textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

A Dense Fog Advisory has been issued until 11 AM this morning for Carbon and Monroe counties.

KEY MESSAGES

1. The marine layer will remain in place across the region through this morning, then scatter out this afternoon. Widespread fog development is expected this morning, along with continued cold and damp conditions. There is the potential for dense fog. Warmer and drier conditions then return for the second half of today.

2. A warm front lifts north of the region Saturday bringing record-challenging warmth across the region before a cold front crosses Sunday, bringing a few rounds of showers and thunderstorms before ushering in more seasonable temperatures.

DISCUSSION

KEY MESSAGE 1...The marine layer will remain in place across the region through this morning, then scatter out this afternoon. Widespread fog development is expected this morning, along with continued cold and damp conditions. There is the potential for dense fog. Warmer and drier conditions then return for the second half of today.

Will go ahead and expand the Dense Fog Advisory to include northeast Maryland, Delaware, and southern and eastern New Jersey as visibilities dropped to 1/4SM or less.

High pressure over the Canadian Maritimes early this morning will exit off to the northeast through the morning hours. During this timeframe, a low pressure system moving northeast out of the Midwest will move into Canada which allows our stationary front south of the area to make progress northward as a warm front. The warm front looks to clear the area by early afternoon.

For this morning, it will remain cool and damp as the marine layer is still in place across the region. Plenty of low clouds will be around during the morning hours with fog also developing as moisture is trapped below a low-level inversion. There is the potential for dense fog to develop. Temperatures through the morning will be mainly in the 40s and 50s.

Improvements are expected this afternoon as the warm front clears the area. As the inversion breaks down this afternoon, clouds decrease in coverage, any fog diminishes, and we quickly warm up. Winds turn from being out of the east in the morning to out of the southwest this afternoon. The warm air moving in allows many locations to reach into the 70s for highs today.

This evening, a prefrontal trough looks to move in from the west ahead of a cold front. An isolated shower is possible late this evening into early tonight and perhaps a rumble of thunder.

Overnight, winds are relatively light and there is a signal for another low-level inversion briefly developing towards daybreak tomorrow. Some low-level moisture looks to get trapped beneath this inversion leading to the potential for some fog development. Lows tonight are in the mid 50s to low 60s for most.

KEY MESSAGE 2...A warm front lifts north of the region Saturday bringing record-challenging warmth across the region before a cold front crosses Sunday, bringing a few rounds of showers and thunderstorms before ushering in more seasonable temperatures.

A warm front is expected to lift north through the region on Saturday as low pressure begins to shift northeastward out of the Great Lakes region. Scattered showers will be possible in the vicinity of the front through the day Saturday, with highest chances across northern parts of the area. There may be enough elevated instability to allow for a few rumbles of thunder. Otherwise, much warmer temperatures will surge into the region, highs on Saturday rising into the mid 70s to low 80s outside of the Poconos and near the coast, where mid 60s are expected. Lows Saturday night look to generally be in the 40s and 50s, but may remain above 60 in parts of Delmarva. These mild temperatures Saturday may challenge some record highs as well as some record warmest low temperatures. See Climate section below for more details.

There will likely be a relative lull in shower chances early Sunday with the region in the warm sector ahead of a cold front that will sweep across the region by Sunday afternoon. High temperatures on Sunday will be highly dependent on the timing of the frontal passage which remains somewhat in question, but there should be enough time for most of NJ southward into Delmarva to rise into the low-mid 70s. Widespread showers and scattered thunderstorms are expected along and just ahead of the cold front. As of right now, any severe weather threat looks quite limited with the primary limiting factor being the degree of destabilization, with meager instability at best depicted in model guidance. Locally heavy rainfall will be possible given rich moisture in place, and PWATs around 1.5", which is well above the 90th percentile for this time of year. However, given that this is expected to be a fast moving system, flash flooding is not currently expected to be a concern. Total rainfall amounts look to be in the neighborhood of 0.5", though locally higher amounts could occur in heavier showers or storms. Breezy conditions are likely on Sunday even outside of any showers and storms with southwesterly winds gusting 25-35 mph ahead of the front, with similar westerly winds behind it.

In the wake of the cold front, temperatures are expected to return to near or even slightly below normal, with highs mostly in the 50s and lows in the 30s and 40s through mid-week. A slow warm up may begin Thursday and beyond.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

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

Today...Low CIGs and VSBYs for much of the morning, with VSBYS near or below 1SM and CIGs less than 500 ft. Conditions improve by 18Z, and should be VFR by 21Z. S winds 5 to 10 kt in the morning, increasing to 10 to 15 kt with gusts up to 20 kt after 18Z out of the southwest. Moderate confidence.

Tonight...Primarily VFR for most of the night. Winds out of the southwest at 5-10 knots. Patchy fog is possible leading to visibility restrictions and low ceilings. Restrictions were added to KABE/KRDG/KACY/KMIV due to fog around 09Z. The exact extent of the fog is low confidence.

Outlook...

Saturday through Saturday night...Mostly VFR with sub-VFR conditions possible at times in showers and perhaps a few thunderstorms.

Sunday...Sub-VFR expected with a period of showers and storms. Gusty winds likely through the day Sunday.

Sunday night...Conditions improve to VFR after the evening hours.

Monday through Tuesday...Primarily VFR. There is a slight chance (around 20%) for a few showers Monday night and Tuesday.

MARINE

A Small Craft Advisory remains in effect for the ocean waters from Sandy Hook NJ to Great Egg Inlet, NJ until 7 AM tomorrow. Winds have diminished to 10-15 knots out of the east. However, seas remain elevated at 5-7 feet. An SCA was also issued for the ocean waters from Great Egg Inlet, NJ to Cape Henlopen, DE from 1 PM this afternoon until 7 AM tomorrow.

For today, winds turn out of the south and then southwest this morning at 5 to 10 kt before increasing to 15 to 20 kt in the afternoon with gusts to 25 kt. Seas of 2 to 4 ft in the morning look to build to 4-6 feet again this afternoon into tonight.

Fog has been developing early this morning with visibility of 1 to 3 NM. Visibility may drop to less than 1 NM. A Marine Dense Fog Advisory was issued for all Atlantic coastal waters and Delaware Bay through this afternoon. Visibility looks to improve this afternoon. Additional fog development may be possible tonight.

Outlook...

Saturday...No marine headlines currently anticipated with winds under 25 kt and seas under 5 feet.

Saturday night through Sunday...SCA conditions likely with gales possible. Southerly winds Saturday night will increase to 15-25 kt with gusts to 30-35 kt. Winds will become southwesterly on Sunday. Seas 4-8 feet.

Sunday night through Monday...Lingering SCA conditions likely. Winds quickly subside to below 25 kt. Seas remain elevated near 5 feet through Monday morning before decreasing below 5 feet by Monday afternoon.

Monday night through Tuesday...Marine conditions are expected to remain below SCA criteria.

CLIMATE

A very warm airmass Saturday may challenge record high temperatures as well as record warmest low temperatures for April 4th.

Record High Temperatures for April 4th:

SITE...................RECORD...YEAR(S) AC Airport (ACY).......78.......2017 Philadelphia (PHL).....80.......1892 Wilmington (ILG).......80.......1950 Allentown (ABE)........79.......1928 Trenton (TTN)..........82.......1892 Reading (RDG)..........81.......1921 Georgetown (GED).......81.......2023/2011/1963 Mount Pocono (MPO).....78.......1928 AC Marina (55N)........77.......1999

Record Warmest Low Temperatures for April 4th:

SITE...................RECORD...YEAR(S) AC Airport (ACY).......56.......1974 Philadelphia (PHL).....60.......2025 Wilmington (ILG).......60.......2025 Allentown (ABE)........60.......1974 Trenton (TTN)..........62.......1981 Reading (RDG)..........58.......2025 Georgetown (GED).......60.......2025/1950 Mount Pocono (MPO).....58.......1981 AC Marina (55N)........56.......2025

PHI WATCHES/WARNINGS/ADVISORIES

PA...Dense Fog Advisory until 11 AM EDT this morning for PAZ054-055. NJ...Dense Fog Advisory until 11 AM EDT this morning for NJZ013-014- 016-020>027. DE...Dense Fog Advisory until 11 AM EDT this morning for DEZ001>004. MD...Dense Fog Advisory until 11 AM EDT this morning for MDZ012-015- 019-020. MARINE...Dense Fog Advisory until 2 PM EDT this afternoon for ANZ430- 431. Dense Fog Advisory until 6 PM EDT this evening for ANZ450>455. Small Craft Advisory until 6 AM EDT Saturday for ANZ450>452. Small Craft Advisory from 1 PM this afternoon to 6 AM EDT Saturday for ANZ453>455.