Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 161424 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 924 AM EST Mon Jan 16 2017 .SYNOPSIS... High pressure over our region will move offshore this afternoon. Low pressure tracking into the Lower Great Lakes Tuesday will redevelop near Long Island Tuesday night and head east. A cold frontal passage occurs Wednesday. High pressure follows to the east coast Thursday and Friday. Weak low pressure forms near the North Carolina coast Friday evening. Much larger low pressure develops over the nations midsection late in the weekend, approaching the mid Atlantic coast on Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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High pressure across the area today will move to the east through the day. Skies will only feature some high clouds much of the day before increasing mid/low clouds arrive from sw to ne during the afternoon. Precipitation is not expected. High temperatures will climb from our frosty morning temps up into the upper 30s/low 40s. Winds will be light mostly from the southwest. How quickly the temperatures rise across northern parts of the region that radiated efficiently last night with a snowcover will be the main issue today.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
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Warm air advection and increasing amts of low level moisture will arrive over the area tonight. It will be cloudy overnight with a small chance for (mostly) light rain across the area. Higher pops will be in the wrn areas (30 pct pop) while these taper back to slgt chc across ern/srn areas. There is some chc that precip could begin as some sleet/freezing rain across the Nrn/Wrn areas tonight. The overall small-ish pops and limited confid in p-types, keep me from issuing any wsw flags at this time. It`s possible this could change later today however. Low temps will range from the low 30s north to the upper 30s across Delmarva and se NJ. Update 9:30 am: Going to evaluate 12z guidance and make a additional update to the forecast in this period once the NAM/RGEM/GFS come in along with the most current RAP/HRRR around 11 am.
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&& .LONG TERM /TUESDAY THROUGH SUNDAY/... 500 MB: Above normal heights prevail with the strong positive anomaly shifting north to Hudson Bay late in the week while strong cold troughs develop in the westerlies between 30 and 40 N: off the west coast, lower Mississippi Valley and western Atlantic by next Sunday night. Temperatures: the first two weeks have averaged above normal... generally 2 to 3 degrees. There is little chance for excessive cold in our outlook for the next two weeks, in a way good news, as we are now in the heart of winter. Everything above normal now is a plus when it comes to heating costs. And above normal it is...statistical guidance indicates averaging about 8 degrees above normal Tuesday, then 10 to 15 degrees above normal daily Wednesday through Sunday. With this in mind, it is difficult to see this month averaging normal, for it would take quite a few days of well below normal temps to lower the monthly average. Forecast basis: Unless otherwise noted, a 50 50 blend of the 00z/16 GFS/NAM MOS guidance Tuesday-Wednesday, thereafter the 00z/16 GFS MEXMOS Wednesday night and Thursday, and then the 05z/16 WPC guidance Thursday night-Monday, at times blended with the 00z/16 GFS MEXMOS guidance or the long term temps were adjusted because of the 00z/16 ECMWF 18z 2m temperatures. The dailies... Hazards: We may need an ice hazard Tuesday morning for portions of ne Pa and far nw NJ but not enough confidence on rain occurrence coinciding with below freezing temps, to issue an advy attm. Tuesday...maybe elevated ice northeast PA to start the day but its probably all non freezing rain by 15z, otherwise rain developing by late in the day everywhere as low pressure forms near or over NJ late in the day. Rain probably continues into the evening. Best chance for most persistent rain is PA and NJ north of I-78. Stratus and maybe some fog at night with a chance of a drizzle. Lowered guidance temps a few degrees, this especially per the 00z/16 ECMWF. Confidence: Above average. Wednesday...morning showers as the sharp trough aloft digs southeast over the area, then north-northeast winds develop north of I-78 in the afternoon where it remains cloudy and cool. meanwhile PHl to ACY southward, west northwest winds gusts 20-25 mph during the afternoon. Clearing likely at night with slowly diminishing north to northwest wind. Confidence: Above average. Thursday...Partly cloudy. Northwest wind. Confidence: Above average. Friday...increasing clouds. Light wind. Confidence: Above average. Late friday afternoon and night...A period of rain. Northeast wind. Small chance of glazing developing north of I 80. Confidence: average due to uncertainty with the northern extent of the rain shield. The 00z/16 GEFS is edging north and so the forecast rain chance may be significantly too low. Saturday into Sunday...Partly cloudy. Confidence: average Sunday night...Rain possible. Confidence: Above average. This rain ahead of a probable large storm system approaching from the central USA. && .AVIATION /15Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. High pressure is cresting across our terminals early this morning and it will move east today and tonight. There are just some high level clouds across the area now and it should remain this way through much of the morning. Light and variable winds will become southwest around 5 knots by afternoon. Increasing clouds and lowering cigs late this afternoon and tonight. MVFR cat cigs and possibly some light fog can be expected overnight. Low chance of a sprinkle or maybe some sleet at KRDG-KABE after midnight. I probably will not mention this in the 12Z TAFS unless pops are higher than slgt chc. OUTLOOK... Tuesday into Wednesday morning...Widespread MVFR conditions develop across the region, especially at TTN, ABE, and RDG (near and to the north of a warm front), where IFR is likely. In addition, fog/stratus Tuesday night should also lead to widespread IFR conditions at times across the area, possibly LIFR vcnty KACY. Light wind. Confidence: above average. Wednesday afternoon...Conditions slowly improving to VFR late in the day or evening. Winds turn north or northwest after a cold frontal passage with gusts of 20 knots possible PHL southward. Confidence: above average. Thursday..Predominantly VFR conditions. Northwest winds. Confidence: average. Friday...VFR ceilings may deteriorate to MVFR from south to north across the terminals. Winds become northeast. Confidence: average due to the uncertainty associated with the north edge of the rain shield. && .MARINE... High pressure across the waters today will move east tonight. Winds and seas will be rather tranquil through the period. Fair weather is expected today and there is a small chc for a shower tonight. OUTLOOK... There is a low probability of southerly winds approaching Small Craft Advisory criteria Tuesday night into Wednesday ahead of a cold front. There is a moderate probability of northwest winds approaching Small Craft Advisory criteria behind the cold front Wednesday and Wednesday night. Seas may also approach 5FT during these time frames. At this time, no advisory issuance due to less than 80 percent confidence that criteria can be equaled or exceeded for 2 hours. With a relatively mild moist air mass (dewpoints 40s) moving over the cooler maritime waters (ssts mid 30s to mid 40s) in association with a warm front Tuesday afternoon into Wednesday morning, we expect areas of fog to develop during this period. Thursday and Friday...Winds and seas are anticipated to remain below SCA thresholds. Confidence: Above average for no SCA headlines. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Drag Near Term...Gaines/O`Hara Short Term...O`Hara/Gaines Long Term...Drag Aviation...Drag/O`Hara Marine...Drag/O`Hara

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