Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 190411 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1211 AM EDT Thu Oct 19 2017 .SYNOPSIS... High pressure remains in control of the weather for much of the rest of the week into the weekend. A weak dry frontal boundary should move through our area Thursday into Friday. A stronger cold front and low pressure moving along it, will bring unsettled conditions for later Monday into Wednesday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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High pressure remains over the mid-Atlantic region. However, this high will undergo gradual weakening tonight as an upstream shortwave trough approaches from the Ohio Valley. Light WAA continues tonight under light SW flow. Dewpoints will gradually creep up through the 40s, approaching 50 by daybreak. Temperatures will gradually fall to the dewpoint, and as a result, patchy shallow ground fog is likely to develop away from the urban centers in the pre-dawn hours. Lows tonight will be in the 40s and low 50s.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/... High pressure sinks southward toward the Southeast U.S. on Thursday. Modest pressure (height) falls at the surface (aloft) occurs across the northern mid-Atlantic region as a weak upper shortwave trough and surface cold front progress eastward. The aforementioned cold front will trail the upper trough enough to remain upstream of the forecast area through the period. The setup will allow us to remain situated in the pre-frontal warm sector and for this warming trend to continue into tomorrow. Sided closer to the warmer MAV guidance for temperatures, yielding forecast highs in the lower to middle 70s (except cooler in the higher elevations of NE PA-NW NJ). Filtered sunshine with high clouds during the morning will give way to sunny skies by the afternoon. Meanwhile, SW winds 5-10 mph in the morning are forecast to increase to 10-15 mph by afternoon. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Thursday night thru Monday...High pressure at the surface and aloft will be in control of the weather with fair weather expected. Temperatures generally 5 to 10 degrees above normal. Monday night thru Wednesday...A pattern change with a sharp h5 trough moving into the ern part of the country. Low pressure and a slow moving front associated with the upper trough will affect the area with occasional rains. Locally heavy rains are possible with an upper trough beginning to take a negative tilt as it crosses the area. The 12Z NA models are showing QPF totals generally in the 1 to 3 inch range across the area for the period Mon_Wed. The higher totals are across the wrn counties. Much colder temperatures will be ushered in behind the system with below normal temperatures for the middle part of next week. && .AVIATION /04Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Generally VFR through Thursday. However, patchy ground fog may develop at the fog-prone, rural TAF sites between 05Z-11Z Thursday which could result in a brief period of MVFR visibility. Confidence in fog development was too low to mention in the 00z TAFs except at MIV. Light southwest winds tonight, increasing to 8-15 kt in the afternoon. OUTLOOK... Thu night thru Monday...VFR expected thru the period. && .MARINE... S-SW winds 5-10 kt will continue tonight and Thursday morning, then increase 10-15 kt across the coastal Atlantic waters during the afternoon. Wind field may become locally enhanced to 15-20 kt off the coast of Ocean and Monmouth Counties via Ambrose jet late in the day. Held off on a SCA at this juncture since poor mixing profiles should inhibit higher winds aloft to reach the surface. Accordingly, capped gusts below 25 kt. Seas will generally be around 3 ft in the coastal waters and 2 ft or less in the Delaware Bay...mostly a se swell of 9 or 10 seconds. OUTLOOK... Thu night...Near SCA winds across the nrn NJ coastal waters Thu evening, but not confid enough for a flag attm. Fair. Friday thru Sunday...Sub- SCA conditions thru the period with fair weather. && .CLIMATE... **Top 5 warmest October on record for PHL and ABE appears likely and its virtually certain a top 10 warmest October for all of our forecast area** Todays max/min plus the Mount Holly 330 PM Wednesday fcst for the next 7 days, the D8-11 GFS 2m max/min temps and then normal temps the last 3 days of the month results in the following. PHL 63.5 degrees or 6 degrees above the October 30 year avg of 57.5. This again pegs PHL for a tie as #2 warmest October on record. 1. 64.5 2007 2. 63.5 1971 (2017?) 3. 62.7 1947 To drop out of the top 10 warmest the PHL avg would have to lower to 61.2 degrees (a 2.4 degree drop from the current projection). Based on the 12z/18 ensembles both GEFS/NAEFS and ECEFS...this will not happen unless todays ensembles completely miss the last 3 days of the month. So while a record is probably out of reach, a top 5 ranking is likely. ABE 59.5 or 7 degrees above the 30 year avg of 52.5. This also projects a tie for #2 warmest October. 1. 60.8 2007 2. 59.5 1984 and possibly 2017? 3. 59.3 1947 4. 58.8 1971 For Allentown to drop out of the top 10, the projected avg would have to lower to 57.2 or a drop of 2.3 degrees from the current projection. Again, thats highly unlikely unless something very unusual and not currently ensembled occurs the last 3 days of the month. It should be pointed out that the D8-14 fcst from the Climate Prediction Center (CPC) .. is for an overall average of above normal temperatures during the last week of the month. We are on the edge of the transition to cold that will be quite noticeable in the nations midsection next week. Uphill (southwest flow at 500MB and the trough axis constantly between 80 and degrees west Longitude [Appalachians or west] during the most intense phase of the troughing makes it difficult for cold air to cross the mountains into our area. Now a moment to share some information from a new tool recently available to us... The last two years in PHL 10/15-10/17/17 is the warmest in the period of record...averaging 3 degrees above normal. Ditto Allentown,,averaging 3.7 degrees above normal! Ditto ILG...averaging 2.5 above normal. We will look at all of this again either Saturday or Sunday morning. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...O`Hara Near Term...Drag/Klein/MPS Short Term...Klein Long Term...O`Hara Aviation...Drag/Klein/O`Hara Marine...Drag/Klein/O`Hara Climate...

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