textproduct: Philadelphia/Mt Holly

SYNOPSIS

High pressure will pass through the region today and offshore tonight. Low pressure will develop over the Southeast tonight before tracking northeast towards our area Tuesday into Tuesday night, bringing widespread precipitation to the area. High pressure and below normal temperatures return for the middle of the week. Another cold front will track through the region Thursday night, with high pressure building back in thereafter. Another system may impact the region Friday night into the weekend.

NEAR TERM /UNTIL 6 PM THIS EVENING/

A brief period of tranquil weather is on tap for today with high pressure in control. The high is quickly transiting from west to east, currently centered over the Great Lakes but will become centered over the region by late this afternoon into the evening.

Skies have largely cleared with the high beginning to build in and the preceding cold front now well offshore, though there is some lingering stratus over the Appalachia that is edging into the higher terrain areas in the northwest portion of the region. Winds have dropped off to around 10 mph, though a few gusts to around 20 mph remain possible early this morning. These gusts may become a bit more frequent during the mid-morning hours after sunrise.

The daytime hours today will remain mostly clear, though some increase in high clouds may come during the afternoon hours ahead of the next system. Lingering gusty northwest winds in the morning will diminish by the afternoon as the high moves overhead and the pressure gradient relaxes. High temperatures will be near freezing in the Poconos, in the upper 30s to lower 40s for eastern PA and much of NJ, and mid 40s for the Delmarva into far southern NJ.

SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/

The main story for the short term will be the strengthening low pressure system moving northeast Monday night and off the coast into Tuesday, which will bring widespread precipitation to the region, including the first accumulating snowfall to portions of the area. There will be a low developing over the southeastern US and our high pressure system will retreat off to the northeast tonight. This low will make its closest approach to the area Tuesday afternoon, and begin departing to the northeast by Tuesday night.

In terms of the details with this system, there have been no significant changes have been made to the forecast or messaging for Tuesday. There are chance to likely PoPs (40-60%) starting late Monday night, with the highest PoPs (90-100%) being during the daytime Tuesday. There continues to be a trend toward a somewhat faster solution in the deterministic guidance. If this trend holds, it could have implications on initial precip type into the I-95 corridor with a little more snow possible. The precipitation will end from west to east pretty quickly by Tuesday evening into Tuesday night as the low moves off to the northeast.

For the precipitation accumulation, QPF remains fairly steady around 0.75-1.25" across the board, greatest across the coastal plain and least farther inland north of I-78. Due to the earlier trend in precip onset, there is the potential for light snow or perhaps some sleet initially for the I-95 corridor and south, perhaps as far south as northeastern Maryland, central and northern Delaware, and portions of interior southern New Jersey. This initial light snow could result in minimal accumulation (a dusting less than 1"), and would not last long as the low draws closer to the area changing the precip to rain. Again, any snowfall occuring this far south will be dependent on exactly how quickly the precip moves into the area. A slower/later onset would probably mean mostly all rain along and southeast of I-95.

Through the day Tuesday, the onshore flow and warm marine influence with the surface low drawing near will impact the temperature profiles. By daybreak Tuesday, the rain/snow line should be near or perhaps just NW of the I-95 corridor. As the warmer air continues to filter in, the rain/snow line is expected to lift quickly northward to near or even north of the I-78 corridor and northwestern New Jersey by Tuesday afternoon. For perspective on this, high temperatures on Tuesday are near freezing in the Poconos, mid 30s northwest of the fall line, near 40 degrees along the I-95 corridor, and in the mid 40s to near 50 degrees in Delmarva and along the coastal areas. Although areas may start as snow, it does not appear that it will last for much of the area. The southern Poconos have the best potential at an all snow event from this system, but even they could see some mixing with sleet or rain Tuesday afternoon.

As for snowfall accumulation, the forecast has remained largely the same as the previous update. The probability for plowable snow (2" or more) remains high (60-90%) in the Poconos and areas along and north of I-78. As you head well south and east of I-78, the potential for plowable snow quickly decreases to near 0% for the I- 95 corridor. Our latest forecast includes snowfall amounts less than 1" for the immediate I-95 corridor, 1-3" for areas just northwest of there, and in the 3-5" range for the I-78 corridor and NW NJ. Higher elevations (especially 1,500 feet and higher) in NW NJ and across the Pocono Plateau have potential for snowfall in the 4-8" range. The Winter Storm Watch remains in effect for the southern Poconos and Sussex County NJ, where probability for warning criteria snowfall (6" or greater) remains a little too low (40-60%) to justify a warning upgrade just yet. If QPF trends a little lighter, the storm continues to speed up, or if more mixing occurs, warning level snowfall may not occur for the watch area.

A Winter Weather Advisory was issued for the counties on the periphery of the watch area, including much of northern NJ and the I- 78 corridor and down into the far northwestern reaches of the Philly metro. These are the areas most likely to experience a troublesome Tuesday morning commute, with snowfall in the 1-5" range. Along the southern-most fringe of the advisory area, probability for reaching the 2-3" criteria is lower (40-60%). However, this will be the first snowfall of the season, which is expected to occur during the Tuesday morning rush hour commute. Thus, impacts may be more significant than usual, even if observed snowfall amounts end up closer to the 1-2" range.

Outside of the Poconos and perhaps the higher elevations in NW NJ, the snow that falls will then be melting through the day with the change to all rain and warm air moving further inland. During the transition period from snow to rain, some sleet is possible briefly. In terms of freezing rain, the overall threat looks minimal given the current set up. The areas that see all rain or a change to rain will have a good soaking all-day type of rain. A few precipitation and/or snowfall records could be challenged. See the Climate section below for more details on the records.

Once the low departs Tuesday night, a high pressure system will build in from the southwest. This will lead to drier conditions through Tuesday night. Lows Tuesday night are in the 20s for most, which may lead to some black ice issues where any slushy snow melt refreezes on roadways (especially north of I-78).

For Wednesday, the high pressure system will be in place, which keeps us dry and mostly sunny with below normal temperatures continuing. High temperatures will be in the mid 30s to low 40s. W- NW winds 5-10 mph. Lows in the 20s again Wednesday night, with clouds beginning to increase late in the night.

LONG TERM /THURSDAY THROUGH SUNDAY/

In the long term period, we stay active with our weather pattern. A cold front looks to cross the area Thursday into Thursday night. As the cold front passes through, there is the potential for some snow showers, especially near/north of I-78. The main factor with this cold front will be the notably colder airmass in its wake. Thursday night looks increasingly likely to be the coldest night so far this season, with widespread low temperatures in the teens for most, and even single digits for the higher terrain. Wind chill values Thursday night will be in the single digits to mid-teens. By Friday, highs are in the upper 20s to upper 30s for most areas. Beyond that, our next system looks to arrive late Friday into the weekend, bringing potential for another round of widespread precipitation, including wintry precipitation. However, details on this system remain very unclear at the moment.

AVIATION /12Z MONDAY THROUGH FRIDAY/

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

Today...VFR with an increase in high clouds late in the day. Northwest winds around 10 kt with gusts up to 20 kt in the morning, before diminishing to around 5-10 kt in the afternoon. High confidence.

Tonight...Primarily VFR. Chance (20-40%) of MVFR conditions after 09Z as rain and snow begin to move in. East-northeast winds around 5 knots or less. Moderate confidence.

Outlook...

Tuesday through Tuesday night...IFR restrictions expected in low clouds and precipitation during the daytime Tuesday. Snow changing to rain at RDG/ABE. For the I-95 terminals, precipitation may begin as snow for a couple hours before a change to rain. All rain for MIV/ACY. Conditions should improve by late Tuesday night, though gusty NW winds will be possible.

Wednesday...VFR. No significant weather.

Thursday...VFR. Gusty WNW winds possible.

Friday...Mainly VFR for Friday. Restrictions possible heading towards Friday night with a chance (40-60%) of rain/snow.

MARINE

A Small Craft Advisory is in effect for all coastal waters until 9 AM Monday. Gusts remain elevated along the Delaware Bay so the SCA for this area was extended to 9 AM along with the continuing SCA for the Atlantic Ocean coastal waters.

Early this morning, winds are northwesterly around 20-25 kt with frequent gusts near 30 kt for all ocean zones and the Delaware Bay. Seas over the ocean are around 5 feet, but are expected to decrease to around 4 feet by mid-morning.

Winds will then begin to diminish by mid-morning today, falling below 25 kt and with seas less than 5 feet. No marine hazards are anticipated beyond the current SCA through tonight.

Outlook...

Tuesday through Wednesday...Advisory conditions with east winds increasing to near 25-30 kts and then becoming northwest Tuesday night into Wednesday. The potential for wind gusts near 35 knots has decreased some, but will leave the Gale Watch in effect as previously issued for now. Winds look to diminish through the day Wednesday. Seas 5-7 feet, also diminishing through the day Wednesday.

Thursday through Thursday night...SCA conditions likely Thursday afternoon into early Thursday night as NW winds increase to near 25-30 kts and seas 4-6 feet.

Friday through Friday night...No marine hazards anticipated. Rain likely developing at night.

CLIMATE

Widespread moderate to heavy precipitation is expected on Tuesday, December 2nd. A few daily precipitation and/or snowfall records could be challenged. Records for our climate sites are listed below:

Record Precipitation (Rainfall) December 2 Site Record/Year Allentown (ABE) 0.86"/1934 AC Airport (ACY) 1.03"/1996 AC Marina (55N) 1.18"/1929 Georgetown (GED) 1.11"/1974 Mount Pocono (MPO) 3.56"/1996 Philadelphia (PHL) 1.48"/1986 Reading (RDG) 1.29"/1981 Trenton (TTN) 2.13"/1986 Wilmington (ILG) 1.27"/1991

Record Snowfall December 2 Site Record/Year Allentown (ABE) 3.6"/1952 AC Airport (ACY) T/2019* Philadelphia (PHL) 2.0"/1903 Reading (RDG) 6.0"/1929 Trenton (TTN) 3.0"/1903 Wilmington (ILG) 1.0"/1952

*Multiple years with a Trace.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Winter Weather Advisory from 4 AM to 1 PM EST Tuesday for PAZ060>062. Winter Weather Advisory from 4 AM to 10 AM EST Tuesday for PAZ101-103-105. Winter Storm Watch from late tonight through Tuesday evening for PAZ054-055. NJ...Winter Storm Watch from late tonight through Tuesday evening for NJZ001. Winter Weather Advisory from 4 AM to 1 PM EST Tuesday for NJZ007-008. Winter Weather Advisory from 4 AM to 10 AM EST Tuesday for NJZ009. DE...None. MD...None. MARINE...Small Craft Advisory until 9 AM EST this morning for ANZ430- 431-450>455. Gale Watch from Tuesday afternoon through late Tuesday night for ANZ450>455.