textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

A Dense Fog Advisory has been issued for much of the area until 7 AM this morning.

The Marine Dense Fog Advisory was extended to 11 AM for all the marine zones.

KEY MESSAGES

1. Dense fog continues into this morning.

2. A cold front moves through the region today leading to continued chances for showers and possibly some thunderstorms.

3. Warmer air will overspread the region early this week before a strong cold front brings more seasonable conditions back for the late week.

DISCUSSION

KEY MESSAGE 1...Dense fog continues into this morning.

A stable airmass remains entrenched over much of the area with low stratus and fog in place. Warm air advection continues from south to north into this morning as a warm front lifts through the area. Soundings already show some of the low-level inversion lessening across parts of Delmarva where the warm front has moved through. However, there remains a strong low-level inversion keeping moisture trapped at/near the surface for much of the area. Due to this, dense fog has developed across much of the area and low stratus continues to persist. A Dense Fog Advisory has been issued for most of the forecast area until 7 AM. Visibility should improve through the morning as the warm air advection continues to erode the low-level inversion with the warm front continuing northward. Temperatures overnight have continued to warm and the additional warm air advection today will result in highs in the mid 60s to low 70s for many.

KEY MESSAGE 2...A cold front moves through the region today leading to continued chances for showers and possibly some thunderstorms.

As a warm front lifts north through the area into this morning, some isolated showers are lingering. Through this morning and into this afternoon, the main focus for any showers or an isolated thunderstorm is south and east of the I-95 corridor as a cold front moves through the region. There looks to be some instability present during the afternoon ahead of the cold front across parts of Delmarva and southern portions of New Jersey. This will allow for the potential for an isolated thunderstorm but nothing severe is expected. Once the cold front clears the area this evening, a high pressure system builds in from the south and west allowing for decreasing clouds and drier conditions into tonight.

KEY MESSAGE 3...Warmer air will overspread the region early this 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 from tonight through Tuesday night. At the surface, high pressure will build into the area in the wake of today's frontal passage. As the high gradually shifts eastward through Tuesday night, light return flow is expected to commence, bringing about a warming trend. On Monday, with light southerly flow and at least some sunshine, temperatures are expected to rise into the 60s across most of the area. The warming trend will continue through Wednesday with highs warming into the low to mid 70s and lows in the 40s and 50s. Highs will be cooler in proximity to the ocean due to sea breeze development each day. In addition, there is the potential for fog each night. Relatively light winds in combination with warm and moist air overspreading the region with very cool ocean temperatures could lead to 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. This will result in increased cloud cover, but at this time singificant precipitation is likely to lag until Wednesday night.

The trough axis is expected to shift eastward across the region late Wednesday night and Thursday, with a surface low and trailing cold front moving through the area. Along the cold front, 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 we can't ruled out a few thunderstorms or at least some gusty winds. After the frontal passage, some lingering rain or snow showers will be possible across the area as colder air blows back into the region.

A return of seasonable temperatures is expected Friday and into the first part of the weekend. Another weak system may glance the region Friday night, bringing a chance for light rain and perhaps a little snow in the Poconos. For now, will feature 20-30% PoPs during this time period, with the higher chances being across northern portions of the area.

AVIATION /07Z SUNDAY THROUGH THURSDAY/

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

Thru 12Z this morning...Generally IFR/LIFR (possibly VLIFR at times) with low ceilings and visibility restrictions from fog. Rain showers continue to move through the area with coverage isolated to scattered. VCSH has been added for the Lehigh Valley and I-95 terminals early this morning. The best potential for -SHRA is at KRDG/KABE. LLWS remains likely at all terminals through 10Z out of the west- southwest at around 40-50 kt. Overall, moderate-low confidence.

Today...Lingering IFR/LIFR conditions early, should gradually improve to MVFR between 12-15Z with showers in the area ending. The exception is MIV and ACY where showers are expected into the afternoon hours. Overall, a gradual improvement is expected with VFR conditions returning by the afternoon from northwest to southeast. West winds around 10-15 kt with occasional gusts up to 20 kt possible in the afternoon. Moderate confidence.

Tonight...VFR. A west wind around 5 knots or less. Some patchy fog is possible but is too low confidence right now to include in the TAFs.

Outlook...

Monday through Wednesday...Primarily VFR. Periods of sub- VFR conditions will be possible in fog each night.

Wednesday night through Thursday...Sub-VFR conditions possible in rain showers. Gusty winds also possible.

MARINE

Marine Dense Fog Advisories have been extended until 11 AM today for all Atlantic Coastal waters including the Delaware Bay. Small Craft Advisories remain in effect until 6 PM this evening for the Atlantic Coastal waters only.

Southwest winds remain around 15-20 kt through this afternoon before shifting west around 10-15 kt in wake of a frontal passage this evening. Seas around 4-6 feet. Seas and winds continue to decrease into tonight.

A chance of showers today with a slight chance for thunderstorms is also present today. Drier conditions are expected this evening and overnight.

Outlook...

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

Wednesday through Thursday...SCA conditions expected. Gales are possible on Thursday. Southerly winds 10-15 kt with gusts to 25 kt are expected Wednesday into Wednesday night. Southwesterly winds 20- 25 kt with gusts 30-35 kt expected Thursday, before becoming west- northwesterly behind a cold front Thursday. Seas 3-6 feet on Wednesday will increase to 6-11 feet Wednesday night into Thursday. Showers are likely, particularly on Thursday, with a few isolated thunderstorms also possible.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Dense Fog Advisory until 7 AM EDT this morning for PAZ054-055- 060>062-070-071-101>106. NJ...Dense Fog Advisory until 7 AM EDT this morning for NJZ013>027. DE...Dense Fog Advisory until 7 AM EDT this morning for DEZ001. MD...None. MARINE...Dense Fog Advisory until 11 AM EDT this morning for ANZ430-431- 450>455. Small Craft Advisory until 6 PM EDT this evening for ANZ450>455.