textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

A Marine Dense Fog Advisory has been issued for all NJ and DE Atlantic coastal waters as well as the Delaware Bay tonight into Tuesday morning.

KEY MESSAGES

1. Areas of fog are expected overnight tonight into Tuesday morning near the coast, and perhaps as far inland as the I-95 corridor.

2. Increasing warmth and humidity through Wednesday with potential record high temperatures.

3. A strong cold front crosses the region Wednesday night into Thursday morning with widespread showers and potential thunderstorms.

4. More seasonable temperatures return for the end of the week and weekend. Unsettled weather possible due to a series of disturbances.

DISCUSSION

KEY MESSAGE 1...Areas of fog are expected overnight tonight into Tuesday morning near the coast, and perhaps as far inland as the I- 95 corridor.

High pressure located off the coast of the Southeast will continue to shift gradually eastward through tonight. This has allowed for continued warm and moist air advection throughout the region. Tonight, dense fog is expected to quickly develop over the Delaware Bay and Atlantic coastal waters as temperatures cool. This fog, and perhaps some low stratus, will attempt to work its way inland overnight and into early Tuesday morning. The primary uncertainty with this forecast is how far inland fog is able to develop, but most guidance suggests it will be possible as far north and west as the I-95 corridor. Regardless, any fog will become decreasingly dense and increasingly patchy with inland extent. While dense fog is likely along the immediate coast, and dense fog advisories may be needed for parts of the area, the uncertainty in inland extent precludes any land advisories at this time.

KEY MESSAGE 2...Increasing warmth and humidity through Wednesday with potential record high temperatures.

High pressure remains anchored off the Southeast and Mid- Atlantic coasts through Wednesday.

Tuesday morning, any low clouds and fog will likely clear out fairly quickly, with temperatures rising quickly and dewpoints mixing down. Ample sunshine is expected after any fog has dissipated, allowing temperatures to climb into the mid 70s for most of the area, with slightly cooler temperatures in the southern Poconos and in proximity to the coast where ocean temperatures remain quite cool.

A warm front lifts north through the region late Tuesday night, and low level moisture will increase over the area as surface dew points rise through the 50s. Patchy fog develops once again, with locally dense fog possible as well. Cannot rule out a few showers across northern zones by early Wednesday morning with that warm front lifting north through the region. Lows Tuesday night will be in the 40s and low 50s.

Southerly flow increases on Wednesday as a strong cold front approaches from the west and the pressure gradient tightens. Winds will increase to around 15 mph with 20 to 25 mph gusts. Even warmer and more humid air spreads into the region with highs inland in the mid to upper 70s, highs along the coast still in the 50s owed to the colder ocean waters, and highs in the 60s within 10 miles or so of the coasts. See the Climate section below for the records. The latest guidance has come in several degrees warmer than the previous forecast, so will follow suit. Some spots well inland may even come close to 80. Surface dew points will climb well into the 50s and even around 60, making it fairly humid, especially for this time of the year.

KEY MESSAGE 3...A strong cold front crosses the region Wednesday night into Thursday morning with widespread showers and potential thunderstorms.

Low pressure will be over the Great Lakes on Wednesday and will track to the north and east Wednesday night. This will drag a cold front towards the region late Wednesday, but it will not cross the region until late Wednesday night or even Thursday morning. Widespread showers will develop with the passage of the front. What remains to be seen, though, is the potential for thunderstorms. What is going against the threat is that the front does not look like it will arrive until late, and there will be a loss of diurnal heating, so SBCAPE will be minimal. However, MUCAPE will be up around 500 J/kg, at least initially, lowering to around 200 J/kg as the night progresses. 0-6 km Bulk Shear will average 50 to 55 kt. This will result in the potential for at least some elevated convection. Surface dew points will also be in the 50s to around 60. Will go ahead and add slight chance for thunderstorms throughout the forecast area for most of the night.

Front does not look like it will clear the region until late Thursday morning, and then strong cold air advection develops throughout the day. It looks like the daily high temperature will occur just after midnight, and then temperatures throughout the day Thursday will fall from the 50s in the morning to the 40s by late afternoon as strong northwest winds develop behind the front.

Showers taper off from west to east through the day, and there may even be some snow mixed with the rain, especially north and west of the Fall Line, before ending. Hope you enjoyed the early taste of Spring.

KEY MESSAGE 4...More seasonable temperatures return for the end of the week and weekend. Unsettled weather possible due to a series of disturbances.

Temperatures return to normal for this time of the year on Friday with highs in the 40s to around 50. Going through the weekend, temperatures may be several degrees above normal, but nowhere near as warm as they are during the first half of the week. A series of disturbances will pass through the region, resulting in a slight chance to chance for rain, but some snow is possible north and west of the Fall Line. PoPs will generally be in the 20 to 40 percent range.

AVIATION /19Z MONDAY THROUGH SATURDAY/

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

Rest of today...VFR. South-southwest wind around 10 kt with gusts 15-20 kt, primarily at RDG and ABE. High confidence.

Tonight...VFR to start. Fog and some low clouds will will begin to work inland after 03-04Z, perhaps as far inland as the I-95 terminals. Will only include restrictions at MIV and ACY for now, which may see IFR visibilities. Wind quickly becoming light and variable to calm. Low confidence.

Tuesday...Any fog is expected to dissipate by 13-15Z, with VFR conditions thereafter. South-southwest wind around 5 kt. High confidence.

Outlook...

Tuesday night...Sub-VFR in BR/FG/stratus.

Wednesday through Wednesday night...VFR during the day, then sub-VFR in SHRA and isolated TSRA, mainly at night. S winds may gust to 30 kt during the day.

Thursday through Thursday night...Sub-VFR early in SHRA, which taper off late, then VFR. Abrupt shift in winds from S to NW late Thursday morning. Gusts up to 30 kt in the afternoon.

Friday through Friday night...VFR during the day, then sub-VFR possible at night in RA and/or SN, mainly north and west of the I-95 terminals.

Saturday...VFR.

MARINE

A Marine Dense Fog Advisory has been issued for all NJ and DE Atlantic coastal waters as well as the Delaware Bay from 8 PM this evening until 11 AM Tuesday. Dense fog is expected to develop tonight, with widespread visibilities under 1 NM likely. In some areas, visibilities could be reduced to 1/4 NM or less.

Southwest wind 5-15 kt tonight through Tuesday, with seas generally 1-3 feet.

Outlook...

Tuesday night...Sub-SCA conditions. VSBY restrictions in fog.

Wednesday through Wednesday night...SCA conditions developing. S winds 15 to 20 kt with 25 to 30 kt gusts. Seas 2 to 4 ft, building to 6 to 8 ft at night. VSBY restrictions in fog, then showers and isolated thunderstorms at night.

Thursday through Thursday night...Abrupt shift in winds from S to NW late Thursday morning through the afternoon with gusts up to 30 kt, diminishing at night. Seas 6 to 8 ft, diminishing to 2 to 4 ft at night. VSBY restrictions in showers on Thursday.

Friday through Friday night...Sub-SCA conditions during the day, then SCA conditions likely at night.

Saturday...Sub-SCA conditions.

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 from 8 PM this evening to 11 AM EDT Tuesday for ANZ430-431-450>455.