textproduct: Wakefield

WHAT HAS CHANGED

Increasing confidence for a major winter storm and very cold temps this weekend, though uncertainties remain regarding coverage, timing, and precip type. Chances for a light wintry mix on Friday have also increased slightly.

KEY MESSAGES

1) Chances for a major winter storm continue to increase this weekend. Exact details remain unclear at this time, but users should keep a close eye on the forecast this week.

2) A prolonged period of very cold temperatures is increasingly likely from Saturday into at least the middle of next week with the potential for temperatures to remain below freezing for several days.

3) A light wintry mix is possible on Friday, however, confidence is low.

DISCUSSION

As of 235 PM EST Tuesday...

KEY MESSAGE 1...Chances for a major winter storm continue to increase this weekend. Exact details remain unclear at this time, but users should keep a close eye on the forecast this week.

There remains a very impressive medium range signal for a major winter storm from the latest deterministic/ensemble guidance. Models have remained fairly consistent with this system and continue to show the primary threat between late Sat afternoon and Sunday night. However, with these WAA setups, it's not uncommon for precip to begin several hours ahead of schedule. However, uncertainties still remain in regards to exact precipitation evolution. Details below:

There will be a very strong push of low-level CAA Saturday, with 850- 925mb temperatures dropping to -5 to -15C across much of the area as 1048+mb Arctic high pressure builds into the midwest. This will translate to temperatures dropping into the teens for much of the area Friday night/Saturday AM. Temperatures will then remain in the low-mid 20s on Saturday outside of far SE VA/NE NC where lower 30s are possible. In fact, the latest NBM guidance has highs on Saturday only around 19F in Louisa! Temperatures drop into the teens for most Saturday night while moderate to heavy precipitation falls. Temperatures remain very cold on Sunday with highs in the lower 20s NW to lower 30s SE (except upper 30s to around 40F possible across extreme SE VA/NE NC. As such, confidence in the cold air ingredient to winter weather is high.

Regarding moisture, the upper pattern appears quite favorable for an active storm track and a major winter storm, with a strong Alaskan ridge, an active/amplified southern stream over the S/SW CONUS, and troughing to our N. This allows for a very favorable synoptic setup for heavy precipitation amidst the generally zonal flow as moisture from the Gulf is open to interacting with the arctic air from the very strong high to the north. For us locally, there still remains several uncertainties with respect to timing and specific precip types (especially S/SE), though the deterministic and ensemble guidance remains consistent in showing a major winter weather event for our area. Both deterministic models and ensemble guidance continue to show moderate-high likelihood for 1.0-1.5+" of liquid equivalent precip with this event. The main question still remains who will see all snow and who will see a wintry mix of snow turning into either sleet or freezing rain (or both). These important details will have to be ironed out as we get closer to the event. However, recent trends this afternoon were for mixed precipitation to push into at least portions of SE VA/NE NC late Saturday night into Sunday as the coastal low develops offshore and a weak ridge aloft amplifies. However, with the strong high/impressive Arctic airmass building in, think p-type would be freezing or frozen everywhere except for maybe southside Hampton Roads and NE NC (and it could very well be mostly snow here as well depending on storm track). Given the very cold temperatures well below freezing, any freezing rain that occurs is of particular concern since with temps below 28F freezing rain is far more efficient at creating black ice on roads (as well as accretion trees and power lines).

Snow probabilities off the 12z suite of models continue to be impressive. The EPS had 50-60% probs for at least 12" of snow whereas the EPS AI had 60-70% probs. These both had 80-90% probs for 6"+ of snow but in different locations (the EPS had the swath across the northern half of the FA whereas the EPS AI had it a bit farther south, centered over the local area. There are even some low probs for higher amounts (18") mainly on the EPS AI. The GEFS had the lowest probs for 12" (20-40%) with the Canadian ensemble showing a 50-60% chance across mainly northern portions of the FA. These chances are likely to waver back and forth some over the next few days as the finer details become clearer. Will also note that recent trends have been for warm air aloft to push farther inland with the potential for a swath (potentially a large swath) of sleet moving into at least SE VA/NE NC with freezing rain also possible. The Canadian has been the most aggressive with the sleet, however, given the ridge over the area, sleet could very well impact snowfall accumulation for a portion of the area. In summary, there is continued, increasing confidence in a major winter storm for the entire area. Exact details regarding precip timing, coverage, and type remain uncertain and should be resolved over the next few days. Stay tuned!

KEY MESSAGE 2...A prolonged period of very cold temperatures is increasingly likely from Saturday into at least the middle of next week with the potential for temperatures to remain below freezing for several days.

A cold area of high pressure (1035mb) centers over the area tonight. This will allow for efficient radiational cooling given dew points in the single digits (below zero dew points possible across the Piedmont), calm winds, and clear skies. As such, have undercut temps with lows in the low-mid teens now expected inland with lower 20s along the coast. Will note that a few locations may even drop into the upper single digits tonight with the best chance for that in Louisa.

A brief warmup is expected through late week before the arctic cold front pushes through Friday. A very strong Canadian high (~1048mb) builds down from the northern Plains into the Midwest Friday into Saturday. Additionally, behind the weekend system, a large trough builds into the region through next week. This combination (along with any snowpack) will allow for very cold temperatures to continue from Saturday through at least the middle of next week. Highs may remain below freezing for an extended period of time from Friday night through Tuesday night (maybe even longer) with extended model guidance showing highs in the 30s through late next week. Meanwhile, lows in the low-mid teens inland (lower 20s along the coast) Friday night, mid teens inland and low-mid 20s along the coast Saturday night, upper single digits west W to mid 20s E Sunday night, and low- mid single digits Monday night are forecast. However, if some of the higher snowfall totals currently modeled are realized, overnight lows in the single digits to potentially below 0F will be possible (potentially for a few nights). That doesn't even factor in the wind chill which could be below zero. This prolonged period of very cold temperatures behind the winter storm could be quite dangerous for those without power.

KEY MESSAGE 3...A light wintry mix is possible on Friday, however, confidence is low.

While all eyes are on the weekend system (and rightfully so), it's worth mentioning that a light period of winter weather is possible on Friday as well. For now, most model guidance is fairly dry on Friday apart from light rain showers ahead of the cold front. However, a few ensemble members and the NAM 12km show the potential for a bit of wintry weather behind the front on Friday. The NAM is the most aggressive and shows the potential for a few inches of snow across a portion of the area along with a bit of freezing rain across NE NC. However, given that this is cold air chasing moisture, confidence remains low in any winter weather on Friday. Nevertheless, will maintain a chance for snow NW of Richmond Friday afternoon, spreading SE into Friday evening. However, given that most model guidance doesn't have snowfall accumulation, currently don't have more than 0.1-0.2" of snowfall in the forecast across the NW half of the area.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

As of 623 PM EST Tuesday...

VFR conditions will prevail through tomorrow evening, with generally clear skies and light winds expected. Some LLWS will likely develop tomorrow night, but currently remains just outside of our TAF period.

Outlook: Mostly dry/VFR through Thursday. A cold front potentially crosses the area Thursday. Low-end precip chances continue into Friday with winter weather possible at the terminals. Winter weather is likely at all terminals this weekend, but it is too early for specifics, though an extended period of degraded flight conditions is becoming increasingly likely.

MARINE

As of 235 PM EST Tuesday...

Key Messages:

- Sub-SCA conditions continue through mid week.

- Increasing potential for a stronger system to impact the waters this weekend with elevated winds and seas.

Strong ~1035 mb high pressure is centered over the Deep South to our SW this afternoon. Light NW winds around 5-10 kt are observed with 12 ft waves and 2-4 ft seas currently. Benign NW winds will continue through tonight before shifting out of the S/SW Wednesday as the high pressure glides offshore and low pressure over the Great Lakes approaches the region. With this low pressure, a weak front will move across the area late Wednesday into early Thursday which may bring marginal SCA conditions to the northern coastal waters and middle bay as SW winds increase to ~15 kt with gusts up to 20 kt in the Ches. Bay and 15-20 kt with gusts up to 25 kt in the northern coastal waters (10-15 kt with gusts to 20 kt in the southern coastal waters). Local probs show a 40-50% chance of gusts to 25 kt off the MD coast and a 10-20% for the middle bay. SCAs may be needed for a brief period, but have held off at this time. Otherwise, winds will remain benign and shift out of the N during the day Friday. Waves and seas will remain below SCA conditions as well, with ~1 ft waves and 2-3 ft seas.

Late week into the weekend will have a stronger system impacting the area as a very strong high pressure (1050+ mb) dives southeast from the Canadian Prairies, which will usher in an extended period of N/NE winds. Low pressure will form along a stalled front to the southeast, moving across areas to the south and offshore the local waters. With the two systems, strong SCA or gale conditions are possible beginning late Friday night/early Saturday morning and lasting through as late as Monday night. Local probs for 34 kt gusts peak early Saturday across the local waters around 10-40%. Waves and seas will rapidly increase as well, peaking on Sunday night/Monday morning with 4-6 ft waves and 7-10 ft seas. The very cold air with this system could additionally cause some concern for freezing spray this weekend into the first half of next week.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...None. NC...None. VA...None. MARINE...None.