textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Added a new key message (1) and updated key message 3.

KEY MESSAGES

1. Surge of warmth and humidity through Wednesday ahead of a cold front.

2. A strong cold front Friday brings an end to the warmth as much colder air arrives for the weekend.

3. Spotty minor coastal flooding will be possible with the Tuesday morning high tide cycle.

DISCUSSION

KEY MESSAGE 1...Surge of warmth and humidity through Wednesday ahead of a cold front.

A frontal zone draped to our north Tuesday will result in surface low pressure riding along it Tuesday night and Wednesday. This will pull a cold front across our area by later Wednesday. Ahead of this feature, southerly flow will boost the low-level warm air advection and this results in much warmer air surging into our area through Wednesday. High temperatures will near 80 degrees for many areas on Tuesday, then into the low to even some mid 80s on Wednesday. In addition, dew points will increase back through the 60s Tuesday and Wednesday, with them peaking on Wednesday (near 70F for parts of the area) ahead of the aforementioned front. This will result in a much more humid feel over the next few days, with it being the most humid on Wednesday (heat index values should approach 90F for areas from about Philadelphia south and east; away from the coast). There does not appear to be all that much in the way of forcing for ascent with the front as it arrives by later Wednesday, therefore just a low chance (20-30 percent) for showers as of now. The dew points will fall from north to south later Wednesday night into Thursday as the front settles southward and the winds turn out of the north and northeast. The front however may not completely clear our region.

KEY MESSAGE 2...A strong cold front Friday brings an end to the warmth as much colder air arrives for the weekend.

A potent upper-level trough is forecast to arrive across the East during Friday, then gradually lift out over the weekend. This will drive surface low pressure just north of our area Friday with an associated strong cold front sweeping through.

A mild and increasingly moist air mass ahead of this feature will provide some instability as the strong cold front arrives on Friday. Large scale forcing for ascent will increase with the arrival of the robust upper-level trough and cold front, therefore showers will increase for a time (peaking on Friday). Some showers though look to develop Thursday night ahead of the main cold front. Some thunderstorms cannot be ruled out given the strength of the system, however this will ultimately depend on the magnitude of the instability and timing of the cold front. In the wake of the cold front, strong cold air advection occurs and this will result in much colder temperatures for the weekend. As of now, high temperatures both Saturday and Sunday look to struggle to get out of the 50s (colder in the higher terrain). A gusty wind Saturday due to cold air advection and a tightened pressure gradient will add to the chill. If the wind drops off enough Saturday night, some frost or freezing temperatures will become a concern for portions of our area. The air mass then starts to modify early next week.

KEY MESSAGE 3...Spotty minor coastal flooding will be possible with the Tuesday morning high tide cycle.

The Coastal Flood Advisory expired at 5 PM for the back bay areas of Sussex County, DE and Ocean County, NJ (mainly Barnegat Bay). There will be the potential for some additional minor coastal flooding with Tuesday morning's high tide cycle for places along the Atlantic coast and Delaware Bay but it should be more spotty in nature as we get farther way from the New Moon.

No tidal flooding concerns expected along the Chesapeake Bay.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

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

Tonight...VFR with decreasing clouds but fog is possible after 07Z. Inserted TEMPO groups for all terminals, primarily with MVFR conditions but some localized IFR conditions are possible. Northwest winds around 5 kts early then calm overnight. Moderate confidence.

Tuesday... VFR expected following any lingering morning fog. Southwest winds increasing 5 to 10 knots. High confidence.

Outlook...

Tuesday night and Wednesday...VFR.

Thursday and Friday...A period of sub-VFR conditions possible with showers. Gusty southwest to west winds on Friday.

Saturday...VFR. Gusty northwest winds.

MARINE

The Small Craft Advisory for Atlantic Ocean coastal waters south of Great Egg Inlet has been cancelled as winds and seas have decreased through the evening. For coastal waters north of Great Egg Inlet, seas continue to linger around 5 feet and the SCA remains in place. However, it's possible that the seas may drop below 5 FT before the SCA is set to expire at 4 AM Tuesday.

Otherwise, fair weather tonight and Tuesday, with winds around 10 kts and seas of 3-5 feet.

Outlook...

Tuesday night through Thursday...No marine hazards are anticipated.

Friday and Saturday...Small Craft Advisory conditions probable, with a period of gale-force wind gusts possible.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 4 AM EDT Tuesday for ANZ450>452.