textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

The Small Craft Advisory has been allowed to expire.

KEY MESSAGES

1. A cold front clears through the region late this afternoon and evening, bringing a chance for a shower or perhaps a thunderstorm across the southern tier.

2. Warmer air will continue to overspread the region through mid week before a strong cold front brings more seasonable conditions back for the late week.

DISCUSSION

KEY MESSAGE 1...A cold front has cleared the land areas as of sunset and will move offshore early tonight.

A cold front has crossed the area as of the early evening. A few showers developed earlier across DE but have now diminished. Following the front, a high pressure system will build in from the south and west tonight and Monday allowing for decreasing clouds and drier conditions.

KEY MESSAGE 2...Warmer air will continue to overspread the region through mid week before a strong cold front brings more seasonable conditions back for the late week.

The region will be beneath a fairly benign upper pattern through Tuesday night. At the surface, high pressure centered over portions of the Southeast and Mid-Atlantic will gradually shift eastward through Tuesday night. This will set the stage for light southerly flow to continue across the area, and a continued warming trend is expected to continue through Wednesday. Daytime highs Tuesday and Wednesday are expected to be in the low to mid 70s for most of the area with morning lows in the 40s and 50s. Highs will be cooler in proximity to the ocean due to potential sea breeze development both Tuesday and Wednesday. In addition, there is the potential for fog development Monday and Tuesday night. Relatively light winds in combination with warm and moist air overspreading the region with very cool ocean temperatures could lead to areas of dense fog, particularly near the coasts.

Beginning on Wednesday, the upper pattern will become much more unsettled as a potent trough over central portions of the US begins to work eastward towards our area. Broad ascent is likely to begin overspreading the region during this time, and will lead to a chance for scattered showers within the warm air advection regime. On Wednesday, shower activity appears most likely along and north of I- 95, with PoPs currently in the 30-50% range, with PoPs around 20% south of it. Rainfall on Wednesday is not expected to be widespread and amounts will be light.

Wednesday night into Thursday morning, height falls associated with the approaching trough are expected to maximize, with the trough axis is expected to shift eastward across the region by Thursday afternoon. A surface low is expected to pass to the north of the region with a trailing cold front moving through the area Thursday morning. Along and ahead of the cold front Wednesday night into Thursday, PoPs increase to 50-70% areawide. Most guidance features a line of showers moving through the region. Very strong wind fields aloft and at least modest instability are forecast to be present, so thunderstorms will be possible. While the timing of this activity is not expected to be ideal for strong to severe storms, gusty winds cannot be ruled out as this activity moves through. After the frontal passage, some lingering rain or snow showers will be possible across the area through Thursday afternoon as colder air filters into the region.

More seasonable temperatures are expected through the weekend in the wake of the cold front. A couple of weak disturbances may glance the area, with the first being Friday afternoon into Friday night and the second being Saturday night into Sunday. This could lead to some light rain or snow across portions of the area, but it still appears that these disturbances may track far enough to the north to bring little or no impacts. Will continue to feature 20-30% PoPs during this time period, with the higher chances being across northern portions of the area.

AVIATION /00Z MONDAY THROUGH FRIDAY/

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

Tonight...VFR. A west wind around 5 knots or less. Some patchy fog is possible, mainly for MIV/ACY, but is too low confidence right now to include in the TAFs. Moderate/high confidence.

Monday...VFR. Winds from the SSW around 5 knots or less. High confidence.

Outlook...

Monday night through Tuesday night...Primarily VFR. Periods of sub- VFR conditions will be possible in fog and perhaps low clouds each night, though how far inland sub-VFR conditions are able to make it remains in question.

Wednesday through Wednesday night...Sub-VFR conditions possible in rain showers.

Thursday...Sub-VFR conditions expected in widespread showers. Some thunder is possible. Conditions will likely improve through the day though lingering rain or snow showers will be possible. Gusty winds expected.

Thursday night...VFR.

Friday...Primarily VFR. Some light rain or snow is possible for the Lehigh Valley terminals.

MARINE

Marine Dense Fog Advisories remain in effect until 8 AM Monday for Atlantic Coastal waters north of Cape May. The Small Craft Advisory that was up earlier has been taken down as seas continue to decrease.

West winds around 10-15 kt in wake of a frontal passage this evening and into the overnight. Seas around 3-4 feet. Seas and winds continue to decrease later tonight. Fair weather.

Sub-SCA conditions for Monday with fair weather overall.

Outlook...

Monday night through Tuesday night...Sub-SCA conditions expected with winds under 25 kt and seas under 5 feet. Marine fog is possible, mainly at night.

Wednesday through Friday...SCA conditions expected. Gales are possible on Thursday. Southerly winds 10-20 kt with gusts to 25 kt are expected Wednesday, becoming southwesterly and increasing to 20- 25 kt with gusts 30-35 kt Wednesday night into Thursday, before becoming west-northwesterly behind a cold front Thursday afternoon. There may be a lull in winds before they again increase out of the south to 15-20 kt with gusts to 30 kt Friday. Seas 4-7 feet on Wednesday will increase to 6-12 feet Wednesday night into Thursday, decreasing back to 4-7 feet Friday. Showers and perhaps a few thunderstorms are likely Wednesday night into Thursday.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Dense Fog Advisory until 8 AM EDT Monday for ANZ450>453.