textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Freeze Watches for Wednesday morning have been converted to Freeze Warnings. A new Freeze Watch was issued for Wednesday night into Thursday morning.

Small Craft Advisories have been issued for today and tonight.

KEY MESSAGES

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

2. Cold temperatures Wednesday morning and Thursday morning will bring widespread freeze and frost conditions.

DISCUSSION

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

Elevated fire weather conditions are likely today as a dry airmass infiltrates the area behind a secondary cold front which will pass through early this morning. Behind the front, dew points will fall into the teens by the afternoon, resulting in a very dry airmass overhead. MinRH values today will be in the 20-30% range with northwest winds around 15-20 mph and gusts around 30-35 mph.

While there is high confidence in the above 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. Upon discussion with our state fire weather partners, it appears that fuels have not dried out enough for Red Flag Warning issuance, as fuels remain generally around 10% or higher. We will check back in with our fire weather partners again this morning in case fuels dry out faster than previously thought. At the very least, suspect a Special Weather Statement may be needed for elevated fire spread risk today.

Winds will be lighter on Wednesday, around 5-10 mph at most, which will reduce the fire spread threat. However, minimum relative humidity values will remain around 20-30% away from the immediate coast.

KEY MESSAGE 2...Cold temperatures Wednesday morning and Thursday morning will bring widespread freeze and frost conditions.

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 the cold front on Tuesday, a reinforcing shot of cold, dry air will arrive tonight 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. As a result, have converted all Freeze Watches that were in effect for Wednesday morning to Freeze Warnings.

Based on coordination with neighboring offices, we have started the growing season for much of the area a few days early, so that 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.

With the surface high pressure centered just offshore, radiational cooling should develop quite efficiently Wednesday evening into early Thursday morning. The easterly wind on Wednesday will help dewpoints to recover some, which will introduce conditions supportive of frost development (unlike tonight). Have lowered forecast low temperatures a bit from guidance, especially across the coastal plain where winds will be lighter. With the chilly east wind during the daytime Wednesday, frost development could occur fairly early across the coastal plain during the evening hours as temperatures fall quickly into the 30s, perhaps even some 20s in the Pine Barrens by midnight.

Forecast low temperatures are mostly in the mid 20s to low 30s once again, thus we have gone ahead and issued a new Freeze Watch for areas with the greatest chance of sub-freezing temperatures where the growing season has been activated. While freezing temperatures are not anticipated along the immediate coastline (including barrier islands), frost development could occur in these areas if winds go calm early enough in the night.

Temperatures will moderate Thursday through Friday, however low temperatures Thursday night into Friday morning could drop into the mid 30s in the usual cooler areas of southern NJ and SE PA where the growing season is active. Thus, could see some frost development in these areas, though another freeze is unlikely Thursday night.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

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

Rest of Tonight (thru 12Z): VFR with SCT/BKN ceilings around 7000 feet through 09Z, before clearing thereafter. A slight chance of rain shower at all terminals, so have included VCSH in TAFs. Variable winds around 5 kt, should become westerly around 5-10 kt late. Moderate-high confidence.

Tuesday...VFR with mostly clear skies. Northwest winds will increase by mid-morning to around 15-20 kt with gusts up to 25-30 kt through the afternoon. High confidence.

Tuesday night...VFR with clear skies. Northwest winds will gradually transition to northerly around 5-10 kt. High confidence.

Outlook...

Wednesday through Saturday...VFR conditions will prevail with fair weather and winds 10 kts or less.

MARINE

Small Craft Advisories have been issued for the Delaware Bay beginning at 9 AM today until 2 AM Wednesday. Small Craft Advisories have been issued on all of the Atlantic Coastal Waters beginning at 11 AM today until 6 AM Wednesday.

Southwest winds around 10-15 kt early will transition to northwest and increase to around 15-20 kt with gusts up to 30 kt by the afternoon in wake of cold frontal passage. Northwest winds tonight will become north-northeast overnight around 15-20 kt with gusts up to 25 kt. Seas of 3-5 feet. Fair weather expected outside of SCA conditions.

Outlook...

Wednesday through Thursday night...No marine hazards expected. Fair weather.

Friday through Saturday...Seas building to near 4-6 feet with medium to long period easterly swells. Otherwise, fair weather.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Freeze Warning from midnight tonight to 9 AM EDT Wednesday for PAZ060-070-071-101>104-106. Freeze Watch from Wednesday evening through Thursday morning for PAZ060-070-071-101>104-106. NJ...Freeze Warning from midnight tonight to 9 AM EDT Wednesday for NJZ013>027. Freeze Watch from Wednesday evening through Thursday morning for NJZ013>023-027. DE...Freeze Warning from midnight tonight to 9 AM EDT Wednesday for DEZ001. Freeze Watch from Wednesday evening through Thursday morning for DEZ001>003. Freeze Warning from 2 AM to 9 AM EDT Wednesday for DEZ002-003. MD...Freeze Watch from Wednesday evening through Thursday morning for MDZ012-015-019-020. Freeze Warning from 2 AM to 9 AM EDT Wednesday for MDZ012-015- 019-020. MARINE...Small Craft Advisory from 9 AM this morning to 2 AM EDT Wednesday for ANZ430-431. Small Craft Advisory from 11 AM this morning to 6 AM EDT Wednesday for ANZ450>455.