Steven Copertino

Public Analysis: Potentially Active Week Ahead With Multiple Thunderstorm Threats

/by

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

John Homenuk

Multiple strong to severe storm opportunities this week

/by

Happy Monday Morning to you all! We’re back in action after a weekend of lovely weather, and the day will start off quite pleasant throughout the majority of the Northeast today as well. Regional observations throughout the entire region showed dry and pleasant air in place, with dew points largely in the 50’s, especially in the higher elevations of the interior Northeast where they are even lower. After a pleasant and relatively crisp morning (we use that term loosely given the lack of a humid airmass), some changes are likely to unfold today.

Read more

Miguel Pierre

Premium Weekly Outlook: More active, progressive pattern this week

/1 Comment/by

Good morning and happy Monday! Overall it was a beautiful weekend, especially as lower humidity settled into the region on Sunday. But a more active, progressive weather pattern is expected this week. This comes as a strong heat ridge begins building over the Rockies and Western Plains this week and the AO/NAO remains positive with lack of high-latitude blocking. This pattern will allow some ridging to build into the region this week with heat and humidity building. Multiple disturbances are expected to move from the Great Lakes/Ohio Valley through the Northeast and Mid-Atlantic, with threats for showers and thunderstorms this week.

First off,  high pressure will be moving off the Mid-Atlantic coast, with a return southerly flow developing over the region today. Mostly sunny skies are expected this morning, then some clouds will be increasing and filtering the sunshine as a warm front approaches.  Humidity will begin increasing later this afternoon as dew points rise into 60s. More lift and instability ahead of warm front may lead to a few isolated showers or thunderstorms popping up over the region later this afternoon. Temperatures will rise into lower to middle 80s area wide. South-southwest winds today will allow for sea-breezes to keep coastal sections in the 70s much of this afternoon.

Read more

Steven Copertino

Public Analysis: Heavy Rain Exits, Calm Weather Sets In

/by

Good Evening! 

After a relatively calm few days, the area of low pressure that developed along the leftover stalled frontal boundary this morning sparked numerous showers and isolated thunderstorms that tracked over eastern Pennsylvania, New Jersey, New York, and portions of Connecticut. Deep tropical moisture ahead on the order of about 2.3″ of PWATs allowed for the overall complex to contain very intense rain rates, upwards of two inches per hours in some locations! To make matters worse, these storms were chugging along with a weak low level flow, so areas of heavy rain were rather slow and this allowed for some spots to experience flash flooding in areas of poor drainage. As the dynamics began to really ramp up as the low pressure intensified, some gusty winds began to be reported with a few embedded storms that tracked through northern New Jersey and into Long Island. There were some reports of small tree limbs being taken down with localized power outages, but due to the time of day, lack of greater instability, and weak mid level winds, these gusts luckily weren’t anything too serious.

As the low moved off the coast and began to intensify some more, the area of rain associated with the low began to accelerate, and this is what likely saved the area from seeing much higher rainfall totals that would have caused more widespread flooding. The rain gradually tapered off as the low pulled away and some more dry low level air worked its way in behind the system, which finally allowed for conditions to calm down. The cloudy, tropical air-mass gave way to mostly sunny skies, which allowed temperatures to rise into the upper 70’s and lower 80’s across the entire area, with light westerly winds. With daytime heating taking place, instability was able to build back to limited values, which promoted the development of some more showers and thunderstorms to our North and West this evening. These showers will gradually slide east/east southeast and likely diminish in intensity as the sun fades, and with it-the fuel they need to survive. The main threat with these storms will be some additional, brief heavy rain, but these storms will be moving at a decent pace, so the overall flood threat is low. Some patchy fog should develop this evening and into tomorrow morning as an inversion in the atmosphere traps the leftover humid airmass. With the inversion in place, lows should be quite mild with most of the area seeing temperatures in the mid 60’s to lower 70’s.

This afternoon/evenings latest regional radar mosaic, surface weather plots, and high resolution visible satellite imagery of the Northeast. showing the remnants of this mornings system exiting to the east.

Saturday looks to start off rather clear despite some areas of patchy fog, which should quickly burn off as the morning progresses. This should allow skies to become mostly sunny, with some spotty clouds as we head into late afternoon. To our north and west, a large mid level trough will be progressing east with a disorganized piece of energy. As the energy from this trough nears the area by the afternoon hours, the leftover tropical airmass and sunshine will allow instability to build to modest levels, with some decent wind shear allowing for the potential of muti-cell thunderstorms to develop over the area. With the upper level jet streak and greatest energy for storm development located to our north over New England, the main focus for storms looks to be over that region, but we expect scattered development at the most, with the main threat being gusty winds, small hail, and heavy rains.

Otherwise, the afternoon will likely be a hot and humid one as temperatures likely reach into the upper 80’s and even to lower 90’s across the region. The area should gradually dry out during the late afternoon hours and early evening hours as the cold front to our west begins to push through. As the front moves through tomorrow evening, the humidity should drop a bit as more stout westerly winds develop, so it should be quite pleasant with lows dropping down into the upper 50’s and lower 60’s.

Sunday will likely be a good deal quieter than the previous day as the cold front moves well to our east and the dry air to the west really begins to work its way into the area. A surface high to the south will begin to build, which will likely allow for mostly sunny skies and low dew points. The overall drier atmosphere will work to negate any threat for afternoon thunderstorms over the entire area. High temperature s on Sunday should be near-normal, with highs likely reaching into the lower 80’s across the entire area. Sunday evening should also continue the theme of being rather calm, with clear conditions and light winds expected, lows should be able to drop into the upper 50’s area-wide.

This evenings Rapid Precision Model showing the development of some afternoon thunderstorms tomorrow, followed by clearing conditions in time for the evening hours (Courtesy of WSI)

Extended Range

A strong heat ridge is expected over Western/Central parts of United States this weekend and into early next week. This will support a more longwave trough over much of the Great Lakes and Northeast with temperatures closer to normal overall. There are some timing differences on model guidance currently with individual disturbances embedded within the longwave trough could still produce some isolated-scattered convection over the region. But much of the time, just warm and dry  with some sunshine each day, as high pressure gradually builds in from the Ohio Valley.

Later in the week, we may have another infusion of deep tropical moisture into the area, with increasing temperatures. Whether or not we see another period of heavy rain will be highly dependent on if we have a trigger mechanism to set off any showers and thunderstorms. At this time, the chance for anything outside of afternoon thunderstorms seems low, and a general increase in both temperatures and humidity seems likely at the very least. We will continue to monitor this period in case anything does try to take shape.

This afternoons ECMWF model showing near-zonal flow across the country, with the main weather features located in the central regions of Canada. (Courtesy of Accuweather Pro)

This afternoons ECMWF model showing near-zonal flow across the country, with the main weather features located in the central regions of Canada. (Courtesy of Accuweather Pro)

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