textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes at this time.

KEY MESSAGES

1. Gusty winds and turning much colder during today with rain mixing with and changing to some wet snow.

2. Gusty winds and dry conditions Saturday may create some fire weather concerns.

3. A strong cold front moves through during Monday bringing precipitation, gusty winds and a surge of colder air.

DISCUSSION

KEY MESSAGE 1...Gusty winds and turning much colder during today with rain mixing with and changing to some wet snow.

A strong cold front will shift offshore early this morning, with strong cold air advection occurring in its wake. This will result in temperatures tumbling today with very early morning highs in the 60s and 70s which then fall into and through the 50s to 40s this morning and then down into the mid to upper 30s this afternoon. Some showers will be around early, then as a ripple of energy rides along the baroclinic zone it will throw moisture back behind the cold front. This will result in an area of developing and expanding rain this morning into this afternoon across much of the area. As the cold air advection deepens through the day, the rain will mix with wet snow and even change to wet snow for a time this afternoon. Some guidance suggests that a ribbon of stronger forcing for ascent slides through by later this afternoon which could enhance the precipitation rates some. If this were to occur, the column may cool even faster and result in a faster changeover to snow and also an increase in the intensity. This may occur from near and south/east of the I-95 corridor. Given the record warmth the last few days and lingering warmth early this morning, despite the strong cold air advection today, not anticipating much snow accumulations. It certainly is possible that during some greater precipitation rates, some slushy snow accumulations can occur mainly on grassy surfaces (road surfaces should remain just wet). This is an interesting setup, however air temperatures during the day are forecast to remain above freezing. The precipitation is expected to quickly end from west to east later this afternoon to early this evening as the system quickly departs. Some clearing is then expected, although a few snow showers cannot be ruled out this evening in the vicinity of mostly the southern Poconos.

There will be a period of deeper mixing beneath an inversion today, and the model forecast soundings show gusty winds mixing down. As a result, it will become rather brisk today with peak wind gusts in the 30-40 mph range. The strongest winds may end up occurring this morning along and for a time behind the frontal passage. The wind will add to the chill as temperatures fall, with wind chills dropping into the upper 20s to low 30s by late afternoon. This will be some 40-50 degrees colder than yesterday afternoon! Most locations drop into the upper 20s by later tonight along with a diminishing wind.

KEY MESSAGE 2...Gusty winds and dry conditions Saturday may create some fire weather concerns.

Low pressure will depart across northern New England early Saturday while high pressure begins to build in from the Great Lakes area. The pressure gradient between these systems will result in a West to Northwest flow across the Middle Atlantic region early this weekend The air that arrives will be close to 30% relative humidity during Saturday afternoon and since winds will be gusting between 25 and 30 mph, this could produce some low- end fire weather concerns. We will continue to monitor this later today and Friday. The main limiting factor will be fuel moistures. Some areas received a decent rainfall last night and this could hinder any fire growth.

KEY MESSAGE 3...A strong cold front moves through during Monday bringing precipitation, gusty winds and a surge of colder air.

As low pressure tracks just to our north Sunday night into Monday, a strong cold front will cross our area late Monday into Monday night. A plume of deeper moisture and stronger forcing for ascent should result in a period of rain ahead of the cold front itself later Sunday night and continuing through Monday. A milder air mass should be in place, therefore rain is expected. Thunderstorms are also possible. As cold air begins to pour in later Monday a transition to snow before ending is possible if enough moisture remains. The amount of precipitation and any snow will be highly dependent on the timing of the system, how much moisture is with it and how quickly the colder air moves in. As low pressure tracks just to our north Sunday night into Monday, a strong cold front will cross our area late Monday into Monday night. A plume of deeper moisture and stronger forcing for ascent should result in a period of rain ahead of the cold front itself later Sunday night and continuing through Monday. A milder air mass should be in place, therefore rain is expected. As some cold air begins to pour in later Monday a transition to some snow before ending is possible if enough moisture remains. The amount of precipitation and any snow will be highly dependent on the timing of the system, how much moisture is with it and how quickly the colder air moves in. A robust period of cold air advection will follow into the middle of next week, resulting in a much colder air mass across our area. This may result in high temperatures Tuesday and Wednesday reaching the upper 30s to low 40s across our region. Winds chills will be in the 30s much of the time. Quite a difference from the recent spell of warmth.

AVIATION /10Z THURSDAY THROUGH MONDAY/

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

Today...VFR ceilings with even a period of MVFR ceilings. Any IFR/LIFR visibility due to fog early this morning improves as the winds increase. MVFR visibilities as rain develops, which then mixes with and changes to some wet snow this afternoon. When all snow occurs and the intensity increases for a time, visibilities can drop to IFR or lower. Variable winds 5-10 knots becoming northwest 15-20 knots with gusts 25-35 knots through this morning, then diminishing some by later this afternoon. Low confidence.

Tonight...VFR as the sky clears. West-northwest winds diminishing to 10 knots or less. Moderate confidence.

Outlook...

Friday/Friday night...VFR expected with gusty winds developing Fri afternoon. Fair.

Sat thru Sunday...VFR expected.

Sunday night thru Monday night...Sub-SCA with IFR probable at times. Rain and chance of tstms. Gusty winds Monday/Monday night.

MARINE

A Small Craft Advisory remains in effect for all waters through the day today, then the Atlantic coastal water zones goes through this evening.

A sharp wind shift from southerly to west and then northwest will occur through early this morning as a strong cold front moves offshore. There will be a period of stronger winds today due to strong cold air advection and deeper mixing, which then starts to diminish later this afternoon and tonight. Seas will also build for a time.

Outlook...

Friday/Friday night...SCA conditions expected with gusts 25 to 30 kts and seas 5 to 7ft on the ocean. Fair weather.

Saturday thru Sunday...Except for a few SCA seas early Sat, sub-SCA thru the period with Fair weather.

Sunday night...Building winds and seas with SCA expected. Showers and tstms possible overnight.

Monday thru Tuesday...SCA with Gales possible Monday. Rains and tstms much of the time.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ430- 431. Small Craft Advisory until 10 PM EDT this evening for ANZ450>455.