Aug 20, 2013: Heat Returns For 3 Days

Forecast Highlights:

f132As clouds exited the region last night, a high pressure will build in today through Thursday, resulting in temperatures warming back up to above average with highs in the mid 80s to near 90 degrees. A cold front will move through on Thursday night, bringing cooler temperatures for Friday and the weekend, followed by a more active pattern towards next week with higher temperatures and an increased risk of rain/thunderstorms (Image credit: PSU e-Wall).


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Monday, August 19 Observations:

8.19.13A weak wave of low pressure exited the area early on Sunday after producing scattered showers, although mainly cloudy skies persisted across the area on Monday, which was more than expected, resulting in cooler high temperatures than forecast. Highs reached the upper 70s across most of the area, with low 80s in northern parts of the area and most of Long Island. The highest temperature was 81 degrees in multiple locations, and the coolest high temperature was 76 degrees in Yorktown Heights, NY.



Today – Thursday: Warmer, Slightly More Humid

A high pressure currently extends across most of the region, allowing for a southwest flow to develop, bringing in a somewhat warmer and more humid air mass into the region. While this will not be nearly as warm and humid as previous heat waves observed in July, this setup still supports above average temperatures as highs rise into the mid 80s to near 90 degrees today through Thursday along with mostly sunny skies through Wednesday. Overnight lows will be warmer as well, ranging from the low-mid 60s inland to the low 70s in NYC and the immediate coast.

A weak mid level shortwave will slowly drift through the Ohio Valley today and tomorrow, keeping scattered clouds and showers to the south and west of the area. This shortwave will reach the region on Thursday ahead of an approaching surface cold front, triggering scattered showers and thunderstorms across the region especially in the afternoon and evening. As with other thunderstorm events this summer, the setup does not support more than isolated severe thunderstorm activity, although storms may be locally heavy with gusty winds possible.

Friday – Next Week: Cooler, Then Storms Return

f132Pattern Overview: The pattern through the first half of August generally consisted of troughing in the eastern half of the US with ridging in the west, keeping the region under a cooler than average pattern; through the first 19 days of August, Central Park has averaged 2.6 degrees colder than average, the first time since July 2009 that a summertime month has been this much cooler than average. The new pattern currently developing, pictured to the left from the 6z GFS (image credit: PSU e-Wall), consists of a strong mid-upper level ridge centered over the central US, where widespread temperatures in the 90s and 100s are expected after a relative absence of sustained heat in that region compared to previous years. Meanwhile, a sustained trough pattern is expected to set up over southeast Canada. The northeast US region will be in between the central US ridging and the SE Canada trough, resulting in a northwest flow aloft, a pattern supporting occasional heat surges towards the region but with shortwave troughs moving through, quickly suppressing these warmth surges and mostly limiting them to the Mid Atlantic region, especially further west, while bringing rain and thunderstorms into the region and a temporary cool down focusing towards New England.

This pattern supports increased storm chances for the region next week, with an increased probability of near-above average precipitation. At this time, the area is likely to remain near the eastern end of these occasional warmth surges, with temperatures occasionally warming back up into the 80s followed by storm chances and a temporary cool down. Some changes are still possible in the exact setup, however, which may result in some changes in the specifics in the forecast for the area next week. The pattern as a whole does not appear to be warm enough to reverse the negative temperature departures observed so far this month; should this be the case, this would be the first cooler than average August since 2008.

Forecast for NYC area: Behind Thursday night’s cold front, partly sunny skies are expected for Friday and Saturday with mostly sunny skies for Sunday, with highs cooling into the low-mid 80s on Friday and the upper 70s-low 80s for next weekend. Overnight lows will be cooler as well, falling into the 50s away from NYC and the coast especially on Saturday night. As the next brief surge of warmth attempts to spread into the region, temperatures are expected to warm back up into the 80s early-mid next week, followed by a higher probability of showers and thunderstorms towards the middle of next week and another possible slight cool down in temperatures. Stay tuned for more information on the longer range outlook.

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