textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

1. A cold front passes through the region this evening.

2. Another cold front is expected to cross through the region Wednesday night into Thursday resulting in additional shower and thunderstorm chances. Likely remaining unsettled late Friday into the first half of the weekend.

DISCUSSION

KEY MESSAGE 1...A cold front will pass through the region this evening. Most surface dew points will reside in the the lower half of the 70s with elevated PWAT values. MLCAPE values will increase to 1000 to 1500, perhaps as high as 2000 J/kg. There remains through the early evening the potential for some brief locally heavy rain. Although shear will be limited and organized convection remains not likely.

Behind the cold front temperatures and dew points will only fall slightly later tonight. There may be areas of patchy fog in rural locations, especially where any early evening showers take place that would moisten the ground even further. High temperatures on Tuesday will be just about identical to Monday, but dew points will drop some with mainly lower and middle 60s further north, and upper 60s to around 70 well south. While warm, it should feel more comfortable compared to Monday.

KEY MESSAGE 2...A cold front is expected to cross through the region Wednesday night into Thursday resulting in more shower and thunderstorm chances.

In the wake of tonight's cold front, weak high pressure will briefly build into the region for Tuesday and much of Wednesday. An upper-low will traverse portions of Ontario and Quebec during this time, passing north of the region Wednesday night. To the south of the upper-low, broad troughing will be in place across much of the northeast, with a few embedded shortwaves pivoting around the base of the trough. At the surface, a cold front will begin to approach the area late Wednesday, and cross through the region late Wednesday night into early Thursday.

Timing discrepancies remain with the frontal passage among the model guidance. Some guidance indicates the front passing through the region primarily during the overnight hours Wednesday night and clearing the region Thursday morning, while there is some guidance suggesting slower timing. At this point, timing uncertainties limit confidence in whether or not there will be any notable severe weather or flash flooding concerns, but this will continue to be monitored in subsequent forecast cycles. If slower solutions come to fruition then the chances of impacts from heavy rain would increase. For now, PoPs peak in the high end chance - low end likely range for the majority of the area Thursday.

Longer range NWP and AI guidance suggests that the pattern remains unsettled later Friday and into the weekend as the front could get hung up just south or even over the area with multiple areas of weak low pressure riding along and mid-level troughing remaining in place. PoPs currently are mainly in the chance to likely range each day due to the present uncertainties in timing and placement of these features and any progression in the long wave pattern. At this time PoPs for this period are relatively higher further south and east.

In terms of temps, Tuesday and Wednesday look to be fairly warm with modestly increasing humidity. Highs look to be mainly in the upper 80s to around 90. Temps currently look a bit cooler in the wake of the front, with highs in the low to mid 80s and lows in the upper 50s to mid 60s late this week and into the weekend. Part of the reason for this will be due to more in terms of cloud cover.

AVIATION /18Z MONDAY THROUGH SATURDAY/

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

Today... A round of SHRA, perhaps a TSRA, may pass across the terminals in the late afternoon/early evening with brief sub-VFR conds. Will include PROB30 groups to handle this potential. NW winds 5 to 10 kt. Moderate confidence.

Tonight...Lingering SHRA possible through 06Z or so. Generally VFR outside of any SHRA. N-NW winds 5 to 10 kt. Moderate confidence.

Outlook...

Tuesday through Wednesday...VFR. No sig wx expected.

Wednesday night through Friday...Periods of scattered showers and perhaps storms are likely, with the greatest chance currently appearing to be late Wednesday night into Thursday. Sub-VFR conditions are possible with any showers or storms.

MARINE

A few showers and thunderstorms possible early evening.

Seas subside to 2 to 4 feet as well. Thus, sub-SCA conditions expected tonight.

Outlook...

Tuesday through Friday...No marine headlines currently anticipated with winds under 25 kts and seas under 5 feet. Scattered showers and perhaps storms could lead to periods of visibility restrictions Wed night through a portion of Thu. Another round of restricted visibilities are increasingly likely late Friday into Saturday.

Rip Currents...

West winds at 10 to 15 mph this afternoon. Breaking waves will average 1 to 2 feet. There will be an increasing southerly swell with a 5 to 7 second period. This results in a LOW risk for the development of dangerous and life threatening rip currents for the Jersey Shore and Delaware Beaches.

For Tuesday, north-northeast winds 5 to 10 mph in the morning will gradually turn to be more southerly at 5 to 10 mph in the afternoon. Breaking waves will average 1 to 2 feet. There will continue to be a southeasterly swell with a 6 to 8 second period. The result of these conditions is a LOW risk for the development of dangerous and life threatening rip currents for the Jersey Shore and Delaware Beaches.

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

PHI WATCHES/WARNINGS/ADVISORIES

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