Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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084 FXUS61 KPHI 140150 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 950 PM EDT Tue Apr 13 2021 .SYNOPSIS... Weak high pressure will continue to influence our weather into tonight. Low pressure is forecast to develop in North Carolina on Wednesday before passing off the Virginia coast on Wednesday night. The low is expected to move slowly northeastward on Thursday and Thursday night, reaching southeastern New England on Friday. The system is anticipated to progress out to sea over the weekend, as high pressure builds into our region from the northwest. A cold front may approach from the west early in the new week. && .NEAR TERM /THROUGH WEDNESDAY/... Clear skies this evening are prompting notable radiational cooling as winds turn light and variable. Otherwise, a quiet night with a few mid-level clouds building by morning. A closed upper low remains to our northwest across the western Great lakes region. This feature will drift slowly eastward through tomorrow and eventually be centered over Michigan by the end of the day Wednesday. An ill-defined and weak area of high pressure will remain strung across much of the East Coast tonight then the surface low associated with the upper low will move slowly closer to the region tomorrow. Northerly surface winds will continue to weaken late this afternoon then become light and variable this evening and into the overnight. Skies should remain mostly clear through most of the overnight period as well, but mid-level clouds will begin increasing around daybreak Wednesday. With the clear skies and not particularly dry airmass in place, could see some patch fog develop overnight in the typical foggy spots. Expect low temperatures in the 40s area wide. On Wednesday, some vorticity maxima embedded in the larger scale zonal synoptic flow south of the upper closed low will begin moving into the region. This will result in increasing cloud cover during the morning hours and ultimately leading to an overcast afternoon. Guidance varies a bit in the robustness and coverage of precipitation with this activity, but generally a chance PoP for rain is forecast. It appears the greatest chance for rain into the afternoon will be across Delmarva and southern New Jersey. QPF should remain light, generally a tenth of an inch or less. A tricky forecast with regard to maximum temperatures since cloud cover will be increasing and light precipitation may impact some areas, but subtle mid-level ridging and light southerly flow should support temperatures warming into the mid to perhaps even upper 60s away from the coasts. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... A mid level low is forecast to be the main feature to affect our weather during the period from Wednesday night through Friday. The low is expected to progress from around Lake Huron on Wednesday night to near Cape Cod on Friday. The low is anticipated to take a slight southward dip, passing over northeastern Pennsylvania and northern New Jersey late on Thursday night. A mid level short wave is expected to move off the Southeast coast on Wednesday night. A surface low is forecast to make its way off the Virginia coast at that time. The surface low will likely be drawn slowly northward in the cyclonic flow around the mid level low. The surface feature should move slowly northeastward over the waters off Delaware and New Jersey on Thursday, reaching the coast of southeastern New England toward daybreak on Friday. The surface low and a short wave rotating around the mid level low will likely bring rain to our region for Wednesday night and Thursday. The resulting flow is expected to bring a fairly robust moisture feed into northern and central New Jersey on Thursday. As a result, those area should receive the heaviest of the rain in our region from this event. The storm total is anticipated to range from 1 to 2 inches in northern and central New Jersey (and perhaps in far eastern Pennsylvania) to generally a quarter to three quarters of an inch in areas to the west and southwest in our region. The expected rainfall amounts should preclude the concern for anything more that some flooding of roadways and areas of poor drainage. However, we will keep an eye on the forecast trends for the Raritan and Passaic River basins in New Jersey. The clouds and rain will likely keep high temperatures from getting out of the 50s in much of our region on Thursday. However, some readings in the lower 60s are possible in the south. The main band of precipitation is expected to lift northeastward and away from our area on Thursday night. As the mid level low passes over our northern counties at that time, the core of cold air associated with it should cause the lingering rain to change to snow in parts of the Pocono Region and far northern New Jersey. Being that the snow will be falling at night, an accumulation is quite possible in the elevated terrain. For now, we are indicating up to an inch or an inch and a half. The lingering showers are anticipated to continue on Friday as the mid level low slowly moves away from our region. Temperatures will remain cool with highs mostly in the 50s. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... The pattern is expected to be fairly progressive for the period from Friday night through Tuesday, so the guidance tends to differ on the timing of some of the relatively weak feature that may affect our weather. Dry air is forecast to build into our region along with weak high pressure for the weekend into the early part of the new week. Temperatures should gradually creep upward during the period, rising to above normal by Tuesday. We will mention a low or slight chance of showers for Sunday, Monday and Tuesday which will be contingent up the development and timing of weak impulses traveling the mid level flow. No significant rain is expected during the period. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through tonight...VFR. Ceilings will increase in coverage and begin to lower after 09Z. Light and variable winds less than 5 kts will initially favor a northerly direction through 00Z. High confidence. Wednesday...Initially VFR ceilings will continue increase in coverage and lower after 12Z. MVFR ceilings will develop starting around 18Z from west to east and these will lower to near IFR after 21Z. Light rain is possible at some terminals after 18Z, but confidence on coverage and intensity is too low to include in the TAFs at this time. Moderate confidence. Outlook... Thursday...IFR/MVFR with rain likely. The rain may become moderate to heavy at times. East to north wind increasing to 10 to 15 knots with gusts around 20 knots. Medium confidence. Friday...MVFR/VFR with a chance of showers. Northwest wind 10 to 15 knots with gusts of 20 to 25 knots. Medium confidence. Saturday...Mainly VFR. Northwest wind 10 to 15 knots. Medium confidence. Sunday...Mainly VFR. Southwest wind 5 to 10 knots. Medium confidence. && .MARINE... Light southerly to variable winds overnight around 5-10 kts then increase to 10-15 kts Wednesday afternoon. Seas around 3 to 4 feet. Outlook... Thursday...East to north wind increasing to 15 to 20 knots with gusts around 25 knots. Friday...Northwest wind 15 to 20 knots with gusts of 25 to 30 knots. Saturday and Sunday...No marine headlines are anticipated. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Iovino Near Term...Davis/Staarmann Short Term...Iovino Long Term...Iovino Aviation...Davis/Iovino/Staarmann Marine...Davis/Iovino/Staarmann

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