textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated Key Message 1 and Marine sections.

KEY MESSAGES

1. Showers and thunderstorms increase in coverage later today and tonight and persist into Monday. There is some potential for areas of heavy rain leading to a risk of flash flooding. There is also a risk for strong to severe thunderstorms.

DISCUSSION

KEY MESSAGE 1... Showers and thunderstorms increase in coverage later today and tonight and persist into Monday. There is some potential for areas of heavy rain leading to a risk of flash flooding. There is also a risk for strong to severe thunderstorms.

An upper-level trough will shift across eastern Canada into early next week. While this occurs, strong energy crests a ridge in the West and this carves the trough out more into the Tennessee and Ohio valleys today and tonight. There continues to be signals in model guidance showing this trough potentially becoming closed off into early next week as it gradually approaches the East. The main trough may detach and depart to the northeast leaving behind a lingering closed low. This scenario would lead to the system slowing its eastward progression through the first half of next week. The model trends continue to show a slower arrival of this system, with the bulk of the showers and thunderstorms occurring later tonight and especially on Monday.

Ahead of the strengthening upper-level trough, deep south to southwest flow will increase and this will ramp up the low-level moisture and temperature advection. It will therefore be a humid time frame as the precipitable waters surge to 2+ inches. There looks to be multiple rounds of showers and thunderstorms, starting with an initial round later tonight into Monday with the increased warm air advection regime. Instability will increase, however the timing at night should limit the thunderstorm intensity especially since it may be more of elevated convection initially. Areas of heavy rain however will be probable given the increasing forcing for ascent and high water content air. When looking at model soundings, the high precipitable water values, warm cloud layer processes, and tall skinny CAPE profiles show the heavy rain potential. For tonight into Monday, the Weather Prediction Center continues with a Marginal Risk (level 1 out of 4) for excessive rainfall.

On Monday, ripples of energy along the incoming cold front during the day may enhance the convective potential and with deep southerly flow, some training convection will be possible. Excessive rainfall rates would enhance the flash flooding risk, especially from the I-95 corridor to the north and west where the elevation rise could boost the ascent some given a southeast to south low-level flow. There is a Slight Risk (level 2 out of 4) for Excessive rainfall for Monday into Monday night for mainly northern portions of New Jersey. There is a Marginal Risk (level 1 out of 4) for the rest of our area.

In terms of the severe weather risk, the SPC has parts of eastern Pennsylvania and northeast Maryland in a Marginal risk for severe thunderstorms today/tonight. On Monday, the Marginal risk moves to cover eastern Pennsylvania and northern/central NJ. The main hazard for both days will be damaging winds which will accompany water loaded downbursts.

Beyond Monday night, the front will weaken across the area Tuesday and we'll have to continue with chances (25% to 35%) for showers/tstms on Tuesday with the very warm and humid airmass remaining in place.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

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

Overnight...VFR with gradually lowering ceilings. Added some showers to KRDG/KABE as a few have been moving across those areas as of late. This is probably the only rains for the overnight. Southeast winds 5-10 kts. Medium confidence.

Sunday...VFR to start. Ceilings will continue to gradually lower, with MVFR ceilings probable for the NW sites by late afternoon. Varying guidance with regards to when steady rains begin limit overall confid. GFS has plenty of daytime showers across most sites while NAM if drier during the day. Generally blended with previous TAFS. AMDs probable. Low/medium confid.

Outlook...

Sunday night and Monday...Periods of sub-VFR conditions along with showers and thunderstorms.

Tuesday through Thursday...Times of sub-VFR conditions are probable as some showers and thunderstorms continue, especially each afternoon and evening.

MARINE

No marine headlines expected through Sunday. South winds around 10-15 kt with a few gusts up to 20 kts. Seas 2 to 3 feet.

Outlook...

Sunday night and Monday...A Small Craft Advisory was issued earlier for all of the nearshore Atlantic coastal waters. We've adjusted the timing a bit with a earlier starting time. South to south- southwest flow increases Sunday night into Monday with wind gusts up to 25 kt. Seas also increase to 4-6 feet. Some gusty thunderstorms possible on Monday.

Tuesday through Thursday...No marine headlines are anticipated.

Rip Currents...

For today, winds turn more southeasterly, which is more directly onshore, and increasing to around 15 mph. While there will be a short 6-7 second period swell, given the strong winds, wave heights in the surf zone may be up to 3 feet, particularly at southeasterly facing beaches. As a result, there is a MODERATE risk for the development of dangerous rip currents for the beaches of Cape May, Atlantic, and Ocean counties of NJ. At the beaches of Monmouth County, NJ as well as the Delaware Beaches, the risk for Sunday remains LOW given that winds at these beaches will be more shore parallel.

For Monday, the risk for the development of rip currents increases to MODERATE for all beaches. Winds will be more shore parallel out of the south-southwest but increasing to around 15-20 mph. Additionally, a strengthening swell will result in offshore seas of 5-6 feet. In the surf zone, this translates to breaking waves of 2-3 feet with a medium 8-9 second period.

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 from 8 PM this evening to 6 AM EDT Tuesday for ANZ450>455.