textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated Key Message 2 and the Outlook periods of the Aviation and Marine sections.

KEY MESSAGES

1. Lingering clouds and a few showers or a thunderstorm into Thursday.

2. A short period of tranquil weather for the end the week and into Saturday before another system arrives Sunday.

DISCUSSION

KEY MESSAGE 1...Lingering clouds and a few showers or a thunderstorm into Thursday.

A closed low will remain over the Northeast and Mid-Atlantic regions through tonight, then it will gradually shift eastward during Thursday. This will take surface low pressure across southern New England this afternoon eventually offshore late tonight and Thursday. Shortwave energy will continue to rotate around this closed low and across our area through Thursday, with a stronger one sliding through tonight. The combination of weak instability with colder air aloft and enough moisture and lift, should result in some showers sliding from north-northwest to south-southeast into this evening. A low-topped thunderstorm cannot be ruled out. The greatest chances of this occurring is roughly from near and north of I-78. While these typically dissipate at night with the loss of heating, some showers may linger through the overnight as a stronger shortwave moves across the area. This should also keep cloud cover around through tonight. A gusty northwesterly breeze will diminish some tonight, then increase again on Thursday.

As the closed low gradually shifts eastward during Thursday, a few showers or a thunderstorm are still possible especially in the afternoon. This looks to be mostly from near and north/east of Philadelphia. Given the continued cooler air aloft combined with boundary layer heating and cyclonic flow, a decent amount of cloud cover is anticipated for most of the area on Thursday. This will also keep temperatures below average for this time of year.

KEY MESSAGE 2... A short period of tranquil weather for the end the week and into Saturday before another system arrives Sunday.

Following the departure of the recent storm up into Canada, high pressure builds back across the area Thursday night into Friday. The high weakens Saturday and is replaced by advancing low pressure from the Ohio Valley area. This low strengthens and moves west of our area later Sunday and into Monday. Thus system will bring increasing chances for showers and a few tstms Sunday afternoon for the western counties and all areas Sunday night and Monday. The PWAT values off the forecast soundings during these times show more 2+ inch PWAT values for our region. So it's possible that excessive rainfall may develop for parts of the region.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

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

This afternoon...VFR ceilings. A shower or thunderstorm by later this afternoon, mainly north of KPHL. Northwest winds 10-15 knots with gusts 20-25 knots. Moderate confidence.

Tonight....VFR ceilings, however some MVFR ceilings are possible at mainly KABE and KTTN. A few showers possible mostly north and west of KPHL. Northwest winds 10-15 knots, diminishing to 5-10 knots. Low confidence.

Thursday...VFR overall. A shower or thunderstorm possible mostly north and east of KPHL. North-northwest winds 10-15 knots with some gusts to around 20 knots. Low confidence.

Outlook...

Thursday night thru Saturday... VFR expected with fair weather.

Sat night thru Monday... Largely VFR but scattered showers and tstms may produce locally lower CIGs/VSBYs.

MARINE

The conditions are anticipated to remain below Small Craft Advisory criteria through Thursday. Northwesterly winds however will gust to around 20 knots at times, especially nearshore.

Outlook...

Thursday night through Sunday... Conditions will remain below SCA levels as high pressure will generally be across the waters. Fair through the period except for Sunday when scattered showers or a TSTM is possible.

Sunday night and Monday... sub-SCA continues,, but winds and seas will be building to just below SCA levels by later Monday. Scattered showers and TSTMs.

Rip Currents...

This afternoon thru Thursday, northwest winds 15 to 25 MPH. Breaking waves will also decrease to around 2 feet or less. While the Full Moon is today, decreasing wave heights, more offshore flow, and no wave period longer than 8 seconds should limit the rip current threat. As a result, elected for a LOW risk for rip currents at all beaches.

For specific beach forecasts, visit weather.gov/beach/phi

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...None.