textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Rainfall forecast totals for Wednesday into Thursday are slightly lower.

KEY MESSAGES

1. A round of much needed rain later Wednesday into early Thursday. Low risk of a stronger thunderstorm for (mostly) Delmarva.

DISCUSSION

KEY MESSAGE 1...A round of much needed rain later Wednesday into early Thursday. Low risk of a stronger thunderstorm for (mostly) Delmarva.

A strong upper-level trough/closed low centered over or just north of the upper Great Lakes Wednesday night and Thursday will gradually pivot eastward. This will drive a strong cold front across our area early Thursday as low pressure develops along the cold front. As of now, this surface low looks to track across the southern half of our our region early Thursday morning.

The precipitable water values are forecast to surge across our area ahead of the cold front to 1.00-1.50 inches. A low-level jet around 850 mb of 40 to 45 knots is forecast to arrive Wednesday evening. This will increase the low-level warm air advection and subsequently augment the forcing for ascent ahead of and with an incoming cold front. An area of low pressure is also forecast to develop along the front in the vicinity of Delmarva. This will all result in an expanding area of showers, or a period of rain, to arrive from the west later Wednesday afternoon with the bulk of the rainfall occurring Wednesday night into early Thursday morning. Some embedded downpours are possible given the higher precipitable water values and stronger forcing, however the overall instability looks to be rather weak. While some thunder (low- topped) cannot be ruled out, the risk of a few stronger thunderstorms looks rather low at this time with the anticipation of cloud cover limiting the instability. If more instability however can become realized, then given the shear magnitude there would be some severe thunderstorm risk especially across our Delmarva zones later Wednesday afternoon and early Wednesday evening.

Overall, storm total rainfall look to be between 0.50-1.00 inches across our entire region. The overnight average is perhaps a little less than Monday's forecast, but not by much. If an embedded stronger convective contribution materializes, then locally higher rainfall totals will be possible. This rain is much needed given the ongoing longer term drought conditions in place. The showers/rain rapidly end early Thursday morning as the cold front and surface low clears our area.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

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

Early this morning (through 12Z)...VFR. Winds light and variable. High confidence.

Tuesday...VFR. South/southeast winds around 5-10 kt. Clouds increasing and bases lowering through the day but high confidence in prevailing VFR and the overall forecast. Perhaps a light shower early afternoon for RDG/ABE; no impacts expected.

Tuesday night...VFR with increasing and lowering clouds. Moderate confidence.

Outlook...

Wednesday...VFR early then lowering to sub-VFR conditions along with showers late in the afternoon and overnight. There is also a slight chance for an evening thunderstorm.

Thursday...Mostly sub-VFR with some showers possible, mainly early, then VFR. Northwest wind gusts up to 20 knots.

Friday...Mainly VFR. West-northwest wind gusts to 20 knots during the day.

Saturday...A period of sub-VFR and showers possible especially for the Delaware Valley sites and S/E.

MARINE

Small Craft Advisory remains in effect through Tuesday due to elevated seas near 5 feet. Winds mostly 10 knots or less. Fair weather.

Outlook...

Tuesday night...Seas may linger at 5 feet for a time on the Altantic coastal zones.

Wednesday and Thursday...A period of Small Craft Advisory conditions possible. Showers later Wednesday and into Thursday morning. A tstm is passable Wed night.

Friday and Saturday...The conditions should be mostly below Small Craft Advisory criteria. Showers possible Friday night and Saturday.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ450>455.