textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

The Aviation section is updated for the 00Z TAFs.

KEY MESSAGES

1. Low pressure passing through the region will bring showers and isolated thunderstorms late Wednesday through Thursday.

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

DISCUSSION

KEY MESSAGE 1...Low pressure passing through the region will bring showers and isolated thunderstorms late Wednesday through Thursday.

An upper trough extending from a closed H5 low over central Canada will move through the Great Lakes and into the Ohio Valley tonight. Surface low pressure associated with this low will stay well north of the area, but the closed low will sag down into the Northeast by Thursday. Behind the departure of the surface low, a cold front slides through the region. Unsettled weather on tap during this period.

The timing of precipitation seems to have slowed down a bit, with scattered showers moving into far northern and western zones by midday Wednesday, but the bulk of the showers will hold off until Wednesday evening.

Showers will overspread the region Wednesday night through Thursday morning. While latest models are indicating that most of the showers will be out of the area on Thursday, will note that with the upper low over the area and several shortwaves passing through the region, unsettled conditions may linger throughout the day Thursday.

With strong shortwaves, at least Wednesday evening, instability will be marginal, and a few isolated thunderstorms are possible in the first half of the night. Not expecting severe thunderstorms.

Storm total QPF continues to be on the lower side, generally ranging from 1/10 to 1/4 inch over Delmarva and southeast New Jersey, and from 1/4 to 1/2 inch mainly north and west of Philadelphia. Locally higher amounts could fall in any thunderstorms.

Mild ahead of the system on Wednesday with highs in the low 70s, then cooler on Thursday with highs in the 60s.

KEY MESSAGE 2...Becoming very warm to potentially hot this weekend through early next week.

As the closed low continues to depart on Friday, 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 mid 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. On Tuesday, the heat builds further with highs forecast to reach the upper 80s to mid 90s (remaining cooler along the coast). By late Tuesday, there are some signs of the ridging starting to lessen and the surface high moving further offshore. This would result in more potential for convection to develop. However, this will largely depend on the timing of the ridging and surface high shifting away from the area which is uncertain given this being at the end of the extended forecast period.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

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

Tonight...VFR. S winds 5 kt or less. High confidence.

Wednesday...VFR. Light SHRA possible late in the day, but restrictions are not expected. S winds increasing to around 15 kt with 20 to 25 kt gusts. Moderate confidence.

Outlook...

Wednesday night through Thursday...Sub-VFR in SHRA. Isolated TSRA possible Wednesday evening. Conditions improve on Thursday. S winds 5 to 10 kt most of Wednesday night, turning NW 10 to 15 kt on Thursday.

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

Saturday through Sunday...VFR.

MARINE

Sub-Small Craft Advisory conditions for the rest of today and tonight. South winds 10 to 15 kt with gusts up to 20 kt. South winds increase to 15 to 20 kt with 25 to 30 kt gusts on Wednesday, diminishing Wednesday evening. A Small Craft Advisory will be in effect from 6 am to 10 pm Wednesday. Winds diminish to 10 to 15 kt Wednesday night, then turn to the west on Thursday. Seas will be 2 to 4 ft tonight, building to 4 to 6 ft on Wednesday, subsiding to 2 to 4 ft Wednesday night and Thursday.

Outlook...

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

Saturday...Small Craft Advisory conditions possible.

Sunday...The conditions are anticipated to be below Small Craft Advisory criteria.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 6 AM to 10 PM EDT Wednesday for ANZ430-431-450>455.