textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Severe Thunderstorm Watch and the Coastal Flood Advisory have been allowed to expire. Updated these key messages and also updated aviation section for 06z TAFs.

KEY MESSAGES

1. The severe weather threat has ended but there are still lingering showers. Showers should be largely out of the area by 3 AM however there may continue to be some lingering areas of flooding through the overnight as water levels on creeks and streams near the I-95 corridor are elevated.

2. The Coastal Flood Advisory has been allowed to expire however another round of minor coastal flooding will be possible with the Monday evening high tide cycle.

3. Some severe thunderstorms possible Thursday afternoon and evening.

DISCUSSION

KEY MESSAGE 1..The severe weather threat has ended but there are still lingering showers. Showers should be largely out of the area by 3 AM however there may continue to be some lingering areas of flooding through the overnight as water levels on creeks and streams near the I-95 corridor are elevated.

As of 1 AM, the cold front is moving through our eastern PA zones. The front will continue moving eastward and will clear the coast by around 5 AM. As this occurs lingering showers will exit the region. However water levels on creeks and streams near the I-95 corridor are elevated so localized flooding will remain a concern through most of the night. No additional severe weather is expected though.

KEY MESSAGE 2...The Coastal Flood Advisory has been allowed to expire however another round of minor coastal flooding will be possible with the Monday evening high tide cycle.

A New Moon is occurring this weekend and resulting in higher than normal astronomical tides. The tidal flooding threat with this past evening's high tide cycle has come to an end but at least one more round of some minor coastal flooding appears likely with the Monday evening high tide cycle for the Atlantic Coast and Delaware Bay.

Tidal flooding is not currently expected along the eastern shore of Chesapeake Bay.

KEY MESSAGE 3...Some severe thunderstorms possible Thursday afternoon and evening.

An upper-level trough centered over south-central Canada is forecast to strengthen eastward and also southward across the Great Lakes to end the week. A strong shortwave rounding the base of this trough may result in a portion of it taking on a negative tilt across the eastern Great Lakes and toward New England late Wednesday and Thursday. This feature is a bit stronger in the ECMWF solution, while the GFS ensembles are mostly a little weaker. A deepening surface low will accompany it and track across the eastern Great Lakes and into adjacent Canada during Thursday. A strong cold front will then arrive into our area Thursday afternoon or Thursday evening.

As the synoptic pattern evolves, the flow will increase out of the south and southwest. This will advect deeper moisture northward, and in tandem with strengthening warm air advection will lead to increased instability during the day Thursday. In addition, a strong mid to upper level jet is forecast to extend eastward from the eastern Great Lakes. While the core of the 500 mb jet (80-100 knots) is forecast to remain mainly northwest of our area, 40-70 knots of flow at 500 mb is still forecast across our area Thursday afternoon into the evening. This increased flow will result in greater shear magnitudes. While there remains some timing differences among the guidance regarding the main features, the consensus is that enough instability should overlap with the stronger shear along with incoming stronger forcing. As a result, there continues to be some severe thunderstorm potential Thursday afternoon and evening. As of now, locally damaging winds are the primary threat especially if convection develops into a squall line. However if shear and instability ends up being even greater, than all severe thunderstorm hazards may come into play especially if the mode is discrete for a time. The details remain much less certain at this time range given the typical uncertainty with instability and the thermodynamic profiles. The forecast synoptic setup however with a deepening surface low tracking to our northwest with strong flow within a warmer and more moist environment suggests some risk for severe thunderstorms. In addition, the main trough may end up arriving on Friday with some additional chances for showers and some thunderstorms.

The I-95 corridor and the coastal plain (away from the immediate coast) looks to be the hottest during Thursday ahead of the convection, with the heat indices potentially getting very close to 100 degrees.

AVIATION /06Z MONDAY THROUGH FRIDAY/

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

Rest of Overnight...Lingering MVFR conditions will improve to VFR between 6 and 9z as a cold front sweeps through the area. As this occurs WSW winds will shift to NW around 10 knots. High confidence.

Monday...VFR with a few/scattered clouds in the afternoon. Northwest winds around 10-15 kt, occasionally gusting up to 20 kt. High confidence.

Outlook...

Monday night...VFR. Northwest winds quickly diminish and becoming light and variable.

Tuesday...Mainly VFR.

Wednesday...Some sub-VFR conditions with a few showers or a thunderstorm possible.

Thursday...A period of sub-VFR conditions probable in the afternoon and evening as showers and some thunderstorms increase.

Friday...Some showers and thunderstorms may linger with areas of sub- VFR conditions possible at times.

MARINE

The Small Craft Advisory for portion of our Atlantic coastal waters and the Delaware Bay has been extended until 3 AM.

Winds will diminish overnight as winds turn northwesterly behind a cold front. Northwest winds will generally remain around 15-20 kt through Monday morning, however a few rogue gusts up to 22-23 kt are possible before further diminishing throughout the day. Seas generally around 2-4 feet, locally 5 feet tonight, and around 2-3 feet on Monday.

Showers and thunderstorms are likely through tonight, which may cause localized higher winds/seas. Some marine fog possible tonight as well. On Monday, fair weather expected.

Outlook...

Monday night through Wednesday...The conditions are anticipated to be below Small Craft Advisory criteria.

Thursday...A period of Small Craft Advisory conditions probable. Southerly wind gusts could near gale force for a time later Thursday. Some gusty thunderstorms late in the afternoon and evening possible.

Friday...The conditions are anticipated to be below Small Craft Advisory criteria.

Rip Currents...

For Monday, winds become northwest 10-20 mph with a continued medium southerly swell of 6-7 seconds. With breaking waves 2 feet or less, have gone with a LOW risk for the development of dangerous rip currents at all beaches.

For Tuesday, winds start northerly before shifting southeasterly, but only at around 5 mph with a continued medium southerly swell of 6-7 seconds. With breaking waves 2 feet or less, have gone with a LOW risk for the development of dangerous rip currents at all beaches.

For specific beach forecasts, visit weather.gov/beach/phi

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 3 AM EDT early this morning for ANZ430-431-450>454.