textproduct: Philadelphia/Mt Holly

SYNOPSIS

A warm front will lift north across the Mid Atlantic this evening followed by a cold front on Saturday. High pressure will build in behind the low pressure system for Sunday and persist through Tuesday. A cold front is expected on Wednesday. More high pressure is expected Thursday and Friday.

NEAR TERM /THROUGH SATURDAY/

As of 940 PM, a few minor adjustments were made along the coastal strip to account for slightly later arrival of low clouds and patchy fog. No changes otherwise.

A round of showers with embedded thunder is expected tonight into early Saturday associated with a shortwave trough. A second round of scattered showers and storms is expected Saturday afternoon into the early evening hours associated with a cold front passage.

Convective showers over the Ohio Valley and Mid-Atlantic will lift northeast this evening and continue through the overnight hours (the bulk of activity will be after midnight). Other than some brief heavy downpours and some rumbles of thunder around, the activity tonight does not look like it will amount to all that much. Greatest potential for showers/storms is north and west of the I-95 corridor, but some of the latest hi-res guidance indicates more of a signal to having some convective showers all the way down to the coast. Lows tonight will be very mild with lows in the mid 50s to low 60s. Patchy to localized dense fog will be possible along the coastal strip as well.

The morning precipitation is expected to exit the area by day break for the majority of the area except for portions of the Poconos and northern New Jersey where shower activity may continue into the late morning hours. All in all, there should be a lull in shower activity during the morning hours in between departing shortwave and approaching cold front. Despite the lull in activity, pesky cloud cover looks to remain in place for much of the day, so skies should primarily be mostly cloudy with occasional breaks of sun in the afternoon. The second round of showers and thunderstorms are then expected to develop by the early afternoon hours. Latest 12Z/HREF probabilities have increased the amount of surface based instability just a bit, with ~1000 J/kg of SBCAPE and ~25 kt of bulk shear available during the afternoon. This of course depends on how much sunshine is able to occur during the day to set the stage on how much the area may destabilize. Considering the above parameters and latest guidance trends by the HRRR/ARW/RRFS, scattered showers and storms may organize into broken clusters as they progress eastward through the afternoon hours ahead of the cold front. Although none of the area is currently outlooked by SPC, do believe there may be a couple strong to severe storms around Saturday afternoon. Primary threat would be damaging wind gusts if any organized clusters are to develop. Convective activity will cease from northwest to southeast during the afternoon as the front progresses through the area.

Aside from the afternoon convection, high temperatures on Saturday are expected to top out in the upper 60s to upper 70s. Winds will also be gusty at times out of the southwest, with a few gusts 20-30 mph possible.

SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/

The period begins with mid-level low pressure to our north. At the surface, a cold front will be just to our east. This cold front will continue to track offshore with a tightening gradient behind it.

Showers will be coming to an end on Saturday night. A good amount of sunshine will be in place on Sunday, especially across the southern half of the forecast area. Definitely more clouds to the north.

The mid-level low will push off to our northeast Sunday night. At the surface, high pressure will begin to build in. While the mid- level NW flow will persist on Monday, the surface high will pass overhead and center itself just off the coast late on Monday.

After a breezy day on Sunday, winds will relax Sunday night and be on the lighter side on Monday.

Saturday and Sunday night lows will will be similar with the upper 30s in the Southern Poconos and in the 40s everywhere else.

Sunday will be the cooler day of the weekend in the post-frontal environment. Highs will be in the 50s across the north and 60s south. Expect 60s and 70s on Monday.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Surface high pressure will remain in place Monday night, but begin to unravel on Tuesday. This will allow a cold front to move through the region on Wednesday. Weak surface high pressure will build once again Thursday. A warm front will first approach the region on Friday followed by a cold front. In short, expect a couple shots of precipitation the second half of the week.

Overnight lows Monday night will be around normal. Temperatures will move into the above normal category on Tuesday and stay there through much of the week. While the guidance has come down from its earlier peak in the mid to upper 80's on Tuesday and/or Wednesday, lower 80s still look reasonable. Thursday's temperatures look normal. Friday could move above normal.

AVIATION /02Z SATURDAY THROUGH WEDNESDAY/

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

Tonight...VFR ceilings will lower to MVFR by 02-04Z and to IFR by 05-07Z. Scattered rain showers with embedded thunder will be possible beginning as early as 03Z and continuing through the night. Confidence in some thunder occurring is now high enough to include for the I-95 terminals after 07Z. South wind around 10 kt. LLWS possible for all terminals developing after 06Z excluding KRDG/KABE. Patchy fog is also possible for KACY/KMIV overnight. Moderate confidence overall, but lower confidence in timing and thunderstorm potential.

Saturday...IFR ceilings should gradually lift to MVFR and scatter out to VFR by the late afternoon hours. Isolated showers in the morning, with scattered showers and thunderstorms possible in the afternoon. A few storms may be strong to severe. Southwest wind around 10-15 kt with gusts up to 25 kt possible gradually shifting to northwest late following a frontal passage. Moderate confidence.

Outlook...

Saturday night through Tuesday...VFR conditions expected. Gusty NW winds likely on Sunday.

Tuesday night and Wednesday...Restrictions expected, at least MVFR.

MARINE

After midnight, a Small Craft Advisory will be in effect for all Atlantic coastal waters through Saturday. A Small Craft Advisory will be in effect for the Delaware Bay beginning at 6 AM Saturday as well. South-southwesterly winds will increase to around 17-22 kt with gusts up to 25-30 kt possible with seas building to around 4-6 feet. Scattered rain showers and isolated thunderstorms are expected after midnight continuing through the day on Saturday.

Also, patchy to areas of dense marine fog are expected to develop tonight into Saturday morning. A marine dense fog advisory may become warranted later tonight, if such fog develops.

Outlook...

Saturday night and Sunday...At the minimum, SCA conditions expected. Gusts between 25 to 35 kt possible.

Sunday night through Tuesday...Sub-SCA conditions expected.

Tuesday night and Wednesday...SCA conditions expected.

FIRE WEATHER

Showers will impact the area tonight through Saturday evening. Overall, between 1/4 and 1/2 inch of rain will fall across most of the area, though up to an inch of rain is possible in the southern Poconos and far northwest New Jersey, and 1/10 inch or so is possible in Delmarva.

On Sunday, northwest winds will increase to 15 to 20 mph with 30 to 35 mph gusts possible. In addition, RH values will drop below 40% south of the PA Turnpike and 195 in NJ. We can't rule out 30 to 35%.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 6 AM Saturday to 6 PM EDT Sunday for ANZ430-431. Small Craft Advisory until 6 PM EDT Sunday for ANZ450>455.