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Steven Copertino

Saturday’s Rain Threat Gives Way To More Variable Conditions Next Week

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Good evening! 

Today started off rather pleasant with clear skies, light winds, and rather moderate temperatures. However, as the broad area of high pressure that remained in control for the past few days began to gradually shift offshore and into the west Atlantic, a broad mid level trough began to edge into the Northeast this afternoon. As this trough gradually progressed east, the airmass change could be felt as dewpoints rose into the middle to upper 60’s across the area, which made for a much more “muggy” feel to the afternoon than the past couple of days. On the lee side of this disturbance, mid levels winds are coming from the southwest, which is acting to advect a good deal of moisture from the south. This moisture has continued to overspread the Northeast this afternoon as a weak warm front moved from north to south across the metro area. With some weak ascent and forcing associated with the front, some showers and thunderstorms have popped up over portions of the Mid Atlantic and portions of Pennsylvania, where severe parameters are supportive of locally severe weather. In fact, an isolated supercell has developed over northern Virginia this past hour, and may eventually reach the DC metro area.

Closer to the NYC metro, the atmosphere remains much more stable than our surroundings (as has been the case this entire year so far). Instead of thunderstorms developing this afternoon, we’ve seen widespread cloudiness take over. Some residual showers from dissipating thunderstorms over Pennsylvania are currently making their way into western New Jersey, but no hazardous weather is expected as any showers/thunderstorms encounter the stable airmass overhead.

As the evening marches on, more leftover showers may entire from the west and bring some brief heavy downpours and occasional lightning, but generally cloudy conditions are likely for the remainder of the night. The combination of the higher dewpoints, southerly winds behind the warm front, and cloudy conditions will almost ensure that raditional cooling will be non-existent this evening. Lows should unanimously mild, reaching the middle 60’s to lower 70’s across the region.

This evenings latest high resolution GOES-16 visible satellite imagery, regional radar mosaic, surface observations, and frontal postilions-showing showers and thunderstorms mainly concentrated to the west of the area this evening (Courtesy of Simuawips)

This evenings latest high resolution GOES-16 visible satellite imagery, regional radar mosaic, surface observations, and frontal postilions-showing showers and thunderstorms mainly concentrated to the west of the area this evening (Courtesy of Simuawips)

Saturday Into Saturday 

Tomorrow morning will likely start off quite unsettled as the mid level warm front to our south and west begins to move over the area with deep tropical moisture entrenched within. Precipitable water values will also increase markedly, into the 1.5-2″ range, so any showers and thunderstorms that develop early Saturday morning have the potential to produce very heavy rainfall in a short period of time. Though, with weak mid level lapse rates, any updrafts that do go up tomorrow morning will be extremely short-lived, and will likely form and die over the same location. Later in the morning, the warm front should lift through the region, possibly clearing out any residual showers and weak thunderstorms out of the area, and allowing for a brief period of sun poking through the clouds. Depending on how much sun the area sees late tomorrow morning and early afternoon will determine just how much the area can destabilize, which will have implications on the rest of the day. Model guidance suggests that the western portion of the New York metro area does in fact clear out enough during the afternoon hours that instability on the order of around 1000-1500j/kg^2 develops. By this time, it appears likely that a mid level trough will begin to nose into the Northeast, with a favorable upper level jet streak also making an appearance.

The combination of these factors could possibly lead to the development of some scattered showers and thunderstorms-some of which may be strong to severe. As of this evening, it appears locations west of NYC will have the best potential to see any robust thunderstorms, with the main threats being gusty winds, sub-severe hail, frequent lightning, and very heavy rains. This activity will be highly dependent on the timing of the best forcing arriving from the west, as well as just how much we can clear up and destabilize tomorrow after the initial batch of rain in the morning. Overall, widespread severe thunderstorm development does not appear likely tomorrow.

As we head into the evening, any residual showers and thunderstorms should gradually head east and weaken as the frontal system associated with the mid level trough begins to push over and out of the area. Behind the front we should have a less humid airmass, but with the risk of cloud cover, temperatures are not that likely to fall all that much-with lows generally in the low to middle 60’s.

Sunday looks to be a huge improvement over today and Saturday, as the shortwave trough that moves through on Saturday heads to our east and begins to usher in a cold front. This cold front not only looks to clear out any substantial cloudiness that may linger over the area, but should also be quite efficient at greatly reducing dewpoints from the 70’s, to lower 60’s over the entire area. With sunny skies, light winds, and low humidity, Sunday will be near-perfect for any outdoor activities , though there may be a risk of rip-current’s along the coasts, so please make sure to monitor beach conditions if you are planning a beach day. Highs will likely be comfortable-with temperatures reaching into the upper 70’s to lower 80’s, and lows getting down to the low to middle 60’s.

This evenings RPM model showing the progression/development of showers and thunderstorms later this evening and into tomorrow afternoon, followed by an eventual clearing on Sunday (Courtesy of WSI)

This evenings RPM model showing the progression/development of showers and thunderstorms later this evening and into tomorrow afternoon, followed by an eventual clearing on Sunday (Courtesy of WSI)

Monday and Beyond 

Previous model guidance runs had Monday being the next potential period for heavy rain, but have since backed off this idea quite a bit. This is due in part to the models incorrectly handling a weak tropical system that has been tormenting forecasters for the better part of the last nine days or so. This low was originally forecast to interact with a stalled frontal boundary located to the south of the region on Monday, which would in turn spawn another wave of low pressure. The tropical low pressure system has once again failed to develop, and this had lead to some significant changes in the model guidance for next week. It now appears that the same frontal boundary will not be able to push as far north as previously thought, mainly due to a lack of a surge in precipitable water values/moisture associated with the tropical system. So in short, this means that any precipitation on Monday will likely be much more spotty in nature than previously thought, with very meager amounts of instability and lift to work with over our area. At this time, we would not be surprised at all if this rain threat continued to deteriorate over time and does not amount to much of anything north of the Mason-Dixon line.

Otherwise, it appears that the northern stream will remain quite active for this time of year and could potentially lead another disturbance down our way by the middle of next week, with moisture surging ahead of this disturbance as we have seen many times before. However, at this time it seems that these rain threats will be transient in nature, with ridges likely building in behind-leading to a brief period of calm weather before the next rain chance.

This afternoons European ensembles, showing another unsettled period shaping up next week, with a trough over the central part of the US, and a ridge positioned over the south. This would lead to multiple disturbances rolling over the ridge, and into the Northeast.

This afternoons European ensembles, showing another unsettled period shaping up next week, with a trough over the central part of the US, and a ridge positioned over the south. This would lead to multiple disturbances rolling over the ridge, and into the Northeast.

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Have a great evening!

Steve Copertino

Steven Copertino

Unsettled Period Taking Shape With Multiple Rain Threats

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Good Evening! 

Today was a rather beautiful day across the entire Northeast, as a elongated area of high pressure centered off the New England coast remains in control. Dry air in the mid levels of the atmosphere associated with subtle mid level height rises over the Mid Atlantic allowed for a mostly clear start to the day across the area, which allowed temperatures to gradually rise into the low to mid 80’s. Today also features some refreshingly low dewpoints courtesy of the high pressure system, and when coupled with light and variable winds, conditions were near perfect for enjoying the outdoors. These conditions lasted throughout the entire afternoon hours and into the evenings hours, and should prevail after dark as well. A weak mid level system passing just to the north of Michigan may be able to create some upper level cirrus clouds to develop late this evening, but no shower activity is expected with this unimpressive system. As the evening progresses, this cirrus activity may actually wind up putting a cap on the potential for radiational cooling as all the other factors are quite favorable, however the increased cloud cover may limit just how much temperatures can fall. Regardless, overnight lows should be able to drop down into the upper 50’s to lower 60’s area-wide, with some inland locations possibly dropping to the lower 50’s.

This evenings latest high resolution 500m GOES 16 visible satellite imagery, regional radar mosaic, and surface observations, showing a very pleasant and calm evening across the entire Northeastern region. (Courtesy of Simuawips.com GOES-16 data is preliminary and non-operational)

This evenings latest high resolution 500m GOES 16 visible satellite imagery, regional radar mosaic, and surface observations, showing a very pleasant and calm evening across the entire Northeastern region. (Courtesy of Simuawips.com GOES-16 data is preliminary and non-operational)

Thursday Into Friday 

Thursday will likely start off with a few high clouds due to the aforementioned weak disturbance gradually moving off to our north. Although with the elongated area of high pressure moving off to our south and east, enough mid level dry air should remain in place so that as the morning hours progress, these high clouds will gradually dissipate, giving way to mostly sunny skies. Another positively tilted mid level trof out over the Great Lakes region will help to build an area of ridging overhead during the day tomorrow, which should advect warmer temperatures into the area once again. With winds out of the south over much of the area, clear skies, and warm mid level temps, expect high temperatures to once again reach into the low to middle 80’s by tomorrow afternoon. A weak wave of low pressure may try to pass to the south of our area tomorrow afternoon, which would potentially bend winds back to the southeast along coastal portions of NJ/LI/CT. This would allow some cooler air via a sea-breeze to work its way inland, but the degree to which this cooler air penetrates the coasts will be something that will need to be monitored tomorrow in real-time. Skies will remain mostly clear up until the evening hours before some thicker high level cirrus clouds begin to move into the area just in time for sunset. Depending on the degree of the southeasterly winds tomorrow, some localized patches of fog may be possible, though this should likely remain patchy in nature. Overnight lows will likely once again drop into the upper 50’s to lower 60’s-with some locations inland seeing slightly lower temperatures.

On Friday, we finally lose our support from the broad area of high pressure, and a large mid level trough from the Great Lakes region will begin to move in early Friday morning. As this trough approaches, the southwesterly flow will begin to advect a moist airmass with higher dew points into the area, which should also increase cloudiness quite a bit during the day. The entire region will likely see more clouds than sun during the day on Friday, and this will also put a cap on just how warm it will be able to get. With mid level temperature remaining rather steady during the day, there won’t be too much of difference, but highs will likely remain in the low to middle 80’s across the area. The increased dewpoints and clouds cover will also make Friday seem much more dreary than the previous two days as well. Any shower activity on Friday will likely remain to the west of the area, as the best mid level forcing and jet stream dynamics will be placed off to our north and west. Cloudy conditions should preside over the rest of the day, lasting into the evening hours as well. With cloudy conditions, warm mid level temps, and increased humidity, temperatures will likely only be able to fall a few degrees, with lows likely reaching into the low to middle 60’s Friday evening.

This evenings NAM model showing the progression of a mid level trough that has the potential to brings some rain to portions of the Northeast Friday and into the weekend (Courtesy of College of DuPage)

This evenings NAM model showing the progression of a mid level trough that has the potential to brings some rain to portions of the Northeast Friday and into the weekend (Courtesy of College of DuPage)

This Weekend and Beyond 

Cloudy conditions should continue to dominate the area on Saturday as a frontal system associated with the mid level trough continues to march eastward and over our area. As this system heads east, better forcing and upper level dynamics will also begin to move over the area on Saturday, so showers and possibly a thunderstorm appear likely during the day. With increasing moisture and a strengthening upper level jet streak providing divergence over the area, some of these showers and isolated thunderstorms may have the potential to produce some locally heavy downpours, but a lack of instability and weak vertical wind shear should mitigate any severe threat during the day on Saturday. Highs during the day on Saturday should once again be limited to the low to middle 80’s due to the threat of showers and enhanced cloud cover over the area. The frontal system will then approach the area late Saturday afternoon and into the evening, but any additional shower activity associated with this frontal system will be highly dependent of the overall strength of the remaining forcing with this wave. At this time, it appears that forcing should not be overly impressive and the jet dynamics may be disjointed just enough to keep the bulk of the heavier showers and potential storms to the north and west of the NYC metro area Saturday evening.

Conditions may briefly clear up on Sunday, but this should be rather short lived as another area of low pressure associated with a mid level trof begins to move out of the central US. The next threat for widespread rainfall appears to be on Monday when a wave of low pressure along a frontal boundary begins to push just to our south. Current model guidance has a very expansive and favorable upper level jetstreak overhead, with deep tropical moisture feeding in from the south. Confidence in this scenario is very low at this time due to the models potentially putting too much emphasis on a tropical area of low pressure interaction with this front and enhancing rainfall. This will likely have to be revisited later in the week when details become more clear. Overall, expect an unsettled and potentially rainy start to work week next week, with temperatures around average for this time of year.

This afternoons European model showing the potential for unsettled conditions starting early next week over the area (Courtesy of Accuweather Pro)

This afternoons European model showing the potential for unsettled conditions starting early next week over the area (Courtesy of Accuweather Pro)

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Have a great evening!

Steve Copertino

Steven Copertino

Severe Weather Possible This Afternoon, Yet Another Unstable Pattern Next Week

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Good Afternoon! 

Despite some heavy showers and thunderstorms that moved through the immediate New York metro area this morning, most of the area was able to clear out quite significantly this afternoon. With high humidity in place and full sunshine, we saw the development of numerous cumulus clouds, especially to the north and west of the city. With instability rising gradually through the early afternoon hours, shear kicking in, and forcing from an approaching upper level trough all coming together, we have seen numerous showers and thunderstorms go up over portions of the Mid Atlantic and Northeast regions. Given rather unimpressive lapse rates, unidirectional shear vectors, and a general broad area of forcing, this activity has mainly been limited to multi-cellular and pulse-cell storms. These storms will mainly be capable of damaging winds and possibly a wet micro burst or two, as the weak mid level lapse rates will fail to sustain any significant updrafts over much of the region. As these updrafts collapse over time, they may do so rather quickly, leading to winds up to 60 mph and torrential downpours, which may cause localized flooding.

However, as we head deeper into western Pennsylvania and New York state, the vertical wind shear profile becomes a little more favorable for more organized convection, and we have seen some embedded supercell structures form within larger convective masses. These storms will have a much higher threat of damaging winds, large hail, and even a brief tornado or two. This stronger activity will likely remain exclusive to this region, as the severe parameters quickly become less supportive for anything too strong the further east you head.

Regardless, the rest of the afternoon should remain quite nice for a typical August day, with highs deep into the 80’s-possibly getting to that 90 degree mark in some locations. As we mentioned before, humidity will be increasing ahead of the front located off to our east, so it will feel quite muggy out, and any locations that saw some of the heaviest rains this morning will have the added moisture in the air from evapotranspiration.

As we head into the evening hours, we should see the development of more showers and thunderstorms over the Northeast, as the previous cells begin to collapse and leave convergent boundaries as to which new thunderstorms can form along. Winds from the south will continue to pump moisture/instability into the area, with CAPE values remaining in the 1200-2800j/kg^2 range until sunset. In addition to the instability in place, a very weak warm front will be passing through the region, and this may work to locally improve wind fields, but only to a small extent. At this time, it appears that the best chance for showers and thunderstorms this evening will be over portions of southern New York, eastern Pennsylvania, and possibly far northwest New Jersey. These showers and thunderstorms should mainly be capable of producing gusty winds and small hail, with heavy rain likely as well.

This afternoons latest regional radar mosaic, high resolution visible satellite imagery, surface observations, and severe warnings. Courtesy of Simuawips)

This afternoons latest regional radar mosaic, high resolution visible satellite imagery, surface observations, and severe warnings. Courtesy of Simuawips)

Saturday and Sunday 

Saturday may start off cloudy and with a few showers and an isolated thunderstorm in spots as the large upper level trough to our west finally begins to move through. This shower and thunderstorm activity should move rather quickly through the northern portions of the metro area, but brief heavy rain, gusty winds, and small hail may all be possible with any stronger areas of activity.

Afterwards, a cold front associated with the large upper level trough will finally move through the Northeast during the afternoon hours, and will likely clear any residual showers out. Behind this front will be some refreshing Canadian air that will also be packing much lower humidity with it as well, so there should be a noticeable change in airmasses by lunchtime tomorrow. With clearing skies, low humidity, and light westerly winds behind the front, highs should be able to get into the low to middle 80s tomorrow, which is right around normal for this time of year. Tomorrow evening will be a very pleasant one, as the skies begin to clear out and winds out of the north and west continue to usher in cooler air. Conditions will be in place for radiational cooling to take place over the entire Northeast, which is somewhat uncommon for this time of year. This will allow for lows to fall into the upper 50’s to low 60’s across our area-with some locations to the far north and west possibly seeing low 50’s tomorrow evening!

Sunday looks to be the “gem” in this forecast period as light winds, low humidity, and warm temperatures in the 80’s will dominate the day region-wide. Clouds may begin to increase later in the evening, but overall Sunday should be an excellent day for any outdoor activities!

CLICK TO ANIMATE This afternoons RPM model showing the evolution of this evenings storms, as well as the cold front passage tomorrow morning/afternoon (courtesy of WSI)

CLICK TO ANIMATE
This afternoons RPM model showing the evolution of this evenings storms, as well as the cold front passage tomorrow morning/afternoon (courtesy of WSI)

Next Week

Our eyes will once again shift to the west, as yet another northern stream disturbance begins to approach our area. As this system approaches, it will begin to dig up a serious amount of warm air and moisture from the south and west and direct it towards the Mid Atlantic and Northeastern states. As the mid to upper level system draws closer, a frontal boundary will likely set up. Below this boundary there will be very warm and muggy conditions, while locations to the north experience more seasonable conditions. Above the surface, a large and very impressive upper level jet streak will be nosing in, which is a tell-tale indicator of potential heavy rain for this area. the questions that remain to be answered at this time are where does this frontal boundary set up, how much instability will be in place, and will these ingredients come together at the right time to produce widespread heavy rain? If these conditions do come together on Monday in the correct manner, then we may have to watch for potential flooding rains and much cooler temperatures to start off the week. We will likely have to revisit this system as more data becomes available.

This system should exit the coast late Monday, and an area of high pressure should begin to take over for Tuesday and into Wednesday. However, we may have another rain chance later in the week as the active northern stream regime shows up once more.

This afternoons GFS model showing the very favorable juxtaposition of an expansive upper level jet streak that could potentially aide in the development of heavy rain on Monday (courtesy of Simuawips)

This afternoons GFS model showing the very favorable juxtaposition of an expansive upper level jet streak that could potentially aide in the development of heavy rain on Monday (courtesy of Simuawips)

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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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(Detailed Discussion With Doug Simonian)  

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Have a great evening!

Steve Copertino & Doug Simonian