textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Severe Thunderstorm Watch discontinued.

Increasing potential for unsettled conditions and hazardous marine impacts from a developing nor'easter beginning Sunday and continuing into next week.

KEY MESSAGES

1. A front will continue to slowly move southeast of the area overnight. Showers will taper across Delmarva and New Jersey late tonight.

2. Frost and freeze conditions are expected for Saturday night into Sunday morning with another round of frost possible for Sunday night into Monday morning.

3. 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 front will continue to slowly move southeast of the area overnight. Showers will taper across Delmarva and New Jersey late tonight.

The remaining part of the Severe Thunderstorm Watch has been cancelled. Low pressure passing north of northern New England will continue to push a potent cold front offshore for the early overnight period. The last of the thunderstorms have moved off the NJ/DE shore, but more scattered showers remain behind the front will linger across southern NJ and Delmarva into the overnight period. Likely POPS will remain S/E and chance pops for the Delaware Valley areas. Additional rains will be rather light, perhaps 0.1 to 0.2 inches.

A tight pressure gradient then develops over the area overnight through Saturday as broad high pressure centered over the Southern Plains begins to build east. Gusty north to northwest winds will develop tonight and will continue through Saturday, with winds ranging from 15 to 25 mph with 30 to 40 mph gusts. Much cooler on Saturday with highs in the 50s and surface dew points falling towards the 30s. Some showers may linger tonight into Saturday morning especially across southern NJ and Delmarva as the front slows for a time, but they should clear out finally later in the day if not before.

KEY MESSAGE 2...Frost and freeze conditions are expected for Saturday night into Sunday morning with another round of frost possible for Sunday night into Monday morning.

The coldest airmass of the season thus far will usher into the region this weekend. With high pressure settling in from the north, skies will become clear by Saturday evening. While it will be a bit breezy early in the night, the pressure gradient is expected to lessen overnight, especially for locales north and west of I-95. In these areas, anticipate a period of good radiational cooling conditions where low temperatures are expected to fall into the upper 20s to low 30s. For this reason, have issued a Freeze Watch for potions of eastern PA and northern NJ for Saturday night. Further south and east, it appears that winds will remain elevated enough to preclude frost formation where temperatures will be in the mid to upper 30s. At this time, no frost/freeze headlines are expected along the I-95 corridor and points south and east.

High temperatures on Sunday will then only be in the 50s for the entire region despite mostly sunny skies. Temperatures will then begin to slowly moderate Sunday night into early next week. Another round of frost/freeze conditions will be possible for Sunday night into Monday morning, 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, so this would favor frost over freeze where the growing season remains active. Too early to determine any headlines at this time, but will be considered in future updates.

KEY MESSAGE 3...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. Some guidance keeps the system suppressed further south due to the strong high to the north, which will then minimize potential impacts to our area. However, if the system is further north (and this has been the trend over the past 24 hours), then more in the way of impacts and unsettled weather may occur. At the very least, it is expected that gusty northeast breezes will occur for the majority of the week with the highest gusts located near coastal areas. While it isn't expected to be a washout by any means, there is at least a chance of showers each day for areas south and east of I-95 beginning as early as Sunday night through the end of the week. More details to come over the weekend once forecast guidance comes into better agreement.

AVIATION /01Z SATURDAY THROUGH WEDNESDAY/

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

Tonight...TSTMs have ended for the terminals, but there will still be some showers lingering especially southern terminals. NW winds increasing to 10 to 15 kt with 20 to 25 kt. High/medium confidence.

Saturday...Mainly VFR, though showers and perhaps some MVFR cigs may linger southern terminals in the morning. NW winds 15 to 25 kt with 25 to 35 kt gusts. High confidence.

Outlook...

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

Sunday night...Primarily VFR. A slight chance of rain showers possible near KACY and KMIV.

Monday through Wednesday...Primarily VFR, although sub-VFR conditions possible at times. A chance of rain showers each day for all terminals except KRDG and KABE. Gusty northeast winds up to 20 kt possible with gusts up to 30 kt possible near KMIV and KACY.

MARINE

A Small Craft Advisory remains in effect for the ocean waters. The front moving across the waters will continue to produce showers overnight and a few TSTMs are possible until around midnight. Gusty winds possible with ant TSTM.

Winds turn north-northwest tonight and increase to 15 to 20 kt with 25 to 30 kt gusts that will last through Saturday. 30 to 40 kt gusts are likely Saturday. Upgraded Gale Watch to Gale Warning Saturday.

Outlook...

Saturday night...Gale Warnings are in effect for offshore waters and Atlantic coastal waters from Great Egg Inlet to Fenwick Island. Small Craft Advisory conditions likely for Atlantic coastal waters from Sandy Hook to Great Egg Inlet and Delaware Bay. North-northeast winds of 20-30 kt with gusts of 30-40 kt. Seas of 6-12 feet.

Sunday...A mix of Gales and Small Craft conditions are likely to continue on all waters. Northeast winds of 15-30 kt with gusts of 30- 40 kt possible. Seas of 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 Watch from late Saturday night through Sunday morning for PAZ054-055-060>062-101-103-105. NJ...Freeze Watch from late Saturday night through Sunday morning for NJZ001-007>009. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ430-431- 450>455. Gale Warning from 6 AM to 6 PM EDT Saturday for ANZ430-431- 450>452. Gale Warning from 6 AM Saturday to 6 AM EDT Sunday for ANZ453>455. Gale Warning from 6 AM Saturday to 7 AM EDT Sunday for ANZ480>483-485.