Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 282018 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 418 PM EDT TUE JUN 28 2016 .SYNOPSIS... Low pressure is forming on a cold front crossing the mid Atlantic states late this afternoon and evening. That front drifts offshore on Wednesday. Weak high pressure builds in for Thursday. A cold front approaches from the west on Friday and moves offshore Saturday. High pressure follows later Saturday into Monday. A strong warm front should be moving northeast toward our area on Tuesday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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A Severe Thunderstorms Watch has been issued for Eastern Pennsylvania, portions of NJ along the Delaware River, as well as New Castle and Kent, Delaware and Cecil, Kent, and Queen Anne`s and Maryland through 10 pm. A cold front is progressing through central Pennsylvania and approaching our this afternoon. Showers and thunderstorms are developing along and ahead of this front as instability has build during the day, and a short wave/vorticity impulse is approaching from the west as well. This activity will all move eastward through late this afternoon and into this evening as the front continues to slowly push eastward. MLCAPE has reached 1,000-1,500 J/KG, or will increase, where the sun has come out and daytime heating has occurred. Bulk shear values are around 30-35 knots, and mid level winds are only 30-40 knots, but with the amount of available CAPE, some storms could build high enough to produce some hail and strong wind gusts. Another concern will be heavy rainfall. Even though PW values are only ~1.5 inches, very heavy rainfall is occuring and could produce over an inch in an hour in some areas, leading to ponding in urbanized and poor drainage areas. The convection should begin affecting the Poconos, Lehigh Valley/Berks County, and Northwest New Jersey areas between 4 and 7 pm. Then continue eastward and reach the Delaware Valley/I 95/295 corridor between 7 and 10 pm, and then eastern New Jersey and central/southern Delmarva by around 10 pm to midnight if it holds together. All shower activity will begin to diminish after midnight, and the remainder of the overnight should end up mostly precipitation free except a few isolated showers/sprinkles. Once the rain ends, some low clouds and patchy fog could develop, especially in areas where winds drop off and become light and variable.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... Wednesday should be a very nice day. The cold front will either be offshore, or moving offshore at the start of the day. We are not expecting any showers to be affecting the area, but if there was any showers, it would be near the frontal boundary. After any morning fog/low clouds burns off, a nice day should develop across the area. Some scattered cumulus cloud build up is expected during the day, but we`ll be precipitation free. We are expecting close to normal, or slightly above normal temperatures for Wednesday, even with the light northwest flow. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... 500MB: A -1SD short wave trough over the eastern Great Lakes Tuesday night weakens during mid week at the expense of a more significant trough (-2SD) developing over southeast Canada late Friday and Saturday. Eventually ridging follows into the northeast USA early next week. Temperatures: June through the 27th has averaged 1 to 2 degrees above normal at PHL, RDG, ABE, and TTN, near normal at ILG/ACY, 0.6F above normal at GED and surprisingly a degree below normal at MPO. Calendar day averages the next week or so should be within 3 degrees of normal... nothing notable. So the monthly average should be very close to the monthly departures posted above and also available in our preliminary CF6 within the MT Holly climate web link. Forecast basis: Unless otherwise noted, a 50 50 blend of the 12z/28 GFS/NAM MOS guidance Wednesday night - Thursday night, thereafter the 12z/28 GFS MEX MOS for Friday-Friday night and WPC Guidance Saturday-Tuesday. I did take into account the 12z/28 ECMWF op run and added several degrees to some of the max`s Thu-Mon, especially north of PHL near I78 north to the northern border and then on Saturday, raised temps almost all the way to the coast where near 90F possible. The dailies... Wednesday night through Thursday...High pressure briefly builds in, in the wake of the cold front. Nice seasonable summer weather. Confidence: Above average. Thursday night...waa may still bring a shower or thunderstorm to the DE coast. Patchy fog probable parts of the area, especially favored nw NJ valleys. Confidence: average. Friday...a chance of showers and thunderstorms ahead of the next cold front, otherwise partly to mostly sunny, very warm and more humid. Heat index lower 90s. Confidence: average. Saturday...Rainfree and very warm, lower dewpoints. Confidence: above average. Sunday through Monday Independence Day...Weak high pressure should build in for Sunday and Independence Day. Thus at this point, we still expect this period to be dry. Nice summer weather for the outdoor celebrations. Confidence: Average. the reason its only average is that am a little concerned about thunderstorms moving into the area Monday afternoon ahead of a developing strong warm front. Tuesday...Depending on how quickly the high shifts off shore, low level flow will shift to southerly sometime on Tuesday, bringing warm air and moisture advection. Forecast is rainfree at this time but warm frontal thunderstorms are a concern. Confidence: below average. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Conditions have improved to VFR and MVFR for all sites this afternoon. These VFR/MVFR conditions will continue through this afternoon and into this evening, with the exception of when any showers/thunderstorms affect a TAF site. A period of heavy rainfall, gusty winds, and low visibilities will occur with any thunderstorms. We`ve updated ABE and RDG to include wind gusts and IFR conditions, and will likely update ILG/PHL/PNE/TTN if the convection continues. The convection should affect ABE/RDG between 21-01z. Then continue eastward and reach ILG/PHL/PNE/TTN between 23z-03z, and then MIV/ACY by around 00z-04z if it holds together. After the rain moves through, low clouds and fog area again expected to develop. Ceilings and visibilities are expected to lower to IFR overnight through daybreak Wednesday. Once any low clouds/fog burns off Wednesday morning, VFR conditions will prevail for the remainder of the day. Winds are mostly southeast across the area, but become variable at times as some southwest winds from aloft mix down to the surface. Once the front moves through overnight, winds will become southwest to west, then northwest during the day Wednesday. Wind speeds are expected to generally be 10 knots or less. Outlook... Confidence on the days listed below is generally above average. Wednesday night through Thursday...VFR. Light northwest wind become southerly late day. Confidence: above average. Thursday night through Friday...MVFR and brief IFR conditions will be possible with any showers and thunderstorms that move through the region during this time...probably mainly Friday. Patchy IFR stratus/fog possible early Friday morning. Saturday...VFR. west to northwest wind. Sunday...VFR. && .MARINE... Sub-Small Craft Advisory conditions will prevail across the waters tonight through Wednesday. A cold front will move across the waters early wednesday, so southerly winds today/tonight will become westerly/northwesterly on Wednesday. A period of showers and possible thunderstorms may affect the waters late this evening, before dissipating overnight. If any thunderstorms do occur, they could locally increase winds and waves. Outlook... Wednesday night through Sunday...winds and seas should remain below SCA criteria. Although gusty winds are possible in the vicinity of any thunderstorms Thursday night or Friday. RIP CURRENTS...The rip current risk will be low to possibly moderate at times during the balance of this week through the weekend, in part dependent on the amount of onshore wind. In other words, not much change from the somewhat active month of June. AWARENESS: weak swimmers for their own safety should swim only in the presence of lifeguards. It is not worth being a rip current victim by swimming near jetties, or after the lifeguards go home, or with untrained weak swimming bystanders who wont be capable of saving a distressed swimmer, except to call 911, which then could be too late. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Drag Near Term...Robertson Short Term...Robertson Long Term...Drag Aviation...Drag/Robertson Marine...Drag

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