Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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927 FXUS61 KPHI 202057 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 357 PM EST Mon Feb 20 2017 .SYNOPSIS...
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High pressure will build over the Mid Atlantic states through tonight, before shifting offshore. A warm front will slide through our region Wednesday morning. A cold front may edge down into eastern Pennsylvania and New Jersey early Friday before retreating northward Friday night. Low pressure over the Great Lakes region Saturday morning will send a cold front off the east coast Saturday evening, as the storm heads across Quebec. High pressure follows across the mid Atlantic states Sunday night.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... While cooler than the weekend, another mild February afternoon in progress with temperatures running warmer than guidance. Boundary layer warmth continues to win out. As a sharp upper-level trough/closed low continues to exit the New England coast through early this evening, a narrow but high amplitude ridge will approach our area through tonight. This will drive strong surface high pressure over our area during the course of tonight, bringing with it subsidence. The flow aloft will start to switch from north-northwest to southwest toward daybreak as the aforementioned ridge axis nears our region. This will result in increasing warm air advection up the Ohio Valley. The ridge axis is very pronounced, which may limit the amount of high level clouds making it to our area through the overnight within the warm air advection pattern aloft to our west. As a result, we slowed down the gradual increase in some of the high clouds through the night. This introduces more of a challenge regarding the low temperature forecast. The dew points have been dropping this afternoon from north to south due to subsidence and more efficient vertical mixing. This should relax some this evening as the mixing diminishes, however the northerly flow should drop the dew points a bit more especially across the northern areas. For now we stayed closer to a MOS blend, which results in no major changes from continuity. Temperatures may drop quicker this evening as the winds diminish more combined with lower dew points, especially for inland and the more sheltered areas. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... A high amplitude ridge will slide across our area through early afternoon Tuesday, before shifting offshore. This will push surface high pressure offshore, allowing for a southeasterly surface flow to develop. Low pressure up near Hudson Bay will have a trailing cold front southward to the Tennessee Valley, with a closed low tracking across the Gulf Coast states. The flow turns more southwesterly aloft ahead of these features across our region, which will contribute to some increasing warm air advection aloft. An upper-level jet streak is forecast to be moving across the Great Lakes Tuesday, which may help contribute to some mid to high level clouds across our area through the day. Overall, some increase in clouds are expected as we go through the day ahead of a developing warm front. Despite some warming aloft Tuesday, the low-level flow is expected to be out of the southeast which will help keep temperatures cooler. This will keep the immediate coastal locales even cooler given the wind off the chilly ocean. High temperatures were mostly a blend of MOS and continuity, with some tweaks especially along the coast. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
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Draft with a 4 PM update probable. 500 MB: A ridge persists over the mid Atlantic states through most of Saturday before a strong short wave departs the Great Lakes for eastern Canada later in the weekend. The ridge reemerges a little further south, off the mid Altantic coast, early next week. Temperatures: As our forecast area proceeds to a 1st or 2nd warmest February on record and a top 10 warmest winter in the period of record dating back to the late 19th century, calendar day averages Wednesday are expected to be 10 to 15 degrees above normal, 17 to 22 degrees above normal Thursday, nearly 25 degrees above normal again Friday (see yesterdays average temperatures in our area), around 15 degrees above normal Saturday depending on the cold air advection subsequent to the late Saturday CFP, still 2 to 7 degrees above normal Sunday and Monday. Forecast basis: Unless otherwise noted, a 50 50 blend of the 12z/20 GFS/NAM MOS guidance Tuesday night; adjusted warmer guidance Wednesday per the 4 Pm max`s on GGEM 2m temp and NAM boundary layer temp; warmer adjusted mav/met guidance, then thereafter close to the 15z/20 WPC guidance Thursday - Monday. The continuing daily cool bias in the daytime max temperature guidance of the last several days is probably related to the lack of snow cover and the persistent and climatologically anomalously warm jet stream pattern. The dailies including any possible significant insight... Tuesday night...Chance of light showers during the night ahead of a warm front. Low probability there could be a touch of freezing rain highest terrain above 1500 feet north of I-80. This ice risk isn`t in the HWO or zones since confidence is below average and guidance favors above freezing min temps during any rain. Confidence: average or below average regarding the occurrence of any rain. Wednesday...Considerable morning cloudiness, then becoming partly sunny and warmer during the afternoon. Near record warmth still (vulnerable records) possible though some of the cooler 2m temp and MOS guidance does raise a cautionary flag. Our 330 PM forecast temps may end up a degree or warmer than now predicted. This fcst is above all available guidance and reflects the recent cool bias in max temps the past several days... the warm regime with a 550DM 1000-500mb thickness. Max temps probably occur around 330 or 4 PM due to the warming southwest flow and boundary layer temps reaching 13C at 21z. southwest wind but much cooler coastal seabreezes. Confidence: average..ie less than yesterday. Wednesday night...Fair (thin high clouds). patchy fog possible in a few countryside locations. Thursday...Mixed clouds and sun. Near record warmth still possible though some of the cooler 2m temp and MOS guidance does raise a cautionary flag. Models may be rain contaminated. So there is uncertainty. Much cooler coastal sea breezes embedded within the southwest gradient wind. BL temp right now only fcst to 14C PHl but 18C Delmarva...all this because of modeled showers which if occurred would reduce max temps to the 60s. Confidence: average...ie less than yesterday and throwing caution to the wind because of a shower risk. Friday...early morning stratus/fog possible along a cool front that may settled into the Nj and PA portion of our area? Maybe a shower north of the boundary during the afternoon or maybe the boundary doesn`t make it down into our forecast area? otherwise considerable clouds. Wind probably southeast turning south to southwest. Confidence: below average on the scenario. Saturday...Models slowing down and warming. It should shower for a few hours along and head of the cold front with a chance for a gusty thunderstorm. Wind fields pretty strong, weak cape but unstable with swi near -2 and tt 50. Dewpoints probably close to 60 in a sliver ahead of the cold front. Could have a squall line and embedded isolated severe thunderstorms if the strong wind field instability maintains. Confidence: average. Sunday...Becoming mostly sunny and cooler but still above normal temps as the sfc low moves northeast into Canada taking the primary chunk of colder air east northeast with it, making it difficult to import too much of the cold air here, from the midwest. Still it will be cold. Breezy. Westerly Gusts to 25 or 30 mph. Confidence: average. Monday...increasing clouds ahead of the next Midwest toward the Great Lakes low pressure system. WAA precipitation may arrive late in the day or at night. Confidence: below average.
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&& .AVIATION /20Z MONDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of this afternoon...VFR. North-northwest winds 10-15 knots with some local gusts to 20 knots at times, diminishing toward early evening. Tonight...VFR. North to northeast winds 5 knots or less, or becoming locally light and variable. Tuesday...VFR with some increase in clouds mainly above 15000 feet. Winds becoming southeasterly during the morning at 10 knots or less. Outlook... Tuesday night...VFR with a small chance of shower. light south wind. Wednesday and Thursday...Mostly VFR conditions with ocnl cigs aoa 5000 ft. There could be a little MVFR fog late each night. south to southwest wind . Friday...VFR but north of a possible quasi stnry front it might become MVFR in a shower. east southeast wind ahead of the warm front and southerly gusty 20 kt south of it and this front should edge north during the afternoon and at night. Saturday...VFR cigs with a period MVFR conds and gusty southwest winds to 30 kt in showers and a possible tstm ahead of a CFP.
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&& .MARINE...
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The conditions are expected to remain below Small Craft Advisory criteria through Tuesday. High pressure will slide across our area tonight before moving offshore during Tuesday morning. This will result in northwest to north winds with gusts up to 20 knots to diminish, and turn northeast to east before becoming southeasterly Tuesday. There could be somewhat of an enhancement to the southeast flow Tuesday nearshore and up Delaware Bay, however winds are expected to remain under 20 knots. Outlook... Tuesday night through Friday...Winds and seas should stay below SCA criteria. A gradual shift from southeasterly to southwesterly is expected Tuesday night. By Thursday night, winds could be light and variable shifting to southeasterly on Friday in response to a weak cool front briefly settling southward into our area. Saturday...SCA south to southwest wind conditions likely ahead of a late day or nighttime cold frontal passage.
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&& .CLIMATE...
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Records for later this coming week. Most of these records will probably remain intact as is, but there appears to be opportunity for approaching within 2 degrees at PHL/ABE/TTN/MPO on 1 to 3 days. Wednesday 2/22 Thursday 2/23 Friday 2/24 ACY 68-1991 72-1985 75-1985 PHL 68-1997/1974 75-1874 74-1985 ILG 69-1997/1974 72-1985 78-1985 ABE 68-1974 71-1985 76-1985 TTN 66-1997 74-1874 74-1985 GED 72-1997 no data no data RDG 70-1974 72/1932/1922 77-1985 MPO 56-1997 60-1977 60-1984 The following monthly and seasonal expectations were number crunched with our forecast at 9am this morning. There is still some large model and forecast variability, but even with daily errors...it should all wash out to the rankings we have posted. We checked our past 24 hr max/mins through 7AM, as well as the new max/min fcst from our office issued at 330 AM and then normal max/min the last two days of the month. That also accounts for possible midnight mins tonight at PHL ILG ABE, and also likely midnight mins Saturday night the 25th. If there is some downside error, it would only lower the monthly average by around half a degree. We continue confident that a widespread top 2 warmest February on record will occur in our forecast area and a top 10 warmest winter season... records dating back to the late 19th century. Confidence: well above average. Details below. February: PHL 43.3. #1 Normal 35.7 Record 42.2-1925 POR 1874 ABE 37.6 #2 Normal 30.7 Record 38.6-1998 POR 1922 ACY 42.2 #1 Normal 35.3 Record 41.6-1890 POR 1874 ILG 42.3 #1 tie Normal 35.1 Record 42.3-1903 POR 1895 Winter (DJF) PHL 40.1 #7 ABE 35.4 #5 ACY 39.6 #10 ILG 39.1 #6 tie Past two years of monthly average temperatures through February 2017, a summary of above normal months listed below: For ABE: 23 consecutive months of above normal temps! FOR PHL: 22 of the past 23 months have been above normal. For ACY: 19 of the past 23 months have been above normal. For ILG: 17 of the past 23 months have been above normal. (Jan Feb March 2015 was the last time we had significant and persistent below normal monthly temps.) Snow: February least on record: Atlantic City should/could end up tied for 5th.
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&& && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Drag 357 Near Term...Gorse Short Term...Gorse Long Term...Drag 357 Aviation...Drag/Gorse 357 Marine...Drag/Gorse 357 Climate...357

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