textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Snowfall amounts were reduced slightly, mainly south and east of the I-95 corridor as confidence has increased in mixing occurring. Impacts are UNCHANGED as the combination of snow/sleet/freezing rain will result in major disruptions over the area.

The narrow corridor of highest ice accumulations has shifted southeast, now focused over South Jersey, central Delaware, and the Eastern Shore of Maryland.

KEY MESSAGES

1. Dangerous cold continues through this morning with wind chills below zero for most. Wind chills as low as -22 expected to continue in the Poconos.

2. A major winter storm is expected to impact the area, beginning tonight and continuing through Monday Morning. This storm will bring significant snow and ice accumulations to the entire area, resulting in major disruptions.

3. Arctic air remains in place through the upcoming week with temperatures below freezing into Friday.

DISCUSSION

KEY MESSAGE 1...Dangerous cold continues through this morning with wind chills below zero for most. Wind chills as low as -22 expected to continue in the Poconos.

In the wake of a strong arctic front, very cold temperatures have settled over the area. Winds were gusting upwards of 40-45 MPH earlier, but have dropped to around 25-35 MPH or so. Forecast is working out well with wind chills from 0 to -10 being observed across most of the area. The southern Poconos, where the Extreme Cold Warning is in place, have seen wind chills between -18 and -22 for most of the night. Wind chills should generally stay in this range as temperatures continue to fall but winds diminish. As a result, no changes are needed to the cold weather headlines. The Extreme Cold Warning for the Poconos and Cold Weather Advisory elsewhere remains in effect through 10 AM.

Ahead of the storm, it will be bitterly cold today, with highs only topping out in the upper teens/low 20s. The Poconos may not even make it out of the single digits.

KEY MESSAGE 2... A major winter storm is expected to impact the area, beginning tonight and continuing through Monday Morning. This storm will bring significant snow and ice accumulations to the entire area, resulting in major disruptions.

A significant winter storm that has resulted in continuous Winter Storm Warnings from Arizona to Maine finally gets to our area, beginning tonight. Snowfall begins after 1 AM from southwest to northeast as low pressure approaches from the southwest. As snow spreads into the region, a secondary area of low pressure begins to form near the Outer Banks, moving up the coast as Sunday goes on. The track of this secondary low looks to be inside the benchmark (40 N, 70 W), which usually results in a mixed precipitation storm for our area and a forecasting headache. That is the case here. However, confidence is increasing in this forecast.

The main changes from the daytime package were cutting snow totals south and east of I-95 as the trend has been a touch west with the track of the low, resulting in more of a sleet/freezing rain mix and even plain rain along the coast. Snow totals were slightly reduced for other areas as well, but not by much. VERY IMPORTANT to stress that while snowfall totals have been reduced slightly, the impacts remain the same. The combination of snow, sleet, and freezing rain will result in MAJOR impacts and that thinking has not changed for days now.

Snowfall envelops the whole region by daybreak Sunday. An area of strong mid-level frontogenesis will lift northward as the morning goes on, and all areas should see a very good thump of snow before a changeover to sleet or freezing rain. Snowfall rates over 1" per hour are likely (60-80%), mainly for New Jersey and Pennsylvania tomorrow morning into the early afternoon, with even a low chance (20%) for rates over 2" per hour. As the day progresses, a warm nose aloft moves in from the southeast. After looking at some model soundings, currently thinking the mix line gets right to about Reading and Allentown in PA and right up to I-78 in NJ. Snowfall amounts will be dependent on how fast or slow that warm air advection aloft is. Given how good the NAM is in these cases, the forecast generally relies on that temperature profile, but not as aggressive, with the thinking that the impressive rates before the changeover can hold back the warm nose aloft. It will be very interesting to see how this plays out tomorrow morning. Important to note that guidance generally underestimated the strength of the cold airmass this morning. Does it matter? That is the question that will be figured out via mesoanalysis as the event begins.

At onset, snow ratios will be around 15-18:1, decreasing to around 7- 10:1 by the early afternoon (and even lower where sleet begins) as warmer air aloft moves in. This will result in a fluffy snow texture. However, add in sleet and/or measurable ice on top of that? It could be very difficult to remove from roads, driveways, and sidewalks. This is mainly why we are stressing major impacts, regardless of snow totals. There is high confidence in at least 6" of snow, and sleet/ice on top of that will just exacerbate impacts (and most areas are highly probable to see more than 6").

In terms of specific amounts, the forecast has 12-16" with localized amounts up to 18" for the I-78 corridor on north. These areas should primarily stay snow. From New Castle County, DE out to LBI and points north up to the I-78 corridor, amounts of 8-12" are expected with a prolonged period of mixing occurring. South of that line, 4- 8" are expected and most locations in this zone likely even see some plain rain.

With a frigid cold airmass overhead and a strong push of warm air aloft, there is a growing threat for freezing rain and ice accumulation. The corridor of highest amounts has shifted southeast a bit, with the current forecast having a stripe of 0.25"-0.4" over the Eastern Shore, extending into central DE, and continuing into Cumberland/Salem/Gloucester/and part of Camden County in NJ. The I- 95 corridor, once the focus of the higher amounts, has trended down a bit, though still somewhat significant - around a tenth to two tenths of an inch of ice. The question is going to be what the depth of the warm nose is. If it is thinner, expect more sleet. If it is deeper, then more freezing rain and ice is likely. There is higher confidence in the highest amounts landing somewhere between the I-95 corridor and Garden State Parkway in central and southern NJ and then somewhere over central and northern Delmarva. These ice accumulations come AFTER anywhere from 4-8/8-12" of snow fall. This will only heighten the impacts, regardless of exactly how much falls.

Overall, no changes to the Winter Storm Warning, which is in place tonight through Monday morning. Snow tapers off by Midday Monday, transitioning to a prolonged stretch of very cold temperatures.

KEY MESSAGE 3...Arctic air remains in place through the upcoming week with temperatures below freezing into Friday.

Arctic high pressure will then be in control for the rest of next week, with Monday possibly being the mildest day, that term is used loosely, with highs in the upper 20s to low 30s. A strong cold front is forecast to cross through Monday night, and then lows will crash into the single digits. The strong winds developing over the area Monday night into Tuesday morning will create widespread wind chills will be as low as 10 below, with wind chills as low as 20 below in the southern Poconos. Cold Weather Advisories and Warnings will likely be needed. Highs will be in the teens and low 20s Tuesday, with highs not much warmer than that through Friday. Lows will be in the single digits.

As a result of this prolonged cold, do not expect the new snowpack to melt much.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

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

Today... VFR expected. Increasing high then mid clouds thru the day. North winds 15 kts with gusts 20 to 25 kts early then decreasing to around 10 kts late. High confid.

Tonight... VFR thru 06Z all sites then VSBY/CIG restrictions towards dawn as snow overspread all areas late. IFR/LIFR quickly realized as snow begins. Northeast to east winds around 5 knots. Medium/high confid.

Outlook...

Sunday/Sunday night... Widespread LIFR conditions with snow, sleet and freezing rain expected much of the time. Snow will predominate Sunday morning with ice/sleet mixing in from South/West to North/East thru the afternoon. Precip may change to all rain KACY during the evening Sunday. East to Northeast winds 10 to 15 kts. Low confid with regards to p-type/timing.

Monday... Lower conditions early then improvement back to VFR by afternoon.

Tue thru Wed... VFR much of the time.

MARINE

A Small Craft Advisory and Freezing Spray Advisory are in place through 1 PM today. Wind gusts out of the northwest around 25-30 kt expected through daybreak, diminishing as the morning goes on with 4 to 6 foot seas. Winds have been a bit slow to wane, so the SCA on Delaware Bay was extended until 9 AM, matching the expiration time of the Freezing Spray Advisory over the Bay.

A period of sub-SCA conditions comes for the afternoon and overnight hours with north/northeast winds around 10-20 kt and seas 2 to 4 feet. Snow moves over the marine zones as the night goes on, likely reducing visibility.

Outlook...

Sunday...A Gale Watch is in effect for all marine zones. Winds out of the east/northeast could get near 35 kt at times, especially over the ocean. Seas of 6 to 9 feet.

Sunday Night through Monday Night...SCA conditions expected with gales possible (40-50%). Seas 6 to 9 feet and winds 20-30 kt, out of the east/northeast on Sunday Night and northwest on Monday.

Tuesday...SCA conditions and freezing spray possible.

Wednesday...Sub-SCA conditions.

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 until 10 AM EST this morning for PAZ060>062-070-071-101>106. Winter Storm Warning from 7 PM this evening to 1 PM EST Monday for PAZ060-070-071-101>106. Winter Storm Warning from 1 AM Sunday to 1 PM EST Monday for PAZ054-055-061-062. Extreme Cold Warning until 10 AM EST this morning for PAZ054- 055. NJ...Cold Weather Advisory until 10 AM EST this morning for NJZ001- 007>010-012>027. Winter Storm Warning from 7 PM this evening to 1 PM EST Monday for NJZ008>010-012>021-026-027. Winter Storm Warning from 7 PM this evening to 7 AM EST Monday for NJZ022>025. Winter Storm Warning from 1 AM Sunday to 1 PM EST Monday for NJZ001-007. DE...Cold Weather Advisory until 10 AM EST this morning for DEZ001>004. Winter Storm Warning from 7 PM this evening to 1 PM EST Monday for DEZ001-002. Winter Storm Warning from 7 PM this evening to 7 AM EST Monday for DEZ003-004. MD...Cold Weather Advisory until 10 AM EST this morning for MDZ012- 015-019-020. Winter Storm Warning from 7 PM this evening to 1 PM EST Monday for MDZ012-015-019-020. MARINE...Small Craft Advisory until 9 AM EST this morning for ANZ430- 431. Freezing Spray Advisory until 9 AM EST this morning for ANZ430- 431. Gale Watch from Sunday morning through Sunday afternoon for ANZ430-431. Small Craft Advisory until 1 PM EST this afternoon for ANZ450>455. Freezing Spray Advisory until 1 PM EST this afternoon for ANZ450>455. Gale Watch from Sunday morning through Sunday evening for ANZ450-451. Gale Watch from Sunday morning through Sunday afternoon for ANZ452>455.