textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Severe thunderstorm and tornado watches have been cancelled.

Flood watch has been cancelled.

Small craft advisory is issued for this evening and overnight.

Made adjustments to the wind forecast for the evening and overnight hours, along with updates to aviation and marine forecasts.

KEY MESSAGES

1. A cold front will cross the region this evening, resulting in widespread showers and thunderstorms. Flash flooding, damaging wind gusts and tornadoes are possible later today.

2. Conditions look to remain unsettled through the weekend, with daily chances of showers and storms each day.

3. Fair weather is expected to return for early next week.

DISCUSSION

KEY MESSAGE 1... Strong winds behind the convective activity appear to be in the wake of the two surface waves moving along the front have keep winds up out of the north and northeast. Have adjusted the forecast for the gusts. Heavy precipitation materialized earlier today with some impressive rainfall totals especially across southern NJ. With the risk of additional flooding low, the flood watch is cancelled. Remainder below is unchanged.

Broad troughing will be the main driving force in the sensible weather into the early to middle part of next week across much of the Eastern Seaboard. A shortwave will round the base of the trough today into this evening providing some mid level synoptic forcing. At the surface a warm front has lifted north into the Philadelphia metro area with a cold front approaching from the west.

The trend for increasing QPF and increasing severe weather potential is being realized this afternoon. Severe thunderstorm, tornado, and flood watches are in effect for most of the forecast area.

Mesoanalysis fields this afternoon show moderate to strong instability centered roughly around the Delmarva peninsula, but extending north into southern NJ and southeast PA. Deep layer shear of 40-60kt along with backed low level flow and strongly curved hodographs will support a tornado risk, most notably from the Philadelphia metro area and points south. Primary mode at the moment is supercellular with all attendant risks, but more multicell clusters may become the primary mode along the cold front.

KEY MESSAGE 2...Conditions look to remain unsettled through the weekend, with daily chances of showers and storms each day.

Mid to long range NWP and AI guidance suggests that the pattern could become unsettled Friday night and into the weekend. The cold front crossing the area tonight will stall in the offshore waters. waves of low pressure will ride along the stalled front resulting in unsettled weather through the weekend. The main periods to watch are early Saturday through Saturday evening, with periods of rain increasingly likely, and again on Sunday. The severe threat appears low at this time but there could be additional flooding concerns, although no day has more than a Marginal (1/5) Risk for excessive rainfall.

Temperatures will be seasonable, but humidity will be uncomfortable.

KEY MESSAGE 3...Fair weather is expected to return for early next week.

Weak high pressure looks to bring quieter and drier weather in the early part of the week, with more unsettled conditions expected later in the week with seasonable temperatures.

AVIATION /01Z FRIDAY THROUGH TUESDAY/

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

Quick update to make wind adjustments in the wake of the front, mostly VFR behind the precipitation but still some risk of MVFR conditions for a few hours this evening. Remainder unchanged below.

Tonight...Sub-VFR conditions probable at times with showers and thunderstorms continuing into the evening hours. Fog and/or low stratus possible at night after the precipitation moves out. Conditions should lift back to VFR near or not long after daybreak. North/northeast winds around 5 to 10 kt. Moderate confidence.

Outlook...

Friday through Friday night...Primarily VFR.

Saturday through Sunday...Periods of VFR and sub-VFR at times. Restrictions expected with daily chances for showers and thunderstorms.

Monday...VFR. No significant weather expected.

MARINE

Have increased gusts in the Delaware Bay and Atlantic coastal waters this evening to account for the strong winds around the surface low moving along the front. The winds should diminish toward morning. Have issued a small craft advisory for all of the waters through daybreak. Remainder below unchanged.

A cold front will move through tonight, with winds becoming more north/northeasterly around 10-15 kt. Seas of 2 to 3 feet. Showers and thunderstorms expected on the waters this evening into tonight.

Outlook...

Friday through Monday...No marine headlines expected. Showers and thunderstorms possible during the day Friday through Sunday.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EDT Friday for ANZ430-431- 450>455.