textproduct: Philadelphia/Mt Holly

SYNOPSIS

High pressure gradually builds into the region tonight through Friday before weakening into Saturday. Low pressure passes through the region Saturday night through Sunday morning bringing a strong cold front through in its wake. Arctic high pressure builds in from the west for the start of next week before sagging into the Southeast and Mid-Atlantic by the middle of next week and then eventually off the east coast.

NEAR TERM /THROUGH FRIDAY/

As the deepening low pressure well to the NE continues to pull away, high pressure builds in from the southern states. A strong pressure gradient between these features will keep gusty winds across the region into the early overnight. Gusts will be mostly 25 to 30 mph early then go less than 20 mph overnight. Precipitation will be scarce, but some snow showers, or perhaps a short duration squall, are possible across the southern Poconos and/or perhaps into north NJ. We will continue the slight chance/chance pops for those areas. Cold overnight with lows in the teens far N/W and low/mid 20s elsewhere. Winds chills will be around 10 degrees less than the air temps, so single digits N/W and teens elsewhere. West to Northwest winds 10 to 15 mph decreasing late.

High pressure moves our way Friday and will crest across the Middle Altantic area late. Therefore, fair weather is expected for the last day of the (standard) workweek. There will be no escaping the below normal temps through with mostly low to mid 30s for highs and wind chills still a few degrees cooler than that. Winds will generally be West at 5 to 10 mph much of the day.

SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/

The Friday night through Saturday period looks to be relatively tranquil. An upper level trough will continue to dominate over the east with a few impulses moving through the flow but at the surface high pressure looks to dominate keeping conditions dry. Skies will be mainly clear Friday evening with increasing clouds by later at night through Saturday ahead of the next system. Expect lows Friday night generally ranging from the teens north to the low/mid 20s south with highs Saturday mostly in the 30s to low 40s.

The forecast gets more complicated for the Saturday night through Sunday period as there will be several different things at play. In the upper levels, there will be an upper level trough digging as it moves from the Great Lakes region towards the east coast. Meanwhile at the surface level, there will be an arctic front pushing into the area from the NW as low pressure pivots through Quebec into northern New England. Forecast guidance continues to indicate that a wave of low pressure will form farther south near the front as it's moving through the mid Atlantic region Saturday night into Sunday morning. However there are differences regarding the strength and track of this system. The latest GFS continues to indicate that the low may not really get going until it's off the coast and if this were to verify, most of the precip with the system would be near and south of the I-95 corridor but mainly fall as snow. The NAM is at the other end of the spectrum indicating a stronger low forming near Delmarva. This would keep the heaviest precip with the system north of the urban corridor with lighter amounts and more of a snow/rain mix farther south. The 12z RGEM lies in between these two extremes. There's also a wide variation in the ensembles. Given this continuing uncertainty, we largely stayed close to the NBM. And the bottom line with this forecast is that we do expect precip to move in either late Saturday evening or overnight Saturday night. It should be mainly snow except near the coast where some mixing with rain is likely...especially at the onset. And if arrives early enough Saturday evening, some rain or mixing could also occur near the urban corridor. The bulk of the precip falls overnight Saturday night through the first half of Sunday morning. This had been looking like a light precip event but some of the latest guidance has also beefed up QPF amounts into the .25 to .50 inch range. The big questions though are where the highest amounts will fall and how this will translate to snowfall. We admittedly still lean a little on the conservative side with forecast snow amounts and continue to indicate a fairly widespread 1-3 inches falling across the area. There is the potential though that some areas could see snow amounts in the 3 to 5 inch range given the general uptick in forecast QPF. The big question though is where these amounts occur. A more northern track would result in these higher occuring over eastern PA into northern NJ where a more southern track would favor higher amounts along the coastal plain. At this point, the main thing to stress is this continuing uncertainty in the details despite overall moderate confidence in there being an accumulating snowfall event affecting the area.

The snow with the system should taper off by early Sunday afternoon with the remainder of the day being blustery and cold. Lows Saturday night will be mainly in the 20s with highs Sunday only a few degrees warmer than this due to the developing strong cold air advection pattern. By afternoon NW winds will be around 10 to 20 gusting up to 30 mph resulting in wind chill values in the single digits and teens!

LONG TERM /MONDAY THROUGH THURSDAY/

Strong, gusty winds continue into Sunday evening before starting to diminish some overnight as low pressure moves farther out to see and arctic high pressure advances eastward towards the area. Overnight lows Sunday night will be mainly in the teens but with the wind, the wind chill will make it feel more like single digits!

High pressure to our south brings fair and dry weather for Monday though there will be a continuing breeze. Highs will be mostly in the 20s to low 30s but the wind chill will make it feel more like teens and low 20s.

Beyond next Monday, there looks to be a gradual warming trend as high pressure over the SE CONUS moves offshore and eventually sets up more of a return flow from the SW. It will still be chilly Tuesday with highs mainly in the 30s (20s over the southern Poconos) with temperatures warming into the 40s Wednesday and then potentially some upper 40s into the 50s by next Thursday. Conditions should stay mainly dry through the first half of the week before the next system approaches by later Thursday bringing chances for rain as temperatures look to be too warm for snow.

AVIATION /19Z THURSDAY THROUGH TUESDAY/

The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight... VFR expected overnight with SCT sky cover mostly and perhaps some BKN at times for KRDG/KABE. A couple snow showers early across the far N/NW areas. Gusty West to Northwest winds 10 to 15 kts G25 kts will decrease overnight. High confid.

Friday... VFR expected. Mostly high clouds expected. West winds 10 to 15 kts developing by mid/late morning. High confid.

Outlook...

Friday night...VFR/NSW.

Saturday...VFR/NSW.

Saturday night through Sunday night...Sub-VFR in SN Saturday night through Sunday morning. VFR thereafter. W-NW winds 15 to 20 kt with 25 to 30 kt gusts Sunday afternoon and Sunday night.

Monday through Tuesday...VFR/NSW.

MARINE

The Gale Warning for the waters will continue until 6PM for Delaware Bay and the southern coastal zones. Further north, Gales continues until 1AM. We will see the West to Northwest winds diminish slowly overnight and SCA conditions will follow for Friday. Fair weather expected.

Outlook...

Friday night through Saturday...Sub-SCA conditions.

Saturday night...Sub-SCA conditions but VSBY restrictions in rain/snow.

Sunday through Sunday night...SCA conditions developing Sunday morning, ramping up to gales late Sunday and Sunday night. VSBY restrictions in rain/snow Sunday morning. Freezing spray possible Sunday night.

Monday...Gales possible in the morning, then SCA. Freezing spray possible Monday morning.

Tuesday...Small Craft Advisory conditions may linger into the first part of the day.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Gale Warning until 8 PM EST this evening for ANZ430-431- 453>455. Gale Warning until 5 AM EST Friday for ANZ450>452.