textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated the rip currents section.

KEY MESSAGES

1. Cold front moves away and high pressure builds in for Saturday.

2. Unsettled weather returns Sunday into Monday.

DISCUSSION

KEY MESSAGE 1...Cold front moves away and high pressure builds in for Saturday.

The front that has been slowly moving across the area the previous few days is now exiting our CWA across southern Delaware and NE Maryland. Showers and a few tstms accompany the front, but will diminish this evening. We'll continue with the chance or low likely pops for the next several hours.

High pressure will build in behind the front tonight and remain for Saturday. Except for some patchy rural fog overnight, fair weather is expected through Saturday.

KEY MESSAGE 2...Unsettled weather returns Sunday into Monday.

The next storm system arrives Sunday into Monday as a surface low moves across the Great Lakes, Ohio Valley, and eventually the Mid-Atlantic, bringing the chance for showers and thunderstorms.

The biggest change with previous guidance is the spread in the timing of precipitation. There are some models that show precipitation moving in as early as 06Z to 12Z Sunday Morning. That being said, there are still a few models not showing rain move in until the afternoon. The net result of this uncertainty is that there are PoPs in place from late Saturday night all the way through Monday. This long period of rain mention is an artifact of the differences between models in the timing, but we don't expect rain to occur for that entire period.

Regardless of the timing, the primary threat at this point is heavy rain leading to flash flooding. Global guidance shows PWAT values surging back into the 2" range, increasing the potential for heavy downpours within any thunderstorms that develop. As a result, WPC does have much of our area in a Slight Risk (level 2 out of 4) in the Excessive Rainfall Outlook for Sunday.

Depending on the timing of the storms, some instability may be in place to support a severe potential. Latest guidance is a bit more robust with upper-level forcing for ascent as well as shear, probably linked to some convectively enhanced features of the incoming trough which are tough to resolve a few days out. At this point, it remains too early to lock down any specifics for severe and flash flood, but we will need to monitor the potential over the next couple days.

AVIATION /20Z FRIDAY THROUGH WEDNESDAY/

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

Rest of today...VFR. Light and variable winds trending more SW or W by sunset. High confid except for wind directions.

Tonight...VFR expected. Patchy rural fog possible. Light variable or calm winds. High confid.

Saturday... VFR expected. Northeast winds 5 to 10 knots developing. high confid.

Outlook...

Saturday night through Sunday Morning... VFR. No significant weather. Increasing clouds Sunday.

Sunday Afternoon through Monday...Sub-VFR conditions likely (60-70%) at times with widespread showers and a few embedded thunderstorms anticipated.

Tuesday and Wednesday...VFR conditions expected.

MARINE

Winds and seas will remain below SCA levels as high pressure builds in tonight and remain into Saturday. Except for a few evening TSTMs near the Delaware coastal waters, Fair weather will be across the waters.

Outlook...

Saturday night and Sunday...No marine headlines expected.

Sunday Night through Monday...SCA conditions possible (30-40%) as seas near 5 feet and southerly wind gusts near 25 kt.

Tuesday and Wednesday...No marine headlines expected.

Rip Currents...

For Saturday, winds turn from northeast to east through the day at 5-10 mph. Breaking wave heights will be around 2 feet or lower. There is an onshore swell with a period of 8-10 seconds. For these reasons, there is a LOW risk for rip currents at all beaches.

For Sunday, winds turn from southeast to southerly through the day while also increasing. Winds out of the south reach 15-20 mph with higher gusts. Breaking wave heights will also be increasing through the day to 2 to 4 feet. An onshore swell remains with a period of 8-10 seconds. For these reasons, there is a MODERATE risk for rip currents at the Jersey Shore and a LOW risk for rip currents at the Delaware Beaches.

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

PHI WATCHES/WARNINGS/ADVISORIES

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