textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Aviation discussion has been updated.

KEY MESSAGES

1. An elevated risk for fire spread is likely on Tuesday as a dry airmass will be in place.

2. Chilly temperatures Wednesday morning and Thursday morning raise frost/freeze concerns where the growing season is currently active.

DISCUSSION

KEY MESSAGE 1...An elevated risk for fire spread is likely on Tuesday as a dry airmass will be in place.

A period of elevated fire weather conditions is likely Tuesday as a dry airmass infiltrates the area. On Tuesday morning, a secondary cold front is forecast to pass through the region. This will cause dew points to fall into the teens, resulting in a very dry airmass overhead. MinRH values for Tuesday afternoon will be in the 25-35% range with northwest winds around 15-20 mph and gusts up to 30-35 mph.

At this time, these conditions will be very close to reaching Red Flag Warning criteria on Tuesday. While there is high confidence in meteorological conditions being met for a Red Flag Warning, rainfall from Sunday may keep 10 hour dead fuel moistures high enough to offset this threat. Most areas received around 1/4 to 1/2 of an inch of rainfall, with locally higher amounts up to 1 inch across southern Delaware and New Jersey. So far, contacts with our state partner fire agencies have indicated fuels will not be quite dry enough for a Red Flag Warning on Tuesday, with a Special Weather Statement being the most likely issuance. However, we will continue to get feedback in case fuels dry out excessively fast, resulting in the need for a warning.

Winds should be lighter on Wednesday, reducing the fire weather threat.

KEY MESSAGE 2...Chilly temperatures Wednesday morning and Thursday morning raise frost/freeze concerns where the growing season is currently active.

Strong Canadian 1040 mb high pressure will settle over New York State on Wednesday morning before shifting off the New England coast by Thursday morning. In wake of a cold front on Tuesday, a reinforcing shot of cold, dry air will arrive Tuesday night and linger into Wednesday night. Low temperatures will fall into the low to mid 20s to low to mid 30s for most locales, with teens in the Poconos by Wednesday morning. Based on coordination with neighbors, we have decided to start the growing season for much of the area a few days early, so that in addition to the Delmarva, frost/freeze headlines may now be issued for most areas along and south of a line roughly along I-195 and the east-west PA Turnpike. There is a decent chance (50-60%) for temperatures at or below freezing on Wednesday morning over Delmarva as skies will be clear and winds light, with higher probabilities further north. Therefore, have issued a widespread freeze watch for all zones now considered active except the Delaware beaches, where marine influences may keep temps just above.

Current forecast indicates temperatures Thursday morning will be a few degrees warmer as the high shifts offshore. However, its possible that guidance is underdoing the radiational cooling this night, such that in some better radiative locales, Thursday morning ends up the colder, while less radiative places end up with Wednesday morning being colder. In any case, another round of headlines will be possible, but we'll cross that bridge when it gets closer.

A return to more normal temperatures well above freezing comes by Friday morning, continuing at least through the weekend.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

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

Tonight... VFR expected. Gusty west winds continue to diminish to 5-10 knots. SCT to BKN clouds at 060-080 for most areas into the early overnight period. High confidence.

Tuesday... VFR. A mostly clear sky is expected. Winds increase out of the west in the morning before becoming more out of the northwest in the afternoon. Wind gusts 10-15 knots with gusts upwards of 25-30 knots develop around 12Z. High confidence.

Outlook...

Fair weather with generally VFR conditions are expected during the midweek to late week time period. The good conditions may last into Saturday.

MARINE

For the rest of today and tonight, we can expect Northwest to West winds 10 to 15 kts which will decrease overnight as then back to Southwest overnight. Fair weather.

For Tuesday, a cold front will cross the waters early and a short period of SCA gusts are possible, but not certain. We did not issue A SCA at this time. Winds will generally be around 15 kts perhaps a bit higher during the afternoon. Fair weather expected.

Outlook...

A prolonged period of sub-SCA conditions and Fair weather for the mid to late week period.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Freeze Watch from late Tuesday night through Wednesday morning for PAZ060-070-071-101>104-106. NJ...Freeze Watch from late Tuesday night through Wednesday morning for NJZ013>027. DE...Freeze Watch from late Tuesday night through Wednesday morning for DEZ001>003. MD...Freeze Watch from late Tuesday night through Wednesday morning for MDZ012-015-019-020. MARINE...None.