textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated Marine and Aviation sections. Minor wording changes for Key Message 1.

Uncertainty continues for Wednesday and beyond with the potential impacts from the nor'easter.

KEY MESSAGES

1. A cold airmass builds into the region this weekend. Freeze Warnings are in effect for tonight. Another round of frost is possible Sunday night into Monday morning.

2. Uncertainty persists regarding a nor'easter developing off the coast of the southern Mid-Atlantic that may cause unsettled conditions and hazardous marine impacts early next week.

DISCUSSION

KEY MESSAGE 1...A cold airmass builds into the region this weekend. Freeze Warnings are in effect for tonight. Another round of frost is possible Sunday night into Monday morning.

The last of the rains have exited the forecast (land) areas. High clouds remain across eastern NJ and Delmarva through. A tight pressure gradient exists between the departing low and high pressure building into the Central and Southern Plains. North winds remain mostly 5 to 10 mph and will continue to diminish overnight.

Tonight, temperatures drop into the 30s nearly throughout, with lows down to or below freezing for the southern Poconos, Lehigh Valley, and northwest New Jersey. Maintained freeze warnings as inherited, but mixing from lingering wind may preclude the southeastern extent of them from verifying. Confidence not high enough to cancel, however.

High temperatures on Sunday will then only be in the 50s for most of the region despite mostly sunny skies. While another night of temperatures below freezing is not expected, conditions will once again potentially favor the development of some frost, mainly confined to the Lehigh Valley, Poconos and northern New Jersey. Lows are expected to be several degrees warmer than Saturday night mainly in the mid to upper 30s. Additional headlines can't be ruled out for Sunday night if frost potential is realized where the growing season remains active, though the growing season may be ended in these areas by the freeze tonight.

Temperatures will then begin to slowly moderate Sunday night into early next week.

KEY MESSAGE 2...Uncertainty persists regarding a Nor'easter developing off the coast of the southern Mid-Atlantic that may cause unsettled conditions and hazardous marine impacts early next week.

The base of a deep trough axis will pass through the region late tonight into Sunday. As it does so, the trough axis will then cutoff into an upper level low which will meander over the southern Mid- Atlantic coast into early next week. At the same time, strong and expansive high pressure will be building over the Ohio Valley. While confidence is increasing regarding a nor'easter developing off the North Carolina coast by Sunday into Sunday night, it must be said there remains a vast amount of uncertainty with regards to potential impacts to our region into next week.

Considerable differences amongst global/ensemble guidance exists with regards to just how close/long this system will get/last in our region. Relative to the previous forecast discussion, there has not been much change. The EC ensemble member spread is fairly tightly clustered through the early part of next week, and then begins to diverge, but generally has the low tracking northward and then meandering off the Mid-Atlantic coast into mid or even late week. The GEFS members are similar until about mid-week when they begin to diverge more substantially. All of this being said, it doesn't appear likely that there will be significant impacts inland from this system, even though they can't be entirely ruled out at this time. What is increasingly likely though is at least some impacts to coastal communities with periods of gusty northeast winds, some showers, and potentially some coastal flooding concerns, potentially for multiple days next week. We will continue to monitor the progress of this developing system.

AVIATION /01Z SUNDAY THROUGH THURSDAY/

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

Tonight...VFR. N winds 10 kt or less. High confidence.

Sunday...VFR. NE winds 10 kt or less. High confidence.

Outlook...

Sunday night...VFR. No significant weather expected.

Monday and Tuesday...VFR. Gusty northeast winds up to 20 kt possible with gusts up to 30 kt also possible near KMIV and KACY.

Wednesday and Thursday...Primarily VFR, although sub-VFR conditions possible at times. A chance of rain showers each day, with chances highest for KMIV and KACY. Gusty northeast winds up to 20 kt possible with gusts up to 30 kt also possible near KMIV and KACY.

MARINE

Gales were converted to SCA for Delaware Bay and the northern NJ waters earlier as Gusts have decreased. But, for all other waters, Gale Warnings remain in effect overnight with gusts to 35 kts expected. These gusts drop down on Sunday morning. Seas 6-12 feet. More Gales expected Monday with a Gale Watch in effect. Fair weather tonight and Sunday.

Outlook...

Sunday night through Thursday...Due to developing nor'easter off the southern Mid-Atlantic coast, a prolonged period of gale force conditions are expected to develop/continue across all marine waters. A Gale Watch has been issued for Monday through Tuesday. Lower confidence for Wednesday and Thursday. Northeast winds of 25-35 kt with gusts of 35-45 kt are possible. Seas of 10-16+ feet possible.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Freeze Warning from 1 AM to 9 AM EDT Sunday for PAZ054-055- 060>062-101-103-105. NJ...Freeze Warning from 1 AM to 9 AM EDT Sunday for NJZ001-007>009. DE...None. MD...None. MARINE...Small Craft Advisory until 10 AM EDT Sunday for ANZ430-431. Small Craft Advisory until 6 AM EDT Monday for ANZ450>452. Gale Watch from Monday morning through Tuesday afternoon for ANZ451>455-480>483-485. Gale Warning until 6 AM EDT Sunday for ANZ453>455. Gale Warning until 7 AM EDT Sunday for ANZ480>483-485.