textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated aviation section for 12z TAFs.

KEY MESSAGES

1) Sunshine returns for today with light winds and highs generally in the low to mid 80s.

2) Rounds of showers and thunderstorms return for Thursday through at least Friday as a cold front approaches and crosses through the region.

3) Some scattered showers and thunderstorms may linger into Saturday for portions of the area before drier conditions return by Sunday.

DISCUSSION

KEY MESSAGE 1...Sunshine returns for today with light winds and highs generally in the low to mid 80s.

Weak high pressure will gradually build in as we head into the day today and this will bring a return to at least partly sunny skies with highs for most areas in the low to mid 80s. Winds will be light but generally onshore so that will keep it a bit cooler near the coast where highs should be mainly in the upper 70s. It will also be cooler over the Pocono Plateau where highs should be in the upper 70s as well. It will still be a little on the humid side but not nearly as oppressive as some of our recent days so the heat index should only be a few degrees higher than the temperatures.

KEY MESSAGE 2...Rounds of showers and thunderstorms return for Thursday through at least Friday as a cold front approaches and crosses through the region.

Isolated showers start to develop Wednesday night into Thursday morning before coverage starts to increase more for Thursday afternoon into Thursday night as a piece of upper-level energy moves through the region. Winds out of the southwest on Thursday will allow moisture to increase through the day. From these showers and thunderstorms, there is the potential for heavy rain. PWAT values will increase to upwards of 2 inches along with a warm cloud layer process. All of this said, these showers and thunderstorms will have the ability to be efficient rainfall producers bringing the potential for more flash flooding. In fact the Weather Prediction Center now has much of the area in MARGINAL risk for excessive rainfall for Thursday. There is also the signal for a marginal severe weather threat. Increasing instability as temperatures reach the 80s for many along with rising humidity and some supportive lapse rates are forecast. The magnitude of shear values supporting storm organization is still a little more uncertain. The primary concern with any strong to severe thunderstorm is damaging wind gusts. The Storm Prediction Center has expanded the MARGINAL risk for severe storms northward to include most of our County Warning with the exception of the Poconos and portions of central and northern NJ.

On Friday, another round of showers and thunderstorms look to develop ahead of the cold front moving southward into the area. Once again, as moisture increases ahead of the front, PWAT values look to increase upwards of 2 inches with these showers and thunderstorms having the potential to produce heavy rain and flash flooding. In terms of any severe weather threat, ML CAPES look to reach at least around 1000 j/kg and shear looks to be a bit stronger than Thursday. So there looks to be at least some threat for severe weather once again with the biggest threat again being damaging winds. Finally worth noting for Friday, temperatures around 90 for many along with higher dew points will result in heat indices peaking in the mid 90s to low 100s.

KEY MESSAGE 3...Some scattered showers and thunderstorms may linger into Saturday for portions of the area before drier conditions return by Sunday.

Tricky forecast for Saturday as some of our forecast guidance clears the front far enough south to keep the area mainly dry while other guidance moves it through more slowly which would keep showers and storms around. We stayed close to the National Blend of Models (NBM) with this forecast and are forecasting POPs around 20-40 percent from the Philly area southward with lower POPs farther north where it stands a better chance of being dry. Expect highs mainly in the 80s with more comfortable humidity levels compared to Friday.

Sunday is shaping up to be free of precipitation with seasonable temperatures, comfortable humidity levels, and a partly to mostly sunny sky.

AVIATION /10Z WEDNESDAY THROUGH SUNDAY/

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

Today...Generally VFR except MVFR cigs could linger at times through the morning at ACY and even potentially at MIV. All sites should be VFR by the afternoon though. Northeast winds 3-7 knots becoming south and then SW through the afternoon at around 5-10 knots. Moderate confidence.

Tonight...VFR through the evening. Overnight, clouds will increase with some low stratus potentially affect TAF sites towards 12z. Winds south to southwest 3-7 knots. Low confidence.

Outlook...

Thursday through Saturday...Prevailing VFR, but scattered showers and storms could result in temporary restrictions to MVFR or even IFR.

Sunday...VFR. No significant weather.

MARINE

North-northeast winds around 10-20 knots early this morning shifting to east and then southeast through the day Wednesday and diminishing some as well. Generally expect seas around 3-4 feet.

Little change for Wednesday night with southwest winds around 10 knots and seas around 3 feet or so.

Outlook...

Thursday through Sunday...Conditions are anticipated to be below Small Craft Advisory criteria. Some showers and thunderstorms are likely over the waters by late Thursday into Thursday night and again for later Friday. Some scattered storms could linger Saturday before fair weather returns Sunday.

Rip Currents...

For today, northeast winds 10 to 15 mph will veer to east and then southeast in the afternoon diminishing to around 5-10 mph. The onshore flow when combined with moderate easterly swell at 7-8 seconds will result in a MODERATE risk of rip currents across northern NJ beaches but LOW further south where winds are a little more relaxed (DE) and/or the shoreline is more parallel to the wind (southern NJ).

For Thursday, winds are more southerly, and the moderate swell also becomes more southeasterly. This combination gives a MODERATE risk for the northern NJ beaches and DE beaches, but a LOW risk for the southern NJ beaches.

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

PHI WATCHES/WARNINGS/ADVISORIES

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