textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

PoPs have increased Saturday night...now likely areawide.

Rip current risk has decreased for tomorrow, with a LOW risk now at all beaches.

KEY MESSAGES

1. A cold front will cross through the area Thursday into Thursday night bringing the potential for a round of showers and storms.

2. Another disturbance will approach the area on Saturday night into Sunday and produce a round of showers and thunderstorms.

DISCUSSION

KEY MESSAGE 1...A cold front will cross through the area Thursday into Thursday night bringing the potential for a round of showers and storms.

High pressure that has been over the region will shift offshore tonight. In the mid and upper levels, ridging will begin to breakdown with height falls through tomorrow as upper-level troughing approaches. A weakening piece of upper-level energy approaches the region tonight which will be associated with decaying showers and thunderstorms from off to our northwest. A more pronounced shortwave will pass through the region Thursday into Thursday night, with a cold front tracking from northwest to southeast across the region during the evening into overnight hours.

Some showers and a few embedded storms are expected tonight into early Thursday morning for mainly the Lehigh Valley, Poconos, and adjacent portions of northern NJ as the decaying line of convection originating from the eastern Great Lakes will be tracking toward the area. There is some potential for this activity to make it all the way to the I-95 corridor by around daybreak Thursday. PoPs during this timeframe are generally 50-60% across the Poconos, 20-40% for the Lehigh Valley and far northern NJ, and around 20% along I-95. Elsewhere, conditions will likely remain dry.

On Thursday, the cold front will begin to approach the region by the afternoon and progress through the area into Thursday night. The strongest shear (0-6 km Bulk Shear exceeding 40 kts) looks to remain across northern parts of the area and weaken with southern extent to around 20 kts. Meanwhile, destabilization looks modest at best and confined to southern parts of the area. Given these factors, the most likely scenario is scattered showers and storms with a very limited severe threat. However, some limited hydro concerns could evolve Thursday afternoon into Thursday night across mainly Delmarva into southeastern PA and southern NJ as PWATs reach upwards of 2 inches and there is warm cloud layer processes allowing for efficient rainfall. WPC has a Marginal (1 of 4) Excessive Rainfall Outlook over these areas. Showers and storms look to clear southern parts of the forecast area by Friday morning.

KEY MESSAGE 2...Another disturbance will approach the area on Saturday night into Sunday and produce a round of showers and thunderstorms.

Behind Thursday's front, a drier and more comfortable airmass will settle into the region on Friday, and into at least the start of Saturday, as high pressure temporarily settles in.

This quick shot of high pressure will push east later in the day on Saturday. This will allow Thursday's cold front to push back north as a warm front, and it will likely be have a weak low with it. Timing adjustments are likely over the next few days, but as of this afternoon, it will be unsettled Saturday afternoon into Sunday. At this point, the highest chances for showers and thunderstorms are on Saturday night with PoPs in the 60-70% range areawide.

The front and associated precipitation look to clear the area late on Sunday, with warm and dry conditions to start next work week.

AVIATION /20Z WEDNESDAY THROUGH MONDAY/

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

Rest of today...VFR. S winds 10 to 15 kt with 15 to 20 kt gusts this afternoon. High confidence.

Tonight...VFR. S-SW winds around 10 kts with gusts upwards of 20 kts. Some SHRA, perhaps a TSRA, may approach KRDG/KABE late which has been handled with VCSH due to coverage. Moderate confidence.

Thursday...VFR. Winds turn westerly in the morning at around 10 kts. There is the potential for SHRA/TSRA for mainly the I-95 terminals and KMIV/KACY after 21Z. Moderate confidence.

Outlook...

Friday and Friday night...VFR conditions expected.

Saturday...Primarily VFR. Isolated to scattered showers and thunderstorms could lead to brief periods of sub-VFR conditions.

Saturday night...Numerous showers and thunderstorms will likely lead to periods of sub-VFR conditions.

Sunday...Primarily VFR. Isolated to scattered showers and thunderstorms could lead to brief periods of sub-VFR conditions.

Monday...With the showers and thunderstorms forecast to push south of the terminals, VFR conditions are expected.

MARINE

Small Craft Advisories remain in effect for the ocean waters starting later this afternoon, then for Delaware Bay and the ocean waters tonight. South to southwest winds will increase to 15 to 20 kt with 25 to 30 kt gusts later today and tonight. Seas will be 2 to 4 feet today, then 4 to 6 feet tonight.

Outside of SCA conditions, fair weather is expected.

On Thursday, SCA conditions to start the day with southwest winds 15- 20 kt and gusts 25-30 kt. Seas 4-6 feet. Conditions are expected to gradually improve through the day, with winds and seas likely falling below SCA criteria by late afternoon.

Outlook...

Friday through Monday...Sub-SCA conditions are expected, meaning no marine headlines are currently anticipated with winds below 25 kt and seas below 5 feet.

Rip Currents...

On Thursday, southwest winds will range from 10 to 15 mph in the morning, gradually diminishing to 5 to 10 mph late. Breaking waves will be 2 to 3 feet with an 8 to 9 second period. Given winds turn more offshore and will gradually be decreasing through the day, elected to go with a LOW risk for the development of rip currents at all beaches.

For Friday, winds turn more northerly and will be around 5 to 10 mph. Breaking waves decrease to 2 feet or less with a period of 6 to 8 seconds. With more tranquil conditions expected to close out the week, there will be a LOW risk for rip currents at all beaches.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ430-431. Small Craft Advisory until 2 PM EDT Thursday for ANZ450>453. Small Craft Advisory until 10 AM EDT Thursday for ANZ454-455.