textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Cold Weather Advisories are now in effect for most of New Jersey, southeast Pennsylvania, Delaware and the eastern shore of Maryland through Monday morning.

The Extreme Cold Warning for Carbon and Monroe counties remains in effect until 10 AM Monday.

KEY MESSAGES

1. Dangerous wind chill values will continue through Monday morning.

2. Temperatures moderating to right around average for the middle of this week. A warm front may bring some light wintry precipitation to parts of the region later Tuesday.

DISCUSSION

KEY MESSAGE 1...Dangerous wind chill values will continue through Monday morning.

Northwest winds will continue to range from 15 to 20 mph with 25 to 35 mph gusts through late this afternoon. Winds will diminish fairly quickly this evening, and then will range from 5 to 10 mph tonight.

Due to how cold it will continue to be, winds remain elevated enough to result in dangerous wind chill values.

Broad Arctic high pressure centered over the Great Lakes and Ohio Valley slowly builds east today, then will be overhead tonight before moving offshore on Monday. Highs today will be in the single digits in the southern Poconos and the teens elsewhere. With the winds, wind chills today will mostly be in the single digits to as low as -10. Tonight, lows will be in the single digits throughout with wind chill values as low as -20 in the southern Poconos and as low as -10 to -15 elsewhere.

As a result, the Extreme Cold Warning for Carbon and Monroe counties remains in effect through Monday morning and Cold Weather Advisories are now in effect for the rest of the area through 10 am Monday.

Heights aloft begin to rise on Monday, and warm air advection will be underway. Highs will mostly be in the upper 20s to around 30.

KEY MESSAGE 2...Temperatures moderating to right around average for the middle of this week. A warm front may bring some light wintry precipitation to parts of the region later Tuesday.

As heights build aloft with a ridge slowly migrating east and arctic surface high pressure shifting off the coast, warm air advection will be underway and this will translate to temperatures moderating Tuesday and then to right around average on Wednesday. This will result in thawing taking place more each day through at least Wednesday. Low temperatures however will drop below freezing each night resulting in thaw and refreeze cycles, with lows Tuesday night looking like the milder night due to southwest winds ahead of a cold front.

The cold front will cross the region sometime later Wednesday as low pressure passes to our north. Given the track of the surface low to our north and this being more of a clipper system, the main forcing for ascent is just to our north and the moisture is limited. This results in lower chances for precipitation. The NBM has some slight chance PoPs (20 percent) across the far north by later Tuesday with an incoming warm front, otherwise the PoPs are trending downward. Some 00z guidance has trended a little stronger though with the isentropic lift with the warm front later Tuesday, which could produce some frozen or freezing precipitation especially across our northern areas. As of now, made no changes to the NBM guidance. It then turns colder for the second half of the week, but not to the magnitude of our current arctic outbreak. A storm may then arrive during the weekend with the potential for some rain and/or wintry precipitation.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

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

Today...VFR. NW winds 15 to 20 kt with 25 to 35 kt gusts, diminishing to 10 to 15 kt with 20 to 25 kt gusts after 21Z. High confidence.

Tonight...VFR. NW winds 10 to 15 kt with gusts up to 20 kt, diminishing to 5 to 10 kt after 03Z. High confidence.

Monday...VFR. NW winds 5 to 10 kt. High confidence.

Outlook...

Monday night and Tuesday...VFR ceilings lower.

Wednesday and Thursday...VFR overall. Northwest winds gusts to around 20 knots possible.

MARINE

Northwest winds of 15 to 25 kt with gusts up to 30 knots will continue through much of tonight, as a result, Small Craft Advisories and Freezing Spray Advisories are now in effect through this period. Even as winds diminish late tonight, seas look to remain elevated above 5 feet through the morning hours on Monday, resulting in the SCA continuing into daytime Monday.

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 over the next few days. Some areas though are forecast to get to around 40 degrees Wednesday afternoon. Significant rainfall, producing river rises, can also break up ice but that is not in the forecast this week.

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

Outlook...

Monday night through Wednesday...No marine headlines are anticipated.

Thursday...A period of near Small Craft Advisory conditions possible.

CLIMATE

Record Low Temperatures February 8 Site Record/Year Allentown (ABE) -5/1935 AC Airport (ACY) 3/1967 AC Marina (55N) -1/1895 Georgetown (GED) 3/1967 Mount Pocono (MPO) -15/1963 Philadelphia (PHL) -2/1934 Reading (RDG) -4/1934 Trenton (TTN) -8/1934 Wilmington (ILG) 0/1895

Record Coldest High Temperatures February 8 Site Record/Year Allentown (ABE) 16/1934 AC Airport (ACY) 20/1951 AC Marina (55N) 14/1895 Georgetown (GED) 27/2007 Mount Pocono (MPO) 10/1936 Philadelphia (PHL) 9/1895 Reading (RDG) 18/1951 Trenton (TTN) 12/1895 Wilmington (ILG) 12/1895

EQUIPMENT

The Fort Dix radar (KDIX) is out of service through Tuesday and perhaps longer depending on how quickly replacement parts arrive.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Cold Weather Advisory until 10 AM EST Monday for PAZ060>062- 070-071-101>106. Extreme Cold Warning until 10 AM EST Monday for PAZ054-055. NJ...Cold Weather Advisory until 10 AM EST Monday for NJZ001- 007>010-012>027. DE...Cold Weather Advisory until 10 AM EST Monday for DEZ001>004. MD...Cold Weather Advisory until 10 AM EST Monday for MDZ012-015- 019-020. MARINE...Small Craft Advisory until 10 AM EST Monday for ANZ430-431- 450>455. Freezing Spray Advisory until 6 AM EST Monday for ANZ430-431- 450>455.