July 25, 2012: Severe Weather Outbreak Tomorrow

Forecast Highlights:


- Widespread severe weather outbreak possible tomorrow
- Slightly cooler for Fri/Sat with clouds/storms
- More storms possible for next week


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Yesterday's Observations:

Tuesday, July 24 was another warm day across the area, with temperatures reaching the lower to mid 90s for most places except for far eastern Long Island and the interior areas, which peaked in the upper 80s. Newark and JFK reached 96 and 95 degrees, respectively. Most of the day was dry, although scattered storms ended up affecting parts of the area towards the evening hours, especially over southern Connecticut and Long Island.

Following a much more seasonable and dry day today, an approaching low pressure will result in what may be one of the biggest severe weather outbreak of the last few years across the region for Thursday, with the NYC area in the southern edge of the highest severe weather risk. Temperatures will slightly cool down for Friday and Saturday with more storms and clouds, with additional storms possible later next week.


Thursday's Outlook: Severe Storms Likely


A low pressure will move through the region tomorrow, bringing what may be one of the biggest severe weather outbreaks for the region over the last few years. The Storm Prediction Center (SPC) already has the region, including the area, in a Day 2 moderate risk; moderate risks are not very common for the area, especially not 2 days out. The day will start out with scattered morning storms in central New England, possibly extending a bit further south to affect the northern parts of the area. Clearing in the cloud cover is expected by the afternoon hours, with temperatures quickly warming up into the lower to mid 90s from NYC and further north/west, possibly passing 95 degrees in the immediate NYC area. Along with the heat, high humidity is expected as well with dew points likely in the upper 60s to possibly lower 70s, resulting in heat index values reaching and/or slightly exceeding 100 degrees.

By the mid afternoon hours, widespread instability will be present across the region with LI down to -8 and CAPE up to 3500 J/kg; as a low pressure moves towards central NY with the cold front slowly approaching, widespread thunderstorms are expected to form from Ohio into central/northern Pennsylvania and southern New York state. Unlike the last severe weather outbreak, however, there is widespread shear present under the areas of higher instability, especially over the area, in southern NY/northern PA, and in southern New England. This appears to be the main area of concern regarding tomorrow's storm activity, with the main risk including damaging winds, hail, and perhaps isolated tornadoes.

The outlook for the NYC area is a bit more uncertain, however, as some models show the storms not making it far south of the area, keeping the biggest activity to the north/west, although especially if a MCS/derecho ends up forming, which is a possibility also highlighted by the latest SREF runs, the area may have a better risk of observing more widespread severe weather. With the more favorable parameters compared to the last events, I placed a widespread 30% risk zone, with a 45% zone extending from central/northern PA into southern New England. There is some uncertainty on whether the area ends up in the higher risk area or not, although it is a possibility that the 45% risk zone may need to be extended to the coast. Stay tuned for afternoon updates on tomorrow's regional severe storm outbreak.


Longer Range: Storms are expected to continue affecting the region on Friday and Saturday with highs cooling down into the mid 80s to lower 90s across the area. Drier conditions are likely to return by Sunday and the early week before more storms possibly return towards the middle of next week. No significant warm spell or cool down is on track to affect the area.