Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 240249 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 949 PM EST Mon Jan 23 2017 .SYNOPSIS... Strong low pressure near the Virginia Capes early this evening will drift northeast toward Long Island through Tuesday morning, before passing east of Cape Cod Tuesday evening. Weak high pressure crosses our region on Wednesday. A cold front passes southeastward off the mid Atlantic coast Thursday and with another cold frontal passage possible again Sunday or next Monday. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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For the 930 PM Update...The Wind Advisory remains in effect for the coastal counties through Midnight. We added a bit more ice to the storm total amounts mainly for locations at and above 1900 feet in the Poconos. We received a report from Tobyhanna, PA at an elevation of 2100 feet of an estimated 0.20 inches of ice with some trees down. The downed trees appear to be due to the combination of the icing and gusty winds. At elevations below this, icing amounts should be lower. This may result in less snow/sleet accumulations overall, although some change to sleet and snow is still possible overnight as some cooling may take place. A very dynamic storm centered to our south, with ample lift to its north due to an intense easterly low-level jet along with robust warm air advection in about the 800-850 MB level. This is occurring as cooler air and some lower dew points have advected southwestward from points to our north. This has lowered the wet bulbing across the far northwest zones, with freezing rain and sleet occurring especially mainly at and above 1000 feet in elevation. Some reports indicate rather icy road conditions in the higher elevations of Monroe and Carbon counties in Pennsylvania. A distinct dry slot has worked northward and is now across about the southern half of our area. This should fill in some on the southern side as additional lift arrives and a pivot may occur with the surface low off the coast moving northward. It appears that the chance of steadier rainfall particularly across our southern zones has decreased quite a bit (some drizzle looks to be occurring though). Otherwise, most of the precipitation will fall as rain with some sleet possibly mixing in overnight just north and west of I-95. For Carbon and Monroe, Pennsylvania and Sussex, New Jersey, portions of these counties especially higher elevations are expected to be below freezing through tonight. So a wintry mix is expected across portions of these counties, especially the higher elevations. The question becomes how much of each P-Type falls across the area. Forecast thermal profiles vary through the night and we could give a period of each, freezing rain, sleet, and some snow. We are expecting 2-5 inches of snow/sleet combination as well as up to about one quarter of an inch of ice. Therefore the Winter Weather Advisory remains in place. It is possible that more freezing rain/sleet ends up occurring, which would make the snow/sleet amounts less than forecast. Generally 1 to 2 inches of storm total QPF are forecast for much of the area, with the Delmarva and southern New Jersey seeing the least and portions of northeast New Jersey seeing the most. We continue with the Flood Watch for northeastern New Jersey which has 1.5 to 2 inches QPF, and isolated higher amounts possible. Winds are expected to diminish some through the night, but will remain gusty at times especially closer to the coast.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... The coastal low will slowly drift to the east northeast during the day Tuesday. As the low moves away from the area, we could get some wrap around moisture across the area which could keep some light precipitation through the day. Current forecast temperatures would keep everything rain for most areas, except where the Winter Weather Advisory is in effect. If temperatures do not rise much during the day, it is possible that some areas could see snow or sleet mix in at times with any rainfall that occurs. For the areas under the Winter Weather Advisory, they have the better chance of seeing a winter mix into the day. For now, we will keep the end time of noon time, but this may need to be extended in time in the future. Winds will become northwesterly as the low moves to farther to our east and will remain gusty through the day with gusts around 20-25 mph expected. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... 500 MB: Weak ridging follows the departure of our coastal storm Tuesday night and Wednesday, followed by a series of short waves that carves out a positive tilt trough in the eastern USA. Temperatures: around 10 degree above normal Wednesday, 10 to 15 above normal Thursday, 5 to 10 above normal Friday, cooling to near normal Sunday and Monday. Forecast basis: Unless otherwise noted, a 50 50 blend of the 12z/23 GFS/NAM MOS guidance Tuesday night-Wednesday night, thereafter the 12z/23 GFS MEXMOS Thursday and Thursday night, and then the 15z/23 WPC guidance Friday-Monday, at times blended with the 12z/23 GFS MEXMOS guidance or the long term temps were adjusted because of the 12z/23 ECMWF 18z 2m temperatures. The dailies... Tuesday night and Wednesday: a little leftover mixed precipitation is possible but it should not last long, if there is any. Conditions dry out Tuesday night as high pressure builds into the region and moves offshore during the day Wednesday. Gusty northwest winds to 20 or 25 mph Tuesday night and Wednesday morning become west or southwest Wednesday afternoon and diminish a bit. Wednesday night and Thursday...warm air advection ahead of cold front. Maybe a few showers. Lots of uncertainty regarding whether it will rain. Blended the MEX POPS with the previously drier forecast. Later Thursday into the weekend...gradual cool down with generally dry weather expected. Breezy at times. Next Monday...by then another cold front has either passed or is passing and the GFS is the first of our usual reviewed global models to suggest low pressure forming on the front over the mid Atlantic states. To say the least, uncertainty and so we stayed with the dry WPC fcst. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. MVFR/IFR ceilings tonight. As areas of rain and drizzle occurs VSBYS will lower especially during any heavier rain. There will be a break in the rain for awhile from about PHL on south and east. Some sleet or snow may mix in at ABE and RDG later this evening and overnight. Conditions are expected to return to MVFR during the day Tuesday. Northeast winds 15-25 knots with gusts 30-40 knots (strongest gusts in the MIV and ACY areas), will diminish some during the remainder of this evening and especially overnight. The winds will turn north and then northwest later tonight and Tuesday, with speeds in the 10-20 knot range Tuesday with some gusts. OUTLOOK... Tuesday night and Wednesday...VFR. NW winds 10-15 KT with gusts to 20 kt with winds backing to west in the afternoon. Late Wednesday night or Thursday...Isolated showers, possibly briefly lowering conditions to sub-VFR. Friday and Saturday...VFR. West winds 10-20 KT with gusts 25 to 30 kt.
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&& .MARINE... An intense easterly low-level jet continues to move northward along with the tightest pressure gradient. This is allowing the winds to diminish some across much of the area. As a result, the remaining Storm Warning has been lowered to a Gale Warning. This ends from south to north later tonight and early Tuesday morning. Small Craft Advisory level winds are then expected on Tuesday. Seas are in the 10-20 foot range (mainly 3-7 feet on Delaware Bay), however these will slowly subside late tonight and during Tuesday. OUTLOOK... Tuesday night...northwest SCA, possible low end leftover gale early in the evening. Wednesday...Sub-SCA conditions expected. Thursday through Friday...West wind gusts 25-30 KT possible. Saturday...West wind gusts 20-25 knots possible. && .HYDROLOGY...
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Flood Watch remains in effect tonight for central and NE NJ, where the flooding risk is highest (heaviest rainfall and most prone to flooding issues in urban locales). Impacts will be due to excessive rainfall, as between 1.5 and 2.0 inches of rain with locally higher amounts are expected through tonight. No main stem river flooding is anticipated. However, minor flooding is possible along small streams and creeks and in areas of poor drainage. The entire region has some positive things working in its favor, precipitation has been below normal the last 30 days, there`s really no consequential snow cover to speak of, there`s no ice on area waterways, streamflows are either running at or below normal as is soil moisture, and last but not least, the ground isn`t frozen. We think all the above will help mitigate the flood threat especially for our counties outside the Flood Watch.
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&& .TIDES/COASTAL FLOODING...
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We experienced areas of minor coastal flooding along the coasts of Delaware and New Jersey this morning. There was widespread minor flooding and areas of moderate flooding during the late afternoon and evening. Numerous roads were affected. A Coastal Flood Warning remains in effect through Tuesday morning along the NJ and DE coasts and along Delaware Bay. Storm surge values of 2 to 3 feet are possible at that time. Fortunately, the astronomical tides are low. Nevertheless, we should see tide levels on Tuesday morning a bit lower than those experienced this evening. Strong wave action and the resulting beach erosion will likely compound the effects of any tidal surge. Waves breaking along the shore may be around 4 to 7 feet on Tuesday morning. Based on the forecast guidance and the expected wind shift to the north then northwest we are not anticipating any coastal flooding on the upper eastern shore of Maryland or on the tidal Delaware River. The wind shift will result in a decreasing potential for flooding along the coast and along Delaware Bay beyond Tuesday morning.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...Winter Weather Advisory until 11 AM EST Tuesday for PAZ054-055. NJ...Flood Watch until 5 AM EST Tuesday for NJZ008-010-012>015-020- 026. Coastal Flood Warning until 11 AM EST Tuesday for NJZ012>014- 020>027. Wind Advisory until midnight EST tonight for NJZ013-014-020- 022>027. Winter Weather Advisory until 11 AM EST Tuesday for NJZ001. DE...Coastal Flood Warning until 11 AM EST Tuesday for DEZ002>004. Wind Advisory until midnight EST tonight for DEZ004. MD...None. MARINE...Gale Warning until 6 AM EST Tuesday for ANZ450>453. Gale Warning until 1 AM EST Tuesday for ANZ430-431-454-455.
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&& $$ Synopsis...Drag Near Term...Gorse/Robertson Short Term...Robertson Long Term...Drag Aviation...Drag/Gorse/Robertson Marine...Drag/Gorse/Robertson Hydrology...Gorse/Kruzdlo Tides/Coastal Flooding...Iovino

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