textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated aviation discussion for 18z TAFs.

KEY MESSAGES

1. Scattered showers and thunderstorms move in this evening as a cold front sweeps through. A Slight Risk (2/5) for severe weather is in place from the I-95 corridor and points north and west with damaging winds as the primary threat.

2. Mainly dry conditions expected through the middle of next week with warming temperatures.

DISCUSSION

KEY MESSAGE 1...Scattered showers and thunderstorms move in this evening as a cold front sweeps through. A Slight Risk (2/5) for severe weather is in place from the I-95 corridor and points north and west with damaging winds as the primary threat.

A cold front will move across Pennsylvania and New York through today. The front will encounter a warm and unstable airmass, with showers and thunderstorms expected to develop well off to our west later today. Storms likely will congeal and form a broken line segment or several broken line segments as they move toward our area. The cluster of storms will move into our area later this evening, likely no earlier than 5 to 6 PM over the Lehigh Valley and Southern Poconos. This cluster of storms likely will push through the I-95 corridor between 8 to 11 PM and then offshore by early tomorrow morning.

With steep low level lapse rates of 7.5 to 8 degrees C/km, strong downdrafts/gusty winds are likely to accompany some of the thunderstorms. A secondary threat with these storms also is the potential for 1" hail in stronger storms. No real changes to the Severe Weather Outlook, with a Slight Risk (2/5) in place for the I-95 corridor and points north and west.

The main failure mode with these storms could be a lack of moisture as the airmass has been quite dry and we don't really have strong moisture advection out ahead of the front. The 00z NAMNest kind of hints at this solution with limited coverage in convection. The timing also isn't favorable for widespread severe weather, especially south and east of the I-95 corridor. Those are two factors to keep in mind after the afternoon and evening goes on.

No flooding concerns as QPF amounts generally will be around a tenth to three tenths of an inch with locally higher amounts possible in any thunderstorms. Convection should be fast moving as well.

As the initial front goes through, things should dry out pretty quickly. Cannot rule out some patchy fog though in areas that see some rainfall. The drier airmass will hold off until the secondary front passes later on Sunday.

KEY MESSAGE 2...Mainly dry conditions expected through the middle of next week with warming temperatures.

The region will remain embedded within a belt of somewhat enhanced mid-level flow through early next week as sharp trough located over New England begins to close off and track slowly eastward away from the region. Thereafter, mid-level ridging will likely begin to take shape across the region through late week. At the surface, a cold front will shift southeastward through the region late Sunday into Monday. In its wake, high pressure will shift into the area, and generally remain in place, though it may begin to break down some by late week.

The cold front late Sunday into Monday looks to usher in slightly cooler temperatures, with high temperatures on Monday generally in the upper 70s to low 80s, and temperatures overnight Monday night falling into the low to mid 50s. The cool down does look to be fairly short lived with the high pressure taking shape across the area afterwards. Steady warming is expected Tuesday and beyond, with widespread low 90s by Wednesday and perhaps even mid or upper 90s by late week.

In terms of precipitation chances, dry conditions are expected through Tuesday night. Thereafter, as the high pressure breaks down slightly, isolated to scattered, primarily diurnally driven convection will be possible mid-late week. For now, PoPs are generally in the 20-40% range each day Wednesday through Saturday.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

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

into the Evening...Primarily VFR.

Showers and thunderstorms are expected to develop off to the west later this afternoon and push into our area this evening.

Decided on the TEMPO groups for timing the initial rounds of tstms (higher confid too) KRDG/KABE/KTTN 22Z/23Z thru 01Z/02Z.

Other terminals still have some uncertainty so the VCTS/VCSH groups retained for now. These areas will have their activity 23Z/00Z thru 03Z/04Z as it appears now. There isn't the greatest confid in this however. KACY/KMIV also keep VC groups for now too. We'll AMD by 20Z/21Z for the Delaware Valley if the threat seems greater confid.

Winds will continue out of the west/southwest around 10-15 kt with gusts 20-25 kt into the evening then decreasing after that. Gusty winds of 30 to 40 kts probable near tstms.

Moderate confidence in the 18Z TAFS at best.

Overnight...Primarily VFR, but cannot rule out patchy fog (15-20% chance) over areas that receive rainfall from showers and thunderstorms this evening. Winds generally out of the west around 5 kt. Low confidence.

Sunday... VFR expected. West to Northwest winds increasing to around 10-15 kts with gusts around 20 kts after 14Z/15Z.

Outlook...

Sunday night through Tuesday night...VFR. No significant weather.

Wednesday/Thursday...Primarily VFR. Brief periods of sub-VFR conditions can't be ruled out in isolated to scattered afternoon showers tstms.

MARINE

Small Craft Advisory are in effect for coastal waters north of Great Egg Inlet as winds continue to increase to around 15 to 25 kt out of the southwest and seas get near 5 feet. Scattered showers and tstms after sunset.

Lower seas and winds are expected over Delaware Bay and south of Great Egg Inlet, where sub-SCA conditions are expected for this afternoon and tonight. Scattered showers and tstms by sunset NW.

Outlook...

Sunday through Wednesday...No marine headlines currently anticipated with winds under 25 kt and seas less than 5 feet.

Rip Currents...

For today, southwest winds of 10 to 15 mph with gusts up to 20 mph. Breaking waves will be 2 to 3 feet with a light easterly swell around 8 seconds. Have maintained a MODERATE risk for the development of dangerous and life threatening rip currents at the Jersey Shore and a LOW risk at Delaware Beaches.

On Sunday, west-northwest winds of 5-15 mph. Breaking waves will be 2-3 feet. There may be an increased south-southeasterly swell around 7-8 seconds. Given the increased swell, there is a MODERATE risk for the development of dangerous and life threatening rip currents at the Jersey Shore. There is a LOW risk at Delaware beaches where it currently appears the increased swell will not have as much influence.

Ocean water temperatures are generally near 60 degrees for much of the Jersey Shore and the low 60s for Delaware beaches. These chilly water temperatures can quickly cause hypothermia and physical incapacitation to anyone suddenly immersed in the water.

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 6 AM EDT Sunday for ANZ450>452.