textproduct: Wakefield

WHAT HAS CHANGED

Increasing confidence for a major winter storm this weekend and very cold temperatures behind it. Recent model guidance has decreased the amount of snowfall and increased the amount of ice, but there remains uncertainty regarding the precipitation types and timing.

KEY MESSAGES

1) Chances for a major winter storm impacting the region remain high, but confidence is still low in regards to specific precipitation types. Users should continue to keep a very close eye on the forecast over the coming days.

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. Precipitation will most likely be rain and if any wintry mix, no accumulation is expected.

DISCUSSION

As of 330 PM EST Wednesday...

KEY MESSAGE 1...Chances for a major winter storm impacting the region remain high, but confidence is still low in regards to specific precipitation types. Users should continue to keep a very close eye on the forecast over the coming days.

What We Know So Far:

- Surface cold air: Very strong low-level CAA will push into the region Friday night/Saturday morning behind a strong Arctic cold front. 850-925 mb temperatures will drop to -15 to -5 degrees C as a very strong high pressure (~1045 mb) builds into the Midwest. With this, the temperatures at the surface will be very cold with temperatures in the teens to lower 20s across the area Saturday morning.

- Favorable upper pattern: The upper air pattern is favorable for an active storm pattern and a major winter storm, with a strong Alaskan ridge, an amplified southern stream over the S/SW CONUS, and troughing to our north. This will allow for Gulf moisture to interact with the cold Arctic air mass.

- Plentiful moisture: The 12z deterministic and ensembles continue to show a widespread 1.0-2.0" of QPF across the local area.

What We Are Still Unsure Of:

- Precipitation types: The 12z model runs continue to lift the "warm nose" of warmer temperatures aloft falling somewhere across the area behind the initial onset of snow. This will change the precip over from snow to a mixed precip. The 12z deterministic GFS shows freezing rain totals primarily in the SE VA/NE NC areas, while the deterministic Canadian and ECMWF bring freezing rain amounts across the majority of the forecast area, actually excluding the far SE coastal areas like VA Beach and Currituck Outer Banks. The exclusion is from the depiction that surface temperatures will reach above freezing from the warmer air mass wrapping around the coastal low that develops along the stalled front to our southwest that then moves offshore just to the south of the area resulting in plain rain. Where this line of warmer temperatures ...both in the mid levels or at the surface... is where there lies much uncertainty. With this said, some sleet or freezing rain is likely behind the onset of snow or the southern portions of the area. The precipitation type forecast will likely change (potentially dramatically) on future forecasts depending on the trends in the guidance.

- Timing: Confidence is continuing to increase in regards to timing, but there are still some differences amongst the models. Currently looks like precip will start around Saturday afternoon/evening mostly as snow for all, then transition to the wintry mix for some areas early Sunday morning, then exiting the area as snow again Monday morning/afternoon. Precip will likely conclude by Monday evening.

Snow Probs:

With this shift towards a wintry mix, the probs for higher amounts of snowfall have decreased for most of the area, with the highest amounts in the north. The GEFS guidance shows a 50-70% chance of >=6" for the area north of Richmond/Petersburg and 20-40% for the southern half of the area. The EPS shows a tighter gradient with a 50-60% chance for >=6" for just the northern counties to a 0% chance for the NE NC counties. Additionally, the LREF probs for ice accumulations for areas south of Richmond and away from the coast between 50-70% chance for 0.25" of ice and a 30-60% chance of 0.50".

In conclusion, confidence is increasing in a major winter storm for the area but the fine details will need to continue to be ironed out. With the onset of the event still far out, have held off on a Winter Storm Watch at this time in collaboration with the neighboring offices, but the midnight update will likely need to issue for the majority, if not all, of the area.

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.

After a brief warm up Thursday, the Arctic cold front will usher in a very cold air mass as a strong Canadian high pressure (~1045 mb) 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, low-mid teens inland and low-mid 20s along the coast Saturday night, lower teens W to mid 20s E Sunday night, and low-mid single digits Monday night are forecast. This doesn't factor in 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. Precipitation will most likely be rain and if any wintry mix, no accumulation is expected.

Although not as impactful as the winter system this weekend, it's still worth mentioning that a light period of winter weather is possible Friday afternoon as well. Model guidance no longer outputs any accumulating snowfall, but a few flurries are possible in the northern half of the area, This is once again a case of cold air chasing moisture, which like last Sunday, often doesn't lead to much accumulation.

AVIATION /00Z THURSDAY THROUGH MONDAY/

As of 548 PM EST Wednesday...

VFR conditions prevail for the 00z/22 TAF period. High pressure is situated just offshore this evening. A dry cold front will bring increased sky coverage overnight, but not expecting low CIGs due to overall lack of moisture. Winds have begun to lighten and are slowly starting to shift out of the SW. Winds become more westerly tomorrow afternoon behind the front. LLWS is also expected for most of the terminals starting late this evening into the overnight hours, with the exception of ECG.

Outlook: Low-end precip chances possible Friday. 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 330 PM EST Wednesday...

Key Messages:

- Small Craft Advisory issued for the northern coastal waters and northern/central Chesapeake Bay tonight into early Thursday.

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

- Potential for freezing spray late this weekend into early next week.

1034mb high pressure is centered over the Delmarva, resulting in erratic winds around 5 kt across the waters this morning. Waves and seas are generally around 1 foot. High pressure moves offshore later today, allowing winds to become SW and increase to 10-15 kt by mid afternoon. A period of SW winds 15-20 kt with gusts to 25 kt is expected overnight for the northern coastal waters. SCA flags remain in effect along the Atlantic coast north of Parramore Island this evening and tonight, mainly for seas building 3-5 ft (highest well offshore), but a few gusts >25 kt are possible. A brief period of SCA winds is also expected this evening into early Thu morning in the Ches Bay, and with Wind Probs increasing slightly to 60-80% have issued a SCA for the Ches Bay N of Windmill Pt.

SW winds decrease later Thursday morning/Thu afternoon, shifting to the west ahead of the next strong cold frontal passage. The front is forecast to cross the waters Thursday night with N winds 5-10 kt expected on Friday. Cold advection strengthens Friday night, as very strong/cold high pressure dives SE out of the upper Midwest. Strong SCA are forecast Friday night into Saturday, with a brief period of Gale force gusts possible (Gale Force gust probs ~40-60%, highest coastal waters and lower Ches Bay). Winds briefly diminish Saturday afternoon into Saturday evening, only to ramp back up again later Saturday night into Sunday, as low pressure is forecast to form along the stalled front/inverted trough along or just inland of the coastal Carolinas late Saturday night/Sunday morning. Resulting quickly compressing pressure gradient brings another period of strong N-NE winds in snow/wintry precip, again with predominately strong SCA with potential for a narrow period of gale force gusts Sun morning, mainly along the coastal front. Seas will build along with the winds, likely peaking in the 6-9 ft range on Sunday. Very cold air will be in place from late this weekend into early next week, will have to keep a close eye on the potential for freezing spray during this period.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until 7 AM EST Thursday for ANZ630-631- 650-652.