textproduct: Philadelphia/Mt Holly

SYNOPSIS

Low pressure tracks northeast towards our area Tuesday into Tuesday night, bringing widespread precipitation. 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, before high pressure builds back in for early next week.

NEAR TERM /THROUGH TONIGHT/

As of 10:15AM, the rain/snow line is moving north and continues to progress NW of the I-95 corridor. There has been a slower progression of this transition zone this morning as the colder air has held on longer. This has led to more mixed precipitation including freezing rain. Due to radar data, observation trends, and reports, the Winter Weather Advisory running from western Montgomery county in PA to Somerset county in NJ was extended to 12PM today. Chester county was allowed to expire as temperature trends are now above freezing and winter precipitation looks to have ended as the transition to rain has occurred. All other Winter Weather Advisories remain unchanged as these areas continue to see winter precipitation.

The previous discussion below remains on track:

The low pressure system remains the main story for the near term period as it continues to approach the area this morning and then off the coast by this afternoon, which will continue to bring widespread precipitation to the region, including the first accumulating snowfall to portions of the area. This low will make its closest approach to the area as it passes offshore this afternoon, and begins departing to the northeast tonight.

In terms of the details with this system, the forecast largely remains on track. The precipitation remains widespread across the area with the highest PoPs (90-100%) remaining during the daytime hours today.

Observations indicate that temperatures continue to increase with subtle warm air advection as the system approaches. Continuing through the day today, the onshore flow and warm marine influence with the surface low drawing near will impact the temperature profiles. For perspective on this, high temperatures today will be near or a couple degrees above freezing in the Poconos, mid 30s to near 40 degrees northwest of the fall line, low 40s along the I-95 corridor, and in the mid 40s to low 50s in Delmarva and along the coastal areas.

Through the morning hours, the rain/snow line will inch closer to I-78. During the afternoon, the rain/snow line has the potential to reach into the Poconos and parts of northwest NJ. With the aforementioned highs being near/just above freezing in the Poconos, there is even the potential for mixing in the higher elevations of these areas above 1,500 feet.

Regarding more details about the precipitation accumulation, QPF has remained about the same with the latest updates. Totals continue to range from 0.50-1.00" with localized amounts to 1.25" with the greatest across the coastal plain and least farther inland north of I-78.

As for snowfall accumulation, the forecast has remained about the same with this 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 of a few tenths of an inch for the very NW portion of the I-95 corridor, up to an inch for areas just northwest of there, and in the 1-3" 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 3-6" range.

Outside of potentially 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. Due to the stronger signal of warmer air advecting in, the transition zone from snow to rain may not be as clean. There is now the potential for a light accumulation of ice from freezing rain in the transition zone northwest of the I-95 corridor. The ice accumulation looks to be a light glaze.

The Winter Weather Advisory for the southern Poconos and Sussex County NJ is unchanged, remaining in place through the day today, as snow and/or mixed precipitation will continue in this area until the system departs this evening.

The Winter Weather Advisory for the next tier of counties southeastward in northern NJ and the I-78 corridor and down into the far northwestern reaches of the Philly metro, has been expanded to include Somerset County in New Jersey. These are the areas most likely to experience a troublesome Tuesday morning commute, with snowfall up to the 1-3" range as well as light glaze of ice from freezing rain.

For the remainder of the region that will see all rain or a change to rain early on 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 late this evening, a high pressure system will build in from the southwest. This will lead to drier conditions through tonight. Lows tonight 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).

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/

By Wednesday morning, the axis of the H5 trough that will lead to Tuesday's widespread precipitation will be in the Gulf of Maine vicinity, rapidly lifting northeast away from the area. A subtle upper-level ridge axis will shift eastward across the area through the day Wednesday. Wednesday night into Thursday, enhanced southwesterly flow aloft will begin to overspread the area as a trough digs southeastward over portions of Ontario and eventually Quebec. The trough axis will pass to the north/glance the region Thursday. Subtle height rises will follow with flow aloft becoming zonal Thursday night. At the surface, high pressure will build in from the west on Wednesday. A surface low will pass well to the north of the area on Thursday with a strong trailing cold front moving through by Thursday evening.

Wednesday should be a partly to mostly clear day. Highs will range from the mid 30s across eastern PA and northern NJ to the low 40s across southern NJ and the Delmarva. Wednesday night will feature increasing clouds from northwest to southeast as the cold front begins to approach the region. Lows will be in the low-mid 20s across most of eastern PA and NJ, with upper 20s to near 30 for the coastal plain, urban corridor, and Delmarva.

Thursday will be partly to mostly cloudy ahead of the front. While not explicitly mentioned in the forecast at this time, a couple of snow showers could occur with the frontal passage across the Poconos. If this were to occur, accumulation amounts would be light. Otherwise, it looks to remain dry. Will defer to future shifts on potential inclusion of PoPs for this region. Highs will generally be in the 30s northwest of I-95 and 40s southeast. Skies should clear behind the front, but breezy northwest winds will ensue, so it will be quite chilly.

With the cold post-frontal airmass in place, decreasing winds, and partly to mostly clear skies, the stage will be set for a very cold Thursday night. Lows are expected to be in the single digits across the Poconos and into far northwestern NJ, the teens across the remainder of eastern PA and NJ, and the low 20s across the Delmarva.

LONG TERM /FRIDAY THROUGH MONDAY/

Friday looks to start with high pressure centered over our area under zonal flow aloft. Deterministic guidance still shows the potential for a weak impulse aloft to track through the region Friday night into Saturday. The surface high will shift eastward and off the coast Friday night into Saturday. Ensemble guidance still suggests the possibility of surface cyclone formation across the Carolinas, though consensus remains that it will be a weaker storm that will stay south of us, with only a glancing blow. We continue to have a chance (30-50%) PoPs across most of the area for Friday night, with the greatest chances across southern DE and far southeastern NJ. These ultimately may continue to come down, but trends will be monitored in the coming days as this potential storm system gets closer in time. The airmass in place will be cold enough that any precipitation that does fall across the area with this system would have the potential to be of the wintry variety.

Regardless of precipitation chances for Friday night into Saturday, the pattern favors well below average temperatures. In fact, temperatures may remain below freezing on Friday for most of eastern PA and northern NJ, and only reach the mid 30s across the Delmarva and into southern NJ. Saturday and Sunday look to remain below average, though slightly warmer than Friday. Another cold front could bring at least low precipitation chances and a renewed shot of cold air Sunday night into Monday.

AVIATION /14Z TUESDAY THROUGH SATURDAY/

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

Today...IFR/LIFR conditions develop between 11z-15z. High confidence in all rain at KACY/KMIV. The trend as of this morning has been warmer and slower with precipitation moving in. This will result in pretty much all rain for KILG/KPHL and have taken snow out of the TAF for now. Cannot rule out a few flakes/mix at onset, but would expect a quick flip to rain once precipitation begins. For KPNE/KTTN, expecting a longer period of snow and/or mix, but a flip to all rain should occur by 14z. A period of all snow expected at KRDG/KABE till about 14z before mixing occurs and eventual flip to all rain after 18z. High confidence in at least IFR through the morning with the potential (25-35%) in prevailing LIFR. Moderate confidence in timing of precipitation type changes. Winds will be out of the east/northeast around 5-10 kt, expecting to shift to north/northwest between 19z-22z. Moderate confidence in timing of wind shifts.

Tonight...Conditions gradually improving with rain coming to and end though MVFR/IFR expected to start, with VFR anticipated to return between 03-06Z. Northwest winds around 10 knots with gusts up to 20 knots possible. Moderate confidence.

Outlook...

Wednesday through Wednesday Night...VFR. No significant weather.

Thursday...VFR. Gusts near 20 kt expected out of the west/northwest

Thursday Night through Friday...VFR. No significant weather.

Friday Night through Saturday...Restrictions possible (40-60%) with rain and snow showers moving through.

MARINE

No marine hazards are anticipated through early this morning with seas 2-3 feet and winds out of the east to then southeast gusting to 10-20 knots.

Winds and seas will then increase later this morning. Winds will gust to 25-30 knots and flip to be out of the north to northwest by this evening. Occasional gusts to 35 knots are possible on the ocean zones tonight. Seas will reach 5-7 feet tonight as well. As a result, a Small Craft Advisory is in effect beginning at 10 AM today for the Atlantic Ocean coastal waters and at 3 PM for the Delaware Bay. The SCA will continue through tonight for all coastal waters.

Outlook...

Wednesday...SCA conditions linger into the first part of the day. While winds are expected to have subsided, seas of 4-6 feet are expected in the morning, decreasing to 2-4 feet through the day.

Wednesday night...No marine headlines are anticipated with winds below 25 kt and seas below 5 feet.

Thursday through Thursday night...SCA conditions are possible with northwest winds 15-25 kt and seas 3-5 feet.

Friday through Saturday...No marine headlines are anticipated with winds below 25 kt and seas below 5 feet.

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 until 1 PM EST this afternoon for PAZ060>062. Winter Weather Advisory until noon EST today for PAZ103-105. Winter Weather Advisory until 6 PM EST this evening for PAZ054- 055. NJ...Winter Weather Advisory until 7 PM EST this evening for NJZ001. Winter Weather Advisory until 1 PM EST this afternoon for NJZ007-008. Winter Weather Advisory until noon EST today for NJZ009-010. DE...None. MD...None. MARINE...Small Craft Advisory from 3 PM this afternoon to 6 AM EST Wednesday for ANZ430-431. Small Craft Advisory until 1 PM EST Wednesday for ANZ450>455.