textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated the aviation section for the 12z TAFs.

KEY MESSAGES

1) Shower and thunderstorm chances increase for the first half of next week with the potential for areas of heavy rain and some strong thunderstorms.

DISCUSSION

KEY MESSAGE 1...Shower and thunderstorm chances increase for the first half of next week with the potential for areas of heavy rain and some 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 gets pushed back some as a potentially strong upper-level trough in eastern Canada sends spokes of energy southeastward across the Great Lakes and Northeast. This will initially allow for the upper-level trough to become more carved out across the Northeast by later this weekend. Some guidance maintains a rather vigorous shortwave sliding southeastward across the Great Lakes Monday and then across the Northeast during Tuesday. This results in some model solutions closing off the trough across the Northeast Tuesday into Wednesday. Some other guidance is slower and thus sharpens or closes off the trough a day or two later. The upper-level system will drive surface low pressure and a cold front our way Tuesday into Wednesday. Some convection from upstream may try and get into parts of our area later Sunday, however while weakening there may be just enough surface high pressure still over our area with dry enough air to protect our area. This will change though as we go through next week.

It looks like we turn convectively active Tuesday into Wednesday. While there remains some 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 (dew points into the low 70s) advecting northward ahead of this feature with eventual cooling aloft and stronger forcing for ascent may result in widespread showers and some thunderstorms. Depending on the evolution of this system, some areas of heavy rainfall and strong thunderstorms are possible. The intensity and coverage of thunderstorms though may ultimately depend on the prior days convective development and then its evolution downstream.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

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

Today...VFR with increasing high clouds. Light and variable winds becoming northeast 5 knots, then becoming east to southeast 8-12 knots. Moderate confidence.

Tonight...VFR. Southeast or east winds 4-8 knots becoming light and variable to calm. High confidence.

Outlook...

Saturday and Sunday...VFR.

Monday...Some showers and thunderstorms in the afternoon and at night with some times of sub-VFR conditions.

Tuesday...Times of sub-VFR conditions with some showers and thunderstorms.

MARINE

The conditions are expected to remain below Small Craft Advisory criteria through tonight as onshore flow continues.

Outlook...

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

Tuesday...Small Craft Advisory conditions possible as southerly flow increases.

Rip Currents...

For today, northeast to east winds 10-20 mph with waves in the surf zone 2-3 feet. There will be multiple swell groups including a longer period swell from the southeast at 9 seconds. Due to the onshore flow and multiple swell groups we will maintain the MODERATE risk for the development of dangerous rip currents at the Jersey Shore and Delaware Beaches.

For Saturday, northeast winds 10-20 mph with breaking waves once again 2 to 3 feet with multiple swell groups. For these reasons, we will continue with a MODERATE risk for the development of dangerous 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.