textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

The timing of the late weekend/early next week frontal system has slowed a bit, with Sunday now looking mostly dry and most precipitation coming in Sunday Night into Monday.

A Slight Risk for Excessive Rainfall was added for areas along and north/west of the I-95 corridor on Monday.

KEY MESSAGES

1. Tranquil weather takes over through Saturday though a few very isolated sea-breeze showers cannot be ruled out this afternoon.

2. A frontal system on Sunday and Monday will bring the next opportunity for widespread showers and thunderstorms. Increasing confidence in potential heavy rain on Monday.

DISCUSSION

KEY MESSAGE 1...Tranquil weather takes over through Saturday though a few very isolated sea-breeze showers cannot be ruled out this afternoon.

Showers have dissipated for tonight and we should be dry through the rest of the morning. However, some patchy fog could develop given the residual ground moisture and some clearing of clouds, particularly in sheltered areas. While confidence is not high in fog development, went ahead and kept patchy fog in the forecast given the potential for lowered visibilities in spots. Any fog mixes out by 7-8 AM.

Surface high pressure settles in today with drier air moving in. Some guidance hinting at a few rather isolated showers this afternoon, mainly focused along the sea and bay breeze. Did add a mention of showers near the NJ and Delaware coast, but only 15% for a brief period this afternoon. A large majority today will stay dry however given the closed low/trough continuing to move away. Some warming aloft along with some increase in sunshine Friday will result in warmer afternoon temperatures. Lighter flow however will result in a sea/bay breeze developing by later in the afternoon. Depending on how far inland this gets by early Friday evening, some increase in the dew points should occur in its wake. Temperatures moderate some more to start the weekend with high temperatures on Saturday right near average along with dry conditions.

KEY MESSAGE 2...A frontal system on Sunday and Monday will bring the next opportunity for widespread showers and thunderstorms. Increasing confidence in potential heavy rain on Monday.

High pressure weakens late Saturday and is replaced by advancing low pressure from the Ohio Valley area. This low strengthens and moves west of our area later Sunday and into Monday. This system will bring increasing chances for showers and thunderstorms later Sunday, with a bulk of the precipitation coming moreso on Monday. The PWAT values off the forecast soundings during these times show more 2+ inch PWAT values for our region, so it's possible that excessive rainfall may develop for parts of the region. WPC did add a Slight Risk (2/4) for excessive rainfall on Monday for the I-95 corridor and points north and west. Moisture and instability will also increase ahead of the front, so we likely will have to monitor the severe weather threat for the Sunday and Monday afternoon periods as well. However, our area is not in any long term severe outlooks, and it is looking increasingly more likely that there are more hydro concerns with this system.

Guidance continues to show this as a slow moving system with a frontal boundary either stalling over our area or slowly pushing to south and east. This could result in another stretch of unsettled weather through next week. The current forecast does have showers/thunderstorm chances each day next week, mainly in the afternoon and evening. Important to note though that each day other than maybe Monday will have periods of tranquil weather but it does turn to look more active after Sunday.

AVIATION /08Z FRIDAY THROUGH TUESDAY/

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

Rest of Tonight (through 12z)...Primarily VFR. Have added patchy dense fog to the KACY through about 10z, with conditions improving back to VFR by 12z. Seeing some MVFR stratus around the I-95 corridor but thinking it will dissipate within the next hour (by 10z). Moderate confidence.

Today...VFR. Winds mainly west/northwesterly around 5 to 8 kt though an afternoon sea-breeze will turn winds more south/southwesterly, getting to KACY by 19z-20z, KMIV by 21z-22z, and the I-95 terminals around 23z-00z. High confidence in prevailing VFR, moderate confidence in timing of wind shifts.

Friday Night...VFR. Winds generally light and variable to calm at 5 kt or less, though a southerly direction may be favored at times. High confidence.

Outlook...

Saturday through Sunday Morning...VFR. No significant weather.

Sunday Afternoon through Tuesday...Periods of sub-VFR conditions expected at times with a slow moving frontal system moving through. VFR conditions should mix in with IFR/MVFR conditions at times.

MARINE

No marine headlines expected through Saturday Night. Light northwesterly winds around 5 to 10 kt with will transition to southerly winds around 10-15 kt for this afternoon, overnight period, and for Saturday. Seas 2 to 3 feet.

Outlook...

Sunday...No marine headlines expected.

Sunday night through Monday night...SCA conditions likely (60-70%) as seas could near 5 feet and winds may gust near 25 kts. Showers and thunderstorms also possible during this period.

Tuesday...No marine headlines expected.

Rip Currents...

For today, light winds less than 10 MPH are expected at all the beaches, starting out northwesterly, then transitioning to a more southerly direction with a sea-breeze forming. Breaking waves of 2 feet or less, combined with a dominant wave period of less than 8 seconds will result in a LOW risk for the development of rip currents at all beaches.

For Saturday, south/southeasterly flow will strengthen a bit with either shore parallel or slightly onshore winds around 10-15 MPH. However, wave heights still should be around 2 feet or less, with an 8 second dominant wave period. This will mitigate the rip current risk and result in another day of LOW risk for 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...None.