textproduct: Philadelphia/Mt Holly

SYNOPSIS

An upper level system will arrives today with surface low pressure also crossing our area. This exits the region Saturday with high pressure building in during the weekend. A weak cold front however may settle across our area Saturday night into Sunday. High pressure shifts offshore Monday into Tuesday, then low pressure looks to arrive from the southwest Wednesday into Thursday.

NEAR TERM /THROUGH TONIGHT/

An upper trough moving towards western Pennsylvania this morning is expected to close off as it moves towards the Delaware Valley later today. While this happens, a surface low deepens on the front which extends from Delmarva and across south NJ. This low and associated front will bring clouds and rains to the area much of today. Some residual CAPE across Delaware and ern MD will help produce scattered tstms across those ares today. Highs will be much below normal with readings only topping out in the upper 50s to low 60s most areas with some higher temps for southern Delaware and low/mid 50s for the far NW areas. Winds will be Northeast to North at 5 to 10 mph. The winds will switch around to NW later today and speeds will increase to 10 to 15 mph with gusts 20 to 25 mph developing.

The upper low will be directly across the lower Delaware Valley this evening while the surface low will be up closer to NYC. Both systems slowly depart to the NE overnight. This will lead to the rains (from today) diminishing and clouds decreasing overnight. Winds will increase overnight with Northwest winds around 10 to 15 mph with gusts to 20 mph at times. Temperatures will dip into the low 40s across the N/W areas while readings bottom out in the upper 40s around Delmarva, south NJ and metro Philadelphia.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/

Turning warmer with drying conditions through the weekend.

The closed low moves farther away from our area during Saturday. High pressure is forecast to build into the Ohio Valley by Saturday night. This combined with the departing low will result in a tight pressure gradient across our area Saturday. As deeper mixing develops during the day Saturday, the west-northwest breeze will increase in strength. The depth of the mixed layer looks to support wind gusts to around 30 mph during the daytime, although this should start to weaken/diminish fairly quickly late in the afternoon and especially Saturday evening.

As we go through Sunday, some cyclonic flow looks to remain in place into our area however surface high pressure is forecast to build across our area. This will result in much less wind and also warmer temperatures. There should be plenty of sunshine given the drier air mass in place, although cannot rule out a touch of high level clouds streaming in from the west and south late with a southern storm system. Given the lighter flow and warmer temperatures on land, sea and bay breeze circulations should develop Sunday afternoon which will offer some cooling closer to the coasts.

LONG TERM /MONDAY THROUGH THURSDAY/

Summary...Dry to start, then an increasing chance for showers.

Synoptic Overview...A mid level ridge is forecast to be across our area as a trough departs the Canadian Maritimes. Meanwhile, a closed low sliding across the Gulf coast states to the Tennessee Valley is forecast to gradually move to the northeast and arrive in our region Wednesday into Thursday. This feature is forecast weaken some as it arrives. At the surface, high pressure shifts offshore as the mid level ridge does as well. Low pressure across the Gulf coast states will lift northeastward and arrive into our region Wednesday into Thursday. After a dry start, it looks to turn unsettled for the middle of the week.

For Monday and Tuesday...A southeast to northwest orientated mid level ridge over our area Monday will gradually shift eastward. This will continue to shift the center of high pressure farther offshore during Monday. A southeasterly wind will therefore develop and start to bring in an increase in the moisture from the south. Meanwhile, a closed low across the Gulf coast states to the Tennessee Valley is forecast to slowly lift northeastward through Tuesday. As this occurs, low-level warm air advection and deeper moisture advection will strengthen across the Mid-Atlantic. Most if not all of Monday looks to be dry given the ridge aloft overhead, although some increase in high clouds should develop. The forecast challenge is how quick the forcing for ascent starts to arrive into our area. Some guidance brings this into at least our southern zones by daybreak Tuesday, then this shifts northward doing Tuesday. As a result, showers are forecast to be on the increase Tuesday from the south and some thunder cannot be ruled out if enough instability develops. While showers are currently in the forecast, it is possible that a more steady rain could develop. Depending on the timing, the showers/rain may start to end from south to north later Tuesday night. While there is a closed low involved, some of the guidance may be to fast with the forward progression although it may tend to weaken some as it shifts northeastward.

For Wednesday and Thursday...This time frame will be driven by the weakening trough across the Northeast and Mid-Atlantic regions. A surface low will accompany this with it tracking near or over our area late Wednesday into Thursday. It looks overall to be unsettled at times however given that at least some heating should occur and with the trough aloft weakening, high temperatures should be warming. The chance/extent and intensity of any thunderstorms will depend on the magnitude of any instability.

AVIATION /08Z FRIDAY THROUGH TUESDAY/

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

Today...Poor conditions with widespread IFR and low end MVFR developing early and persisting into the afternoon. Improvement beginning late SW and spreading E/NE across the other terminals into the evening. NE winds 10 to 20 kts shifting to NW this afternoon. Low/medium confid overall.

Tonight...Improving conditions with decreasing clouds and improving CIGS from SW to NE this evening then VFR expected overnight. Gusty NW winds 10 to 15 kts with gusts around 20 kts at times. Medium confid.

Outlook...

Saturday...VFR. West-northwest winds 15-20 knots with gusts to around 25 knots, diminishing in the evening.

Sunday and Monday...VFR.

Tuesday...Sub-VFR conditions and showers possible.

MARINE

Poor conditions across the waters today and into the evening with widespread rains and a few tstms as well. Winds and seas will remain below SCA levels until early tonight when winds will become NW and gusts will increase to around 25 knots at times. Rains diminish this evening with fair weather overnight.

Outlook...

Saturday...Small Craft Advisory conditions expected with wind gusts up to 30 knots across all coastal waters, including the Delaware Bay, as well as seas up to 5 feet along the ocean coastal waters. Conditions begin to improve during the afternoon.

Saturday night through Tuesday...The conditions are anticipated to be below Small Craft Advisory criteria.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 10 PM this evening to 1 PM EDT Saturday for ANZ430-431. Small Craft Advisory from 10 PM this evening to 3 PM EDT Saturday for ANZ450>455.