872  
FXUS21 KWNC 202056  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST DECEMBER 20 2017  
 
SYNOPSIS: A SERIES OF COLD FRONTS ARE PREDICTED TO MOVE ACROSS THE CENTRAL AND  
EASTERN CONTIGUOUS U.S. DURING THE 3-7 DAY PERIOD, RESULTING IN A VERY VARIABLE  
WEATHER PATTERN. FOR THIS PERIOD, THE BEST CHANCES FOR LARGE SCALE, STORMY  
CONDITIONS ARE OVER THE APPALACHIANS AND EAST COAST STATES, WHICH ARE LIKELY TO  
HAVE SOME IMPACT ON CHRISTMAS TRAVELERS. BY THE END OF THE 3-7 DAY PERIOD, COLD  
HIGH PRESSURE AT THE SURFACE IS FORECAST ACROSS MOST AREAS EAST OF THE ROCKIES,  
WITH THE EXCEPTION OF AREAS NEAR THE GULF COAST. DURING WEEK-2, COLD AIR MASSES  
FROM CENTRAL CANADA ARE EXPECTED TO MOVE SOUTHEASTWARD ACROSS THE BORDER,  
EVENTUALLY SPREADING POLAR AIR OVER MOST OF THE CONTIGUOUS U.S. EAST OF THE  
ROCKIES. THE FREQUENT PASSAGE OF LOW PRESSURE SYSTEMS ARE LIKELY TO MAINTAIN  
STORMY CONDITIONS OVER MUCH OF ALASKA DURING THIS OUTLOOK PERIOD, WITH PERHAPS  
THE STRONGEST SYSTEM AFFECTING THE STATE ON OR AROUND DECEMBER 23RD.  
 
HAZARDS  
 
HEAVY RAIN FROM EASTERN TENNESSEE TO SOUTHEASTERN NEW YORK, SAT-SUN, DEC 23-24.  
 
HEAVY PRECIPITATION FOR THE NORTHEAST, SAT-MON, DEC 23-25.  
 
HIGH WINDS FOR THE NORTHEAST COAST, SAT, DEC 23.  
 
MUCH BELOW-NORMAL TEMPERATURES FOR MOST OF THE WESTERN AND CENTRAL CONUS,  
SAT-MON, DEC 23-25.  
 
MUCH BELOW-NORMAL TEMPERATURES FROM THE NORTHERN DIVIDE EASTWARD ACROSS THE  
UPPER MIDWEST, GREAT LAKES, AND NORTHEAST, TUE-WED, DEC 26-27.  
 
ENHANCED WILDFIRE RISK FOR SOUTHERN CALIFORNIA, SUN, DEC 24.  
 
MUCH ABOVE-NORMAL TEMPERATURES FOR WESTERN AND NORTHERN ALASKA, SAT-SUN, DEC  
23-24.  
 
HEAVY PRECIPITATION FOR PARTS OF THE SOUTHERN ALASKA COAST, SAT-SUN, DEC 23-24.  
 
HIGH WINDS FOR WESTERN AND SOUTHERN PORTIONS OF ALASKA, SAT, DEC 23.  
 
SIGNIFICANT WAVES FOR SOUTHERN ALASKA COAST, SAT-SUN, DEC 23-24.  
 
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR NEARLY ALL AREAS EAST OF THE  
CONTINENTAL DIVIDE (THE EXCEPTION BEING SOUTHERN FLORIDA). WEST OF THE DIVIDE,  
THIS INCLUDES NORTHERN AND CENTRAL IDAHO, WASHINGTON STATE, AND NORTHERN AND  
WESTERN OREGON (THU-MON, DEC 28-JAN 1).  
 
A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR THE NORTHERN PLAINS, THE  
LOWER CENTRAL PLAINS, THE NORTHERN MISSISSIPPI VALLEY, MOST OF THE GREAT LAKES  
REGION, NORTHERN NEW YORK, AND NORTHERN AND CENTRAL NEW ENGLAND (THU-MON, DEC  
28-JAN 1).  
 
A HIGH RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR THE NORTHERN PLAINS AND MUCH  
OF MINNESOTA (THU-MON, DEC 28-JAN 1).  
 
A SLIGHT RISK OF HEAVY PRECIPITATION IS INDICATED OVER THE SOUTHERN PLAINS AS  
FAR NORTH AS EASTERN KANSAS, THE LOWER AND MIDDLE MISSISSIPPI VALLEY, AND MUCH  
OF THE TENNESSEE/OHIO VALLEYS, THU-SAT, DEC 28-30.  
 
LONG-TERM DROUGHT (D2 OR WORSE) IS INDICATED OVER THE MIDDLE/LOWER MISSISSIPPI  
VALLEY, SOUTHERN GREAT PLAINS, NORTHERN GREAT PLAINS, SOUTHERN ARIZONA, AND  
HAWAII.  
 
DETAILED SUMMARY  
 
FOR SATURDAY DECEMBER 23 - WEDNESDAY DECEMBER 27: A COLD FRONT APPROACHING THE  
APPALACHIANS EARLY IN THIS PERIOD IS FORECAST TO BRING A VARIETY OF  
PRECIPITATION TYPES TO APPROXIMATELY THE EASTERN QUARTER OF THE CONUS. HEAVY  
RAIN (UP TO 2 INCHES) IS FORECAST FROM THE SOUTHERN AND CENTRAL APPALACHIANS TO  
SOUTHEASTERN NEW YORK STATE ON DEC 23-24. A MIX OF SNOW, SLEET, AND/OR FREEZING  
RAIN IS POSSIBLE ACROSS THE REMAINDER OF NEW YORK STATE AND NEW ENGLAND DURING  
THIS SAME PERIOD. A SECONDARY LOW PRESSURE CENTER MAY FORM FARTHER SOUTH ALONG  
THIS COLD FRONT AND TRACK NORTHEASTWARD NEAR THE NEW ENGLAND COAST ON DEC  
24-25. THIS MAY BRING ANOTHER ROUND OF HEAVY SNOW TO THE INTERIOR NORTHEAST,  
EXTENDING INTO CHRISTMAS DAY. AN AREA OF GUSTY WINDS IS ALSO FORECAST ALONG THE  
NORTHEAST COAST ON DEC 23.  
 
MAXIMUM AND MINIMUM TEMPERATURES ARE PREDICTED TO RANGE FROM ABOUT 12-24  
DEGREES BELOW NORMAL DURING THE 3-7 DAY PERIOD OVER TWO REGIONS. THE FIRST  
REGION INCLUDES MUCH OF THE WESTERN AND CENTRAL CONUS, AS FAR EAST AS THE UPPER  
PENINSULA OF MICHIGAN IN THE NORTH, AND THE CENTRAL GULF COAST REGION IN THE  
SOUTH (DEC 23-25). THE SECOND REGION OF PREDICTED MUCH BELOW-NORMAL  
TEMPERATURES RUNS FROM THE NORTHERN CONTINENTAL DIVIDE GENERALLY EASTWARD  
ACROSS THE UPPER MIDWEST, GREAT LAKES REGION, AND NORTHEAST (DEC 26-27).  
 
THERE IS AN ENHANCED RISK OF CRITICAL WILDFIRE CONDITIONS OVER THE VICINITY OF  
THE L.A. BASIN ON DEC 24, DUE IN PART TO EXPECTED STRONGER PRESSURE GRADIENTS  
AT THE SURFACE AND STRONGER OFFSHORE WINDS.  
 
SOUTHERLY FLOW OF RELATIVELY MILD AIR IS ANTICIPATED ACROSS NEARLY THE ENTIRE  
STATE OF ALASKA DURING THE FIRST FEW DAYS OF THIS PERIOD, WITH DEEP LOW  
PRESSURE SITUATED OVER THE ALEUTIANS. MOST OF MAINLAND ALASKA (EXCEPT  
SOUTH-CENTRAL AND SOUTHEASTERN PORTIONS) HAS ELEVATED ODDS OF MUCH ABOVE-NORMAL  
TEMPERATURES ON DEC 23-24 (AT LEAST 25 DEGREES ABOVE NORMAL). HEAVY  
PRECIPITATION (2-3 INCHES OF LIQUID EQUIVALENT IN A 24-HOUR PERIOD) IS ALSO  
POSSIBLE OVER THE WINDWARD (EAST-SOUTHEAST-FACING) SLOPES OF KODIAK ISLAND, THE  
KENAI PENINSULA, AND WESTERN PRINCE WILLIAM SOUND ON DEC 23-24. HIGH WINDS (IN  
EXCESS OF 40 MPH) ARE FORECAST ACROSS WESTERN AND SOUTHERN PORTIONS OF ALASKA,  
PRIMARILY ON DEC 23, WHILE SIGNIFICANT WAVE HEIGHTS (EXCEEDING 20 FEET) ARE  
PREDICTED ALONG THE SOUTHERN COASTLINE ON DEC 23-24, GENERATED BY AN EXPECTED  
LONG TRAJECTORY OF SOUTHERLY WINDS ACROSS THE GULF OF ALASKA. ON DEC 24TH,  
THERE IS ALSO THE POSSIBILITY OF A GROUND BLIZZARD OVER THE EASTERN NORTH SLOPE  
AREA, WITH STRONG EASTERLY 850-HPA WINDS EXPECTED.  
 
FOR THURSDAY DECEMBER 28 - WEDNESDAY JANUARY 03: DURING MOST OF THIS PERIOD,  
CONTINENTAL POLAR AIR MASSES ARE FORECAST TO DOMINATE MOST OF THE LOWER 48  
STATES. A SLIGHT RISK (20-PERCENT CHANCE) OF MUCH BELOW-NORMAL TEMPERATURES IS  
PREDICTED FOR NEARLY ALL AREAS EAST OF THE CONTINENTAL DIVIDE (THE EXCEPTION  
BEING SOUTHERN FLORIDA). WEST OF THE DIVIDE, THIS INCLUDES NORTHERN AND CENTRAL  
IDAHO, WASHINGTON STATE, AND NORTHERN AND WESTERN OREGON (DEC 28-JAN 1). A  
MODERATE RISK (40-PERCENT CHANCE) OF MUCH BELOW-NORMAL TEMPERATURES IS  
INDICATED OVER THE NORTHERN PLAINS, THE LOWER CENTRAL PLAINS, THE NORTHERN  
MISSISSIPPI VALLEY, MOST OF THE GREAT LAKES REGION, NORTHERN NEW YORK, AND  
NORTHERN AND CENTRAL NEW ENGLAND. A HIGH RISK (60-PERCENT CHANCE) AREA IS  
FORECAST FOR THE NORTHERN PLAINS AND MUCH OF MINNESOTA. THESE RISK AREAS DEFINE  
REGIONS WHERE THE GEFS MODEL PREDICTS TEMPERATURES WILL BE WITHIN THE LOWEST 15  
PERCENT OF THE HISTORICAL TEMPERATURE DISTRIBUTION.  
 
A SLIGHT RISK (20-PERCENT CHANCE) OF HEAVY PRECIPITATION IS INDICATED OVER THE  
SOUTHERN PLAINS AS FAR NORTH AS EASTERN KANSAS, THE LOWER AND MIDDLE  
MISSISSIPPI VALLEY, AND MUCH OF THE TENNESSEE/OHIO VALLEYS, DEC 28-30. THIS IS  
GENERALLY CONSISTENT WITH WEEK-2 REFORECAST PRECIPITATION GUIDANCE. DUE TO THE  
LIKELIHOOD OF BELOW-NORMAL TEMPERATURES, THERE IS A RISK OF WIDESPREAD WINTER  
WEATHER HAZARDS ACROSS THE CENTRAL AND EASTERN CONUS.  
 
THE U.S. DROUGHT MONITOR, UPDATED ON DEC 12, SHOWS AN INCREASE IN AREAS OF  
EXCEPTIONAL DROUGHT (D2-D4) TO 6.49% FROM 5.99%. MOST OF THE NEWLY INDICATED  
SEVERE DROUGHT WAS OVER THE SOUTHERN PLAINS.  
 
FORECASTER: ANTHONY ARTUSA  
 

 
 
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