textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Made minor changes to each section. No significant changes to the forecast overall.

KEY MESSAGES

1. Breezy conditions will continue across the area today.

2. A coastal storm/nor'easter is forecast to impact the region Thursday through Friday night.

DISCUSSION

KEY MESSAGE 1...Breezy conditions will continue across the area today.

Another upper-low centered over eastern portions of Ontario today will shift southeastward today, with a sharp trough axis with strong shortwave energy pivoting through the region by this afternoon. At the surface, low pressure will pass north of the area today with a trailing cold front moving through the region. High pressure will begin nudging into the region from the southwest by this evening.

Winds aloft today will be stronger than they were on Sunday, with the pressure gradient remaining fairly tight. Under similar mixing conditions, winds will likely be even breezier than they were on Sunday, with gusts up to 30-35 mph possible. No wind headlines should be needed, but the gusty winds will certainly be noticeable. With much of the region near or past past peak fall foliage, these breezy conditions will likely defoliate much of the seasonal vegetation across the area.

Temperatures will be near normal with highs in the lower 60s.

KEY MESSAGE 2...A coastal storm/nor'easter is forecast to impact the region Thursday through Friday night.

A vigorous upper-level trough is forecast to evolve across the eastern U.S. later this week and into the weekend. This would support a surface low that may initially track near the Ohio Valley, before a secondary low develops in the vicinity of the northern Mid- Atlantic. The model guidance, including ensemble data, continues to be in good agreement that a deep upper-level trough evolves in the East later this week. There are however some differences with the handling of the embedded shortwaves and thus the details of the surface low. The details will be important because they will determine where the surface low tracks and where the main forcing for ascent becomes established along with some colder air on the west/northwest side of the developing coastal storm/nor'easter.

The strength of the parent upper-level trough would result in a colder air mass moving in with time, however the initial air mass is not looking all that cold with the lack of a cold antecedent air mass. As a result, dynamic cooling would have to come into play. This could allow for the air mass to become sufficiently cold enough for a rain/snow mix or even some snow across our far western to northwestern zones (elevation dependent). There remains a variety of solutions across model guidance. It continues to appear at this time that the greatest probabilities for some snow is across the I-80 corridor (Poconos). Otherwise, a decent rain event remains possible. The amount of precipitation (rain and/or snow) will depend on the ultimate development and track of the main surface low and the associated thermal profiles that evolve across our region. The GEFS and ECMWF members suggest a spread still with the placement/track of the surface low. The coastal impacts, including the potential for stronger winds and also tidal flooding, are less certain because if the surface low tracks right over our area that would lessen the residence time of the (stronger) onshore flow. The uncertainty remains with the details for Thursday through Friday night, therefore this time frame will continue to be monitored. It does look to turn colder Friday and over the weekend.

AVIATION /06Z MONDAY THROUGH FRIDAY/

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

Early this morning...VFR. W winds 5 to 10 kt. High confidence.

Today...VFR. NW winds 15 to 20 kt with 25 to 30 kt gusts. High confidence.

Tonight...VFR. W-SW winds 5 to 10 kt. High confidence.

Outlook...

Tuesday and Wednesday...VFR. West-southwest wind gusts to 20 knots possible Tuesday.

Thursday and Friday...Sub-VFR conditions develop, especially Thursday night, and continue Friday with rain developing (rain/snow possible, particularly north of KABE/KRDG). North to northwest wind gusts 20-25 knots possible Friday.

MARINE

A Small Craft Advisory remains in effect for all of the Atlantic coastal waters and the lower Delaware Bay through 7 PM. For the upper Delaware Bay, the Small Craft Advisory is in effect from 5 AM through 7 PM.

Winds will become west-northwesterly and increase a bit more to 20-25 kt with gusts around 30 kt. Seas will increase to 4-6 feet. Winds and seas will begin to diminish by late afternoon or early evening.

Outlook...

Tuesday...A brief period of Small Craft Advisory conditions are possible.

Wednesday...The conditions are expected to be below Small Craft Advisory criteria.

Thursday and Friday...Small Craft Advisory conditions probable mostly Thursday night and continuing Friday. Gale force wind gusts possible on Friday.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 5 AM early this morning to 7 PM EST this evening for ANZ430. Small Craft Advisory until 7 PM EST this evening for ANZ431- 450>455.