Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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324 FXUS61 KPHI 300815 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 315 AM EST Wed Nov 30 2016 .SYNOPSIS...
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Low pressure will slowly track across the Great Lakes today into tonight, then across southeastern Canada by late Thursday. An associated cold front will cross our area during tonight. High pressure approaches later Friday, then settles over our region during Saturday into Sunday. A warm front lifts to our northwest late Monday as low pressure lifts into Canada, then a cold front approaches later Wednesday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Early this morning...Light wind field and high boundary layer RH is permitting fog to develop and some of it will be dense. Whether we issue a dense fog advisory is not known at this time though the worst of the fog conditions are not expected until between 6 am and 9 am. Today...Rain overspreads the entire region during the morning, then shifts to mostly the I-95 region northward during the afternoon as the little leftover wind shift that develops by this morning over southern DE shifts northwest during the afternoon in response to the next impulse of strong southwesterly 850mb winds. Instability is significant enough to put in an isolated tstm this morning over the Delmarva as modeled by the SPC WRF and NSSL WRF. Thereafter, am not sure about thunder. GFS/EC have good instability fields of NJ and DE near 21z/30-00z/01 but little in the way of lift so not much convection may occur at that time in the gusty southerly sfc flow of 15 to 25 mph. Winds will be light and variable from KRDG and KMQS northward through the Lehigh Valley and Poconos into far northwest NJ. A large north to south temperature gradient is forecast late this afternoon across the forecast area with highs ranging from the lower 70s (near record KGED) in southern DE to between 50 and 55 from I-80 north. Highs will be generally 15 to 20 degrees above normal. The fcst temps this aftn may be 1 to 3 degrees too warm from KMQS-PHL-ACY northward.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... Showers with maybe an isolated tstm will accompany a cold frontal passage, probably mostly in the 9 PM to 3 AM time frame tonight. Clearing from west to east toward sunrise Thursday. Patches of dense fog possible early tonight near near and north of I-78 where sfc winds will be light and variable prior to the cfp. Fcst was a 50 50 blend of the 00z/30 gfs/nam mos leaned toward the warmer nam. For qpf totals: I have storm totals of .6 to 1.25 inches. That might be a tad high and will reevaluate at 6 am. Lows will generally be around 15 to 20 degrees above normal. && .LONG TERM /THURSDAY THROUGH TUESDAY/...
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The synoptic setup starts with a closed low Thursday that eventually elongates and weakens eastward to the Canadian Maritimes Thursday night and Friday. The southwestern flank of the trough then pivots across the Northeast later Friday into Saturday before shifting east. The flow tries to go more zonal over the weekend, however a short wave undercutting a ridge looks to move through Sunday night into Monday. There is however more uncertainty with this feature. As a trough amplifies across the West later Monday, downstream ridging builds across our area Tuesday. The western trough looks to amplify quite a bit across the central part of the nation later Tuesday and Wednesday, and its eastward progression may be slowed due to this. As a result, did not rush in an associated cold front as the parent surface low lifts up into Canada Wednesday. We used a model/continuity blend Thursday through Friday night, then blended in the 00z WPC Guidance. Some adjustments were then made following additional collaboration with our neighboring offices. For Thursday and Friday...An upper-level trough/closed low from the Great Lakes to Ontario Canada is forecast to weaken and become elongated during this time frame. This occurs as a surface low develops on the triple point just to our northeast as the parent low north of the Great Lakes gradually spins down. This places a cold front offshore to start Thursday with cyclonic flow occurring. Cooling will allow for lake effect precipitation to occur however the flow looks westerly enough to keep it northwest of our area. There will be stratocumulus though with this more notable across our northwestern zones each day (potentially thinning out at night). A breeze especially Thursday will add some chill to the air. The axis of the trough looks to pivot across the area Friday night, however it looks generally dry except for perhaps a snow shower or flurries in the Poconos. For Saturday and Sunday...The upper-level trough shifts east early Saturday with the flow attempting to turn more zonal. Some ridging though arrives Sunday before perhaps a weakening short wave trough arrives Sunday night. The guidance is mixed with this feature, however some solutions suggest it may shear out some as it runs into a confluence area downstream (the 00z ECMWF is rather wet starting Sunday night, which looks to phase systems resulting in a stronger and faster scenario). The shearing out option is seen via some guidance as a weakening precipitation shield. For now given the uncertainty, we kept the PoPs on the low side and limited the amount of precipitation types. There should be more cloudiness especially later in the weekend with the incoming system. For Monday and Tuesday...This time frame features an amplifying upper-level trough across the West, which will drive some ridging downstream. There is the potential for a lead short wave trough, potentially robust, that ejects northeastward from the Gulf coast states well ahead of the main trough. This would toss some precipitation our way Monday into Tuesday as high pressure sits to our north. As noted above, there is quite a bit of variability in the guidance with this possible short wave and also timing differences. The main system may be low pressure running northeastward from the Plains to the Great Lakes then into Canada. Given the sharpening associated trough, the eastward progression of this system might be slowed and therefore delaying any precipitation for our area. Given much more uncertainty, tried to keep the forecast closer to continuity.
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Early this morning prior to 12z...Light wind with MVFR and IFR cigs slowly degrading to widespread IFR fog/stratus by 12z/30 with patches of LIFR. Today after 12z...IFR conds in stratus fog will improve with the onset of rain..some briefly heavy. IFR Conditions should improve to MVFR CIGS during mid-late afternoon KTTN/PHL/KPNE/KILG/KMIV/KACY as southerly winds increase, however, IFR/LIFR conds in st/fog/periods of rain continue KRDG/KABE. Thunder potential, especially this morning over the Delmarva. Tonight...MVFR and IFR conditions in st/fog and band or two of moderate to heavy showers with a small chance of thunder. Clearing and eventual improvement to VFR from west to east after 06z. Low level wind shear is possible in the evening due the the expectation of a 40 to 50 knot low level southwesterly jet at that time, especially affecting airfields from KTTN, KPHL and KILG eastward. OUTLOOK... Thursday and Friday...VFR overall. West-northwest winds 10-15 knots with gusts to 20 knots, however diminishing during each night. Saturday and Sunday...VFR for much of time. A storm system may approach Sunday night with some precipitation, however there is uncertainty with this system.
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&& .MARINE...
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SCA continues through at least tonight. Right now its for seas of 5 feet or greater but the southerly wind will once again gust 25-30 kt this afternoon/evening, then gusty westerly late tonight. There could be an hour of gales either side of the cold frontal passage tonight. A thunderstorm is possible this morning over the DE waters and then late today or this evening any of the waters but confidence is below average on thunder occurrence. OUTLOOK... Thursday through Saturday...Pressure gradient hangs on enough for much of this time frame with cooler air, therefore gusts to about 25 knots are anticipated mainly for the Atlantic coastal water zones. This will keep seas elevated as well. Small Craft Advisory extended through the day Thursday for now. The conditions should then be below advisory criteria Saturday night. Sunday...Winds and seas are currently forecast to be below advisory criteria due to weaker flow.
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&& .HYDROLOGY...
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For today and tonight...Additional rainfall is expected to favor the 0.60 to 1.25 inch range. We are still not expecting main stem flooding or even smaller basin flooding since these rainfall amounts will be spread out and the antecedent conditions were rather dry. Poor drainage flooding is always a possibility especially during heavier rainfall rates but impacts from this type of flooding are generally minor, except for travel during the morning and evening commutes.
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&& .CLIMATE... PHL should average 50 degrees for the month or 2.4 above the average of 47.6. Will post the expected monthly rankings of temperature if top 15, around 5am Wednesday. Meanwhile... Daily record High temperatures for Wednesday 11/30 where they appear vulnerable to being within 2 degrees of record. GED 74 - 2006 Daily record rainfall values for Nov 30. NOV 30 ACY 1.25 1923 PHL 0.96-1972 ILG 1.28-1934 ABE 0.86-1923 TTN 0.76-1898 GED 1.71-1987 RDG 1.52-1987 MPO 3.00-1923 We just missed a record equaling amount for the 29th at ABE by about .04 hundredths. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EST Thursday for ANZ450>455. Small Craft Advisory from 7 PM this evening to 3 AM EST Thursday for ANZ430. Small Craft Advisory from 4 PM this afternoon to 3 AM EST Thursday for ANZ431.
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&& $$ Synopsis...Gorse Near Term...Drag Short Term...Drag Long Term...Gorse Aviation...Drag/Gorse Marine...Drag/Gorse Hydrology... Climate...

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