Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 210735 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 335 AM EDT THU JUL 21 2016 .SYNOPSIS... High pressure builds south and east of the area today and tonight. A frontal boundary is expected to into the area overnight Friday into Saturday, and slowly sag south of the area through Sunday. Another frontal boundary is expected late Monday into Tuesday. High pressure should then briefly build back into the area Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... As the high continues to shift further off shore, southwesterly flow will start the warming trend that will continue right into the weekend. For today however, the upper level ridge remains to our west, keeping highs generally in the 80s and lower 90s for our region today. Today should be prime conditions for an afternoon sea breeze to develop, keeping the shore a few degrees cooler than interior locations. However, no showers are expected to develop along the sea breeze as subsidence with the building ridge is expected. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... Dew point temperatures will continue to increase thanks to persistent low level southerly flow. Therefore, expect a warmer night as compared to Wednesday night. The other concern will be how quickly the pre frontal trough will approach the region. We could see showers and thunderstorms developing along or just ahead of this trough. The 00Z model runs though for the most part depicted this trough staying well west of our region through overnight period, keeping dry conditions again tonight. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Hot and humid conditions are continued to be forecast for much of the extended period, with Saturday, Sunday, and Monday expected to be the warmest days. Thicknesses and 925/850 mb temperatures are expected to continue to climb during this period. With the building thicknesses and 925/850 mb temperatures, daytime highs are expected to climb into the low to mid 90s Friday, followed by mid to upper 90s Saturday, Sunday, and Monday, followed by low to mid 90s again by Tuesday. Heat index values will begin approaching the upper 90s to 100 degrees by Friday, but the dangerously high heat index values over 100 degrees are expected over the weekend into Monday, and possibly into Tuesday. With several days of dangerously high heat index values expected, we have issued an Excessive Heat Watch starting Saturday and continuing into Sunday for all of our forecast area except Carbon and Monroe counties in Pennsylvania and Sussex county in New Jersey. This watch will likely need to be extended into Monday, and possibly Tuesday. Rain chances through the extended will be centered around a couple of frontal boundary passages. The first is late Friday into Friday night, and the second period being Monday into Monday night. On Friday, a pre-frontal trough will be to our west, with a frontal boundary approaching the area late in the day as well. As these features move eastward, along with the associated short wave aloft, scattered showers/thunderstorms could begin moving into the area late in the day Friday into Friday night. There is a fair amount of instability forecast with the heat and humidity, and there will be some weak shear present as well. If any thunderstorms do develop, the could produce a brief period of heavy rainfall and gusty winds. A similar situation is forecast to occur on Monday as a frontal boundary is forecast to approach late in the day into Monday night. Instability increases during the day into the evening, and as the frontal boundary and associated short wave move into the area, showers and thunderstorms may develop and move across the area. The rest of the extended forecast is expected to be dry. && .AVIATION /07Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Patchy MVFR visibility restrictions are possible, primarily for more rural TAF sites (especially KMIV), with BR between 09 and 12Z both this morning and Friday morning. Otherwise, VFR conditions are expected through the TAF period. Winds will be mostly light (10 kts or less) and southwesterly. The one exception to this is the sea breeze which should develop early this afternoon and affect at least KACY and KMIV (and may propagate as far inland as the Delaware Valley TAF sites). Behind the sea breeze, southerly winds near 10 kt, with higher gusts will be possible. OUTLOOK... Friday-Friday night...Generally VFR. A chance of showers and thunderstorms which may briefly lead to lower conditions. Gusty southwest winds 15-20 knots. Saturday-Sunday...VFR. Monday-Monday night...Generally VFR. A chance of showers and thunderstorms which may briefly lead to lower conditions. Gusty southwest winds 15-20 knots. && .MARINE... Southerly winds may gust just above 20 kt this afternoon and evening along the northern NJ coastal waters, but are expected to remain below SCA criteria at this time. Seas should generally be 3 ft or less. OUTLOOK... Friday-Friday night...Small Craft Advisory conditions possible with increasing winds ahead of an approaching cold front later Friday into Friday night. Saturday-Sunday...Sub-Small Craft Advisory conditions expected. Monday-Monday night...Near Small Craft Advisory conditions possible with increasing winds ahead of an approaching cold front. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Excessive Heat Watch from Saturday morning through Sunday afternoon for PAZ060>062-070-071-101>106. NJ...Excessive Heat Watch from Saturday morning through Sunday afternoon for NJZ007>010-012>027. DE...Excessive Heat Watch from Saturday morning through Sunday afternoon for DEZ001>004. MD...Excessive Heat Watch from Saturday morning through Sunday afternoon for MDZ008-012-015-019-020. MARINE...None. && $$ Synopsis...Robertson Near Term...Johnson Short Term...Johnson Long Term...Robertson Aviation...Johnson/Robertson Marine...Johnson/Robertson

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