textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Precpitation has ended for today, with the main concern now being gusty winds and low wind chills tonight into Friday morning.

For the long-term, PoPs were increased slightly on Sunday as chances are increasing that some snow may reach the coast. Confidence remains high in a prolonged cold stretch beginning on Sunday, continuing through at least Wednesday, where wind chills could drop into the single digits or even below zero.

KEY MESSAGES

1. Blustery and cold through Friday morning. Wind chills in the single digits in many areas and below zero in the southern Poconos by Friday morning.

2. Multiple rounds of precipitation possible this weekend, some of which could fall as snow. Continuing to watch an area of low pressure expected to develop off the coast.

3. Prolonged period of below normal temperatures expected from Sunday into the middle of next week.

DISCUSSION

KEY MESSAGE 1...Blustery and cold through Friday morning. Wind chills in the single digits in many areas and below zero in the southern Poconos by Friday morning.

Cold front has cleared the region with its associated precipitation. Can't rule out a stray wraparound flurry or snow shower, especially in the southern Poconos, but now the main attention is the wind and cold. Today is already a very different day from yesterday and tonight will even be more different than last night was, with winds remaining sustained at 15-25 mph and gusts of 30-35 mph, with temps falling well below freezing. This will bring wind chills into the single digits for much of the area, and slightly below zero in the southern Poconos. That all having been said, while this is gonna feel like night and day compared to last night, we aren't expecting any wind or cold thresholds to be met, so no headlines through Friday. THAT having been said, this kind of cold is no joke, so cold weather precautions should be taken.

KEY MESSAGE 2...Multiple rounds of precipitation possible this weekend, some of which could fall as snow. Continuing to watch an area of low pressure expected to develop off the coast.

A longwave trough sets up over the Eastern US, with a series of shortwaves moving over the area, resulting in some unsettled weather this weekend. The first system looks rather weak and should move through on Saturday. Precipitation looks to start as mainly snow with onset occurring near or just after daybreak when temperatures are at their overnight lows. Weak warm air advection and daytime heating will quickly result in temperatures increasing though, transitioning to mainly rain for everyone except the northern Lehigh Valley, northwest New Jersey, and southern Poconos, where snow could hang on longer. Precipitation should be rather light though. Snowfall amounts up to an inch are possible in the Poconos, with up to half an inch possible north and west of the I-95 corridor. Nothing more than a trace for areas along and south/east of I-95. QPF amounts are less than a tenth of an inch across the region.

The second more organized system has more high-end potential but also could end up being nothing, depending on the track of an area of low pressure offshore Sunday into Sunday Night. Latest trends in the guidance have depicted a slight northwest trend and a closer approach by the surface low. In particular, the GEM/GEPS have joined closer to the operational GFS and its AI counterpart (which remain the furthest northwest solution). The ECMWF and its ensemble members did shift slightly northwest as well but remains the furthest southeast of all the solutions and mainly offshore. As a result, PoPs were increased slightly again, up to around 35-45% along the coast, and up to 25-35% inland to as far as the Lehigh Valley. With the passage of a cold front on Saturday Night, there should be an abundance of cold air available for most precipitation to fall as snow, its just a matter if the surface low and precipitation shield get close enough. Confidence remains relatively low overall but is a bit higher than at last forecast issuance. NBM snow accumulation probabilities have ticked up as well. 1"+ or more of snow is around a 25-35% chance for the coast with a 10-20% chance for 3" or more. Probabilities of 1"+ of snow in the I-95 corridor and areas northwest is around 15-25%. This system will continue to bear watching given the latest trends.

KEY MESSAGE 3...Prolonged period of below normal temperatures expected from Sunday into the middle of next week.

A deep trough sets up over the eastern US, ushering in an arctic airmass. High pressure at the surface will be in control keeping things dry. Several days of below normal temperatures begin on Sunday, continuing through at least Wednesday. Highs struggle to get above freezing, and may even struggle to get out of the 20s on some days (especially Tuesday). Main concern will be overnight lows and wind chills though as most nights will feature apparent temperatures in the single digits. Areas in the Poconos likely (60-70% chance) have wind chills below zero. Cold Weather Headlines may be needed, especially on Tuesday Night.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

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

Rest of Today...VFR ceilings and no visibility restrictions. Westerly winds 15-20 kts with gusts up to 30 kts. High confidence.

Tonight...Mostly VFR, although there is potential for MVFR ceilings, as guidance indicates cloud heights lowering to around 3,000-3,500 feet overnight. The best chance of MVFR ceilings is at RDG/ABE, which is included in the TAF. West to northwest winds remaining around 15-20 kts with gusts up to 30 kts through 06Z, then winds lessening a little toward dawn. High confidence in prevailing conditions, but lower confidence and lower probability in any MVFR ceilings occurring.

Friday...VFR. West wind gusts up to 20-25 kts to start, gradually diminishing through the day and shifting more southwesterly.

Outlook...

Friday Night...VFR. No significant weather.

Saturday through Sunday...Primarily VFR, though sub-VFR conditions possible (30-50%) with periods of rain and snow moving through.

Sunday Night...Primarily VFR. Chance of snow (20-30%) around KACY/KMIV may result in restrictions.

Monday...VFR. No significant weather.

MARINE

Small Craft Advisory in effect for all coastal waters through this afternoon. Westerly winds 20-30 kts and seas 4-6 feet.

Winds increasing this evening, with gale force gusts 35 to 40 kts anticipated to develop for several hours into the overnight period before diminishing into Friday morning. Seas 4-7 feet. Freezing spray is possible (20-40% chance) tonight through Friday morning as air temperatures fall into the mid to upper 20s. Gale Warning in effect for all marine zones from 6 PM this evening through 10 AM Friday. Thereafter, winds should fall off pretty quickly, ending up below SCA levels by evening.

Friday Night...Small Craft Advisory conditions expected with seas 4 to 6 feet and wind gusts near 25 kt out of the west/southwest.

Saturday...SCA conditions likely (50-70%) with seas right around 5 feet.

Sunday...Mainly sub-SCA conditions expected.

Monday...SCA conditions possible with seas of around 5 feet and wind gusts near 25 knots.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ430- 431-450>455. Gale Warning from 6 PM this evening to 10 AM EST Friday for ANZ430-431-450>455.