Aug 25, 2013: Storms Return Mon Night, Weds

Forecast Highlights:

nam-hires_namer_030_sim_reflectivityA high pressure remained stationed over the region today, keeping mostly sunny skies and temperatures slightly cooler than average. A significant heat wave is developing in the central US, however, and while the sustained heat will not reach the area, warmer temperatures and noticeably more humidity is expected especially for the first half of this week along with several rounds of heavy thunderstorms, possibly strong-severe, focusing on Monday evening and Wednesday, followed by a temporary late week cool down and a possible return of heat for early September.


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Saturday, August 24 Observations:

8.24.13Clouds from a cold front that moved through on Thursday night cleared the area early in the morning hours after a mid level shortwave triggered an isolated thunderstorm in coastal New Jersey. Throughout the rest of the day, a strong high pressure entered the region from the northwest, giving way to mainly sunny skies across the area, north winds, and temperatures slightly cooler than average, peaking in the upper 70s to low 80s for most. The highest temperature was 81 degrees in Somerset, NJ, and the coolest high temperature was 74 degrees in Montauk, NY.



[notice]Today’s discussion is more in-depth than usual. For those looking for a quick forecast, a simplified summary of the forecast discussion updated daily can be found in the 5-Day Forecast page.[/notice]

Tonight – Wednesday: Stormy, Warmer, More Humid

For the first time this summer, a strong stationary ridge is setting up over the central US, pulling a warm air mass from the Rockies into the central US with widespread 850 millibar temperatures over 20C, resulting in widespread high temperatures in the 90s and 100s, making it one of the most widespread heat waves of the year despite occurring at the end of meteorological summer. The region will remain in between the ridging to the west and troughing to the northeast, with a NW flow aloft bringing several mid level shortwaves through in the early-mid week period, triggering showers and thunderstorms, possibly strong/severe. The main uncertainty with the early-mid week outlook is regarding the exact timing and location of the shortwaves and the thunderstorms/MCS, with today’s discussion focusing on the timing but with some changes possible to the outlook.

Monday: Tomorrow’s outlook is a slightly complicated one with two clusters of thunderstorms/potential MCS complexes moving through the region. Latest observations show a cluster of thunderstorms in southern Canada, which is likely to move through New York State while weakening tonight into Monday morning while producing locally heavy rain and thunder. These storms are likely to stay north of the area, with cloud cover spreading in towards the early afternoon. This MCS will be accompanied by a mid level warm front tracking southeast through the area, bringing a much more moist air mass from the north as precipitable water values increase to 2 inches by the afternoon and evening. With this anticipated setup, partly cloudy skies are expected on Monday afternoon with highs rising into the low to mid 80s as dew points begin to climb into the 60s. By the evening, another and stronger shortwave will move through the region, likely triggering a cluster of thunderstorms tracking through SE NY and the area towards the evening hours. Some of the short range models indicate a potential MCS, although this potential is uncertain at this time and will be watched more closely tomorrow. Severe weather parameters are marginal, given low bulk shear and marginal instability, although storms will be capable of producing heavy rainfall.

Tuesday-Wednesday: Partly sunny skies are expected for Tuesday with highs climbing into the mid to upper 80s, along with more humidity as dew points likely reach the mid 60s. Another shortwave currently in the southwest US associated with tropical storm Ivo in the Pacific Ocean will track around the northern end of the ridge, reaching the Great Lakes and western Pennsylvania towards Tuesday night, potentially triggering another MCS which reaches the region, including the NYC area, on Wednesday, producing another round of thunderstorms and possibly strong-severe thunderstorms. This shortwave will be accompanied by a surface low pressure, likely to move through the area on Wednesday. There is some uncertainty regarding the timing of the storms, with some models bringing the storms in the morning to early afternoon hours, while others show a slower scenario with thunderstorms throughout the afternoon. At this time I am leaning towards a compromise with thunderstorms through the mid afternoon hours, although the timing is subject to change. Unlike Monday, more instability will be present, and some of the storms could be strong or severe. Due to the cloud cover and storms, cooler high temperatures are forecast, back in the low-mid 80s, but may be lower depending on the exact timing of the storms. Storms are likely to clear the area by the late evening-night hours.


Thursday – Beyond: Temporarily Drier, Then Possibly Stormy Again

For the late week, 500mb heights aloft will slightly lower over the region with more sunshine and a drier and slightly cooler air mass returning. Temperatures are likely to reach the mid to upper 80s across the area on both days, with low temperatures falling back into the upper 50s to low 60s as opposed to mid 60s-low 70s during the early-mid week.

By the weekend, the model guidance diverges with the key uncertainty focusing around the ridge; some models shift it west, with a brief warmth surge followed by a more sustained trough pattern, while others shift the ridge further east, with a widespread heat wave affecting the Northeast US region for the first week of September. Should ridging shift east into the region, however, the trough pattern in eastern Canada is likely to moderate, which would support a more widespread and further north/east extent of the warm air mass into the region; this scenario may result in warmer high temperatures for early September than the highest August temperature in NYC. Some of the models are likely too aggressive in pushing the ridge and heat into the region, although the ridge is likely to make at least some progress into the region during the weekend into the first week of September, with at least a brief return of heat possible during this time frame, possibly lasting longer should the warmer scenario verify.

Temperatures during the weekend are likely to end up at least slightly cooler, back into the upper 70s to low 80s, but are expected to warm up towards early-mid next week into the 80s again, possibly into the 90s in the warmer case scenario, along with potential return of storminess towards the middle of next week. Stay tuned for more information on the longer range outlook.

10 thoughts on “Aug 25, 2013: Storms Return Mon Night, Weds

  1. Eduardo Berroa Reply

    Are heavy T’storms possible late this afternoon/evening?

    What’re the threat you’ve expected for heavy thunderstorms?

    • NYC Area Weather Post authorReply

      Yes, thunderstorms are likely to affect the area especially in the evening and early overnight hours. Given marginal instability and a lack of bulk shear, severe storms are unlikely today, although storms could be capable of producing heavy rainfall and frequent lightning, especially north and west of NYC.

        • NYC Area Weather Post authorReply

          Thunderstorms don’t always weaken prior to reaching NYC; it depends on many factors, although in the occasions that storms do weaken prior to reaching NYC, some factors that are sometimes involved include the marine layer, dry air at the surface or aloft, and low instability. In some cases, the timing of the day also plays a role.

          • Eduardo Berroa

            Because NYC hasn’t gotten’ severe T’storms in couple of Months, although the upper boroughs of NYC has gotten’ morning strong T’storms. Actually It’s great news We haven’t gotten’ Thunderstorms.

  2. Anonymous Reply

    Is there a potential for a pattern similar to that of June 23-July 3, with hot temperatures near 90 degrees and widespread afternoon and evening thunderstorms to return after the Labor Day Weekend?

    • NYC Area Weather Post authorReply

      There are several differences compared with that pattern, most notably that the source of the heat is different, originating from western Atlantic ridging and focusing close to the coast with high humidity in the early July period, while in this case the heat originates in the central US, with ridging attempting to expand east into the region at times but failing to settle in. While a surge or two of heat is possible during the first week of September, given the upper level pattern in place any heat shouldn’t be long lasting and will be interrupted by frontal passages and troughs entering the region. Temperatures may reach the upper 80s and possibly the low 90s again, but with humidity likely not as high as the early July period, although with additional frontal passages expected, showers and thunderstorms are possible again at some point in the first week of September.

  3. Anonymous Reply

    Are any pop-up thunderstorms expected again during the hottest days?

    • NYC Area Weather Post authorReply

      It’s still a bit too far out with not enough confidence on the exact setup to determine the exact thunderstorm risk; isolated storms can’t be ruled out, with more organized thunderstorm activity possible with the frontal passages that push any heat surge out of the region, as unlike the July setup, in this case the warm air mass will come in surges that are followed by frontal passages, as opposed to a stationary warm air mass settling over the region before being pushed out by a strong front.

  4. Anonymous Reply

    Also, is there any sea breeze expected for Long Island during those days?

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