textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes to the forecast, all previous headlines continue to remain in effect. The mid- week system for next week continues to trend weaker, with little to no impacts increasingly likely.

KEY MESSAGES

1. Dangerously cold and windy conditions will continue through Sunday morning as arctic high pressure builds into the region.

2. Temperatures moderating closer to normal during upcoming week, with a weak system possibly impacting the region mid- week.

DISCUSSION

KEY MESSAGE 1...Dangerously cold and windy conditions will continue through Sunday morning as arctic high pressure builds into the region.

Strong cold air advection continues behind the passage of the Arctic front. 925mb- 850mb temperatures drop to -21C to -25C by late this afternoon. As a result, the max temperature for today already occurred during the pre-dawn hours, generally in the mid and upper 20s.

Meanwhile, as arctic high pressure builds into the Great Lakes and Ohio Valley, low pressure over the western Atlantic will intensify and deepen. This results in a tight northwest pressure gradient over the Northeast and Mid-Atlantic. Winds increase to 20 to 35 mph with gusts up to 55 mph for most of the region and as high as 60 mph across Delmarva and the southern coast of New Jersey. The High Wind Warning and Wind Advisory remain in effect and will be in effect through midnight tonight.

The strong winds and very cold daytime temperatures will result in wind chills below zero during the daytime hours today, ranging from around -5 to -15 degrees for most areas, and as low as -25 in the southern Poconos.

Temperatures tonight will drop into the single digits by Sunday morning for most of the region and as low as -5 degrees in the southern Poconos and far northwest New Jersey. Wind chills will be as low as -30 degrees tonight in the southern Poconos and far northwest New Jersey. Minimum wind chills will range from -10 to -20 for the rest of the region tonight. The Extreme Cold Warning remains in effect for the entire region through noon Sunday. High temperatures Sunday will range from the mid 10s to low 20s, but northwest winds will be 10 to 20 mph with gusts up to 30 mph and this will result in maximum daytime wind chills in the single digits Sunday afternoon. Lows Sunday night will be in the single digits, and wind chills will be below zero; as low as -10 degrees north and west of the Fall Line and as low as -15 degrees in the southern Poconos. A Cold Weather Advisory will likely be needed through Monday morning following the ending of the Extreme Cold Warning.

A slow moderation of temperatures will occur as the new week progresses.

KEY MESSAGE 2...Temperatures moderating closer to normal during upcoming week, with a weak system possibly impacting the region mid- week.

High pressure will dominate early in the coming week, and with heights building aloft as a ridge slowly migrates east and the high shifting east off the coast, temps should see some substantial moderation, at least compared to current values. Highs will approach freezing in many areas on Monday, then likely pass freezing in many areas Tuesday, and possibly touch 40, especially in southern locales, on Wednesday. Lows will stay mostly in the teens Monday night and may not get much, if at all, below freezing Tuesday night thanks to the southwest flow ahead of an approaching cold front.

Said front will cross the region sometime Wednesday into Wednesday evening as low pressure passes north. Guidance has grown decidedly dry with this system, so while we can't rule out some precip with it yet, odds are starting to turn against it. Kept some slight chance POPs around. Temps turn cooler again behind said cold front, but not nearly to the magnitude of the current outbreak...highs Thursday, Friday and Saturday, while staying a bit below normal, appear likely to break the freezing mark in most areas. Lows will stay below, which will keep the melt down slow. POPS increase at week's end as guidance remains all over the place with any potential systems for next weekend.

AVIATION /20Z SATURDAY THROUGH THURSDAY/

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

Tonight...VFR. NW winds 20 to 30 kt with 40 to 50 kt gusts, diminishing to 15 to 20 kt with 25 to 30 kt gusts by 06Z. High confidence.

Sunday...VFR. NW winds 10 to 15 kt with 20 to 25 kt gusts. High confidence.

Sunday night...VFR. Northwest winds diminishing to around 10 knots. High confidence.

Outlook...

Monday through Thursday...VFR most likely prevails.

MARINE

Northwest winds of 25 to 35 kt with 40 to 50 kt gusts are expected across much of the coastal waters through late this evening. Storm Warnings are in effect for the ocean waters south of Manasquan Inlet and for Delaware Bay and Gale Warnings remain in effect for ANZ450, the zone from Sandy Hook NJ to Manasquan Inlet. Heavy Freezing Spray Warnings are also in effect through Sunday morning.

Gale Warnings will be needed late tonight after the Storm Warnings end with winds beginning to decrease, and then Small Craft Advisories will be needed Sunday-Sunday night as winds decrease further. Freezing Spray Advisories will also be needed in this period.

Regarding the river/bay ice...Ice continues across area bay waters and inland estuaries. This includes, but is not limited to the Delaware estuary. On rivers, the ice has grown in thickness enough to cause some restrictions in the flow. Per satellite imagery and ice analysis data, the Delaware River is mostly ice covered from the entrance to Delaware Bay northward, or upstream, to at least Washington Crossing.

The most common ways river ice can break up is either through a thermal or mechanical means. We would like to see temperatures rise into the 40s for a few days, but that's not expected within the next several days. Significant rainfall, producing river rises, can also break up ice. But again, that's not in the forecast either this coming week.

As a result, ice will continue to expand before it contracts, especially with another deep freeze expected this weekend. For next week, there may be a pause in the growth during the daylight hours as temperatures warm above freezing, however temperatures at night will continue to support expansion.

Outlook...

Monday through Tuesday...mainly sub-SCA conditions expected.

Wednesday through Thursday...Marginal SCA conditions more likely.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Extreme Cold Warning until noon EST Sunday for PAZ054-055- 060>062-070-071-101>106. Wind Advisory until midnight EST tonight for PAZ054-055- 060>062-070-071-101>106. NJ...Extreme Cold Warning until noon EST Sunday for NJZ001-007>010- 012>027. High Wind Warning until midnight EST tonight for NJZ016- 020>027. Wind Advisory until midnight EST tonight for NJZ001-007>010- 012>015-017>019. DE...Extreme Cold Warning until noon EST Sunday for DEZ001>004. High Wind Warning until midnight EST tonight for DEZ001>004. MD...Extreme Cold Warning until noon EST Sunday for MDZ012-015-019- 020. High Wind Warning until midnight EST tonight for MDZ012-015- 019-020. MARINE...Storm Warning until 4 AM EST Sunday for ANZ430-431-451>455. Heavy Freezing Spray Warning until 10 AM EST Sunday for ANZ430- 431-450>455. Gale Warning until 10 AM EST Sunday for ANZ450.