Jan 7, 2017 Winter Weather Event Decision Support Briefing # 4 Assessment for northeast South Carolina & southeast North Carolina National Weather Service Wilmington NC 8 AM EST Friday January 6, 2017 Steven Pfaff, WCM Steven.Pfaff@noaa.gov Weather Forecast Office Wilmington, NC weather.gov/ilm @NWSWilmingtonNC 1
New Information Winter Storm Watch remains in effect for Darlington, Marlboro, Dillon, Robeson, and Bladen counties, and a decision will be made this morning if a Winter Storm Warning or only a Winter Weather Advisory will be needed for this event. More information forthcoming. Lowered snow accumulations across northwest areas, but did expand slight accumulations closer to the southeast NC coast and parts of the Pee Dee with some snow possible as the system begins to exit the area. Included peak wind gust and wave height graphics. Delayed onset of changeover to wintry weather by a few hours. There could be a few patches of rain around by later this afternoon, while most areas will initially receive rain during the evening. 2
Impact Summary Greatest expected impacts Snow/Sleet None Elevated Moderate High Extreme -Highest far northwest areas Ice None Elevated Moderate High Extreme Wind Surge/ Inundation None Elevated Moderate High Extreme -Gusts to 30 mph possible (higher over ocean) None Elevated Moderate High Extreme Marine None Elevated Moderate High Extreme -Gale conditions likely *These impacts do not apply to all areas of southeast NC or northeast SC, check the following slides for details on where impacts will be greatest. 3
Impact Overview, Timing, & Confidence Potential Impacts Hazardous driving conditions expected, especially bridges, overpasses, & elevated road surfaces beginning early Sat morning, especially across inland areas Confidence Confident that any snow accumulations will occur much farther inland, less confidence along the coastal and southern areas. Confident of a swath of freezing rain accumulation generally <0.1 High confidence with cold temperatures through Monday night. Approximate Timing Black ice possible on area roadways Saturday night into Sunday morning as arctic air arrives in force Isolated power outages possible Saturday Dangerously cold weather Sunday into Monday with arctic air-mass in place 4
Expected Storm/Sleet Total Snowfall Highest snow accumulations remain across northwest areas but a dusting is possible farther east and slightly southward as the system exists the area during Saturday. Accumulations will primarily be on grassy surfaces and elevated areas. 5
Probability of Snow Accumulating 1 WPC Probability of Snowfall Accumulating 1 valid 7 PM EST Today through 7 PM EST Saturday Consistency remains with the axis of highest snow accumulating to 1 probabilities from near Greenville, SC to Charlotte, Raleigh and Rocky Mount, NC. While a few outlier scenarios bring accumulating snowfall farther south and east. 6
Expected Ice Accumulation Total Highest ice accumulations are expected to occur across northwest areas, while a glaze is possible across remaining areas. Freezing rain will accumulate more efficiently on elevated surfaces. 7
Probability of Freezing Rain Accumulating 0.01 WPC Probability of Freezing Rain Accumulating 0.01 valid 7 PM EST Today through 7 PM EST Saturday The axis of highest freezing rain accumulating to 0.01 probabilities continue across inland portions of the forecast area. have increased across inland areas for Saturday. However, the probabilities for freezing rain accumulating 0.10 (not shown) are only less than 30% for a portion of the area. 8
Wind Chill Period of Coldest Wind Chill Wind Chill Advisory is possible early Sunday morning and Monday morning for portions of the area. 9
Arctic Temperatures Arctic air-mass in place into Tuesday morning Coldest temperatures Monday morning, temperatures recovering beginning Tuesday 10
Wind Gusts and Seas Gale Warning in effect for the adjacent coastal and offshore waters Conditions will deteriorate tonight with the worst maritime weather Saturday, slow improvement Sunday. 11
Key Points A changeover to a mix of wintry weather is expected by daybreak Saturday far inland areas and later during Saturday morning for coastal areas. The high temperature during Saturday will occur in the morning, with temperatures dropping throughout the day as the arctic air-mass plunges across the Carolinas. Ice accumulations of <0.10 are possible across portions of forecast area Saturday. This freezing rain along with any snow/sleet accumulations farther inland will create hazardous travel conditions. Very cold temperatures and single digit wind chill values (combination of wind and temperature) are expected Sunday morning and again during Monday morning. The arctic air-mass will begin to lose its grip on the area Tuesday into Wednesday. NEXT PDF BRIEFING: 4 PM EST - today January 6, 2017 12