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Steven Copertino

Heavy Rain Threat Friday, Monday’s Eclipse Conditions Coming Into View!

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Good Evening! 

Today was another warm and relatively clear day across the entire northeast, but we did see higher dew points begin to creep in which allowed for a “muggier” feel to the day during the peak of the afternoon. With a northwesterly flow in place in the mid levels of the atmosphere, more dry air from Canada allowed for mostly sunny conditions across the region, with come occasional cumulus clouds rising up and eventually collapsing due to any kind of support. As the day progressed, an area of  surface high pressure off to our north and west also helped to keep conditions relatively calm, with light northwesterly winds lasting the entirety of the afternoon. With light winds, dry mid levels, and predominately sunny skies, temperatures were able to gradually rise into the mid to upper 80’s across the area, with cooler temperatures located over portions of interior Connecticut and New York.

Conditions remain quite pleasant this evening as much of the metro area is sandwiched in between two stalled fronts, with the northern front holding back cooler temps and lower dew points, and the southern front holding back oppressive dew points and warmer temperatures. Regardless, as the sun begins to set, the area should be able to cool down quite a bit thanks to a hefty amount of radiational cooling likely to take place due to the aforementioned high pressure, light winds, dry mid levels, and clear skies. This should allow low temperatures to bottom out into the upper 50’s to lower 60’s-with some of the more interior locations possibly dropping into the lower 50’s by early tomorrow morning.

This evenings latest high resolution visible satellite imagery from the GOES 16 satellite, regional radar mosaic, surface observations, and frontal positions from the Weather Prediction Center (courtesy of Simuawips)

This evenings latest high resolution visible satellite imagery from the GOES 16 satellite, regional radar mosaic, surface observations, and frontal positions from the Weather Prediction Center (courtesy of Simuawips)

Thursday and Friday 

Tomorrow morning should start off much like how today did, with relatively clear skies and cool temperatures to begin with. The main difference will be that the area of high pressure will begin to retreat and move off the coast, which will lead to more winds coming from the Atlantic, which will lead to increasing dew points as temperatures begin to rise. While we will have prevalent onshore winds to deal with during the day, a mid level ridge axis will be moving over the area, which should allow temperatures to rise into the low to middle 80’s area-wide-with some cooler conditions possible along the immediate coasts. As the mid level ridge pushes up and over our area early tomorrow afternoon, a shortwave trough will be moving over the Great Lakes region, which will drape a warm front over portions of Pennsylvania and the Mid Atlantic states.

As this front continues to advance east, it will bring an increasing chance of showers and possibly a few thunderstorms over the Northeast. Conditions will likely stay more tame back towards the metro area as the onshore flow keeps the atmosphere relatively stable, so only a gradual increase in mid to high level clouds is expected through the mid to late afternoon hours. Later in the evening, the threat of showers and an isolated thunderstorm will be increasing as the front draws closer and moisture convergence gradually increases. Expect lows to be much more mild Thursday night due to increased cloud cover and the threat for showers-with temps likely staying in the upper 60’s to lower 70’s.

Friday looks to be the most unsettled day in the forecast period as the area of low pressure associated with the large trough over the Great Lakes continues to move to the north and east. This will allow for the warm front to completely overspread the region by early Friday morning, likely bringing a period of locally heavy rainfall with it as it marches north and east. At this time it appears that the heaviest rain may fall over portions of New Jersey, Pennsylvania, C/S New York, and Connecticut, but this could easily change if thunderstorm development becomes more prominent during the morning hours further to the south of the NYC area. Otherwise, Friday will likely feature at least a moderate chance of showers and an isolated thunderstorm up until the later portion of the afternoon, when a renewed threat for heavy showers and thunderstorms may redevelop over Pennsylvania and warm air advection surges north over the Northeast. It seems that the overall severe threat on Friday will be quite low due to the increased cloud cover, but if some patches of sun do develop, then stronger destabilization of the atmosphere may take place, which could lead to more widespread/strong storm development. The primary threat will be heavy rains on Friday, which should last into the evenings hours and possibly even into the early morning on Saturday. Overall, confidence in flash flooding is low at this time, but with deep tropical moisture nearby and forcing from the warm front present, it would not take that much to chance for heavy showers and storms to develop and drop torrential rainfall within a short period of time. Details will likely need to be fine-tuned over the next 48 hours, so be sure to check back for the latest.

This afternoons European model, showing very high precipitable water values surging in behind a warm front progged to move through the area Friday AM with a chance at some locally torrential rainfall.

This afternoons European model, showing very high precipitable water values surging in behind a warm front progged to move through the area Friday AM with a chance at some locally torrential rainfall.

Saturday and Beyond 

Most of the area should still be within the residual warm sector on Saturday morning, but with the best jet dynamics and lift displaced off to the west, the threat for heavy rain will begin to gradually fall. The shortwave trough should continue to move east during the day, with conditions likely improving as the day goes on. Highs will likely be able to reach into the low to middle 80’s ahead of a cold front tracking east from the Ohio Valley. This front should usher in much drier air and bring in some cooler temperatures as well, as it mixes out the atmosphere.

Sunday will likely be much-improved from the previous two days as high pressure begins to build over the area. This should allow for clear skies, light winds, and generally pleasant conditions across the region, with highs likely reaching into the low to middle 80’s across the area-which is right around normal for this time of year. Conditions will be ripe for radiational cooling on Sunday evening, so expect low temperatures to drop down into the lower 60’s with relatively low dewpoints.

Monday will be the day that will have the most focus on the weather, not for any severe weather or tropical cyclones, but for the partial solar eclipse that will take place during the afternoon hours. While we are not in the path of totality, most of the area will still be able to experience a rather cool and rare occurrence. However, the big question right now looks to be if there will be any cloud cover. As of right now, the conditions look to be quite favorable for safely viewing the partial eclipse, with mid level ridging overhead and surface high pressure just offshore-providing light onshore winds over much of the metro. This is however five days away, and predicting cloud cover for a three-hour window is rather difficult, but we can say that signs are encouraging at this time for a pleasant viewing experience! Be sure to check back over the next few days for updates!

The European 51 member ensembles showing cloud cover percentage. Monday the 21st is highlighted, with little cloud cover expected from a vast majority of the ensembles! (Courtesy of WxBell)

The European 51 member ensembles showing cloud cover percentage. Monday the 21st is highlighted, with little cloud cover expected from a vast majority of the ensembles! (Courtesy of WxBell)

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Have a great evening!

Steve Copertino

Steven Copertino

PM Rain Exits, Storms and Cooler Weather Possible This Weekend!

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Good Evening!

After a relatively hot and humid day across the entire Northeast and Mid Atlantic regions, we have seen large-scale thunderstorm development courtesy of the mid level shortwave that we discussed back on Monday. This shortwave was located to the west of the area, and with CAPE values of around 2000-3000 j/kg^2, PWATS near 1.5″, and strong low level lapse rates, the weak amount of energy associated with the disturbance was more than enough to set off numerous showers and thunderstorms around 2pm. Due to a significant lack of vertical wind shear, these storms were not able to move all that much from where the initial updrafts formed, and thus most cells rained themselves out over time. However, when these updrafts collapsed and the rain cooled air rapidly sunk to the surface, it created new boundaries which served to provide breeding grounds for renewed storm development. In some locations we saw this happen three to even four times over, which caused serious street flooding.

In addition to the street flooding, cool/dry air aloft allowed for some of the more robust thunderstorms to develop marginal to severe hail stones, with some reports of stones reaching the 1.75″ mark! Some folks may have noticed that these storms were also producing a cooler rain than one would expect during August, and this also can be attributed to the cooler air aloft. These drops were whats know as “Big Drops” (I know, very creative) and form when an updraft just isn’t able to keep ice suspended long enough to freeze sufficiently to reach the ground as hail. However, a few thousand feet up in the atmosphere, these drops were frozen, and when they crashed into one another, they create a negatively charged particle in the atmosphere, called an electron. When enough of these electrons build up in an updraft, they connect with positively charged particles (protons) at the surface, the path they take to get to one another creates lightning! With a ton of ice in the atmosphere from numerous updrafts this afternoon, there was a very impressive amount of lightning that went up across the area. Some of this lightning even caused damage to houses and property, with some areas losing power. Otherwise, today’s storms mainly posed a very heavy rain, lightning, and gusty wind threat.

As of six o’clock this evening, most of the showers and thunderstorms that formed early this afternoon were finally beginning to wind down. Lightning activity over the area has greatly weakened over the past hour or so, and this also points towards a gradual dissipation of the rest of the thunderstorm activity. As this time, we think that the heaviest showers and thunderstorms should dissipate by sundown, with only a few lonely cells remaining thereafter. Some residual cloud cover is likely as we head into the overnight hours, and this will help to keep overnight lows rather mild, with temperatures dropping to around the low to middle 60’s.

This evenings latest regional radar. high resolution visible satellite, surface observations. and severe warnings, showing the bulk of the heavy rain dying off. This trend should continue as we head deeper into the evening (Courtesy of Simuawips)

This evenings latest regional radar. high resolution visible satellite, surface observations. and severe warnings, showing the bulk of the heavy rain dying off. This trend should continue as we head deeper into the evening (Courtesy of Simuawips)

Thursday and Beyond

Thursday should start off just as the past few days have, with any low clouds quickly burning off by the mid to late afternoon hours. This will allow afternoon temperatures to climb significantly during the afternoon hours, with highs likely reaching the middle 80’s to lower 90’s across the area. With a moist airmass in place tomorrow, we should see the region destabilize once again by the mid to late afternoon hours, similar to as we saw today. The main difference will be that tomorrow does not look to have a coherent area of forcing to initiate thunderstorm development, so any thunderstorms tomorrow afternoon will likely have to rely on convergent boundaries from local sea breezes. This activity will likely be limited to a heavy rain and lightning threat given the lack of favorable parameters for anything outside of heavy thunderstorms. Storms should gradually fade tomorrow evening, leaving generally mild and humid conditions in their wake.

As we head into the first half of the weekend, a large shortwave trough diving out of Canada will provide a threat of heavy rain and possibly some thunderstorms over the area as moisture begins to surge north from the Gulf States. This system will be watched closely, as it does have a very favorable upper level jet streak which could potentially enhance a heavy rainfall threat over our area. A strong cold front looks to push through late Saturday and into Sunday, which should bring not only cooler temperatures to our area, but also much lower humidity compared to what we’ve been seeing-which should make for an enjoyable end to the weekend!

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Steve Copertino & Doug Simonian 

 

Steven Copertino

Public Analysis: Oppressive Heat and Humidity, Strong Thunderstorm Threat Thursday and Friday

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Good Evening! 

As we stated earlier this week, conditions were once again going to become unstable as a deep tropical airmass works its way over the region over the next few days. This was quite noticeable today as dew points rose into the uncomfortable (66-70) and oppressive (71-75) degree ranges! Coupled with highs in the mid to upper 80’s, heat indices were able to climb into the middle 90’s in some locations, promoting the issuance of a Heat Advisory for counties in Pennsylvania, New Jersey, and New York-for now. A Heat Advisory is issued when the combination of heat and humidity is expected to make it feel like it is 95 to 99 degrees for two or more consecutive days, or 100 to 104 degrees for any length of time.-NWS 

With this increased instability and plentiful moisture trapped in the atmosphere, all we needed today was a little daytime heating to really destabilize the atmosphere. The first in a series of quick-moving shortwaves in a general west to east flow was today’s trigger mechanism that set off numerous strong to severe thunderstorms over portions of southern New England, and even portions of Connecticut. These storms were mainly very heavy rain producers as the atmosphere did not have enough energy in place to keep the significant amount of moisture lofted within the low to mid levels of the atmosphere. As the updrafts that held all of this moisture began to collapse, they created very high rain rates, with some nearing close to 2″/hr! As the more robust updrafts quickly collapsed  and the rain cooled air rushed to the ground, this created localized instances of wet microbursts, which were the cause of some tree damage in Connecticut.

As the forcing mechanism for this afternoon convective outbreak begins to quickly move off to our east, showers and thunderstorms should gradually sink further south and east with time. As they do so, they will also encounter a slightly less favorable environment needed to sustain themselves, however it would not be out of the realm of possibilities that a few more short-lived cells go up near sunset, capable of small hail, heavy downpours, and occasional lightning.

The rest of the evening will likely remain quite muggy, as the tropical-like airmass remains locked in place due to rather stout low level winds from the west/southwest. Lows this evening will be lucky to get down into the lower 70’s, so expect a rather muggy night ahead with a slight chance of some showers in the very early morning hours.

This evenings latest regional radar mosaic, regional surface observations, and high resolution visible satellite imagery, showing left-over showers and thunderstorms over the area gradually moving to the east/southeast (Courtesy of Simuawips.com)

This evenings latest regional radar mosaic, regional surface observations, and high resolution visible satellite imagery, showing left-over showers and thunderstorms over the area gradually moving to the east/southeast (Courtesy of Simuawips.com)

Thursday Into Friday 

Thursday is likely to start off with a few broken or scattered clouds, with some “hazy” conditions likely as well. As the daytime heating gets off to a rather quick start tomorrow morning, temperatures will quickly shoot into the upper 80’s to lower 90’s once again, and when factoring in the very high dewpoints, conditions will become quite miserable in some locations. Heat indices may swell into the upper 90’s and even into the lower 100’s during the peak heating hours of the afternoon! As another in a series of mid level disturbances rushes over from the Great Lakes region, mid level shear ahead of this wave will begin to increase in earnest, creating a conducive initial environment for afternoon thunderstorms to fire in over the area.

While the initial setup of parameters over the area will be primed and ready for thunderstorm development by the afternoon, the main question is regarding the timing and location of the mid level disturbance that would be able to trigger thunderstorm development. What may wind up happening is that the initial thunderstorms may fire over portions of southern New England (like they have many times this year before) and then begin to sag southward along a frontal boundary to our north. The problem with this is that by the time that the showers and thunderstorms begin to propagate to the south, the best parameters over our area will begin to fade. This would mean that as any storms move south, they would gradually weaken with time, which would mitigate the overall severe threat. Regardless, the setup tomorrow looks to support at least torrential downpours, frequent lightning, gusty winds-with the potential for more damaging wind gusts and hail in the strongest cells.

This afternoons RPM model showing the progression of the frontal boundary tomorrow morning and through the afternoon hours (Courtesy of WSI)

On Friday, a broad area of low pressure will begin to stretch over into our area, likely starting the day off with rather thick cloud cover and cooler temperatures. Though the model diverge on this quite significantly, there does appear to be a rather good chance that a frontal boundary will be stalled somewhere along the Metro area, or just to our north-which will dictate much of Friday’s weather. This stalled frontal boundary will act as a near-perfect source for lift, as deep low-level flow ushers in PWATS of around 2.25″-2.5″. Additionally, CAPE will also become quite plentiful due to this tropical airmass, and this instability will be met with increasing low to mid-level shear from the stalled frontal boundary. Due to the amount of dynamics riding on this frontal boundary, even a small deviation would be able to turn a potential severe weather event into a heavy rain/flooding threat with very little notice-or vice versa.

The first threat of thunderstorm development will likely be in the early afternoon hours, with the second, and more impactful taking place towards the late afternoon/early evening hours. Regardless, all modes of severe weather will be possible on Friday, with damaging wind gusts, large hail, and even an isolated tornado being quite possible. Very heavy rain will also be a large concern as the atmosphere will be “water logged”-for the lack of a better term. Both time frames will likely need adjusting over the next 36 hours or so, so make to stay up to date with our daily updates.

This afternoons European model, showing very high precipitable water vales (PWATS), modest mid level winds, and an approaching mid level trough to help kick off a two-pronged event on Friday with severe weather and localized flooding possible.

This afternoons European model, showing very high precipitable water vales (PWATS), modest mid level winds, and an approaching mid level trough to help kick off a two-pronged event on Friday with severe weather and localized flooding possible.

This Weekend and Beyond

Improving conditions are looking likely heading into the weekend, with some clouds or showers may linger into Saturday morning as shortwave trough and frontal boundary exits the region. Otherwise high pressure from Ohio Valley builds into region with a drier northwesterly flow, for rest of the weekend. It will be more pleasant, with lower humidity, more sunshine and high temperatures in the lower to middle 80s. Latest GFS and ECMWF models are keeping the next chance of more scattered showers and thunderstorms with cold front and upper-level trough coming from Great Lakes, away until Monday or Tuesday. Temperatures will likely be at seasonable levels through early next week.

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Have a great evening!

Steve Copertino & John Homenuk

Steven Copertino

Public Analysis: Stormy Start to the Holiday Weekend, Possible Break for the Fourth of July?

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Good Evening! 

As was mentioned all the way back on Monday, today has featured quite an extensive development of showers and thunderstorms over much of the Northeast. These storms were fueled mainly by the built up heat and humidity which created modest levels of instability to build during the afternoon hours today. Additionally, the storms were aided by strong vertical wind shear in the atmosphere, which helped some storms to produce damaging wind gusts, and even some rotation which prompted at least three tornado warnings. Radar images also indicate that there is a rather high amount of moisture in these showers and thunderstorms, which can be attributed to the impressive resurgence of tropical moisture over the area that occurred yesterday when the high pressure that was over our area on Tuesday began to back away to our east, causing winds to surge from the south. As opposed to most days this year that featured decent convective development, these storms were generated by a strong mid level short wave at around 700mb, in contrast to the traditional cold front.

While the vast majority of any actual severe weather was confined to areas well north and west of our area, some locations in southern New York and portions of Connecticut did see some wind damage, frequent lightning, and very heavy rainfall. As the evening rolls on and the sun gradually fades away, the heat and instability that we had will begin to drop off quite significantly, and any remaining strong storms will weaken below severe limits, while heading generally eastward. Some storms in southern Connecticut may still be capable of producing damaging winds as they feed off residual instability and favorable parameter space that had not been touched by previous cells.

The rest of the evening should feature improving conditions, with partly cloudy skies likely for most of the area. Due to the lack of a coherent frontal system, the humid airmass that spawned these storms will linger around and make for another muggy night, with lows likely staying in the lower 70’s and into the middle 60’s.

Animated loop of the evenings latest regional radar mosaic, regional surface observations, and high resolution visible satellite imagery (Courtesy of College of DuPage)

Saturday should start off quite nice, with a mix of sunshine and scattered clouds to start off the day. Although, with warm mid level temperatures, winds from the south, and a humid airmass in place, the conditions will be ripe for temperatures to quickly rise into the upper 80’s and even pass the 90 degree mark in locations like NE NJ and SNY. As we go through the late morning and early afternoon hours, a shortwave trough and associated cold front will be working its way east towards the area. This will set the stage once again for instability to begin to pool up ahead of the frontal system, which will act as a forcing mechanism for thunderstorm development later into the afternoon. Like today’s threat, the best wind shear and parameters are likely to stay to the North and West of the immediate New York City area, but more isolated strong storms will be possible towards the area as the day progresses on. The main threats tomorrow appear to be gusty winds, frequent lightning, and very heavy rainfall. Due to this risk, the Storm Prediction Center in Norman, Oklahoma has placed locations to our north and west in a Slight Risk for severe thunderstorms.

Showers and storms may continue to longer through the late afternoon and evenings hours as the lift associated with the cold front will trigger additional shower and possible thunderstorm development if there is any left over instability to work with. The main threat from these storms later in the day appear to be confined to gusty winds and heavy rain. Lows tomorrow evening will remain quite warm, with upper 60’s and lower 70’s likely.

This evenings latest Rapid Precision Model, showing scattered showers and thunderstorms developing mainly to the north and west of the city tomorrow afternoon/evening (Courtesy to WSI)

This evenings latest Rapid Precision Model, showing scattered showers and thunderstorms developing mainly to the north and west of the city tomorrow afternoon/evening (Courtesy to WSI)

Sunday should feature a less humid start to the day as the cold front moves through during the early morning hours and mixes out the tropical airmass that has been lingering over the past few days. As dry air behind the front moves on in, mostly sunny conditions are likely to hold up for the rest of the day on Sunday. With mostly sunny skies and a much less humid airmass over the region, high temperatures will gradually build up towards the upper 80’s-with some locations possibly reaching that 90 degree mark once again!

Monday will likely features much of the same conditions as Sunday, with low humidity, clear skies, and an overall low threat for afternoon storms. Highs should also be quite similar, with temperatures likely peaking around the middle to upper 80’s. Overall, both days will be very pleasant and a great lead up to Independence Day.

Tuesday (Fourth of July) – the day that everyone has been wondering about for over a week now actually looks to have quite an excellent setup in place during the day! A stationary front-the remnants of the cold front that passed on Sunday-will be located to our south, which will leave a large area of high pressure in control for the day, providing light winds, low humidity, and clear skies! Highs should continue their warm, but not outrageously hot trend, with temperatures likely reaching the middle 80’s over much of the area! In summary, it should be an excellent outdoors day, with near perfect conditions for firework-viewing, with only high cirrus clouds likely during the day!

We hope everyone has an excellent Holiday Weekend!

A quick summary of the conditions for the Fourth of July-orange colors denote areas of higher than normal pressure

A quick summary of the conditions for the Fourth of July-orange colors denote areas of higher than normal pressure

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Have a great evening!

Steve Copertino