textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Marine Dense Fog Advisories for the coastal waters extended through this morning.

KEY MESSAGES

1. Cloudy skies with fog and periods of rain through tonight.

2. Turning very mild especially this weekend and early next week along with several chances for showers.

DISCUSSION

KEY MESSAGE 1...Cloudy skies with fog and periods of rain through tonight.

A stationary front extends from low pressure over the Ohio Valley across the Delmarva Peninsula and southern New Jersey. That low tracks to the north and east throughout the day and will pull that stationary front north a a warm front. Temperatures will gradually creep up through the night, and then highs will be in the low 50s, through possibly into the upper 50s in Delmarva.

Cloudy and foggy conditions persist through tonight with ceilings lowering through daybreak or so. While some locally dense fog is possible, most fog will be generally as low as 1/2 to 1 mile through daybreak. Fog gradually dissipates through the morning, and while skies remain cloudy today, ceilings will gradually lift. Some shortwave energy and weak low pressure passes through the southern half of the forecast area ahead of the main low this afternoon. This will touch off some rain late this afternoon and into this evening, mainly over the Delaware Valley, southern New Jersey, and Delmarva.

More fog develops tonight with ceilings lowering once again. Another shot of rain is possible late as that low draws nearer. Lows tonight generally in the 40s.

KEY MESSAGE 2...Turning very mild especially this weekend and early next week along with several chances for showers.

A much warmer air mass is forecast to overspread our area this weekend and especially early next week. In addition, there will be several opportunities for showers and perhaps a few thunderstorms across the area.

A shortwave trough is forecast to slide along the northern side of a building ridge that becomes anchored/centered in the western Atlantic Thursday and Friday. The trough should exit the New England coast Friday morning, however strong high pressure across eastern Canada is forecast to build southward. As this occurs, the ridge amplifies west and northward aloft. This setup forces a boundary to our south and west with an east to northeast low-level flow. This will drive a much cooler air mass across our region along with more cloud cover and perhaps some fog. This cold air damming scenario will likely lead to a strong temperature gradient, although this may end up being to our south and west Friday given the stronger onshore push from the northeast. As a result, the NBM is showing a cooling trend for Thursday and especially Friday although likely not enough for Friday. Therefore, used a NBM/NBM10 blend for temperatures on Friday. Ahead of and with the aforementioned shortwave trough, warm air advection aloft will result in a zone of ascent and therefore an increase in shower activity Thursday morning with perhaps another round moving through Thursday night when also some isolated thunder cannot be ruled out due to some increase in elevated instability. Precipitable water values are forecast to be 1.00-1.25 inches Thursday into Friday, therefore rainfall amounts could reach or exceed 1-inch in some areas.

Another upper-level disturbance tracks to the north of our area Saturday night, with a trailing cold front moving through. This looks to bring additional showers and perhaps a few thunderstorms to our region. We become more embedded within the warm sector over the weekend and especially early next week. This should result in a much warmer air mass surging into the region. Highs Saturday through Tuesday are forecast to be in the 60s with 70+ for may areas as we go through early next week. The flow may be light enough and also more southerly during the weekend and early next weak, which would introduce cooling along the coast with perhaps even a robust sea breeze racing inland.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

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

Early this morning...IFR/LIFR CIGs/VSBYs. LGT/VRB winds. High confidence in IFR/LIFR conds, but low confidence in just how low conds will get an corresponding timing.

Today...IFR CIGs lifting to MVFR from time to time in the afternoon. VSBY restrictions in BR in the morning, then IFR or MVFR VSBYs lift to VFR. Some RA possible in the afternoon with additional VSBY restrictions. High confidence in conds overall, but low confidence in timing.

Tonight...IFR or LIFR conds in stratus and BR. RA possible late. E winds less than 5 kt. Moderate confidence overall.

Outlook...

Thursday...Sub-VFR conditions with showers and some fog, and some thunder is possible at night.

Friday...Sub-VFR conditions due to low clouds and possible fog. A few showers possible.

Saturday...Times of sub-VFR conditions with some showers. Showers more numerous mostly at night with some thunder possible.

Sunday...Conditions may improve to VFR. A few showers still possible.

MARINE

Visibility restrictions 1 nm or less in fog will persist through this morning on the coastal ocean waters and Delaware Bay. As a result, the Marine Dense Fog Advisory is now in effect until 10 am. Though the Marine Dense Fog Advisory will expire later this morning, visibility restrictions in fog and periods of rain will continue this afternoon and tonight.

Southwest winds around 10 kt will become light and variable this afternoon before taking on an easterly flow around 10 kt tonight. Seas on the ocean will be around 5 feet through this afternoon, then seas subside to 3 to 4 feet. As a result, the Small Craft Advisory on the ocean remains in effect until 1 pm.

Outlook...

Thursday and Friday...The conditions are anticipated to be below Small Craft Advisory criteria. Fog possible.

Saturday and Sunday...A period of Small Craft Advisory conditions possible.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Dense Fog Advisory until 10 AM EST this morning for ANZ430-431- 450>455. Small Craft Advisory until 1 PM EST this afternoon for ANZ450>455.