Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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143 FXUS61 KPHI 232350 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 650 PM EST Tue Jan 23 2018 .SYNOPSIS...
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In the wake of a strong cold front, high pressure will build east through the remainder of the week, before moving out to sea Saturday. A cold front and low pressure then arrives from the west on Sunday and proceeds offshore next Monday.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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Low pressure continues to move across eastern Canada and far northern New England this evening. Its cold front has shifted off the Mid-Atlantic coast, with cooling now overspreading the region. The dew points are also dropping from west to east. The last of the showers have shifted offshore, and any showers well to our west and northwest associated with the southern extent of the closed low are expected to remain there. Much of the cloud cover has thinned out, however some stratocumulus associated with the cold air advection are lurking to our west. Some of this may spill into our western zones for awhile. A west-northwest wind has taken over now and this has become gusty for much of the region, as the boundary layer is still on the mild side and with cooling aloft better mixing is occurring. This should continue for awhile longer before some decoupling occurs for may spots. Therefore, increased the winds some for a time tonight. This update also adjusted the temperature and dew point grids based on the latest observations, then the LAMP guidance was blended in to help assist with trends.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... A secondary cold front crosses the region early in the morning with the remainder of the day featuring breezy NW winds due the pressure gradient between the low over Atlantic Canada and high pressure over Ontario. Conditions will be dry under a mix of sun and clouds as some Cu develops due to diurnal heating. Highs range from the upper 20s to low 30s across the southern Poconos to the upper 30s to mid 40s elsewhere. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... With ongoing weather earlier today, few changes made in the long term from the previous forecast. 500MB: Another short wave trough moves a cross the mid Atlantic coast Wednesday night followed by substantial ridging Friday and Saturday, then another trough develops to the east coast next Sunday and Monday. Temperature: Calendar day averages should range between 3 and 7 degrees above normal Wednesday, near normal Thursday and Friday, on Saturday near 10 degrees above normal, Sunday probably 12 to 18 degrees above normal, cooling a bit to 5 to 10 degrees above next Monday. Forecast basis: Wednesday-Thursday is based on a blended 00z/22 GFS/NAM MOS, Thursday night-Friday was based on the 00z/22 GFS MEX MOS and then D4-8 was based on the 0441z WPC guidance. Thursday...Mostly sunny and brisk. Northwest gusty 20-25 MPH. Max temps 2 to 7F below normal. The Thu night mins about 2F below normal. Confidence: Above average. Friday...Mostly sunny. Wind becoming light southwest. Max temps near normal. Confidence: Above average. Saturday...Increasing clouds and milder. Southwest gust 20 to 30 MPH. Chance of showers at night. Max temps 10 to 15F above normal. Sat night mins. probably 15 to 20 degrees above normal! Confidence: Above average. Sunday...Showers with a coldfront and developing low pressure on the front. This part of the fcst differs considerably than what I`d anticipated earlier and it is a GEFS combo with the GGEM and ECMWF both pretty confidence on a wet 12 to 24 hours much more so than the 00z/23 GFS op. So have followed WPC guidance POPS. Max temp 10 to 15 above normal. Gusty southerly flow with a wind shift to west probable at night. Confidence on overall scenario: Above average but below average on details including timing CFP. Monday...cooler but daytime max temps still probably 5F above normal. GFS continues to depict a mid or upper level short wave trough digging south through this period, allowing for snow showers on the back side of this. However, other models have slight differences in the track and intensity of the trough, keeping our area dry. Thus, expect showers to be ending or gone by this period. Confidence: average. Tuesday...strong cold air advection continues behind the cold front. High temperatures are expected to be slightly be normal. Confidence: average. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR. West-northwest 10-15 knots with gusts up to 25 knots, diminishing some later this evening and overnight. Wednesday...VFR. Some cloud bases (scattered to perhaps broken) at or above 3,500 feet. Northwest winds 10-15 knots with gusts up to 25 knots. Outlook... Wednesday night and Thursday...VFR. West to northwest wind gusts 20-25 kt Thursday. Friday...VFR. Light wind becoming southwest. Saturday...VFR gusty southwest wind 20-30 kt. Chance of MVFR conds later at night in showers. Sunday...MVFR or lower conditions with low clouds and rain likely. Light southwesterly winds.
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&& .MARINE...
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The Small Craft Advisory for Delaware Bay has been extended through 17z/12pm Wednesday. Winds are expected to increase overnight and continue for awhile Wednesday, with gusts to 25 knots. Otherwise through tonight, winds drop below SCA levels for a time this evening, especially over Delaware Bay, but will pick up again to SCA levels later tonight. Seas remain elevated this evening but will start to subside overnight. Wednesday....SCA conditions with west to northwest winds gusting to around 25 knots. Outlook... Wednesday night through Thursday...A west northwest wind could gust around 25 knots and the Small Craft Advisory may need to be extended in time. Thursday night through Friday...No marine headlines are anticipated. Saturday... A southwest wind small craft advisory may be needed. Sunday...No marine headlines anticipated.
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&& .HYDROLOGY...
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Forecast Points...with up to two inches of rain across portions of Schuylkill county, rises were quick this morning at the Landingville USGS gauge. Landingville has crested and water is currently working down the Schuylkill. Crest forecasts have been updated for all points on the Schuylkill. Although Berne has reached Caution/Action Stage, no flooding is expected at any forecast point on the Schuylkill. Snow...any remaining snow on the ground, which is near zero across much of the HSA, is hydrologically insignificant. River ice...we continue to receive reports of solid ice cover on the Delaware River, but conditions are not as widespread as last week. We know of solid ice near Trenton from about the Route 1 Bridge south down to about Borderntown, or near the head of the tide. We also know of ice further north near and in the Delaware Water Gap. With the warm temperatures the last few days combined with today`s precipitation and rising water levels, melting and fracturing ice will occur. Restrictions in flow or ice jams are possible as ice breaks up and begins to move. Since ice jams can not be predicted with certainty, the best approach is awareness and to take notice of day to day changes on a river or stream of concern.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EST Wednesday for ANZ450>455. Small Craft Advisory until noon EST Wednesday for ANZ430-431.
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&& $$ Synopsis...Drag/Johnson Near Term...Gorse Short Term...Fitzsimmons Long Term...Drag/Johnson Aviation...Drag/Gorse/Johnson Marine...Drag/Fitzsimmons/Gorse/Johnson Hydrology...Kruzdlo

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