textproduct: Wakefield

WHAT HAS CHANGED

Winter Weather Advisories have been expanded a bit southwest to include Middlesex, King William, and King and Queen counties. Snow totals for south-central VA into interior NE NC have also increased to 0.5-1". Uncertainty continues to remain higher- than-normal given marginal temperature conditions which could limit accumulations.

KEY MESSAGES

1) Confidence is moderate-high in portions of the area seeing some wet snow today, with the most likely timing for snow from the afternoon through early evening. 1-2" is expected across the VA Northern Neck and MD Eastern Shore, where Winter Weather Advisories have been issued. 0.5- 1" is expected elsewhere, with lesser amounts for southside Hampton Roads and coastal NE NC. However, uncertainty remains due to marginal surface temperatures.

2) A strong push of Arctic air arrives for early next week, with below normal temperatures to continue through the first half of next week. Tuesday is expected to be the coldest day, with single digit wind chills possible Tuesday morning.

3) Another storm system may impact the area next weekend, but it is way too early for specifics at this time.

DISCUSSION

As of 545 AM EST Sunday...

KEY MESSAGE 1...Confidence is moderate-high in portions of the area seeing some wet snow today, with the most likely timing for snow from the afternoon through early evening. 1-2" is expected across the VA Northern Neck and MD Eastern Shore, where Winter Weather Advisories have been issued. 0.5- 1" is expected elsewhere, with lesser amounts for southside Hampton Roads and coastal NE NC. However, uncertainty remains due to marginal surface temperatures.

An upper trough to our west pushes E today. A fast moving shortwave at the base of the trough is forecast to strengthen as it takes on a slight negative tilt just before it crosses the area during the afternoon and evening. At the surface, low pressure develops off the Carolina coast this morning before deepening while tracking NE during the remainder of today. Light rain is encroaching on on the SW Piedmont early this morning, with dew points increasing a few degrees over past hour or so. This initial push of precip will likely focus from the I-95 corridor and points W, increasing in coverage through 7 AM or so. The precipitation will increase in intensity throughout the day (while also spreading east) as the trough axis approaches. Weak CAA also ensues from the NW. 925-850mb temps are progged to drop to -1 to -4C across the NW two-thirds of the area by the afternoon as precip intensity peaks. The key to whether precip can change over to snow will be the thermal profiles in the lowest 1000-1500 ft AGL. If it can drop to 32-33F for a few hours due to wet-bulb/column cooling effects, then a period of accumulating snow is likely (mainly on grassy/elevated surfaces). On the other hand, if it doesn't drop below 34-36F, precip would be predominantly rain with perhaps a brief period of snow at the tail end of the precip during the early evening. Additionally, snow will be more likely where precip rates are heavier.

Significant model inconsistencies remain as of this writing, which is particularly frustrating given this event is within 24 hrs. Most of these differences can be traced to resolving the aforementioned thermal profiles, with there now being good agreement on the synoptic details and QPF placement. There has been some trend among the 00z model runs, particularly among the higher-res guidance (HRRR/3km NAM/ARW/NSSL), of showing a notable burst of snow accum (1- 2") from central NC into S-Central VA this evening as the precip changes over to snow. The latest 00z EPS also depicts a similar scenario with a swath of 1-2" from central NC into SE VA and the Eastern Shore. While confidence is too low to go this high in the forecast, did up totals to 0.5-1" in these areas. Still think the best chance for 1-2" is from the Northern Neck onto the Eastern Shore, coinciding with the best overlap of dynamic cooling effects and mid-level frontogenesis. Winter Weather Advisories remain in effect for these areas, with a small expansion SW for areas that have >1" in the forecast (to maintain consistency with the previous forecaster's rationale). SE VA and NE NC still look to struggle to see much, if any, snow despite the higher QPF, mainly due to temps struggling to drop until precip departs this evening. However, we will be closely monitoring the evolution of the temperatures and precip through the day in case additional short-fused advisories may be needed.

Regardless of any headlines, would expect any accums to be mostly confined to grassy and elevated surfaces and not roadways. We could see accums on roadways if it snows hard enough for a couple of hours, though not that confident in this. A reasonable worse case scenario would be 2-3" for most of the area with 1-2" for SE VA and NE NC, mainly if precip intensity can overcome marginal sfc temps. Colder and drier air arrives from NW-SE this evening bringing a rapid end to the precip. Will also have to monitor for any freezing of residual wet/slushy surfaces tonight.

KEY MESSAGE 2...A strong push of Arctic air arrives for early next week behind a secondary dry cold front, with below averages temperatures to continue through the first half of next week.

Arctic air arrives Monday night behind a secondary cold front. Frigid temperatures are expected for at least the first half of next week, with the coldest air occurring Monday night, Tuesday, and into early Wednesday morning. EPS/GEFS continue to show 2m temperature anomalies 15F to nearly 20F degrees below average. Overnight lows in the upper teens to mid 20s are expected Sunday night, and primarily teens Monday/Tuesday night. Cold Weather Advisories are possible Mon night given forecast wind chills in the single digits across far northern portions of the FA (particularly the Eastern Shore). While day-time temps will be rather chilly each day Monday through Wednesday, Tuesday is forecast to be the coldest day with highs struggling to make it above freezing north of I-64.

Temperatures may attempt to moderate a bit by the middle and end of the week as the upper flow turns more zonal. However, daily highs still look to be slightly below normal. While it also looks mainly dry, a series of fronts toward the end of the week could bring sporadic/light precip.

KEY MESSAGE 3...Another storm system may impact the area next weekend, but it is way too early for specifics at this time.

Despite the slight moderating trend is expected late this week, Arctic air is expected to remain entrenched across north and northeast portions of the CONUS through late week into next weekend. The flow aloft largely remains zonal but strong (1045+mb) Arctic high pressure is progged to build into the north-central CONUS by next Saturday. A couple of fast moving shortwaves may track over the area next Sat and or Sun, which could bring chances for more widespread precip. There is some ensemble support (including from the Euro AIFS) for wintry wx across northern portions of our area, which seem reasonable given the strong supply of cold air to our N. Ultimately, exact precip types will be highly dependent on impossible-to-resolve (at this range) storm tracks. Will continue to monitor over the next several days.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

As of 545 AM EST Sunday...

Widespread rain is moving in this morning. CIGs have been slowly lowering, but remain VFR at this hour. Expect them to quickly drop to MVFR over the next few hours and then IFR after 14-16z. LIFR CIGs are also possible by this evening. Lowered VSBY (2-4 SM) is also likely in the rain. The rain likely changes to snow or a rain/snow mix at RIC and SBY during the afternoon, with light to occasionally moderate snow possible for a few hours mid-late afternoon. The most likely timing for snow at RIC and SBY is 18-01z. There could be a few hours of -SN with IFR VSBYs at PHF/ORF between 20-01z, with mainly rain at ECG (brief mix possible ~23z). Winds become N-NW around 5-10 knots today, though no significant wind is expected with the precip. Conditions improve later this evening and tonight as the precip moves offshore.

Outlook: Dry/VFR prevails Tuesday morning through Wednesday. A cold front potentially crosses the area Thursday with only a 20% chance of showers at this time.

MARINE

As of 635 AM EST Sunday...

Key Messages:

- Small Craft Advisories have been issued for the Chesapeake Bay and coastal waters later this afternoon into tonight due to the potential for 20 to 25 knot wind gusts.

- Another round of SCAs is possible Monday night into Tuesday as another cold front crosses the waters.

SCAs have been expanded to include the coastal waters and Currituck Sound late this afternoon into tonight. A brief window of gusts around 30 knots will be possible ~00z/7 PM this evening.

Previous Discussion: Early this morning, a stalled cold front is located just off the coast. Low pressure is expected to develop along this front later this morning, eventually lifting northeast of the local area by this evening. Winds are currently light and variable over the waters. Seas range from 2 to 3 feet and waves in the Chesapeake Bay are 1 foot or less. Winds increase and become N to NW today, generally ranging around 10 to 15 knots. Winds increase further this later this afternoon into early tonight as the pressure gradient briefly tightens due to the area of low pressure. Low-end SCA conditions are expected across the Chesapeake Bay, with latest wind probs now up to ~60-70% chances for 20+ knot gusts around 00z/7 PM this evening (especially across the northern bay). With the guidance showing the increasing SCA potential, opted to issue a SCA for the Chesapeake Bay from 21z/4 PM EST Sunday until 06z/1 AM EST Monday. There is less confidence across the coastal waters for SCA conditions, but local wind probs do show a 3-4 hour window from ~23 to 03z for 25+ knot gusts (especially out 20 nm). Winds diminish to 10 to 15 knots after Midnight, becoming W and eventually SW by Monday morning. SW winds increase Monday afternoon ahead of a strong cold front which is expected to cross the waters Monday evening into Monday night. In the wake of the front, winds become NW and average ~15 to 20 knots. Additional SCAs may be needed for at least portions of the Chesapeake Bay and the northern coastal waters Monday evening into Tuesday morning. Generally benign, sub-SCA, conditions take hold through the midweek timeframe before another system potentially approaches next weekend.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...Winter Weather Advisory from 10 AM this morning to 10 PM EST this evening for MDZ021>025. NC...None. VA...Winter Weather Advisory from 10 AM this morning to 7 PM EST this evening for VAZ064-075>078-085-517>522. MARINE...Small Craft Advisory from 4 PM this afternoon to 1 AM EST Monday for ANZ630>632-634-650-652-654. Small Craft Advisory from 4 PM this afternoon to 10 PM EST this evening for ANZ633-656-658.