textproduct: Philadelphia/Mt Holly

SYNOPSIS

The region will remain between low pressure over Quebec and an expanding high centered over the South Central US through mid- week. A weak area of low pressure will pass to the north with a trailing cold front moving through the area Wednesday night. High pressure looks to build in beginning late Thursday and continuing into Friday. A couple of weak disturbances could approach the region this weekend into early next week.

NEAR TERM /THROUGH TONIGHT/

An upper trough remains over the Northeast, and a tight pressure gradient remains over the area between low pressure over eastern Canada and high pressure over the Central and Southern Plains. West winds will begin to ramp up to 20 to 30 mph with with 40 to 50 mph gusts this morning as some shortwave energy passes through the region. The pressure gradient slackens somewhat in the afternoon, and winds diminish to 15 to 20 mph with 25 to 30 mph gusts. Shortwaves touched off some widely scattered light snow, and that is beginning to taper off with no accumulations. Conditions otherwise remain dry, but the shortwaves passing through the region will keep skies partly to mostly cloudy. A cold day, even by late December standards, with highs in the low to mid 30s. Wind chills this morning will range from the single digits to low teens, and then will be in the teens to low 20s this afternoon.

The Wind Advisory remains in effect through late afternoon for the southern Poconos and into midday for southeast Pennsylvania and New Jersey. Will go ahead and extend the Wind Advisory until midday for Delmarva due to that surge in winds after sunrise.

The pressure gradient continues to slacken tonight, but shortwaves passing through the region will keep skies cloudy. In fact, some of those shortwaves may be strong enough and will be accompanied by a 60 to 80 kt jet streak that may touch off some isolated snow showers late tonight and into daybreak Wednesday. Will go ahead and bump up PoPs to slight chance for snow showers. Minimal snow accumulation is possible, generally a dusting or so, given how dry it will be. West winds 10 to 15 mph with gusts up to 20 mph this evening will diminish to around 10 mph late. The combination of cloudy skies and somewhat elevated winds will keep optimal radiational cooling conditions from developing, but it will still be cold with lows in the teens to low 20s. Wind chills will be in the single digits in the southern Poconos and otherwise in the teens.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/

Broad upper-troughing will be in place across the northeastern CONUS through the period as an upper-low meanders over Quebec. A couple of shortwaves will pass near or through the region. The first looks to move through Wednesday night, with a second passing just to the north of the area Thursday evening. Northwesterly flow aloft and rising heights appear likely Thursday night as the trough axis begins to slide eastward. At the surface, A weak low will pass to the north of the area Wednesday night, with a trailing cold front passing through. Weak high pressure will build into the area in its wake.

Wednesday looks to feature partly to mostly cloudy skies. Temperatures will be in the upper 20s to near 30 across the Poconos and into far northern NJ, the low to mid 30s for the remainder of eastern PA and most of NJ, and upper 30s to near 40 across the southern Delmarva and far southern NJ.

As the cold front approaches and moves through the region Wednesday night, snow showers will be possible, with the greater chances generally along and north of I-78. However, a few snow showers could extend southwestward along the I-95 corridor as far southwest as northern DE late Wednesday night into Thursday morning. With cold temperatures firmly in place, some light accumulations are possible, with a dusting north of I-78 and perhaps near an inch across the Poconos. South of I-78, any snow amounts appear negligible at the moment. Lows Wednesday night look to be in the teens across the Poconos and into far northern NJ, and low-mid 20s elsewhere.

Behind the cold front and any associated snow showers, skies should clear during the day Thursday, but the reinforcing shot of cold air will keep temperatures below freezing for most of the area, with only portions of the Delmarva and far southern NJ rising into the mid 30s. It will also likely be breezy, with northwest winds gusting 20-30 mph. This could lead to wind chill values 10-15 degrees below actual air temperatures. The shortwave passing to the north of the area Thursday evening is not expected to result in any precipitation as the area will be devoid of any moisture. Skies should start mostly clear, but increasing clouds are expected late. Temperatures look to bottom out in the teens areawide Thursday night, with some upper single digits possible across the Poconos and into far northern NJ.

LONG TERM /FRIDAY THROUGH MONDAY/

At the moment, the extended range forecast looks fairly uneventful, with only a couple of chances for light precipitation.

The upper-air pattern appears fairly benign, with troughing remaining in place over the much of the Northeast. There are some indications that a more progressive pattern could begin to take shape early next week. At the surface, a weak wave of low pressure looks to develop off the Eastern Seaboard Saturday and track eastward, with high pressure taking shape for Sunday. By Monday, the high should start to slide eastward with another area of low pressure potentially approaching from the Great Lakes region.

Depending on the placement of the wave of low pressure Saturday, some light rain could make its way into portions of the Delmarva, but amounts currently appear negligible. In fact, many deterministic models keep precipitation south of the area entirely. The next chance for meaningful precipitation appears to be on Monday. Some of it could be of the wintry variety, but for now amounts appear insignificant.

Temperatures through the entire extended range look to be cold, with highs generally in the 30s to near 40 and lows in the teens and 20s.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas.

Today...VFR. W-NW winds 20 to 25 kt with 30 to 40 kt gusts in the morning, diminishing to 15 to 20 kt with 25 to 30 kt in the afternoon. There may be some light snow this morning, but restrictions not expected. High confidence.

Tonight...Mostly VFR. There is a slight chance for some SHSN that may result in highly localized sub-VFR conditions. W-SW winds 10 to 15 kt with gusts up to 20 kt in the evening, diminishing to 5 to 10 kt late. Low confidence on sub-VFR SHSN, high confidence in wind forecast.

Outlook...

Wednesday...VFR. No significant weather.

Wednesday night through Thursday...Primarily VFR. Brief sub-VFR conditions can't be ruled out in snow showers, particularly overnight Wednesday into early Thursday morning.

Thursday night through Saturday...VFR. No significant weather.

MARINE

Gale Warnings remain in effect for the ocean waters and Delaware Bay until 6 PM. West winds 20 to 30 kt with 35 to 40 kt gusts will persist through the day, then will diminish to 15 to 20 kt with 25 to 30 kt gusts tonight. A Small Craft Advisory will be needed after the Gale Warnings end. Seas will be 6 to 8 feet today, subsiding to 2 to 4 feet late tonight.

Cannot rule out a passing snow shower with minimal VSBY impacts late tonight and into daybreak Wednesday.

Outlook...

Wednesday through Thursday night...SCA conditions are possible with west winds 15-25 kt. Seas 3-5 feet.

Friday through Saturday...No marine headlines currently anticipated with winds below 25 kt and seas below 5 feet.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Wind Advisory until 1 PM EST this afternoon for PAZ060>062-070- 071-101>106. Wind Advisory until 5 PM EST this afternoon for PAZ054-055. NJ...Wind Advisory until 1 PM EST this afternoon for NJZ001-007>010- 012>027. DE...Wind Advisory until 1 PM EST this afternoon for DEZ001>004. MD...Wind Advisory until 1 PM EST this afternoon for MDZ012-015-019- 020. MARINE...Gale Warning until 6 PM EST this evening for ANZ430-431- 450>455.