textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Increasing chances for showers and thunderstorms on Thursday. Otherwise, no significant changes to the forecast.

KEY MESSAGES

1. A weak cold front will gradually sink south through the region through today, with isolated thunderstorms possible this afternoon.

2. Another cold front is expected to cross through the region on Thursday, resulting in greater chances for showers and thunderstorms. Likely remaining unsettled through the weekend, with daily chances of showers and storms each afternoon and evening.

DISCUSSION

KEY MESSAGE 1...A weak cold front will gradually sink south through the region through today, with isolated thunderstorms possible this afternoon.

An isolated shower or rumble of thunder will remain possible overnight, but no significant weather is expected.

A weak cold front will gradually sink south today into tonight. Behind the cold front, temperatures and dewpoints will only fall slightly. There may be areas of patchy fog in rural locations, especially where any evening showers took place. High temperatures today will be just about identical to Monday, but dewpoints 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.

Th main story today will be the potential for some diurnally driven isolated showers and storms developing this afternoon. These will be focused along and south of the front, with greater coverage of convection more probable along and southeast of I-95. Aside from lightning, no hazardous weather is anticipated with this activity.

Any convection will diminish after sunset, then dry overnight with patchy fog possible again. Dry and seasonable Wednesday with lower humidity, though highs will still be in the mid to upper 80s.

KEY MESSAGE 2...Another cold front is expected to cross through the region on Thursday, resulting in greater chances for showers and thunderstorms. Likely remaining unsettled through the weekend, with daily chances of showers and storms each afternoon and evening.

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, though a slower trend has begun. 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. PoPs have increased for the area on Thursday, especially along and southeast of I-95, but much of the region now has 60-80% PoPs for Thursday afternoon and evening.

Longer range NWP and AI guidance suggests that the pattern remains unsettled later Friday and into the weekend. The frontal boundary 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, highs will be mainly in the upper 70s to mid 80s through the weekend 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 cloud cover, and humidity will increase.

AVIATION /09Z TUESDAY THROUGH SATURDAY/

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

Through 12Z...Generally MVFR to IFR ceilings developing for most areas outside of RDG/ABE, where confidence in restrictions is lower. Variable winds favoring a northerly direction less than 5 kts. Moderate confidence.

Today...Restrictions from low ceilings early, then scattering out to VFR by 16Z. Isolated SHRA/TSRA possible (10-20% chance), but coverage is too low to warrant a TAF mention at this time. North winds shifting northwest around 5-10 kts. High confidence in prevailing VFR following restrictions early, low confidence on timing of improvements.

Tonight...VFR early, though some patchy fog may develop after 04Z. Northwest winds around 5 kts or less. Low confidence on any fog restrictions.

Outlook...

Wednesday...VFR. No significant weather expected.

Wednesday night through Friday...Periods of scattered showers and perhaps storms are likely, with the greatest chance and coverage on Thursday. Restrictions are possible with any showers or storms.

MARINE

No prevailing marine hazards expected. Isolated showers or storms with locally gusty winds and higher seas possible through this evening.

Outlook...

Wednesday through Friday...No prevailing marine hazards currently anticipated, with winds under 25 kts and seas under 5 feet. Scattered showers and perhaps storms could lead to periods of visibility restrictions Wednesday night through Thursday. Scattered showers and storms are likely again late Friday into Saturday.

Rip Currents...

For today and Wednesday, northeast winds 5 to 10 mph this morning will gradually turn to be more easterly at 5 to 10 mph this afternoon. South to southwest winds near 10 mph on Wednesday. Breaking waves will average around 1 foot. 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.