textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

An Extreme Cold Warning was issued for the southern Poconos as wind chills as low as -20 degrees F are expected. No other headline changes with the Cold Weather Advisory in place elsewhere. Confidence increasing in significant and dangerous cold for tonight.

For mariners, a Freezing Spray Advisory was issued for all marine zones Friday Night into Saturday. See the marine section below for more information.

Confidence continues to increase in significant impacts across the area from a major winter storm Saturday night through early Monday afternoon. Potential for mixed precipitation including sleet and potentially substantial ice accumulations is increasing. A Winter Storm Watch remains in effect for Saturday night through late Monday morning.

KEY MESSAGES

1. Dangerous cold expected tonight, with wind chills below zero for most. Wind chills as low as -20 degrees F expected in the southern Poconos.

2. A major winter storm will impact the area Saturday night through early Monday afternoon. Significant impacts from accumulating snow, sleet, and freezing rain are expected.

3. Arctic air will remain in place into late next week. Temperatures will likely remain below freezing across much of the area through Thursday.

DISCUSSION

KEY MESSAGE 1...Dangerous cold expected tonight, with wind chills below zero for most. Wind chills as low as -20 degrees F expected in the southern Poconos.

Following the passage of a cold front this afternoon, an arctic airmass comes in via strong cold air advection. 850 mb temperatures tonight drop to -15 C (mainly south) to -25 C (over the Poconos up north). This will result in temperatures taking a steep dive from the 30s and even low 40s down into the single digits or even below zero. In addition to the cold, it will be quite breezy in the wake of the front. A strong arctic high will be moving in with low pressure departing over the Canadian Maritimes. This will result in a tight pressure gradient setting up tonight, with wind gusts increasing once the front passes. Initially, gusts will be around 25-35 MPH, gradually diminishing through the night. Once air temperatures reach their low point, gusts will mainly be around 15-25 MPH.

The combination of single digit (or even below zero in the Poconos) temperatures and breezy winds will result in wind chills below zero, potentially getting as low as -10 F for most locations. The exception being the Poconos where temperatures near or below zero and gusty winds have an outcome of wind chills near -20. Given this and the fact that many may get up early to prepare for the incoming winter storm on Saturday morning, the Cold Weather Advisory was upgraded to an Extreme Cold Warning. Just 30 minutes of exposed skin could cause frostbite and/or hypothermia, so for anyone making last minute preparations for the storm tomorrow morning, bundle and layer up! Or, stay inside and stay warm.

No changes were made for the rest of the area, where the Cold Weather Advisory remains in place.

With such deep cold overhead, highs on Saturday will only get into the mid to upper teens and low 20s. Areas in the Poconos may struggle to get out of the single digits.

KEY MESSAGE 2...A major winter storm will impact the area Saturday night through early Monday afternoon. Significant impacts from accumulating snow, sleet, and freezing rain are expected.

A closed H5 low will gradually pivot northeastward across the southwestern US on Saturday, eventually phasing with the northern jet as it approaches our area beginning Saturday night and continuing through Sunday. This will place our entire region within the left exit region of the approaching large scale trough for a prolonged period. At the surface, low pressure will track out of the Mid-South Saturday into Saturday night, with additional surface cyclogenesis anticipated off the Eastern Seaboard.

As synoptic scale ascent overspreads the region, precipitation will begin overspreading the region from southwest to northeast overnight Saturday night. Very cold temperatures will be in place at the surface and throughout the vertical column. Therefore, precipitation is expected to begin as all snow. As the column moistens towards daybreak Sunday, snow will likely become moderate to heavy at times.

Strong warm air advection aloft will likely start to lead to the development of a warm nose during the day on Sunday near 750 mb, and snow may mix with or change to sleet and freezing rain. Of particular concern is a corridor roughly from the Eastern Shore of Maryland northeastward along the I-95 corridor. Sleet and freezing rain may reduce snow totals, but will create their own problems, with freezing rain in particular leading to the potential for damage to trees and powerlines. In addition to the mixed precipitation concerns for these areas, as the surface low develops off the Eastern Seaboard and tracks northeastward, marine influence is likely to be felt across portions of the Coastal Plain. This may lead to precipitation mixing with or changing to plain rain for this area. This is not expected to occur until during the day on Sunday, so substantial snow accumulations are still anticipated for these areas prior to any potential changeover.

The areal extent of potential mixing remains in question, and tied in large part to the exact track of the coastal low. With that said, guidance continues to support the idea of a low track close enough to the coast to lead to at least some mixing for a large portion of the area, potentially as far north as the I-78 corridor. North of I- 78, the anticipation is still for an all snow event. Sunday night through early Monday morning, as the low begins to pull away and cold air from the northwest begins to filter back in, precipitation should change back to all snow for most of the area with additional accumulations likely. Breezy northeast winds on Sunday and northwest winds on Monday could lead to some minor blowing and drifting of snow, especially where mixing does not occur and where snow-to- liquid ratios are highest.

All-told, snow amounts around 12-15" appear likely across all of eastern PA and northern NJ. Higher amounts (potentially exceeding 18") are expected across the Poconos and into adjacent areas of far northwestern NJ. For the lower Delmarva into much of southeastern NJ, 6-12" of snow are expected, with mixing limiting totals more in those areas. Right now, ice accretion of generally 0.10-0.25" is expected along the I-95 corridor. Amounts exceeding 0.25" are possible for portions of the Eastern Shore of Maryland. Further refinements will likely be needed in future updates as the event draws closer.

A Winter Storm Watch remains in effect for the entire area Saturday night through early Monday afternoon.

KEY MESSAGE 3...Arctic air will remain in place into late next week. Temperatures will likely remain below freezing across much of the area through Thursday.

After the departure of the expected winter storm, high pressure will build in from the west. Arctic air will remain in place across the area through Thursday. Temperatures will likely remain below freezing across the entire region through Thursday, with most locations struggling to make it out of the low 20s. In addition, the breezy conditions Monday and Tuesday will lead to dangerously cold wind chills. Monday and Tuesday night, wind chills are likely to be below zero areawide, and below -10 across much of eastern PA and portions of NJ. There won't be much in the way of relief during the day, with wind chills remaining in the single digits. Wednesday and Thursday look to feature similar temperatures, though wind chills should improve some as winds will likely subside.

This period of prolonged cold will be dangerous to those that are outside without proper clothing for prolonged periods of time. Cold weather headlines will likely be needed for parts of next week.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

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

Today...VFR. Winds increase between 14z-16z out of the west/northwest with 15-20 kt sustained winds and gusts 25-30 kt or so. Between 22-00z, winds go more northwesterly, with gusts up to 30 kt possible.

Tonight...VFR. Northwest winds 15-20 kt, gusting up to 30 kt for the first half of the night. Winds diminish gradually around 08z, settling to around 10 kt by daybreak Saturday.

Saturday...VFR. No significant weather.

Outlook...

Saturday night...VFR early, with sub-VFR conditions developing late in periods of snow.

Sunday through Monday...Sub-VFR conditions expected in periods of snow. Sleet and freezing rain may also occur, particularly during the day Sunday. Conditions will gradually improve Monday afternoon.

Monday night through Tuesday...VFR.

MARINE

No marine headlines in for most of the morning as seas will be around 2 to 4 feet with winds out of the west/northwest around 10-15 kt.

A Small Craft Advisory goes into effect for waters north of Little Egg Inlet at 11 AM, with the rest of the marine zones getting added to the SCA at 4 PM. The SCA goes through the night and into tomorrow morning (for the ocean) as wind gusts around 30 kt out of the west/northwest are expected with seas 3 to 6 feet.

With very cold air moving overhead along with gusty winds and choppy seas, there is an increasing threat for freezing spray Friday Night into Saturday morning. A Freezing Spray Advisory was issued for all marine zones through that time period.

Winds and seas will diminish by Saturday afternoon, with the threat for SCA conditions and freezing spray ending around that time. Winds out of the north/northwest around 10-20 kt and seas 2 to 4 feet for tomorrow afternoon and evening.

Outlook...

Saturday night...SCA conditions likely developing late with northeast wind increasing to 15-20 kt with gusts to 25 kt. Seas 3-5 feet. Visibility restrictions possible late in rain/snow.

Sunday though Monday night...SCA conditions expected with periods of gales likely. Northeast wind 25-30 kt with gusts around 35 kt and seas 5-9 feet Sunday and Sunday night. Winds shift to northwesterly Monday night. Visibility restrictions expected in periods of heavy precipitation.

Tuesday...SCA conditions likely with west wind 20-25 kt and seas 4-8 feet early. Gradual improvement likely through the day.

CLIMATE

An impactful winter storm bringing significant snow accumulations to the area is expected on Sunday. Here are the 1-day daily record totals for January 25th from our snow observing sites. Some of these could be challenged.

January 25th Daily Snowfall Records

Allentown (ABE) 10.4" (1988) AC Airport (ACY) 8.3" (2000) Philadelphia (PHL) 8.5" (2000) Reading (RDG) 9.0" (1905) Trenton (TTN) 14.0" (1905) Wilmington (ILG) 10.0" (2000)

PHI WATCHES/WARNINGS/ADVISORIES

PA...Cold Weather Advisory from midnight tonight to 10 AM EST Saturday for PAZ070-071. Winter Storm Watch from Saturday evening through Monday afternoon for PAZ070-071-101-102-104. Cold Weather Advisory from 10 PM this evening to 10 AM EST Saturday for PAZ060>062-101>106. Winter Storm Watch from late Saturday night through Monday afternoon for PAZ054-055-060>062-103-105-106. Extreme Cold Warning from 7 PM this evening to 10 AM EST Saturday for PAZ054-055. NJ...Cold Weather Advisory from midnight tonight to 10 AM EST Saturday for NJZ012>014-016>027. Winter Storm Watch from Saturday evening through Monday afternoon for NJZ016>019-021>025-027. Cold Weather Advisory from 10 PM this evening to 10 AM EST Saturday for NJZ001-007>010-015. Winter Storm Watch from late Saturday night through Monday afternoon for NJZ001-007>010-012>015-020-026. DE...Cold Weather Advisory from midnight tonight to 10 AM EST Saturday for DEZ001>004. Winter Storm Watch from Saturday evening through Monday afternoon for DEZ001>004. MD...Cold Weather Advisory from midnight tonight to 10 AM EST Saturday for MDZ012-015-019-020. Winter Storm Watch from Saturday evening through Monday afternoon for MDZ012-015-019-020. MARINE...Small Craft Advisory from 4 PM this afternoon to 6 AM EST Saturday for ANZ430-431. Freezing Spray Advisory from 9 PM this evening to 9 AM EST Saturday for ANZ430-431. Small Craft Advisory from 10 AM this morning to 1 PM EST Saturday for ANZ450-451. Freezing Spray Advisory from 7 PM this evening to 1 PM EST Saturday for ANZ450-451. Small Craft Advisory from 4 PM this afternoon to 1 PM EST Saturday for ANZ452>455. Freezing Spray Advisory from 10 PM this evening to 1 PM EST Saturday for ANZ452>455.