textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Dense fog advisories cancelled for land areas as fog has already started to scatter out.

KEY MESSAGES

1. Dense fog has already begun scattering out, and should dissipate entirely not long after sunrise.

2. Warm temperatures expected through Wednesday, possibly record breaking in some spots. Dense fog possible at night.

3. A strong cold front will cross through the region late Wednesday into Thursday, bringing the potential for widespread showers and possibly some thunderstorms.

4. Seasonable temperatures late week into the weekend with a couple disturbances bringing some more unsettled weather.

DISCUSSION

KEY MESSAGE 1...Dense fog has already begun scattering out, and should dissipate entirely not long after sunrise.

While we had areas of dense fog develop overnight, they appear to already be starting to scatter out, possibly due to the drier air behind the cold front finally infiltrating the region. Thus, dense fog advisories for land areas have been cancelled, with a Special Weather Statement issued for lingering patches until 9 AM. After the remaining fog burns off, plenty of sunshine will push temps back well into the 60s to near 70 once again.

KEY MESSAGE 2...Warm temperatures expected through Wednesday, possibly record breaking in some spots.

The region will be beneath a fairly benign upper pattern through mid- week. At the surface, high pressure will be stationed out over the western Atlantic. This high will essentially act as a heat pump, bringing very mild temperatures to the region as much as 20 to 25 degrees above average! Daytime highs will mainly be in the low to mid 70s for most, with 60s in the Poconos with lows in the 40s and 50s. The exception is along the coast, where highs will likely only top out in the 50s each day with lows in the 40s due to cold Atlantic water temps. As of now, records look to be safe on Tuesday, but there are some low hanging records on Wednesday that could be broken in some spots (see more in the Climate Section below). Given the light flow, there should be a hefty sea breeze that occurs each day as well.

In addition, there is fairly high confidence that there will be an abundance in fog development at night given increasing dew points and cool ocean temperatures. This will be mainly near coastal locales, but will spread inland overnight.

KEY MESSAGE 3...A strong cold front will cross through the region Wednesday night into Thursday, bringing the potential for widespread showers and possibly some thunderstorms.

By later Wednesday, the upper pattern will become more much active as a potent trough over the central US begins to work its way east. Broad forcing for ascent is likely to begin overspreading the region during the day on Wednesday, leading to the return of some showers mainly north and west of the I-95 corridor. Elsewhere, should remain mostly dry.

Continuing into Wednesday night and Thursday, height falls with the trough are expected to maximize with the trough axis reaching the area by Thursday afternoon. The associated surface low is expected to pass well north of the area, cutting up through the Great Lakes and into southern Canada. A trailing cold front is then expected to cross through the region early Thursday morning. At this point, categorical PoPs are expected for Wednesday night before gradually decreasing on Thursday. Most guidance continues to depict a line of showers moving through the region. While the timing of this is at night, this should limit the potential for severe weather, however guidance does indicate the potential for some elevated instability. For this reason, have included a slight chance of thunder mentioning for Wednesday night. Also, a strong background wind field is expected so while gusty winds may not be in direct correlation from precipitation, winds will still likely be gusty throughout the period. Behind the front, shower activity is expected to wane, however, a few rain or snow showers may linger as colder air filters in late in the day.

KEY MESSAGE 4...Seasonable temperatures late week into the weekend with a couple disturbances bringing some more unsettled weather.

By late week and into the weekend, a much more seasonable airmass is expected to return to the region. During this time, a few weak disturbances are expected to pass north of the area, which may impact parts of the region. The first would be later Friday into Friday night and the second would be Saturday night into Sunday. For now, PoPs are only in the 20-40% range, but a period of rain and/or snow showers may be possible at times across the northern half of the area.

AVIATION /12Z MONDAY THROUGH FRIDAY/

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

Today...VFR after any lingering fog breaks mid-morning. Winds from the SSW around 5 to 10 kts. Maybe a few gusts 15-20 kts in the afternoon, most likely at ABE. Moderate confidence.

Tonight...VFR to start, then low clouds/fog may start creeping inland from the coast, with MIV/ACY most at risk. Winds becoming light/variable. Low confidence.

Outlook...

Tuesday through Wednesday...VFR expected during the day, with sub- VFR conditions possible at night due to BR/FG. A slight chance for showers on Wednesday.

Wednesday night through Thursday...Sub-VFR conditions likely with periods of showers and a slight chance of thunderstorms. Winds may occasionally gust in excess of 30 kt on Thursday.

Thursday night through Friday...VFR. Winds may occasionally gust up to 25 kt. A chance of rain/snow showers at RDG and ABE.

MARINE

Marine Dense Fog Advisories continue for all waters thru 6 PM this evening, and may need further extension through tonight. Winds and seas will remain sub-SCA thru tonight.

Outlook...

Tuesday through Tuesday night...Sub-SCA conditions expected. Winds generally less than 15 kt and seas around 2-3 feet. Dense marine fog likely.

Wednesday through Wednesday night...SCA conditions likely to develop late in the day. Wind gusts up to 20-30 kt. Seas around 2-4 feet during the day building to 4-7 feet at night. Dense marine fog possible with a chance of rain showers.

Thursday through Thursday night...SCA conditions likely, diminishing into Thursday night. Wind gusts up to 20-30 kt. Seas around 4-7 feet during the day, lowering to 2-4 feet at night. Rain showers likely.

Friday...SCA conditions possible. Wind gusts up to 25 kt with seas around 2-4 feet.

CLIMATE

Near record high temperatures are forecast for Wednesday, March 11th. Records for our climate sites are listed below:

Record High Temperatures: March 11 Site............................Record/Year Allentown (ABE).....................73/2021 AC Airport (ACY)....................79/1967 AC Marina (55N).....................70/1879 Georgetown (GED)....................77/2021 Mount Pocono (MPO)..................66/1977 Philadelphia (PHL)..................74/2021 Reading (RDG).......................77/2021 Trenton (TTN).......................73/2021 Wilmington (ILG)....................74/2021

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Dense Fog Advisory until 6 PM EDT this evening for ANZ430-431- 450>455.