Aug 19, 2013: Heat Briefly Returns

Forecast Highlights:

northeast2A warm and more humid air mass is gradually making a return to the region, with temperatures returning into the low to mid 80s today and the mid 80s to low 90s for Tuesday through Thursday. A cold front is expected to move through on Thursday night, with seasonable conditions returning for Friday and Saturday and another brief warmth surge possible the following week as the region remains near the eastern end of strong ridging.




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Sunday, August 18 Observations:

8.18.13The high pressure previously in place moved offshore as a frontal boundary and a weak wave of low pressure slowly advanced to the northeast. This wave of low pressure spread light rain showers across Pennsylvania, New Jersey and southern New England; although the shower extent was north of the forecast, the storm only produced very light rainfall rates for most especially with dry air still present aloft, with less than 0.05 inch across most of the area. The clouds and scattered showers interrupted the gradual warming trend that began on 8/14, with highs in the mid to upper 70s across the area. The highest temperature was 78 degrees in JFK airport and the lowest high temperature was 73 degrees in Sussex, NJ and Port Jervis, NY.



Today – Thursday: Increasingly Warm, Humid

Behind yesterday’s wave of low pressure, a high pressure is rebuilding over the southern Mid Atlantic states, resulting in a widespread west-southwest low level flow covering the majority of the east-central US. This will bring a warmer and somewhat more humid air mass from the Gulf of Mexico, with dew points climbing into the 60s and temperatures aloft at 850 millibars reaching the 15-17C range. Along with mostly sunny skies, this setup will bring temperatures back to warmer than average, with 90s returning for some locations for the first time in a month.

Today will be partly cloudy with highs expected to reach the low to mid 80s across the area. Temperatures will peak in the Tuesday to Thursday time frame with widespread highs in the mid to upper 80s across the area, with parts of NE NJ and NYC likely to peak near or a little over 90 degrees. The wind direction will generally be from the southwest except for Tuesday, with west winds expected away from coastal locations and a SW wind near the coast. The warmth will mostly remain north of Washington DC to Philadelphia, as a weak mid-upper level shortwave producing clouds and scattered thunderstorms remains further south, over Virginia. The latest model guidance is trending towards faster timing of this shortwave, moving into the area on Thursday, as opposed to Friday, and producing more widespread cloud cover and scattered thunderstorms ahead of the surface cold front; at this time I included a 30% risk of scattered storms in the 5-day forecast for Thursday, although the outlook is subject to change with the possibility of a slightly higher risk of storms and lower high temperatures.

Friday – Next Weekend: More Seasonable

By Friday and next weekend, the new pattern will continue to settle in with strong ridging centered over the central US, where widespread temperatures in the 90s and some 100s are expected. The northeast US region will be under a NW flow aloft at the east end of the ridge as a trough pattern develops and persists over eastern Canada, with the first shortwave diving through the region on Friday, bringing a trough into the region for Friday and Saturday. A surface high pressure will gradually sink south through the region, setting up for a N/NE wind on Friday and Saturday and later a west wind as it drops to the south, allowing for the warmer air mass in the central US to briefly surge east towards the area. With the NW flow persisting, however, any surges of heat in this pattern are forecast to be short lived and followed by frontal passages producing some showers/storms, although sustained cooler temperatures like the early-mid August pattern are unlikely to set up.

The cold front is expected to move through on Thursday night with a cooler air mass returning for Friday. High temperatures are forecast to reach the low to mid 80s with partly sunny skies and a north wind, with highs on Saturday in the upper 70s to low 80s with a northeast wind. A brief surge of warmth may take place on Sunday and Monday which would bring temperatures back into the mid-upper 80s briefly, although the models vary regarding this potential, ranging from the GFS with brief warmth to the ECM with the frontal boundary remaining near the area producing scattered showers/storms. More information will be posted regarding the weekend and next week’s outlook in the next few days.

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