textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes for low pressure passing through the Mid-Atlantic Sunday night through Monday.

Above normal temperatures return to the area by the middle of next week.

Several waves of low pressure may affect the area late next week.

KEY MESSAGES

1. Snow showers are possible late Friday Night into early Saturday Morning, mainly for areas north of I-195 in New Jersey and north of I-78 in Pennsylvania.

2. Low pressure moves through the Mid-Atlantic Sunday night through Monday, bringing some rain and snow to the area.

3. Above normal temperatures return to the area by the middle of next week.

4. Several waves of low pressure may affect the area late next week.

DISCUSSION

KEY MESSAGE 1...Snow showers are possible late tonight into early Saturday morning, mainly for areas north of I-195 in New Jersey and north of I-78 in Pennsylvania.

A fast moving mid level short wave trough will spark some snow showers which could progress as far southeast as northern New Jersey very late tonight into early tomorrow morning. Initially dry air in the boundary layer could result in mostly virga. However, some model soundings depict that dry air will erode and snow will begin to reach the surface. Hi res guidance was less bullish on precipitation coverage, so POPs were lowered to around 20-30%. Given the fast moving nature of this system, the window for accumulating snow from these showers is quite brief, thus, any snow accumulations are likely to be a few tenths of an inch at most.

Overall, this is unlikely to produce widespread impacts, but with temperatures in the 20s and teens as the snow is falling, if there are any light accumulations then untreated surfaces could be slippery. By the time the sun comes up on Saturday, precipitation should be out of the area.

Lows tonight will be below normal for one more night with temperatures into the mid teens to low 20s.

KEY MESSAGE 2...Low pressure moves through the Mid-Atlantic Sunday night through Monday, bringing some rain and snow to the area.

Low pressure will track along the Gulf Coast states this weekend, emerging over the Southeast by Sunday evening. A warm front will extend out from this low, and overrunning precip will develop from south to north Sunday afternoon. The heaviest precipitation will impact the area Sunday night, tapering off Monday morning. The big question is going to be how far north the precipitation gets. 12Z/13 NAM pretty much has precipitation confined to Delmarva, while the 12Z/13 GFS is a bit farther north with heavier QPF in Delmarva, and precipitation as far north as into the Lehigh Valley. The 12Z/CMC is similar to the NAM in that it keeps the system south. In terms of p- type, generally looking at rain in Delmarva and extreme southern New Jersey, and snow along and north of the I-95 corridor. 12Z/ECMWF is similar to the GFS, and the 12Z ECMWF-AI remains an outlier producing Warning level snowfall across the region. Since it is an extreme outlier, will not factor the ECMWF-AI in the forecast. With precipitation amounts heavier in the southern portions of the area, generally expecting less than an inch of snow where snow falls, mostly Sunday night into Monday morning.

Will generally follow the NBM guidance for this timeframe due to the low confidence in the forecast.

KEY MESSAGE 3...Above normal temperatures return to the area by the middle of next week.

High pressure builds into the Eastern Seaboard on Monday, then establishes itself offshore Tuesday through Wednesday. Return flow sets up at the surface and zonal flow sets up aloft. This allows for warm air advection to develop, and temperatures will finally push to above normal levels. Normal highs on Tuesday and Wednesday range from the mid 30s in the southern Poconos to the low 40s in the Lehigh Valley to the mid 40s along the I-95 corridor, Delaware Valley, and into southern New Jersey, and in the mid 40s in southern Delmarva. High temperatures will mostly range from the mid 40s or so in the southern Poconos and Lehigh Valley to the upper 40s and low 50s along the I-95 corridor, Delaware Valley, and southern New Jersey. Highs will be in the mid and upper 50s in southern Delmarva. Lows for the most part will be down into the low to mid 30s. Although relatively warm for this time of the year, it will also remain cloudy. The temperatures should allow for some of the abundant snowpack to start to melt, but it may not melt as much as it could due to the cloudy skies.

KEY MESSAGE 4...Several waves of low pressure may affect the area late next week.

Conditions then turn somewhat active for the middle to the end of next week. The first wave of low pressure will pass through Pennsylvania and New Jersey late Wednesday and Wednesday night. Precipitation at this point looks to be plain rain along and south of the I-95 corridor and a wintry mix of rain and snow, possibly mixed with some freezing rain, across the southern Poconos, far northwest New Jersey, and the Lehigh Valley.

Another system may affect the area for the end of the work week.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

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

Tonight...Primarily VFR. West/southwest winds around 5 kt or less. 15-20% chance of light snow showers at KTTN/KABE which could result in brief restrictions down to MVFR. Moderate confidence.

Saturday...VFR. West/northwest winds around 10 kt. High confidence.

Outlook...

Sunday through Monday...MVFR or IFR in RA or SN. Best chances for SN will be at KRDG/KABE/KTTN, RA and SN at KPHL/KILG, and RA at KMIV/KACY.

Monday night through Tuesday night...VFR.

Wednesday...Sub-VFR possible from time to time, mostly in RA.

MARINE

Sub-SCA conditions expected through Saturday with west/northwest winds around 10-15 kt and seas 1 to 3 feet.

Regarding the river ice threat...Ice remains across area bay waters and inland estuaries. This includes, but is not limited to the Delaware estuary. On rivers, the ice has grown in thickness enough to start causing restrictions in flow. An example of this can be seen at the Trenton River gauge. Per satellite imagery, the Delaware River is pretty much ice covered from just south of Trenton upstream to about Washington Crossing, though growth has stalled with warmer afternoon temperatures.

The most common ways river ice can break up is either through a thermal or mechanical means. We would like to see temperatures rise into the 40s for a few days, which is forecast this weekend and into next week. Rainfall, producing river rises, can also break up ice. The current forecast does include light rainfall across the Delaware Bay area Sunday into Monday with light snowfall for the Delaware River.

With afternoon temperatures warming above freezing, but overnight temperatures remaining below freezing, we have seen ice growth stall with some minor improvements in some areas, mainly across the southern waterways given the warmer afternoon temperatures. With afternoon temperatures warming into the 40s over the next several days, there is a better chance for gradual improvement during this stretch.

Outlook...

Saturday night through Wednesday...Generally a prolonged period of sub-SCA conditions expected.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...None.