textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated Rip Current section.

KEY MESSAGES

1. Some showers around into tonight before a tranquil stretch takes over.

2. A frontal system on Sunday and Monday will bring the next opportunity for widespread showers and thunderstorms.

DISCUSSION

KEY MESSAGE 1...Some showers around into tonight before a tranquil stretch takes over.

A closed low will continue to gradually shift eastward and exit off the New England coast this evening. The cyclonic flow remaining over our area along with lingering cool air aloft is resulting in quite a bit of cloud cover this afternoon. This looks to continue for a while tonight before some thinning starts to occur. More clearing may occur sooner across parts of Delmarva however. A shortwave will rotate across our area into this evening and this will support some showers. While a few lightning strikes cannot be ruled out into this evening, there is currently meager MLCAPE and the visible satellite trends so far are not all that supportive for thunderstorms. As a result, opted to remove thunder from the forecast especially given the even lower probability. The visible satellite imagery this afternoon also shows a weak low spinning southward off the New Jersey coast. This feature may enhance the shower development some along portions of the New Jersey coast. A northwesterly breeze will ease into this evening.

Surface high pressure will then begin to settle in during tonight with some drier air. Some guidance hinting at a few rather isolated showers Friday afternoon, however given the closed low/trough continuing to move away, opted to continue with a dry forecast. Some warming aloft along with some increase in sunshine Friday will result in warmer afternoon temperatures. Lighter flow however will result in a sea/bay breeze developing by later in the afternoon. Depending on how far inland this gets by early Friday evening, some increase in the dew points should occur in its wake. Temperatures moderate some more to start the weekend with high temperatures on Saturday right near average along with dry conditions.

KEY MESSAGE 2...A frontal system on Sunday and Monday will bring the next opportunity for widespread showers and thunderstorms.

High pressure weakens late 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. This 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. Latest outlook from WPC shows a marginal risk of excessive rainfall. Moisture and instability will also increase ahead of the front, so we likely will have to monitor the severe weather threat for the Sunday and Monday afternoon periods as well. However, our area is not in any long term severe outlooks, so there is a chance that there are more hydro concerns with this system.

AVIATION /20Z THURSDAY THROUGH TUESDAY/

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

This afternoon...VFR ceilings, with some localized MVFR ceilings lingering for a time. A few showers around, with a very small chance of a localized thunderstorm. Used a VCSH for now given uncertainty on coverage. Northwest to north winds 8-15 knots with some gusts to around 20 knots, with the winds diminishing by later this afternoon. Low confidence.

Tonight...VFR overall. A local shower possible early. North- northeast winds diminishing to 5 knots or less, then light and variable to locally calm. Low confidence regarding if any MVFR ceilings develop.

Friday...VFR. North-northwest winds 5-8 knots, becoming southeast or south-southwest in the afternoon as sea/bay breezes develop. Moderate confidence.

Outlook...

Friday night through Saturday night...VFR. No significant weather.

Sunday through Tuesday...Primarily VFR but a frontal system will slowly move through the area late Sunday into Monday, likely (60-70% probability) resulting in restrictions at times over this period. Some showers/storms may linger into Tuesday.

MARINE

The conditions are expected to remain below Small Craft Advisory criteria through Friday. Northwest to north wind gusts to 20 knots this afternoon will diminish tonight, then southerly winds develop on Friday. The southerly winds should become enhanced some Friday afternoon with a sea/bay breeze, and therefore some gusts to 20 knots especially nearshore are forecast.

Outlook...

Friday night through Sunday...No marine headlines expected.

Sunday night through Monday night...SCA conditions possible as seas could near 5 feet and winds may gust near 25 kts. Showers and thunderstorms also possible.

Tuesday...No marine headlines expected.

Rip Currents...

For Friday, light west-northwest wind in the morning will transition to south-southeast winds in the afternoon around 10 to 15 mph. Breaking wave heights are expected to remain around 1 to 2 feet with a 2 foot 7 to 8 second southeasterly swell. Have opted to maintain a LOW risk for the development of dangerous rip currents at all beaches.

For Saturday, light southerly winds in the morning around 5 to 10 mph will increase in the afternoon to around 10 to 20 mph. Breaking wave heights will range between 1 to 3 feet with a 2 foot 7 to 8 second southeasterly swell. As a result, went with a LOW risk for the development of dangerous rip currents at all beaches. However, could consider a MODERATE at some southeastward facing beaches late in the day.

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

PHI WATCHES/WARNINGS/ADVISORIES

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