situation will have to be monitored closely tomorrow afternoon to gauge the overall threat

Wednesday and Beyond

After a calmer and more seasonable day Wednesday, another disturbance approaches the region on Thursday with a surface low tracking north into Western New York State. While it is too early to discuss individual parameters, especially given the degree of uncertainty surrounding convective evolutions prior to the disturbances approach, it appears probable that another threat for strong to severe thunderstorms will evolve during the afternoon and evening hours throughout the Northeast.

Notable height falls are present on most models and ensembles during the afternoon and evening hours, with marginally favorable instability parameters (again including a modified elevated mixed layer and favorable surface instability. Future forecast shifts will have to monitor trends among ensembles and models to attempt to identify local threat regions.

The European model showing another shortwave trough setting up in the Great Lakes region, with multiple disturbances embedded in a west to east flow. This would make it possible for at least a few storm chances later in the week

The European model showing another shortwave trough setting up in the Great Lakes region, with multiple disturbances embedded in a west to east flow. This would make it possible for at least a few storm chances later in the 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 evening!

Steve Copertino