Impactful Snow/Sleet/Ice Possible Northwest of I-95
POSTED ON: Wednesday, December 16, 2020 8:51 AM by METEOROLOGIST A.R. DAVIES
Overview: A coastal storm will intensify along the Carolina coast today and will move through the Mid-Atlantic region. High pressure to our north will help to reinforce cold air at the surface. The storm track will likely be further west than the model guidance was indicating 48 hours ago. This track is favorable for mostly rain south and east of I-95, a mix of snow, sleet, freezing rain, and rain along and just north of I-95, and mostly snow with some sleet and/or freezing rain well north and west of the metros. The map (above) shows the most probabilistic outcome based on data overnight and early this morning. There is a threat for impactful sleet and/or freezing rain accumulations > 0.1 inches within the dashed orange lines, which would cut-back on the forecasted snow/sleet totals in those regions. The percent chance of greater than/less than scenarios are also listed and these values reflect the uncertainty in the forecast. The light blue and blue shaded regions along and just northwest of I-95 are the biggest “wild cards” as precipitation types will likely be variable and unpredictable.
Storm Forecast for Annapolis: The precipitation will likely arrive in Annapolis between 1100 and 1400 on Wednesday as light snow/mix with little accumulation anticipated. This will likely transition to cold rain by mid- to late-afternoon and continue through the evening. The rain could be steady/heavy at times with 1.0 to 1.5 inches of rain possible. The National Weather Service has issued a Flood Watch through early Thursday morning for Anne Arundel County. Temperatures will likely hover in the mid- to upper-30s throughout the afternoon and evening. Once the storm is latitudinally past Annapolis (around midnight), the winds will shift out of the north and a transition back to sleet or snow is possible between 0200 and 0600. Surface temperatures early Thursday morning will likely drop below freezing. The current forecast for Annapolis is for a trace to an inch of slushy accumulation (generally on grassy/elevated surfaces, sidewalks, if any). Some icy patches are possible Thursday morning regardless of whether the rain transitions to a snow/sleet mix because the ground will likely be wet from the rainfall and could freeze overnight. In terms of forecast uncertainty, there is a 35% chance of no wintry accumulation in Annapolis and a 20% chance the storm is colder than anticipated with 2.0 to 4.0 inches of snow/sleet. Sustained winds out of the northeast 18-23 mph with gusts as high as 45 mph are possible Wednesday night into Thursday morning.
Storm Forecast for the Region: Along and just north of I-95 (light blue shaded region on the map) can expect 2.0 to 4.0 inches of snow/sleet mix with up to 0.1 inches of freezing rain possible. This region has the highest degree of uncertainty with a 25% chance of < 2.0 inches of snow/sleet if more freezing rain/rain mixes, and 25% chance of > 4.0 inches of snow/sleet accumulation. In the blue shaded region north and west of the immediate suburbs, 4.0 to 8.0 inches of snow/sleet mix is possible with up to 0.15 inches of freezing rain. There is a 25% chance of < 4.0 inches if more freezing rain/rain mixes and 15% chance of > 8.0 inches if snow dominates. In the dark blue shaded region across northern MD and Southern PA, expect 8.0 to 12.0 inches of mostly snow with some sleet and little freezing rain mixing in. There is a 20% chance of <8 inches if there is more sleet/freezing rain and 10% chance of > 12.0 inches of snow. This scenario is mostly probable where the precipitation type is all snow. Winter Weather Advisories and Winter Storm Warning have been issued for these regions by the National Weather Service.
Category: Press Releases, General Interest