textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated the aviation section for the 12z TAFs.

KEY MESSAGES

1) A much drier air mass will be in place through the end of the week and to start the weekend.

2) Shower and thunderstorm chances increase early next week with the potential for areas of heavy rain and strong thunderstorms.

DISCUSSION

KEY MESSAGE 1...A much drier air mass will be in place through the end of the week and to start the weekend.

Much drier air has filtered in from the northwest early this morning in the wake of a cold front. An upper-level trough will gradually weaken across the Northeast and northern Mid-Atlantic later today, tonight and Friday. Surface high pressure builds across the Northeast and down into the Mid-Atlantic through the end of the week before shifting offshore of New England on Saturday. A northerly flow will keep a much drier air mass across our area along with cooler temperatures. The lighter low-level flow due to high pressure in place will result in some enhancement to the sea/bay breezes later today and again on Friday.

KEY MESSAGE 2...Shower and thunderstorm chances increase early next week with the potential for areas of heavy rain and strong thunderstorms.

As a strong upper-level ridge expands into the Plains early next week, northwesterly flow aloft will occur across much of the East. This ridge looks to get pushed back some as a potentially strong upper-level trough in eastern Canada sends spokes of energy southeastward across the Great Lakes and Northeast. Some guidance has stronger shortwave energy which results in the trough closing off across the Northeast with time during the first half of next week. This will also drive surface low pressure and a cold front our way around the Tuesday time frame. Some convection from upstream may try and get into parts of our area later Sunday, however this is less certain.

It looks like we may turn convectively active early next week, especially Tuesday into Wednesday. While there are differences among the model guidance on the timing and strength of the features diving southeastward early next week, the setup would tend to favor upstream convective development given northwesterly flow aloft. This would be enhanced if the trough aloft closes off. Deeper moisture advecting northward ahead of this feature with eventually colder air aloft arriving may result in widespread showers and some thunderstorms. While the specifics are uncertain at this time range, some areas of heavy rainfall and strong thunderstorms are possible given the overall synoptic setup that is forecast.

AVIATION /12Z THURSDAY THROUGH MONDAY/

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

Today...VFR. Light and variable winds to north-northwest 5-10 knots, becoming north-northeast. The winds then become east to southeast or south less than 10 knots later in the afternoon. Moderate confidence.

Tonight...VFR. Southeast or south winds less than 10 knots, becoming light and variable or locally calm. Moderate confidence.

Outlook...

Friday and Saturday...VFR.

Sunday...Mainly VFR.

Monday...Times of sub-VFR conditions along with some showers and thunderstorms possible.

MARINE

The conditions are expected to remain below Small Craft Advisory criteria through tonight. Northwest to northeast winds may increase for a time today, then turn east to southeast this afternoon and evening and also decrease some. Seas below 5 feet.

Outlook...

Friday through Monday...The conditions are anticipated to be below Small Craft Advisory criteria.

Rip Currents...

For today, north to northeast winds 10-20 mph will become east to southeast later this afternoon and evening. Breaking waves in the surf zone are expected to be 2-4 feet with a 7 second period. With the onshore component of the wind and multiple swell groups expected, will maintain a MODERATE risk for the development of dangerous rip currents at all beaches.

For Friday, very similar conditions to Thursday so we will go with a MODERATE risk for the development of dangerous rip currents for all beaches once again.

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

PHI WATCHES/WARNINGS/ADVISORIES

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