textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Aviation section updated for 12Z TAFs.

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.

A cold front continues to work through southeast New Jersey and Delmarva this morning as low pressure moves into the Canadian Maritimes. Any lingering light rain showers will taper off as the morning progresses. A tight pressure gradient develops between the departing low and high pressure building into the Central and Southern Plains. North winds will increase to 15 to 20 mph with 25 to 35 mph gusts going into this morning, with the strongest winds from late morning through early afternoon after skies clear out and peak mixing develops.

Much cooler and drier today with highs in the 50s.

Tonight, temperatures drop into the 30s throughout, with lows down to or below freezing for the southern Poconos, Lehigh Valley, and far northwest New Jersey. The Freeze Watches that were in effect for tonight were upgraded to Freeze Warnings.

High temperatures on Sunday will then only be in the 50s for the entire 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.

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 later Saturday. 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 later this weekend, 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 /12Z SATURDAY THROUGH WEDNESDAY/

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

Today...VFR. Light rain tapers off this morning, but conds remain VFR. N winds 15 to 20 kt with 25 to 35 kt gusts, diminishing after 20Z. High confidence.

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

Outlook...

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

Monday through Wednesday...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

Gale Warnings in effect for all waters for today for north winds 15 to 25 kt with 35 to 40 kt gusts. Winds diminish a bit on northern NJ ocean waters and DE Bay tonight, and Small Craft Advisories will be needed. For all other waters, Gale Warnings remain in effect.

Outlook...

Sunday...Advisory conditions will likely continue through the day, with gales possible on the outer waters. However, winds will be decreasing through the day and there may be a relative lull where winds dip below 25 kt. Seas 6-12 feet.

Sunday night through Wednesday...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. It should be noted that forecast confidence is low though. 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...Gale Warning until 6 PM EDT this evening for ANZ430-431- 450>452. Gale Warning until 6 AM EDT Sunday for ANZ453>455. Gale Warning until 7 AM EDT Sunday for ANZ480>483-485.