textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

1. An Arctic front will pass through the region this morning, possibly with isolated heavier snow showers or snow squalls.

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

3. Temperatures moderating close to normal during next week, however some wintry precipitation possible around midweek.

DISCUSSION

KEY MESSAGE 1...An Arctic front will pass through the region this morning, possibly with isolated heavier snow showers or snow squalls.

The Arctic front is currently through the Great Lakes and Ohio Valley and will track through western New York and western Pennsylvania early this morning before moving offshore by late morning. This will be accompanied with a deep H5 trough and strong shortwave energy.

Light snow ahead of this front will wind down, but then with the passage of the front and the shortwave, a round of snow showers and possible brief snow squalls will develop around daybreak. Though additional snow accumulation will be minimal with any snow showers, there may be visibility restrictions to under one mile along with brief gusts of 30 to 40 mph.

KEY MESSAGE 2...Dangerously cold and windy conditions develop this morning and will continue through Sunday morning as arctic high pressure builds into the region.

Strong cold air advection develops behind the passage of the Arctic front, and temperatures will be crashing throughout the day. 925mb- 850mb temperatures drop to -21C to -25C by late this afternoon. As a result, the max temperature for today will occur in the pre-dawn hours, generally in the mid and upper 20s. Temperatures crash into the single digits and teens late this morning.

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 beginning this morning 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 3...Temperatures moderating close to normal during next week, however some wintry precipitation possible around midweek.

A weak ridge aloft will begin building in over the area during a portion of next week. This will dislodge the arctic air and allow for some milder air to advect in. Temperatures from Tuesday onward look to be much closer to normal, with highs mainly in the 30s (even low 40s in Delmarva).

For the mid-week time frame, an upper-level trough develops to our west. At the surface, a low looks to develop near the Great Lakes region and then track eastward. The passage of this low looks to bring an opportunity for some wintry precipitation to at least parts of our region late Tuesday night and Wednesday. If the overrunning precipitation moves in quick enough, then enough cold air may linger near the surface to result in a wintry mix. Details remain uncertain this far out, but overall the system may have a limited amount of moisture with it. If there is more moisture and mixed precipitation, then impacts may change. However with the passage of the main dynamics currently sliding by to our north, this tends to reduce the precipitation chances across much of our area. The main thing is that our region exits out of the deep freeze during the course of next week.

AVIATION /07Z SATURDAY THROUGH WEDNESDAY/

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

Through early this morning...Generally VFR, though brief MVFR conds in -SN through 08Z or so. W-SW winds 5 to 10 kt turn NW 10 to 15 kt with 20 to 25 kt gusts by 09Z, then to 15 to 20 kt with gusts up to 30 kt prior to 12Z. Moderate confidence overall.

Today...VFR. NW winds 20 to 30 kt with 40 to 50 kt gusts. The strongest winds will occur at KMIV/KACY. High confidence.

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.

Outlook...

Sunday night...VFR. Northwest winds diminishing.

Monday...VFR.

Tuesday and Wednesday...A period of sub-VFR conditions and wintry precipitation possible later Tuesday night and Wednesday.

MARINE

An Arctic front passes across the waters later this morning, and winds will quickly turn northwest and ramp up to 25 to 35 kt with 40 to 50 kt gusts. 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 tonight after the Storm Warnings end, and then Small Craft Advisories will be needed on Sunday. Freezing Spray Advisories will also be needed on Sunday.

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...

Sunday night and Monday...SCA conditions subside, especially on Monday. Light to moderate freezing spray diminishes by later Sunday night into Monday.

Tuesday and Wednesday...No marine headlines are anticipated.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Extreme Cold Warning from 6 AM this morning to noon EST Sunday for PAZ060>062-070-071-101>106. Wind Advisory until midnight EST tonight for PAZ054-055- 060>062-070-071-101>106. Extreme Cold Warning until noon EST Sunday for PAZ054-055. NJ...High Wind Warning until midnight EST tonight for NJZ016- 020>027. Extreme Cold Warning from 6 AM this morning to noon EST Sunday for NJZ001-007>010-012>027. Wind Advisory until midnight EST tonight for NJZ001-007>010- 012>015-017>019. DE...High Wind Warning until midnight EST tonight for DEZ001>004. Extreme Cold Warning from 6 AM this morning to noon EST Sunday for DEZ001>004. MD...High Wind Warning until midnight EST tonight for MDZ012-015- 019-020. Extreme Cold Warning from 6 AM this morning to noon EST Sunday 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.