textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated the Aviation section for the 12Z TAFs.

KEY MESSAGES

1. High pressure will result in tranquil conditions through Wednesday.

2. A cold front will cross the area Thursday bringing the potential for a round of showers and storms.

DISCUSSION

KEY MESSAGE 1...High pressure will result in tranquil conditions through Wednesday.

Broad high pressure over the Great Lakes and Northeast slides towards the Mid-Atlantic later today, then will be offshore tonight. A cold front approaches from the west on Wednesday.

Mostly sunny and mild today with highs in the low to mid 80s with low humidity. Clouds increase somewhat tonight, and with a light southerly flow, lows will be a bit warmer tonight.

Southerly pressure gradient tightens on Wednesday as that cold front approaches from the west. A bit warmer and more humid on Wednesday with highs in the mid 80s or so and surface dew points rising into the low to mid 60s. Showers and thunderstorms will stay to the north and west during the day.

KEY MESSAGE 2...A cold front will cross the area Thursday bringing the potential for a round of showers and storms.

Mid-level ridging will begin to break down on Wednesday across the region as an upper-low traverses portions of the Hudson Bay into Quebec. On Thursday, a more pronounced shortwave will pass through the region. At the surface, a cold front will pass through the region Thursday.

Scattered showers and storms could begin moving into northwestern portions of the area as early as overnight Wednesday night as the front begins to approach. PoPs through Thursday morning are currently 20-40% and confined to the Lehigh Valley, Poconos, and adjacent areas of far northern NJ.

On Thursday as the front makes its way southeastward through the area, scattered showers and storms will likely accompany it. Despite somewhat impressive kinematics, most model guidance features modest destabilization at best ahead of the front, with MLCAPE generally around 500 J/kg to 1000 J/kg. Discrepancies do remain with respect to timing of the frontal passage and associated shower and storm chances. A slower front progression through the region could allow for a bit more destabilization than is currently anticipated. All of this being said, the threat for severe storms currently appears fairly low, but not zero. Any potential hydro concerns look limited by the progressive nature of the front and storms.

Behind the front, a drier and somewhat cooler airmass looks to settle into the region for Friday. The forecast beyond Friday is a bit more uncertain as some guidance hints that the frontal boundary may stall somewhere to the south of the region with a few waves of low pressure riding along it. This will need to be monitored as it could lead to somewhat unsettled conditions for the weekend.

AVIATION /10Z TUESDAY THROUGH SATURDAY/

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

Today...VFR. W-NW winds less than 10 kt. High confidence.

Tonight...VFR. Light S winds. High confidence.

Outlook...

Wednesday...VFR. No significant weather.

Wednesday night through Thursday night...Scattered showers and storms could lead to sub-VFR conditions at times, beginning with the northwestern most terminals Wednesday night and spreading southeastward Thursday into Thursday night.

Friday through Friday night...VFR. No significant weather.

Saturday...Primarily VFR. An isolated shower or storm can't be ruled out.

MARINE

Sub-Small Craft Advisory conditions today through tonight. West to northwest winds less than 10 kt, becoming south to southwest 10 to 15 kt this afternoon and tonight. Seas around 2 feet.

Outlook...

Wednesday through Thursday...SCA conditions probable. South- southwest winds of 15-20 kt with gusts 25-30 kt likely beginning Wednesday afternoon and continuing through Wednesday night into part of the day Thursday before diminishing. Seas 4-6 feet.

Thursday night through Saturday...No marine headlines currently anticipated with winds below 25 kt and seas below 5 feet.

Rip Currents...

Today, west to northwest winds 5 to 10 mph in the morning, will turn to the south-southwest around 10 mph in the afternoon. Breaking waves will be 1 to 2 feet. There will be a light easterly swell with a period around 9 sections. As a result, there is a LOW risk for the development of dangerous and life threatening rip currents for the Jersey Shore and for Delaware Beaches.

On Wednesday, south to southwest winds 5 to 10 mph will increase to 15 to 20 mph with gusts up to 25 mph in the afternoon. Breaking waves will be 2 to 3 feet. There will be a light easterly swell with a period of 9 to 10 seconds. Currently a LOW risk for the development of dangerous and life threatening rip currents is expected for the Jersey Shore and for Delaware Beaches, but that risk may be upgraded to a MODERATE risk for most shores depending on the strength and direction of the winds.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...None.