Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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991 FXUS61 KPHI 272047 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 447 PM EDT MON JUN 27 2016 .SYNOPSIS... A cold front from the eastern Great Lakes through the Ohio Valley will cross eastern sections of Pennsylvania and Maryland Tuesday afternoon where low pressure will form. The front and area of low pressure will drift east, off the mid Atlantic coast Wednesday morning. Weak high pressure follows Thursday. Another cold front will move through the region Friday night or Saturday and then stall to our south later in the weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Showers are moving across eastern Pennsylvania late this afternoon and will progress eastward through this evening. These showers are associated with a weak surface trough and short wave/vorticity impulse aloft. There is not much instability, so lightning activity has been minimal, and should continue into this evening. We will still keep a slight chance of thunderstorms in the forecast however. The weak trough will stall our near the area overnight, and another stronger short wave/vorticity impulse is expected to approach the area toward daybreak Tuesday. This may help enhance increase showers potential across the southern areas overnight into daybreak. PW values increase overnight, so if showers or thunderstorms do develop, they could produce some moderate to heavy rainfall. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... Showers could be ongoing at the start of the day Tuesday across the eastern portions of the area as the initial short wave/vorticity impulse moves across the area. By the late morning into early afternoon, the first round of showers may begin to move out and we could get a brief break in shower/thunderstorm activity. However, showers and thunderstorms are expected to develop to our west during the day as the cold front approaches from the west. There is a moderate amount of instability and shear to our west, so thunderstorms could become strong during the day. The instability weakens some as does the shear moving into our area, so the greatest threat for severe weather may be north and west of our area. However, there will still be the possibility for gusty winds and small hail across our northern areas, so we`ve included this in the forecast. PW values drop some during the day, but should still be near 1.5 inches, so there could still be the possibility for some moderate to heavy rainfall with some showers/thunderstorms. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
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500 MB: A -1SD short wave nearing Buffalo NY Tuesday Night weakens eastward Wednesday. A developing -2SD short wave trough moves across Lake Huron Friday night. Temperatures: The month of June through the first 26 days has averaged 1 to 2 degrees above normal at PHL, RDG, ABE, TTN, within .5 of normal at GED ACY and ILG and surprisingly -1F at MPO. the final monthly departures should be within 3 tenths of degrees of those listed above. Calendar day averages over this coming long term period of Wednesday- Sunday should average near normal, some days a bit above, others a bit below. Forecast basis: Unless otherwise noted, a 50 50 blend of the 12z/27 GFS/NAM MOS guidance Tuesday night - Wednesday night, thereafter the 12z/27 GFS MEX MOS for Thursday and WPC Guidance Thursday night-next Monday. Max temperature guidance was on some days modified warmer by the previous 330 am PHI forecast as well as the warmer 12z/27 ECMWF 18z 2m forecast temperatures. Nighttime lows were lowered below guidance Wednesday morning and Friday morning across e PA and nw NJ, where the radiating countryside should get down close to the 12z/27GFS forecast 09z 2m temps. Rainfall: not a bright outlook for alot of needed rainfall...it certainly doesn`t look as if above normal rainfall can transpire in this pattern. To me it looks like too strong a cyclonic flow at mid levels. The dailies... Tuesday night...Any showers and scattered thunderstorms during the evening, will tend to die out late at night. At most a marginal risk of svr with 1000J of MLCape to start Delmarva area and 0-6KM bulk shear increasing late evening but appears to arrive too late for much impact in our CWA. Seems more like an SPS/MWS evening...marginal. PWAT decreasing from 1.5". Confidence: average. Wednesday...Tending to dry out and looking like a very nice summers afternoon after morning skycover clears. PWAT around 1 inch. Cooling afternoon sea breeze possible along the immediate coast. Seasonable temps. Confidence: above average. Thursday...Dry and nice with cooling coastal seabreezes. Small chance of a shower or thunderstorm along the coasts Thursday night in response to the western edge of an instability burst developing northeastward near the mid Atlantic coast. PWAT overall near 0.85 inches. Seasonable temps. Confidence: above average. Friday...much less confidence on the days outcome both temps and rainfall. Chance of a shower. Very warm...a bit above normal in some areas of the interior. Confidence: below average Saturday...Hot. Could be strong thunderstorms on the Delmarva late day or Saturday night where pretty good instability and significant 0-6km bulk shear (40 kt) are modeled though MLCAPE is so far, is modeled relatively low. Temps could reach the lower 90s in the I-95 corridor. Confidence: average. Sunday...Could have a lingering shower or thunderstorm threat in association with the se Canada trough. Confidence: below average. Monday (July 4)...For now it looks like a good day for outdoor activity. Warm. Confidence: average or above average.
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&& .AVIATION /21Z MONDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR conditions continue across the area late this afternoon/early this evening across the TAF sites. An area of showers is moving into our western areas, and will continue eastward through this evening. It is possible that some showers may be heavy enough to lower visibilities to 5-6 miles, so we will continue our TEMPO group with the potential. This line of showers will move eastward and dissipate through the evening, then we could be mostly dry for a good portion of the overnight. More shower activity could develop and move into the area around daybreak from the south and spread northward through the morning. Additional showers and possible thunderstorms are expected late in the day Tuesday as a cold front approaches from the west. Ceilings and visibilities are expected to begin to lower to MVFR then IFR late this evening and overnight as moisture gets trapped underneath a low level inversion. This will likely continue through the day tomorrow ahead of the approaching cold front, although the IFR may lift to MVFR during the day. South-southwest winds continue for most inland areas, while closer to the coast winds are more south-southeast. Sustained winds are around 10 knots, with some gusts 15-20 knots. The winds will lighten some after sunset, and become south-southeast everywhere 5-10 knots. OUTLOOK... Confidence for the periods discussed below is average or above average, Tuesday night...scattered leftover showers and isolated thunderstorms should diminish and end. Patchy IFR stratus/fog should develop late. Light winds. Wednesday...becoming VFR after any early morning IFR stratus/fog rapidly clears. Light west wind except possible afternoon sea breezes coasts. Thursday...VFR. Light west wind with coastal afternoon sea breezes. Patchy IFR stratus/fog may develop late. Friday...VFR. Chance for a shower. (least confidence of all the days listed in this long term section) Saturday...VFR. Chance of late day-or night time thunderstorms Delmarva. Right now the northern fringe is in our area and some of those storms could be strong.
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&& .MARINE...
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Winds on the waters will continue to gust in the low 20s for this afternoon into the early evening. A few gusts around 25 knots may occur across the far northern waters off the coast of Monmouth, but we believe they will be infrequent and brief enough to preclude the need for a Small Craft Advisory. Winds will diminish some overnight, but should increase in gusts again Tuesday. Wind direction will continue to be from the south to southeast tonight into Tuesday. A few isolated thunderstorms are also possible tonight into Tuesday. There is a moderate risk of rip currents today, and this may continue into Tuesday. OUTLOOK... Tuesday night through Saturday... Winds and seas expected to remain below SCA criteria. A chance for showers and scattered thunderstorms with a slow-moving cold front Tuesday night and then again Saturday. Small chance of a shower Thursday night or Friday. RIP CURRENTS...low to possibly moderate at times this week, 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.
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&& .CLIMATE...
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Presuming less than one half of rain falls between now and the end of June, Allentown could end up top 10 driest June on record with the period of record back to 1922. Currently, as of 440 PM (0.08 since 4P), Allentown`s 1.45" ranks #8 driest. Elsewhere, with no additional rainfall, Atlantic City (1.32") would rank 15th driest and Philadelphia (1.24") 14th driest. For the month so far, deficits were generally 1.5 to 2.5 inches except nil at KILG and near 1.5" KGED and KACY. That is generally 25 to 50 percent of normal (except near normal parts of DE). Until we get any tropical rains, or the trough sharpens in the Ohio Valley, the northeast states trough pattern is unfavorable for persistent high humidity and associated widespread substantial thunderstorm generated rainfall. Operational and ensembles so far for at least the next 7 days, tend to keep paths of heavier rains to the south and north of our forecast area. In other words no significant change in we`ve been seeing the past month.
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&& .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 447P Aviation...Drag/Robertson 447P Marine...Drag/Robertson Climate...447P

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