textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Aviation section updated for the 12Z TAFs.

No significant changes in the extended forecast.

KEY MESSAGES

1. Some light rain early this morning as low pressure passes through the region, followed by some light rain along the coast owed to offshore low pressure.

2. Freezing conditions possible in the southern Poconos tonight.

3. Marginal fire weather conditions are possible on Sunday.

4. A series of systems on Wednesday and Thursday likely brings the next widespread rainfall.

DISCUSSION

KEY MESSAGE 1...Some light rain early this morning as low pressure passes through the region, followed by some light rain along the coast owed to offshore low pressure.

Weak low pressure will drag a cold front through the region early this morning. The front will remain offshore today, and then another area of low pressure will track along that front later today.

Light rain will pass through the region early this morning with rainfall totals generally less than 1/10 inch. Most rainfall will later today with the offshore low will stay offshore, though some wraparound rain may make it to New Jersey and Delaware coasts. PoPs will be minimal, as well as any additional rainfall.

Skies remain cloudy today with generally cooler conditions. Highs will top off in the 50s to low 60s.

KEY MESSAGE 2...Freezing conditions possible in the southern Poconos tonight.

Low pressure departs this evening, and surface high pressure builds over the Tennessee Valley and Gulf Coast states. Meanwhile, an upper trough remains over the Northeast. This allows for a northwest flow over the area with cold air advection. Lows will drop into the 30s and low 40s with temperatures as low as the low 30s in the southern Poconos. A Freeze Watch remains in effect for Carbon and Monroe counties tonight.

KEY MESSAGE 3...Marginal fire weather conditions are possible on Sunday.

Departing low pressure and incoming high pressure will result in a tight pressure gradient setting up for the back half of the weekend. This will translate to a breezy Sunday, with downsloping northwest flow and wind gusts around 20-25 MPH through the late morning and the afternoon.

With breezy and dry northwest winds, combined with deep mixing setting up (tapping into very dry air aloft), there is a marginal fire weather threat as minimum RH values will fall into the 25-35% range. The saving grace and limiting factor may be the recent rainfall that has fallen over the area. Given that it is also May, we have mostly greened up, which also can limit the fire weather threat. Will coordinate with our partners later this morning to see if any statements are needed.

KEY MESSAGE 4...A series of systems on Wednesday and Thursday likely brings the next widespread rainfall.

A cold front approaches from the west on Wednesday and will stall out over the area. A potentially more dynamic area of low pressure develops over the southeast and cuts inland to our west on Thursday. This will result in widespread rainfall over those two days.

The latest guidance has the bulk of the precipitation falling with that second system sliding through Thursday into Thursday Night. This period also features the highest PoPS (70-90%) in the forecast. Taking a peak at some of the model soundings from some of the medium range guidance, cannot rule out some severe weather, mainly on Thursday, but still a long way off to get into specifics. The NBM Probability of total rainfall from those two systems is about 40-60% for 1 inch or more from Philadelphia on north and about 20-40% south of Philadelphia. Flooding concerns appear minimal based on how dry we have been but will have to watch to see what, if any, the severe threat will be.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

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

Today...VFR. Some light RA possible at KACY, but restrictions not expected. NW winds around 10 kt. Ocnl gusts to 20 kt this morning. Winds turn SE at KACY this afternoon. Moderate confidence.

Tonight...VFR. NW winds around 5 kt. High confidence.

Outlook...

Sunday...VFR. Northwest wind gusts 20-25 kt.

Sunday Night...VFR. No significant weather.

Monday...VFR. Southerly wind gusts around 20 kt.

Monday Night...VFR. No significant weather.

Tuesday through Tuesday Night...VFR. South/southwesterly wind gusts 20-25 kt.

Wednesday...Primarily VFR. Some showers move in for the afternoon and evening which could result in some restrictions. South/southwest wind gusts 20-25 kt.

MARINE

Sub-Small Craft Advisory conditions today and tonight. South to southwest winds 10 to 15 kt, becoming northwest later this morning, then southeast this afternoon. Northwest winds 10 to 15 kt with gusts up to 20 kt tonight. Seas 3 to 4 ft.

VSBY restrictions in rain possible from time to time today over the open ocean waters.

Outlook...

Sunday...No marine headlines expected, but cannot rule out the potential (15-20%) for SCA conditions as northwest wind gusts will get close to 25 kt.

Sunday Night...No marine headlines expected.

Monday through Wednesday...SCA conditions expected (90-100% confidence). Wind gusts out of the south around 20-30 kt. Gale conditions possible (30-40%) on Tuesday Night. Seas of 4 to 7 feet anticipated.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Freeze Watch from this evening through Sunday morning for PAZ054-055. NJ...None. DE...None. MD...None. MARINE...None.