textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Confidence with regards to amounts and placement of heaviest rainfall has increased. Increasing potential for rain and/or snow showers Sunday afternoon with passage of cold front. Gusty winds expected Sunday afternoon and Sunday night.

KEY MESSAGES

- Showers late this afternoon into early tonight then more rains Saturday. - Isolated rain and/or snow showers Sunday afternoon. Gusty winds then develop Sunday afternoon and Sunday night.

DISCUSSION

KEY MESSAGE 1...Showers late this afternoon into early tonight then more rains Saturday.

A cold front will cross the area late today and early tonight and then a wave of low pressure forms along it to the south and rides across the northern Middle Atlantic Saturday. Showers are already evident on regional radar to the South/West. As the warm advection develops ahead of the front, these showers will translate across our region. Pops will be in the likely to low categorical range (70% to 80%). Total rainfall of a tenth of an inch or up to two tenths of an inch possible. Rains end overnight with patchy fog. Possible VSBY travel impacts in fog.

More rains develop Saturday as a wave of low pressure moves up from the South/West. Pops (90% to 100%) for the area with rains arriving S/W first for the late morning and then arriving N/E for the afternoon. Rains with this second batch will be three- quarters of an inch to one-inch. Possible impacts could poor drainage flooding and possibly fog for areas near cooler rivers of the ocean.

KEY MESSAGE 2...Isolated rain and/or snow showers Sunday afternoon. Gusty winds then develop Sunday afternoon and Sunday night.

Strong, nearly vertically stacked, low pressure will be over the Province of Ontario Sunday morning and will track east into the Province of Quebec Sunday afternoon. From this low, a deep upper trough will extend back into the Great Lakes and Ohio Valley, and a strong surface cold front will be associated with that trough. The cold front and base of the trough will pass through the region Sunday afternoon, and there will be strong shortwave energy associated with that trough. Strong cold air advection will develop behind the passage of the front, and this should be strong enough to touch off isolated rain and/or snow showers Sunday afternoon. For now, will make sure the forecast has 15-20 PoPs (slight chance) for the afternoon period, as conditions should be dry starting in the morning behind the initial departing system. Cannot rule out the possibility for some localized snow squalls either, but it is a little too soon for those details to be developed.

From there, a tight pressure gradient develops over the area between low pressure over the Canadian Maritimes and high pressure building into the Midwest and Gulf Coast states. Winds shift to the west- north west and increase to 20 to 30 mph with gusts up to 40 mph late Sunday afternoon and Sunday night for most of the area. However, for the southern Poconos, gusts could be as high as 45 to 50 mph, and a Wind Advisory may be needed.

AVIATION /18Z FRIDAY THROUGH THURSDAY/

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

Tonight...MVFR CIGS expected with IFR possible at times. Rain showers with lower VSBYS too especially before 04Z/05Z. Areas of fog possible after that. South to Southwest winds around 10 knots becoming West overnight. Low/Medium confid.

Saturday...VFR early then lower CIGS as rains arrive for the late morning (S/W) and afternoon (N/E). Light winds the mostly East to Northwest around 10 knots by afternoon. Medium confid.

Outlook...

Saturday night...MVFR/IFR in rain and fog.

Sunday through Sunday night...Conds improve to VFR Sunday morning. Isolated SHRA and/or SHSN Sunday afternoon may briefly reduce VSBYs. W-NW winds increase to 15 to 20 kt with 25 to 35 kt gusts late Sunday afternoon and continue for most of Sunday night before diminishing late.

Monday through Tuesday...VFR.

Wednesday through Thursday...Potential for sub-VFR conds in SHRA.

MARINE

Winds and seas will remain sub-SCA tonight and Saturday. Showers will arrive late this afternoon and continue into the evening. Fog possible. More rains Saturday moving across the southern waters first (morning) and then for the northern NJ waters during the early afternoon.

Outlook...

Saturday night...SCA conditions possible for SW winds 20 to 25 kt. Seas building to 4 to 6 feet late. VSBY restrictions in rain and fog.

Sunday through Sunday night...Winds turn W-NW and increase to 15 to 20 kt with 25 to 30 kt gusts in the morning, then increase further late in the afternoon and at night to 20 to 30 kt with 35 to 40 kt gusts. A Gale Watch is now in effect for Sunday night. VSBY restrictions in the morning in rain and fog, then there is the potential for isolated rain and/or snow showers late Sunday afternoon through early Sunday evening.

Monday through Monday night...SCA conditions Monday morning, diminishing to sub-SCA levels Monday afternoon and continuing through Monday night.

Tuesday through Wednesday...Sub-SCA conditions mainly expected, however a period of SCA conditions is possible Tuesday night.

Thursday...Sub-SCA conditions.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Gale Watch from Sunday evening through late Sunday night for ANZ430-431-450>455.