Short Term Forecast – Page 19 – New York Metro Weather

Rare July Nor’Easter Possible This Weekend With Heavy Rains and Wind

July 26, 2017/by Steven Copertino

Good Evening!

Today was yet another in a series of days with below average high temperatures and low humidity. The difference with today, was the fact that we were able to mix out some early morning clouds and have a mostly sunny day across the vast majority of the area, as well as the Northeast. The area of high pressure that contributed to some pleasant and cooler weather yesterday moved directly over the NYC metro area this afternoon, and this further helped to conditions quite pleasant, with light winds generally from the south. With low humidity, clear skies, and a fresh high pressure system over the area, we saw highs limited to the mid to upper 70’s, with a few locations off to the west and north over Pennsylvania and northern New England reaching into the lower 80’s this afternoon. Overall these temperatures were around 5-10 degree below the norm for this time of year, and quite the contrast to the miserable heat and humidity we had over the entire Northeast just a week ago.

As the area of high pressure that was in control for most of the day continues to head eastward, it will begin to kick up more of a southerly flow in its wake later this evening. As it does so, this will lead to increased low level moisture building over the region as well as mid level temperatures increasing ever so slightly. The gradual increase in low level moisture should allow for the development of cloudier conditions for the rest of the evening, which should allow for overnight lows to not be quite as low as they were the past few nights, with temperatures getting down into the lower to middle 60’s across much of the area.

This afternoon/evenings latest high resolution visible satellite imagery, regional radar mosaic, and surface observations, showing relatively pleasant conditions with some high clouds beginning to move in as the high pressure to our east gradually fades (Courtesy of Simuawips.com)

(Click To Animate) This afternoon/evenings latest high resolution visible satellite imagery, regional radar mosaic, and surface observations, showing relatively pleasant conditions with some high clouds beginning to move in as the high pressure to our east gradually fades (Courtesy of Simuawips.com)

Thursday into Thursday Evening

Thursday should start off with mostly broken clouds, with some overcast further inland as the area of high pressure really begins to back off to the east and begins to introduce a brand new moist airmass into the Mid Atlantic and Northeast regions during the late morning and afternoon hours. Additionally, south-southwest flow will also begin to increase markedly ahead of a mid level shortwave that will be located over the Great Lakes region as well as the Ohio Valley. As this south-southwest flow begins to increase, mid level temperatures will begin to increase once again, which should support a round of warmer temperatures by the mid afternoon hours. Despite the possibility of some cloud cover, highs should be able to get into the low to middle 80’s-which will be right around normal for the area during late July. It should be noted that some influence from afternoon sea breeze activity could work to cut highs along coastal sections tomorrow by five or so degrees. In addition to the increasing temperatures, the dreaded dewpoints will once again be on the rise tomorrow afternoon-with values ranging in the mid 60 to lower 70 range, making for a muggy afternoon tomorrow, reminiscent of the days last week.

With all of this increasing moisture in the low levels of the atmosphere, we will likely also see instability begin to increase tomorrow afternoon and into the evening hours. Though not as impressive as it looked a few days ago, tomorrows setup should still yield a marginal risk for severe thunderstorms across the Northeastern states as a weak mid level system will gradually work its way east and potentially spark some showers and thunderstorms during the late afternoon and evening hours. The main limiting factors for any widespread/impressive thunderstorm development will be relatively meager mid level lapse rates, as well as any impressive shear to help keep potential updrafts organized and coherent. However, more favorable parameters may come together over portions of Pennsylvania and New York, so those with interests in those locations may have a better shot at seeing strong to severe thunderstorms capable of damaging winds and possibly a brief tornado. Otherwise, any storms that form near the NYC metro area will likely be capable of producing gusty winds, heavy rainfall, and frequent lightning before they gradually fade to the east by sunset. Expect another humid evening with lows ranging in the middle to upper 60’s once again.

This evenings latest RPM model showing the general evolution of Thursday weather, with some showers and thunderstorms possible. Widespread severe thunderstorm development is not anticipated (courtesy of WSI)

This Weekends Potentially Impactful Nor’Easter

Back on Monday we highlighted the possibility that the Northeast would have to deal with an area of heavy rain moving in from the west during the evening on Friday and into the early morning hours of Saturday, however since that time there have been some marked changes with regards to the duration, timing, and overall severity of this potential system. While the overall main players remain the same, with the initial monsoon energy moving up and around the periphery of the large heat ridge located in the Plains, as well as a small, but potent shortwave diving out of Canada-how these two interact remains to be far from settled at this time.

This afternoons model guidance suggests that as the initial monsoon energy heads into the Ohio valley, the potent Canadian shortwave trough will begin to interact with this energy and begin to phase together to some degree. This setup is something we’d typically be talking about in the Winter months, but the overall outcome may wind up being quite similar-just with warmer temperatures this time around. As these mid level systems interact and potentially phase, this will cause a surface low to develop over the Mid Atlantic states during the afternoon hours on Friday. As this surface low begins to become more established, it will have a very warm and moist feed of tropical air pumping into it from the south. Additionally, it looks quite likely that there will be a favorable upper level jet configuration overhead of this system, which should promote a healthy amount of upper level divergence and convergence at the surface levels. In short, when all of these factors come together in just the right manner, its a rather strong signal that very heavy rain will be likely for portions of the Mid-Atlantic.

So what could go wrong? Though this system will have some potentially favorable synoptic support, there are some serious questions that still remain with this system that make this a very difficult forecast. First off, the trough diving down from Canada is whats known as “positively tilted” in nature, meaning that the majority of its energy is located in the bottom left quadrant of the trough, which often allows the system to be progressive in nature. It also does not help that we have been stuck in a rather progressive west to east pattern for the past week or so, with no upstream blocking to help slow things down. This pretty much eliminates the chances of a large, wrapped up system along the coast unless something drastically changes. Next off, the initial monsoon energy out ahead of the Canadian system will be moving quite quickly to the east, and as the Canadian system drops south, it may wind up shearing out the energy ahead. This would create a much weaker and disjointed system that would likely have the heaviest rain offshore.

Taking all of this into account and carefully looking at this afternoons model guidance, I have decided to go with a blend of the ECMWF/NAM/ECMWF-ENS/UKMET at this time. This would lean towards a more progressive solution for this system, bringing the surface low from the Mid Atlantic coast, to well southeast of New England. This track would likely still bring moderate to heavy rain to the NYC area, but areas south of NYC would likely feel the brunt of this system (PA/MD/SNJ). At this time, it seems likely that the heaviest batch of rainfall should be able to drop 1-2″, with some higher amounts possible along the coasts of NJ and LI. This system is forecast to exit the region by Saturday afternoon, with some showers and gusty winds lingering around thereafter.

We will be carefully monitoring this system over the next few days and providing updates as needed!

This afternoons ECMWF model showing a rather impressive Nor’Easter for this time of year affecting the Mid Atlantic and portions of the Northeast with heavy rain and gusty winds (Courtesy of Accuweather Pro)

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Have a great day!

Steve Copertino

Public Analysis: How Long Will the Cooler Weather Last? Increasing Storm Threat Later This Week

July 24, 2017/1 Comment/by Steven Copertino

Good Evening!

Last evening we saw the development of numerous showers and heavy storms primarily focused to the south of the immediate NYC metro area. These showers and embedded thunderstorms were responsible for producing absolutely torrential downpours over southern Pennsylvania, southern NJ, and as well as Maryland. A record 4.27″ of rain fell between 6-7pm, with 1.83″ of that falling in just 21 minutes! Radar estimates also showed numerous areas of intense rainfall ranging from 4-6″/hr in some locations which caused localized street flooding into the early evening hours. In addition to the very heavy rainfall last night, there were actually two cases of low-topped supercells developing over NJ and Maryland, one of which actually dropped a strong tornado that injured one person and caused damage to a few homes. This tornado was given a preliminary rating of an EF-2 on the Enhanced Fujita scale, with winds topping out around 125 mph! The second tornado supercell formed right near Ocean City, New Jersey and may have produced a brief, weak tornado over that area before moving off the coast where it looks to have strengthened according to radar observations.

Three-Dimensional Volumetric Scan of velocity data from KDIX, showing a rather pronounced mesocyclone reaching towards the surface levels last evening near the New Jersey coast (Courtesy of GRLevel2AE)

As the evening hours progressed, the upper level disturbance moving through the Northeast wasn’t quite as organized as most guidance had showed, thus the overall widespread heavy rain and flooding threat was much lower than what it could have been. Eventually showers and storms did redevelop over Central Pennsylvania and gradually moved eastward, affecting the NYC metro early this morning with gusty winds and localized heavy rainfall. The area gradually cleared out, with only gusty showers left by noon. During the afternoon hours, we saw a pronounced dry patch associated with the upper level jet streak begin to punch its way over the area from west to east.

This dry punch allowed for skies to become mostly cloudy, but with occasional peeks of sunshine mixed in. Additionally, synoptic winds (not associated with thunderstorms) began to increase, which made today feel quite cool as high temperatures were only in the upper 60’s with some locations just hitting the 70 degree mark! This is an incredible difference from a few days ago when we were discussing highs in the middle to upper 90’s combined with high dewpoints, allowing for heat indices to reach into the lower 100’s!

During the late afternoon hours, we saw a relatively similar setup to yesterday, with a wedge of instability located over Pennsylvania, and modest wind shear overspreading the warm sector. With a shortwave trough working its way in from the west, we saw the development of a sew severe thunderstorms over Central PA, with a few cells even becoming tornado warned due to the rather decent surface to 500mb vertical wind shear. As the late afternoon and evening marches on, these showers and thunderstorms should continue to gradually head east/east southeast, and weaken with time as they run into a more stable airmass over the NYC metro area by an area of high pressure to the north. While it is quite likely that these showers and thunderstorms will dissipate before reaching the area, some heavy rain and gusty winds may be possible with any stronger remnants of these storms. The aforementioned high pressure will allow for tonight’s lows to remain 5-10 degrees below normal, with lows ranging in the upper 50s, to lower 60’s across the area.

This afternoon/evenings latest regional radar mosaic, high resolution visible satellite imagery, and regional surface observations, showing the redevelopment of showers and thunderstorms over PA. These storms are expected to weaken before reaching the NYC metro area (Click to Animate)

Tuesday into Wednesday

Tuesday morning should start off rather cloudy, with overcast likely in some places as the lower levels of the atmosphere remain quite saturated. A weak area of low pressure may be located just to our tomorrow morning, and this should allow winds to funnel from a much cooler airmass located to the north. With the skies likely only improving ever so slightly, temperatures tomorrow afternoon should only be able to rise into the upper 60’s to middle 70’s, which will be well-below normal for this time of year (10-15 degrees). Some locations may be able to rise into the upper 70’s tomorrow afternoon depending on just how quickly the residual mid level moisture decides to move. If things are able to dry out sooner, than cloud cover may become more scattered, with peeks of sunshine likely. Additionally, some added sinking air courtesy of a building high pressure system from the west ma also allow some improving conditions later in the day, but at this time widespread clearing does not seem all that likely for the entire region. Tomorrow evening should be yet another well-below normal night in terms of low temperatures, as the area of high pressure continues to build in from the west and clears out the area.

Wednesday will likely be the most quiet day in this forecast period as the area of high pressure fully extended over the region and takes control of our weather. We may start off the day with a few clouds due to the northwesterly flow, but as the column begins to dry out and the sun starts to warm things up, we should see a transition to cool, but relatively sunny day with scattered clouds and light winds. Wednesday will likely also be the nicest day of the week due to the low chance of rain, low humidity, and sunny skies. Highs will likely range from the low to middle 70’s, with some locations with prolonged sunshine possible reaching a few degree warmer. Wednesday evening will likely be below normal once again, but it is uncertain as to how much below normal temps will be able to reach. The models suggest that some increasing cloud cover may exist over the area as the high pressure system begins to move to our east, ushering in a more southerly flow. If this does indeed occur, then lows will likely be right around normal, with temperatures getting down to the middle to upper 60’s.

This afternoons European model showing a large area of high pressure moving in over the Northeast during the early morning hours on Wednesday, making for a very cool and pleasant day with low humidity and few clouds! (Courtesy of Accuweather Pro)

Late Week Rain Threat

Later in the period, the models suggest that the near-zonal pattern that we’ve been stuck in for the last week will produce yet another heavy rain threat late Thursday evening, and possibly into Friday morning. Energy from a monsoonal system currently located over the desert Southwest will begin to move north and east around the northern periphery of a large heat ridge centered over Texas over the next few days. As it does so, another disturbance will be moving briskly across southern Canada to the east. Depending on the degree of interaction between these two systems, the mid level disturbances may briefly phase over the Ohio Valley, allowing for the development of a surface low pressure system to form. A blend of this afternoons European/NAM models shows that as this low pressure moves over western New York, it would begin to drag up a very moist airmass from the south. Additionally, an impressive upper level jetstreak may be positioned over the Northeast, which could promote modest amounts of lifting in the atmosphere.

Though the exact details of this scenario will largely depend on small details like the degree of interaction, timing, and location of each disturbance, there does appear to be an increasing threat of heavy rain late Thursday evening, and into the morning hours on Friday, especially for locations to the North and West. We will continue to monitor this potential storm system over the next few days and provide more details on potential impacts!

Evolution of the mid level disturbance first tracking north, then east over the large ridge centered over the Plains states. Depending on the degree of interaction with another northern stream disturbance, this system may be another heavy rain producer

Have a great day!

Steve Copertino

Public Analysis: Third Heatwave of the Year Possible, Increasing Thunderstorm Threats This Weekend

July 19, 2017/by Steven Copertino

Good Evening!

Today has been another day in this string of hot and muggy weather. This semi-tropical airmass can be attributed to a large area of high pressure over the western Atlantic, which is in a perfect position to pump the uncomfortable dewpoints and heat northward. This airmass is likely to remain in place through the weekend and possibly even into the first half of next week, before a cold front associated with a strong disturbance originating from the Pacific Ocean sweeps through.

Regardless, after some low level clouds and patchy fog that built up during the early morning hours burnt off, temperatures were able to quickly rise into the upper 80’s and lower 90’s-with some locations reaching the middle 90’s! As stated earlier, the high pressure out in the western Atlantic has been pumping in very impressive dewpoints over the region. Dewpoints will range in the 65-75 degree area, which is right around the “uncomfortable” and “oppressive” tiers of the spectrum for this area. When you take temperatures in the upper 80’s to middle 90’s and factor in these very high dewpoints, the apparent temperature-or how hot it feels rises quite a bit. Due to this, the National Weather Service has issued a Heat Advisory, which will likely last until Thursday evening. Day time highs in the low 90s combined dew point temps around 70 will produce heat index values in the upper 90s across the advisory area, which is forecast to continue through Thursday. “The heat and humidity may cause heat stress during outdoor exertion or extended exposure. Extreme heat can cause illness and death among the at-risk population who can not stay cool.”

Additionally, all of this low level moisture will allow for instability to rise over the area as well. Some showers and thunderstorms are currently going up over central and eastern Pennsylvania. These storms formed as a result of some residual energy from a dying upper level low interacting with the warm/unstable airmass over the region. Thankfully, the trigger energy from this disturbance is not all that strong or organized, so widespread thunderstorm development does not seem likely over the area. However, any showers and thunderstorms that do develop may have very heavy rainfall associated with them as the atmosphere is loaded with precipitable water.

The hot and humid conditions will last well into the evening hours, likely until sunset, and even then temperatures will be well-above normal tonight as the muggy airmass keeps the entire area locked into the low to middle 70’s for overnight lows.

This evenings latest high resolution satellite imagery, regional radar mosaic, and surface observations,showing a very warm and humid day across the area with some scattered shower and thunderstorm activity to our west (Courtesy of Simuawips.com)

Thursday into Friday

Thursday will likely start off quite clear, which should allow temperatures to skyrocket during the early afternoon hours. Light west/southwest winds will also be ushering in another round over very high dewpoints, and with slightly higher mid level temperatures, we expect highs tomorrow to be slightly higher than they were this afternoon, with much of the area in the upper 80’s to middle 90’s. This combination will make apparent temperatures (Real Feel) rise into upper 90’s and even lower 100’s across the area. This heat and humidity combo can be dangerous to some people, so make sure to stay hydrated and do not overexert yourself. Weak seabreeze fronts may develop along the shores of Connecticut, Long Island, and New Jersey, and this could help to knock the temperatures and humidity down a few degrees as the afternoon marches onward.

Instability will once again build over the region, and with an active quasi-zonal flow being established over the region, we may have to worry about a complex of showers and thunderstorms moving through the area late tomorrow afternoon and into the evening. Precipitable water values will still be quite high and there will be some weak shear present, so any showers and thunderstorms that develop will have a risk of torrential downpours that can potentially cause flash flooding, as well as some locally damaging winds.

Friday looks to be another very hot and humid day with clear skies and increased low level moisture. It is looking quite possible that if Thursday and Friday both produce highs in the 90’s, then numerous stations will record their third “heatwave” of the year. It is also quite possible that the Heat Advisory for the area gets extended until Friday evening, as dewpoints and temperatures will still be high enough to make conditions seriously oppressive.

This evenings latest Rapid Precision Model, showing the potential for gusty showers and thunderstorms moving through the area by late Thursday afternoon/evening. Some of the stronger storms may be able to produce flash flooding and locally damaging winds. (Courtesy of WSI)

This Weekends Severe Thunderstorm Threat

As we mentioned before, the Northeast will be within a west to east “zonal flow” this weekend, which will have numerous short wave trough embedded withing the flow. This looks to change on Sunday, when a large Pacific disturbance (that is currently off the West coast) gets caught in the flow and is located just to our northwest. The massive area of high pressure to our east over the Atlantic will still be supplying very moist and unstable air directly into the area while yet another area of high pressure over the central part of the country advects what is known as an Elevated Mixing Layer (or EML for short). This EML is very favorable for thunderstorm development, especially severe thunderstorm development. With the shortwave to the northwest in Canada providing upper level support and shear, the very moist and unstable airmass being pumped in from the south, and the support from the EML, it seems quite possible that widespread thunderstorm development will be possible on Sunday, with a higher than average chance that at least some of the storms become severe over a good portion of the Northeast/Mid Atlantic.

The main questions right now appears to be just how much influence will the previous nights possible convection last into the day on Sunday, and how far north will the surface low develop to our west. If we can get a strong enough surface low to develop over the eastern Great Lakes region with increased instability, then we may have to watch for the development of quite a few severe thunderstorms capable of wet microbursts, large hail, and flash flooding. We will have an update later this week to go over this potential threat once again.

This afternoons European model showing modest amounts of instability, decent wind shear, along with good timing for the possible development of strong to severe thunderstorms over the Northeast on Sunday

Have a great evening!

Steve Copertino

AM Update: Calm start, but transitional weather ahead

July 17, 2017/by John Homenuk

Good morning and Happy Monday to you all! As you make your way out the door this morning, you’ll notice a change to the sensible weather conditions in place throughout the majority of the Northeast states. You can thank a strengthening south/southeasterly flow for that — it has replaced the cooler, northwest breeze with a warmer and slightly more humid airmass. Warmer and more humid air will advect into the Northeast states for the remainder of today.

Near the coast, these southeasterly winds have already resulted in the presence of some stratus clouds along the shores of Long Island and even parts of New Jersey — with some localized fog in other locales as well. This will burn off as the day goes on, but the progression of disturbances in the mid and upper levels of the atmosphere will bring more unsettled weather into the picture by this afternoon.

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