textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated all sections.

KEY MESSAGES

1. A strengthening storm over our area this afternoon moves offshore tonight and Friday.

2. A stretch of below normal temperatures begins on Friday, continuing through the weekend as a much colder airmass moves overhead.

DISCUSSION

KEY MESSAGE 1...A strengthening storm over our area this afternoon moves offshore tonight and Friday.

A vigorous upper-level trough continues to evolve across the Eastern U.S. for tonight and into the weekend. This supports the surface low deepening over our CWA this afternoon/evening. The low then heads NE our across the waters off New England Friday. While there are still some differences with the handling of the embedded shortwaves, there is better model clustering with the surface low placement/track. Overall, it will be unsettled across our region tonight and Friday.

The showers and tstms have develop across the area as of early afternoon and a Tornado Watch has also been issued. There was some activity earlier across Monmouth County NJ but more has developed for ern PA and New Castle County DE. This activity will move NE across the NW half of our CWA over the new few hours. Be aware of Severe weather threats and take appropriate action if a warning is issued.

Not much has changed with regards to the cold air following the system and the subsequent change in p-type for NW areas. The strength of the parent upper-level trough results in a colder air mass moving in with time, however the initial air mass is not all that cold (the lack of a cold antecedent air mass). As the surface low consolidates off the northern Mid-Atlantic coast, the winds will turn more out of the northwest and this will increase the cold air advection. This will result in some colder air seeping southeastward later tonight but especially Friday into Friday night. The air mass may become sufficiently cold enough mostly across our far northwestern zones for some snow across the higher elevations, confined mainly to the Pocono Plateau. Any snowfall accumulation is expected to be less than an inch. Some elevated locations across the Lehigh Valley and Northwestern NJ may see a few wet flakes mixing in, but no accumulations are expected. Otherwise, a rain event is forecast. The amount of precipitation (rain and/or snow) will depend on the ultimate track of the surface low and whether a deformation zones wraps back into our northern to central areas. At the moment, rainfall amounts north of the PA Turnpike to I-195 corridor range around the 0.50-1.25" range while further south across Philly and south, we are expecting less than 0.50" of rainfall, with less than 0.10" expected for the southern Delmarva.

KEY MESSAGE 2...A stretch of below normal temperatures begins Friday, continuing through the weekend as a much colder airmass moves overhead.

In the wake of the storm, as it deepens and tracks toward the Canadian Maritimes over the weekend, a colder air mass will be in place across our area. In addition, a tightened pressure gradient coupled with deeper mixing will result in a period of breezy to windy conditions over the weekend. The strongest winds look to occur on Saturday, with peak gusts to about 30 mph, then while still gusty on Sunday it appears the speeds come down a little. Daytime temperatures on Friday and Saturday should not get out of the 40s for many areas, with temperatures at night dropping into the 20s to low 30s. Where the growing season is still active across Delmarva, parts of southern New Jersey and far southeastern Pennsylvania, frost/freeze headlines may be necessary. There could even be some lake effect snow and/or rain showers into the southern Poconos on Saturday.

Temperatures start to moderate a bit Sunday through Tuesday. Despite that, high temperatures are only in the upper 40s to low 50s each day which is still below average for this time of year.

While we are likely to get our first freeze sometime during this stretch, the Frost/Freeze program area-wide ends on Sunday November 15th. Beyond that, no further frost/freeze headlines will be issued.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

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

Rest of today... Increasing amounts of showers/tstms across the terminals into the evening. Largely MVFR conditions develop with IFR at times. Conditions expected for KRDG/KABE first then spreading E/SE reaching KMIV/KACY later. The chances for thunder are lower S/E then other areas. SE/E winds shifting to W/NW by evening. Gusts 20 to 40 kts in tstms. Low confid.

Tonight...Cigs gradually diminish to IFR with showers. Winds north to northwest 5-10 kts. Low/Moderate confidence.

Friday...Low CIGS expected (IFR and LIFR) with periods of rain (rain/snow possible later Friday, mainly well north/west of KABE/KRDG). North to northwest wind gusts 20-25 knots. Low/Moderate confid.

Outlook...

Saturday and Sunday...Mainly VFR. Northwest wind gusts 20-30 knots.

Monday...VFR. No significant weather.

MARINE

Decided to start the SCA flag for the waters earlier with the deepening low pressure area moving offshore this evening. Winds and seas will build overnight. Behind the low, winds will remain in SCA range through Friday. A few Gale gusts are possible too. Showers and tstms this evening and more showers on Friday. Outlook...

Saturday...Small Craft Advisory conditions probable. Near gale force wind gusts possible.

Sunday...Small Craft Advisory conditions possible.

Monday...Marine conditions will be below advisory criteria.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...Coastal Flood Advisory until 2 PM EST this afternoon for NJZ020-026. DE...None. MD...None. MARINE...Small Craft Advisory from 6 PM this evening to 6 PM EST Friday for ANZ430-431-450>455.