Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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695 FXUS61 KPHI 081445 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 945 AM EST Thu Dec 8 2016 .SYNOPSIS... An area of low pressure will continue to slowly drift across eastern Canada today through Friday, and end up south of Greenland by Saturday. With high pressure to our west, a strong west to northwest flow will remain through the end of the week. High pressure briefly affects the area Saturday night, then moves offshore Sunday. A warm front is expected to lift across the area Sunday night, before an area of low pressure is forecast to move near or just north of the area around Monday. This system will pull a cold front across the area Monday, then another quick moving frontal boundary may move across the area around Tuesday night. && .NEAR TERM /THROUGH TONIGHT/... 930 AM ESTF: little change to the 735 AM update. 12z version of the NAM/HRRR and reality observed data continue to advertise a period of light showers for the Delmarva into midday asstd with trough aloft and 100m+ 500 mb hfc heading east from OHIO Valley w PA this morning and the asstd sfc wind convergence. Gusty west wind to 25 MPh developing mid afternoon. Highs were raised a deg or 2 for mid afternoon highs subsequent to the abrupt west to east clearing expected Noon-2PM. Tonight...from the mid shift and will update at 2 PM. colder air will continue to settle in over the region thanks to the continued northwesterly flow (and associated cold air advection). The pressure gradient across the region will continue to increase as the trough moves further east, so winds are not expected drop off much overnight. This will mean we won`t have efficient radiational cooling conditions, but given the cold air advection, lows tonight will as much as 10 degrees lower than what we will see this morning. && .SHORT TERM /FRIDAY/... Cold air advection and streamers from the Great Lakes as well as cold trough aloft increase the snow squall probabilities tomorrow and so at least sct flurries. W ill update the details at 2 PM. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... FB posted and tweeted WPC mid shift Day 4 winter prob 1/4" w.e. outlook. Low pressure continues to drift across eastern Canada Friday, then moves offshore and ends up south of Greenland by Saturday. Meanwhile high pressure remains across the central part of the country. This will keep a steady west to northwest flow across the area. On Friday, although the strong vorticity impulse is expected to be east of the area, there will remain steep low-mid level lapse rates across the area with enhanced moisture as well. With the strong northwest flow, it is possible that some lake effect streamers could set up and bring some snow showers/flurries to portions of the area. The best chances would be across the northern portions of the area, so we keep scattered/isolated snow showers/flurries there. Elsewhere we will keep isolated flurries/sprinkles. On Saturday, the steep lapse rates and moisture combination lifts northward some. We`ll keep isolated snow showers/flurries for the far northern counties, but will keep flurries/sprinkles for the middle half of the area as the northwest flow begins to weaken some, so the flurries may not have as great of a reach southward as on Friday. While most areas probably won`t see much snow accumulation Friday and Saturday, if any snow bands or squalls do develop, it would not be surprising to see some accumulating snow in some areas. High pressure briefly affects the area Saturday night, providing dry conditions. Friday and Saturday will be a cold and windy period, with Friday being the windiest, and Saturday being the coolest of the two. The high builds offshore Sunday ahead of the next storm system. As this happens, it is possible that some showers could develop during the day across the area as a short wave passes just to our north and spreads an area of moisture across the area. However, the best chance of precipitation looks to be Sunday night into Monday. A warm front is forecast to lift across the area late on Sunday night into Monday as an area of low pressure is forecast to move near or just north of the area. Conditions should be cold enough overnight Sunday into Monday for a period of snow to affect a good portion of the area, before much of the area warms up and precipitation turns to rain during the day Monday. There is the potential for an accumulating snow for much of the area, with the northern half having the greatest potential. As the low continues to lift northward, a cold front is expected to move across the area late in the day Monday and overnight. Precipitation chances should diminish behind the cold front. On Tuesday and Tuesday night, the GFS is indicating another cold front moving across the area as low pressure passes to our north. It in turn brings a period of rain and snow to the area late Tuesday into early Wednesday. The ECMWF does not have as strong of a cold frontal passage, so it does not bring any precipitation to the area. For now, we`ll introduce a small chance into the forecast. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR cigs aoa 4000 ft this morning becoming sct clouds this afternoon. scattered brief shower for an hour or two near and south of KMIV later this morning. west wind with gusts increasing 22 to 28 kt during mid afternoon. Tonight...VFR mostly clear. wnw wind with scattered gusts 15 kt possible. Friday...Generally VFR sct-bkn aoa 4000 ft, although CIGS may briefly lower to MVFR in scattered snow showers e PA nigher terrain. Gusty west to northwest winds 22-30 knots. OUTLOOK... Friday night - Saturday...Generally VFR, although CIGS may occasionally lower to MVFR. Scattered showers or flurries/sprinkles are possible during the daytime of each day which may temporarily lower conditions. Gusty west to northwest winds 15-25 knots, strongest winds Friday which may approach 30 knots at times. Sunday...VFR early, possibly lowering to MVFR by the afternoon. Rain or snow possible late in the day. Sunday night-Monday...Conditions continue to lower to MVFR and then IFR. Rain or snow becoming likely. Accumulating snow possible for eastern Pennsylvania, much of New Jersey, and the northern portions of the Delmarva. && .MARINE... Winds will increase around midday today for what will be a prolonged small craft advisory event. Considered a gale warning for lower De Bay and adjacent 453, 54, 55 for the prd 21z today - 11z Friday. Am pretty sure we`ll see mid 30 kt gale gusts some time this evening but no issuance at this 930 am issuance, at least not until can categorically be sure. The wind orientation down De Bay, steep lapse rates possibly manufactures several more kts of wind than modeled in the caa pattern. NAM sounding indicates mid 30s gales possible. May need a marginal mid 30s gale for the remainder NJ waters 10z Friday - 06z Saturday but no decision until late today. OUTLOOK... Friday night-Saturday...Small Craft Advisory in effect through Friday night, which may need to be extended into Saturday. Winds may approach gale force at times on Friday. Saturday night...Winds expected to drop below Small Craft Advisory levels, but pick up again late Sunday. Sunday-Sunday night...Winds may increase and approach Small Craft Advisory levels at late in the day into the overnight. Monday...Small Craft Advisory conditions possible. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EST Saturday for ANZ430-431- 450>455. && $$ Synopsis...Robertson Near Term...Drag/Johnson 945A Short Term...Drag 945A Long Term...Robertson/Drag 945A Aviation...Drag/Robertson 945A Marine...Drag/Robertson 945A

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