textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

A new key message was added for the dry conditions this week.

Aviation section has been updated.

KEY MESSAGES

1. Freeze and/or frost conditions later tonight and Wednesday morning and again Wednesday night into Thursday morning.

2. A dry weather pattern continues for the remainder of the week and potentially most of this upcoming weekend.

DISCUSSION

KEY MESSAGE 1...Freeze and/or frost conditions later tonight and Wednesday morning and again Wednesday night into Thursday morning.

The center of strong Canadian high pressure will settle over New York State early Wednesday morning before shifting off the New England coast by Thursday morning. A very dry and colder air mass will settle in tonight and linger through Wednesday night. Given the incoming surface high, the pressure gradient will weaken tonight and decoupling will come into play therefore the gusty northwest winds will diminish tonight. Low temperatures will bottom out into the 20s to low/mid 30s, with upper teens in the Poconos, by Wednesday morning. As a result, Freeze Warnings remain in effect for later tonight and early Wednesday morning where the growing season has already started. Due to the air mass being so dry and at least some wind occurring through the night at most places, frost formation should be rather limited.

With the surface high centered just offshore Wednesday night into early Thursday morning, radiational cooling should develop quite efficiently. The east to southeast wind on Wednesday will help the surface dew points to recover some, which will introduce conditions supportive of frost development. With the chilly onshore wind during the day Wednesday, frost development could occur earlier across the coastal plain during the evening hours as temperatures fall quickly into the 30s, perhaps even some 20s in the Pine Barrens toward midnight.

Forecast low temperatures are in the mid to upper 20s to low/mid 30s once again, thus a Freeze Watch is in effect Wednesday night and early Thursday morning for areas with the greatest chance of sub- freezing temperatures where the growing season is active. While freezing temperatures are not anticipated along the immediate coastline (including the barrier islands), frost development could occur in these areas if winds go calm early enough in the night. A possible fly in the ointment is that as the low-level moisture starts to increase during Wednesday night and especially closer to daybreak Thursday, some cloud cover could develop especially closest to the coast.

Temperatures will moderate Thursday and Friday, however low temperatures Thursday night into Friday morning could drop into the mid 30s in the usual cooler areas of southern New Jersey and southeast Pennsylvania where the growing season is active. Thus, could see some frost development in these areas.

KEY MESSAGE 2...A dry weather pattern continues for the remainder of the week and potentially most of this upcoming weekend.

Our expansive area of high pressure remains in control across the region through the remainder of this week. As a result, it is a dry week precipitation wise. This high pressure system is moving overhead into tomorrow. At the surface, a very dry air mass will be in place tomorrow with min RH values in the 20-30% range. One difference from today's fire weather concerns is that the wind will be much less tomorrow as the pressure gradient has lessened from the high pressure system moving overhead. Towards the end of the week, RH values do increase as winds are out of the southeast Thursday and southwest Friday from our high pressure system departing offshore. However, there will continue to be a lack of precipitation due to the region still feeling the influences of the high pressure system.

A cold front sinking southeast Friday night into Saturday morning is the next potential at some precipitation, but this potential currently looks pretty limited. Behind this cold front, another high pressure system looks to build in leading to dry conditions for the remainder of the weekend.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

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

Tonight...VFR. Northwest winds 10-15 knots with gusts to around 20 knots, diminishing to 10 knots or less and becoming north to north- northeast. High confidence.

Wednesday...VFR. North-northeast winds 5-10 knots becoming east to southeast. High confidence.

Outlook...

Wednesday night through Sunday...VFR.

MARINE

A Small Craft Advisory remains in effect for Delaware Bay until 2 AM Wednesday. A Small Craft Advisory remains in effect for all the New Jersey and Delaware Atlantic coastal waters until 6 AM Wednesday. Northwest winds will increase with gusts up to 30 knots through much of tonight before diminishing quickly Wednesday morning. Seas 3-5 feet. The conditions may linger very near advisory criteria for a time Wednesday morning, otherwise the winds and seas will be subsiding.

Outlook...

Wednesday night and Thursday...No marine hazards anticipated.

Friday and Saturday...A period of Small Craft Advisory conditions possible mainly due to seas building to 4-6 feet within an easterly swell.

Sunday...No marine hazards anticipated.

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 NJZ012>027. Freeze Watch from Wednesday evening through Thursday morning for NJZ012>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 until 2 AM EDT Wednesday for ANZ430-431. Small Craft Advisory until 6 AM EDT Wednesday for ANZ450>455.