textproduct: Wakefield

WHAT HAS CHANGED

Precipitation (and snowfall) amounts have continued to increase for Sunday. Winter Weather Advisories have been issued for the VA Northern Neck and MD Eastern Shore for up to 2" of wet snow. However, uncertainty remains given marginal temperature conditions which could limit accumulations.

KEY MESSAGES

1) Confidence in a period of accumulating snow is increasing on Sunday, with the most likely timing for snow from 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 along the I-64 Corridor, with lesser amounts farther south. However, there is a lot of uncertainty in the forecast and advisories may need to be expanded to the Richmond Metro if snow amounts continue to trend upward.

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 230 PM EST Saturday...

KEY MESSAGE 1...Confidence in a period of accumulating snow is increasing on Sunday, with the most likely timing for snow from 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 along the I-64 Corridor, with lesser amounts farther south. However, there is a lot of uncertainty in the forecast and advisories may need to be expanded to the Richmond Metro if snow amounts continue to trend upward.

An upper trough to our west pushes E tonight into Sunday. 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 Sunday AM before deepening while tracking NE during the remainder of the day into the evening. Rain moves into the area from the SW well in advance of the shortwave between 3-7 AM Sunday AM. This could possibly be mixed with snow in the Piedmont, but not expecting any accums through sunrise. The precipitation will increase in intensity throughout the day with weak CAA 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.

There is still a lot of disagreement in the guidance given that it is only a day out, with the 12z models generally falling into two camps. The NAMNest/NSSL/GFS show temps dropping to 32F, resulting in a swath of 1-3" of snow across central/eastern VA and part of the eastern shore. The deterministic ECMWF/HRRR/RRFS are a couple degrees warmer and show less than 1" of accum area wide with little to no snow in srn VA/NE NC. With the sharpening shortwave as depicted by synoptic model fields and decently strong lift for a few hours during the afternoon thanks in part to a zone of mid-level frontogenesis, have enough confidence in 1-2" across northeast portions of the area to issue a Winter Weather Advisory. Surface temps may be a degree or two cooler here than in areas farther south. Also, more QPF (higher precip rates) are expected closer to the coast). However, if things continue to trend upward and it looks like the RIC Metro will see 1-2" of snow, the advisory may need to be expanded southward. Some of the models (particularly the NAM/NAMNest/GFS), show 1-2" accums to the RIC Metro so trends will need to be monitored closely.

Regardless of any headlines, would expect any accums to be mostly confined to grassy and elevated surfaces and not roadways. Though we could see accums on roadways if it snows hard enough for a couple of hours (though not that confident in this). For now, the current official forecast is for near 2" of snow over the MD Eastern Shore, 1-2" over the northern neck, up to 1" for the Piedmont, central VA, and SE VA, and no accumulation expected for those near the Albemarle Sound. A reasonable worst case scenario would be 2-3" for the MD Eastern Shore, and ~2" back through most of central/eastern VA. Colder and drier air arrives from NW-SE later Sunday evening bringing a rapid end to the precip. Will also have to monitor for any freezing of residual wet/slushy surfaces overnight Sunday.

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. 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. Low-end precip chances also return by Thursday.

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 rain and/or a wintry mix. Will continue to monitor over the next several days.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

As of 650 PM EST Saturday...

VFR as of 00z with increasing clouds with bases ~4-6kft. Primarily VFR through the early overnight hours, before cigs fall to MVFR late tonight into Sunday morning (08-14z). Rain arrives later tonight with vsby varying between 2-5SM during the day Sunday. The rain likely changes to snow at RIC/SBY during the aftn, with light to occasionally moderate snow (1/2-2SM VSBYs) possible for a few hrs mid to late aftn. The most likely timing for snow at RIC/SBY is 18-00z. There could be a few hours of -SN with IFR VSBYs at PHF/ORF between 20-00z, with mainly rain at ECG. CIGs drop to IFR/LIFR by 11-14z Sunday. A W/SW wind diminishes this evening. The wind becomes N-NW at 5-10 kt on Sunday (no significant wind is expected with the precip).

Improving conditions are expected Sunday night into Monday morning with VFR conditions prevailing through Wednesday. A cold front potentially crosses the area Thursday with only a 20% chc of showers at this time.

MARINE

As of 230 PM EST Saturday...

Key Message:

- Benign, sub-SCA conditions are expected this afternoon through the daylight hours of Sunday, with another round of SCAs possible Monday into Tuesday.

Afternoon weather analysis shows a weak low pressure tracking just north of the Great Lakes and a high pressure off the East Coast. The pressure gradient from these two system have weakened causing the winds to lower. Winds continue out of the WSW around 10-15 kt. Seas remain low as latest buoys are showing 1-2 ft across the bay and 3- 4ft across the ocean. Through tonight and into tomorrow a series of weak cold fronts will move through the area. Winds however will be light tonight behind the front with winds shifting from the WSW to N. Winds tonight will remain around 5 kt and seas around 1 ft across the bay and 2 to 3 ft across the ocean. By sunrise Sunday, a low pressure is expected to develop along the stalled out cold front off the East Coast. As the low develops it will tighten the pressure gradient across the waters and winds will increase out of the north. There continues to remain some uncertainty with the strength of the low pressure. Winds by late Sunday afternoon are expected to be between 10 to 15 kt with some gusts nearing 20 kt. Local wind probs for gusts >= to 18kt are now between 60 to 70% across the bay. However, due to the disagreement in the models on the strengthen of the low no SCA have been issued at this time. Better chance for SCA come Late Monday into Tuesday as an arctic high pressure is moving into place ushering colder and drier air over the area.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...Winter Weather Advisory from 10 AM to 10 PM EST Sunday for MDZ021>025. NC...None. VA...Winter Weather Advisory from 10 AM to 7 PM EST Sunday for VAZ064-075>078-521-522. MARINE...None.