textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated the Aviation section for 06Z TAFs.

KEY MESSAGES

1. High pressure builds through the region today.

2. Unsettled weather returns Sunday into Monday.

DISCUSSION

KEY MESSAGE 1...High pressure builds through the region today.

Broad high pressure is centered over central Canada north of the Great Lakes with a second center over western New York and western Pennsylvania. High pressure builds east today, and one center of the high will be along the Canada/New York border with the second center offshore, east of New Jersey and south of Long Island.

The weather will be fair today with highs in the 80s to near 90 inland and cooler at the coasts. Humidity levels will be fairly comfortable for most northern and inland areas where dew points will be in the 50s to around 60, and a touch humid for Delmarva and southern New Jersey where dew points will be in the mid and upper 60s.

An upper trough will be over the northeast, and some weak shortwave energy will pass through the region and will interact with low level moisture and a surface sea breeze to touch off a few weak showers across extreme southern New Jersey and portions of Delaware.

KEY MESSAGE 2...Unsettled weather returns Sunday into Monday.

Our next system arrives Sunday into Monday as a low pressure system tracks from near the Great Lakes region into the Northeast bringing showers and thunderstorms to the area.

There continues to remain variations among guidance in terms of the exact timing of precipitation. Right now, the general trend is by mid to late morning on Sunday, precipitation is moving into the area. The coverage increases into the afternoon and evening as warm air advection sets up allowing for an increase in ascent across the region. Additional showers and thunderstorms carry over into Sunday night. By Monday, we trend drier through the day. Although, some lingering chances for precipitation will remain before we truly dry out by Monday night as a high pressure system builds in.

Regardless of the exact timing, the primary threat Sunday into Sunday night is heavy rainfall leading to the risk of flash flooding. There continues to be a signal among model guidance showing PWAT values surging into the 2-2.5 inch range Sunday into Sunday night. This combined with warm cloud layer processes shown in model soundings, and strengthen flow at 850mb, all showcase the risk for heavy rainfall, especially with any training that occurs. As a result, WPC has our whole area in a Slight Risk (level 2 out of 4) in the Excessive Rainfall Outlook for Sunday into Sunday night with rainfall rates upwards of 2-3 inches per hour possible.

One aspect that remains a bit more uncertain is the threat for severe thunderstorms. The extent of instability is a key part that remains uncertain given cloud cover and rounds of precipitation through the day Sunday. However, there continues to be the trend of increasing shear and upper-level forcing for ascent from synoptic scale features. SPC has areas south of Philadelphia highlighted in a Marginal Risk (level 1 out of 5) for isolated severe thunderstorms with the primary concern being damaging wind gusts.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

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

Early this morning...VFR. There is a low probability for patchy fog/mist to develop with MVFR or lower conds, mainly away from the I-95 corridor terminals. Will not include in the TAF. LGT/VRB winds. Moderate confidence.

Today...VFR. LGT/VRB winds or NE winds less than 10 kt in the morning, backing to the NW in the afternoon, then veering to the NE late. Cannot rule out a spot SHRA at KMIV or KACY after 21Z. High confidence.

Tonight...VFR. Light SE winds. High confidence.

Outlook...

Sunday through Monday...Sub-VFR conditions with widespread showers and a few embedded thunderstorms expected.

Tuesday and Wednesday...VFR conditions expected.

Thursday...Sub-VFR possible with the chance for showers and thunderstorms.

MARINE

Sub-SCA conditions today and tonight. Northeast winds 10 to 15 kt, becoming southeast late this afternoon and tonight. Seas 23 to 4 feet.

Outlook...

Sunday through Monday...SCA conditions probable with wind gusts reaching 25-30 kt and seas 4-6 feet.

Tuesday and Wednesday...No marine headlines expected.

Wednesday night into Thursday...A brief period of SCA conditions are possible Wednesday night into Thursday morning as seas reach 5 feet.

Rip Currents...

Today, winds will be out of the northeast at 5 to 10 mph, and will turn east by this afternoon, then southeast late. Breaking wave heights will be 1 to 2 feet with an onshore swell with a period of 8-10 seconds. As a result, there is a LOW risk for the development of dangerous and life threatening rip currents for the Jersey Shore and Delaware Beaches.

On Sunday, southeast winds will turn south at 15 to 20 mph with gusts up to 25 mph. Breaking waves will be 2 to 4 feet. There will be an onshore swell with a period of 8 to 10 seconds. As a result, there is a MODERATE risk for the development of dangerous and life threatening rip currents for the Jersey Shore and a LOW risk at 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.