textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Aviation section updated for the 12z TAFs.

KEY MESSAGES

1. A drier airmass spreads into the region today. A Frost Advisory continues for the southern Poconos through 8 AM today.

2. Showers (a few thunderstorms possible) Wednesday afternoon and Wednesday night, then some showers continuing into Thursday morning.

3. Becoming very warm to potentially hot this weekend through early next week.

DISCUSSION

KEY MESSAGE 1...A drier airmass spreads into the region today. A Frost Advisory continues for the southern Poconos through 8 AM today.

Now that the cold front has moves through, high pressure will build across the area today. A cooler and drier airmass has arrived across the northern parts of the area and dew points and temperatures continue to trend down. As winds will remain light, there still remains the possibility of some patchy frost formation across Carbon and Monroe counties. We'll continue the Frost Advisory until 8 AM.

KEY MESSAGE 2...Showers (a few thunderstorms possible) Wednesday afternoon and Wednesday night, then some showers continuing into Thursday morning.

An upper-level trough moves into the Eastern U.S. Wednesday into Thursday before lifting out Friday into Saturday. This trough looks to become a closed low over the Mid-Atlantic and Northeast by Thursday. The details will depend on the timing of the closed low and its track, however as it arrives showers will be on the increase Wednesday afternoon and especially Wednesday night before tapering off into Thursday as a cold front shifts offshore.

The low-level warm air advection will increase ahead of the trough during Wednesday as will the low to mid level flow. This will result in an increase in forcing for ascent, and some instability should develop ahead of the main forcing. A warm front should also lift across our area Wednesday with some ascent associated with it. As a result, showers increase Wednesday afternoon from west to east with forcing peaking Wednesday night as the cold front arrives. Guidance continues to show some instability which could be enough to support a few thunderstorms. The intensity of any thunderstorms however will depend on the magnitude of the instability and shear. Given the later arrival time of the showers, instability looks to be rather weak with an isolated severe thunderstorm risk well to our west Wednesday afternoon.

The main forcing shifts to our east and northeast Thursday with the bulk of the showers ending. However, the presence of the closed low especially overhead with the core of the cold air aloft could result in additional shower development on Thursday before the system departs our region. Rainfall totals look to be on the lighter side (0.20-0.50 inches), although locally higher amounts are possible if more organized showers/thunder occur.

KEY MESSAGE 3...Becoming very warm to potentially hot this weekend through early next week.

As the closed low continues to depart going into the weekend, a ridge starts to build across the East this weekend and into early next week. This along with high pressure centered offshore will result in southerly flow advecting in a much warmer air mass across our area. As a result, high temperatures get into the 70s to low 80s Saturday with widespread 80s on Sunday. Given a southerly wind component though, it should be cooler along the coast. The heat looks to build into early next week with even hot conditions possible. Highs Monday are forecast to be in the 80s with even some areas reaching 90 degrees (again cooler along the coast). Given the presence of the ridge aloft, no precipitation is currently anticipated. However near the edge of the ridge/surface high, there is a slight chance (20 percent) for convection near the southern Poconos Monday afternoon and evening.

AVIATION /10Z TUESDAY THROUGH SATURDAY/

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

Today...VFR. Some high clouds later today. Light and variable to calm winds becoming north-northwest 5-10 knots this morning, then becoming west to southwest and south this afternoon. High confidence.

Tonight...VFR with increasing high clouds. Light south winds. High confidence.

Outlook...

Wednesday...VFR conditions during most of the day, then conditions lower to MVFR or IFR mainly at night as showers arrive from west to east. A few thunderstorms possible late in the afternoon and evening. Southerly wind gusts up to 25 knots during the afternoon.

Thursday...Times of sub-VFR conditions with some showers possible, otherwise VFR. West-northwest wind gusts to 20 knots possible.

Friday...Mostly VFR. An isolated shower possible.

MARINE

High pressure across Pennsylvania and New Jersey this morning will move offshore this afternoon. Fair weather is expected today and tonight. Winds will begin the day mostly North or Northwest on the waters and will remain light as the high moves overhead. Later today winds will turn Southwest or South and increase to 5 to 10 knots. Tonight, winds speeds will further increase to 10 to 15 knots with gusts around 20 knots. Conditions will remain below SCA levels but seas will increase close to 4ft by Wednesday morning.

Outlook...

Wednesday...Small Craft Advisory conditions are probable.

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

PHI WATCHES/WARNINGS/ADVISORIES

PA...Frost Advisory until 8 AM EDT this morning for PAZ054-055. NJ...None. DE...None. MD...None. MARINE...None.