textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

1) A storm system will bring light rain to the area this afternoon and evening. Rain will change to snow before ending Thursday morning. Rapidly falling temperatures behind a cold front may result in icy roads and hazardous travel for the Thursday morning commute.

2) Below normal temperatures and blustery conditions will result in wind chills in the single digits across much of the area Thursday night into Friday morning.

3) The risk of wintry weather through early next week remains low, but cold temperatures mean any changes could result in a return of the chance of snow.

4) An extended period of below normal temperatures is forecast beginning Sunday and through the middle of next week, with wind chills in the single digits and teens possible for multiple consecutive nights.

DISCUSSION

KEY MESSAGE 1...A storm system will bring light rain to the area this afternoon and evening. Rain will change to snow before ending Thursday morning. Rapidly falling temperatures behind a cold front may result in icy roads and hazardous travel for the Thursday morning commute.

Low pressure will develop over central Pennsylvania this afternoon, strengthening as it tracks into interior New York later tonight. Its associated cold front will track east across the Mid-Atlantic region tonight as well. Out ahead of the front, light rain is expected to develop later this morning and continue through the afternoon, primarily for areas north and west of the I-95 corridor as lift increases. Elsewhere, dry conditions under mostly cloudy to overcast skies are expected. Warm air advection will continue under southwest flow resulting in very mild temperatures ranging from the upper 40s to mid 50s this afternoon.

As the low deepens as it lifts off to the north and east tonight, should gradually start to see periods of light rain overspread the remainder of the area. Cold air will also be rapidly surging in on the backside of the strengthening low and behind the cold front. This will cause temperatures to rapidly tumble overnight as the front progresses east where light rain is expected to changeover to light snow or at the very least a rain/snow mix. The best chance for accumulating snow will be across the Pocono Plateau where 1-2 inches of snow are possible. For areas, north and west of the I-95 corridor, including the Lehigh Valley and northern New Jersey a quick dusting/coating to up to a half inch of snow is possible. For areas south and east of I-95, some flakes are possible, but no accumulations are expected. Precip should wind down from west to east as the front moves offshore by Thursday morning. Some residual snow showers may linger though.

While most of the precip is expected to end by daybreak on Thursday, the strong cold air advection and gusty WNW winds in wake of the front will likely result in temperatures below freezing. Thus, anything that does not dry out has the potential to result in roadways and bridges becoming icy for the Thursday morning commute. This risk is higher especially for areas where snow accumulates before precip ends. As mentioned above, this greatest threat is in the Poconos, and generally anywhere northwest of I-95. Making matters more complicated will be that the rain before the changeover, may wash off any pre-treatment of surfaces. Recommend to take it slow and use caution while traveling Thursday morning.

KEY MESSAGE 2...Below normal temperatures and blustery conditions will result in wind chills in the single digits across much of the area Thursday night into Friday morning.

Following cold frontal passage Thursday morning, strong cold advection will persist through Friday morning. This will keep temperatures steady in the low to mid 30s much of the day, with westerly winds 15-20 mph gusting 30-35 mph. Wind chills during the daytime Thursday will only max out in the upper teens to 20s in most areas. Temperatures are forecast to fall into the mid teens to near 20 degrees in most areas by dawn Friday morning. While inland winds will subside some overnight, still expecting sustained westerly winds around 10-15 mph much of the night. Thus, wind chills will fall into the single digits area wide by dawn Friday, and below zero in the southern Poconos.

The strong cold advection will cease Friday morning, and gradient winds will shift southwesterly allowing for some airmass modification. Highs Friday will range from the upper 20s to mid 30s. However, winds remaining near 10-15 mph will keep wind chills in the 20s for much of the area during the day.

KEY MESSAGE 3...The risk of wintry weather through early next week remains low, but cold temperatures mean any changes could result in a return of the chance of snow.

Following a brief warm up to near normal temperatures ahead of a cold front Saturday, a cold pattern with below normal temperatures looks likely to persist through at least the middle of next week (more details on the cold in Key Message 4). A few different shortwave troughs will pass across the region during this time, which could combine and result in a risk of wintry weather (given conducive temps). At the moment, none of these appear particularly interesting or impactful, however we could certainly see some light accumulating snowfall at some point if everything aligns just right. It's also within the realm of possibility that these waves just bring us some flurries or nothing at all. Have stuck with NBM PoPs through this period due to the low predictability, which is mostly 20-30%. We will need to keep a close eye on this period given the cold that will be present, but at this time the risk of significant wintry weather beyond Thursday through early next week is low.

KEY MESSAGE 4...An extended period of below normal temperatures is forecast beginning Sunday and through the middle of next week, with wind chills in the single digits and teens possible for multiple consecutive nights.

There is increasing confidence that our region will experience an extended period of below normal temperatures beginning Sunday through at least the middle of next week. Daytime temperatures will be in the 20s and 30s and nighttime temperatures in the 10s and 20s, and as low as the single digits north of I-78. This combined with persistent winds will result in the potential for multiple consecutive nights of wind chills in the single digits and teens in many areas, and in below zero in the southern Poconos.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

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

Today...Primarily VFR with mostly cloudy to overcast skies. South-southwest winds around 5-10 kt. Light rain possible at KRDG and KABE after 15Z. Elsewhere, a stray shower possible after 21Z. Moderate-high confidence overall.

Tonight...VFR early will lower to MVFR and IFR overnight, primarily after 02-03Z from west to east. Periods of light rain expected, gradually changing over to a rain/snow mix or all snow from west to east. Southwest winds around 5-10 kt early in the evening, becoming west-northwest around 10-20 kt late. Low- moderate confidence.

Outlook...

Thursday...VFR. Gusty WNW winds.

Friday...VFR. Gusty SW winds possible. LLWS possible Friday night.

Saturday and Sunday...VFR most likely, but low chance of restrictions if light rain/snow develops.

MARINE

Small Craft Advisories on the Atlantic Coastal Waters have been extended through Thursday. A Small Craft Advisory for the Delaware Bay has also been issued beginning at 3 AM Thursday.

South-southwest winds around 15-25 kt will diminish to around 10-20 kt later this morning and through the afternoon. Seas of 4-6 feet will lower to around 3-5 feet this afternoon. Southwest winds around 10-20 kt tonight will gradually turn to west- northwest overnight as a cold front passes through. Winds may gust up to 25-30 kt as the front passes with seas building back to 4-6 feet. Light rain expected tonight, may mix with light snow at times.

Outlook...

Thursday...Small Craft Advisory in effect. WNW winds 20-30 kts. A brief period of gale force wind gusts near 35 kts possible Thursday morning as a cold front pushes offshore. Seas 4-6 feet.

Thursday night...Small Craft Advisory conditions expected, with potential for gale force wind gusts near 35 kts developing much of the night into Friday morning. Gale Watch was issued for all coastal waters. Freezing spray possible. Seas lingering near 5 feet across the Atlantic waters.

Friday through Sunday...Advisory conditions likely at times. A slight chance of rain and snow Saturday and Sunday.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 3 AM to 6 PM EST Thursday for ANZ430- 431. Gale Watch from Thursday evening through Friday morning for ANZ430-431-450>455. Small Craft Advisory until 6 PM EST Thursday for ANZ450>455.