432  
FXUS21 KWNC 192004  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST DECEMBER 19 2017  
 
SYNOPSIS: A LOW-PRESSURE SYSTEM AND ASSOCIATED COLD FRONT ARE FORECAST TO PUSH  
EASTWARD FROM THE CENTRAL TO THE EASTERN PART OF THE U.S. EARLY IN THE PERIOD.  
THE FRONT IS FORECAST TO STALL OVER THE EASTERN U.S. WHILE AN ARCTIC AIR MASS  
SPILLS SOUTHWARD INTO THE NORTHERN PLAINS. HAZARDOUS WINTRY WEATHER IS POSSIBLE  
ON THE COLD SIDE OF THE STALLED FRONTAL BOUNDARY OVER THE EASTERN U.S. ON OR  
NEAR CHRISTMAS DAY. ARCTIC HIGH PRESSURE IS FORECAST TO DOMINATE MUCH OF THE  
CONTIGUOUS U.S. BY THE END WEEK-1 AND INTO WEEK-2. A STRONG LOW-PRESSURE SYSTEM  
IS FORECAST TO AFFECT ALASKA LATER IN WEEK 1 AND INTO THE WEEKEND, BEFORE THE  
PATTERN IS FORECAST TO RELAX.  
 
HAZARDS  
 
HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE TENNESSEE  
VALLEY, THE SOUTHERN APPALACHIANS, THE SOUTHERN PLAINS, AND THE OHIO VALLEY,  
FRI-SAT, DEC 22-DEC 23.  
 
HEAVY PRECIPITATION FROM THE SOUTHERN PLAINS TO THE OHIO VALLEY AND NORTHWARD  
TO NEW ENGLAND, SUN-MON, DEC 24-DEC 25.  
 
HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST AND THE MID-ATLANTIC, SUN, DEC 24.  
 
HIGH WINDS ACROSS COASTAL PORTIONS OF NEW JERSEY AND THE NORTHEAST, SAT, DEC 23.  
 
MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE GREAT PLAINS, THE  
ROCKIES, THE GREAT BASIN, THE MIDDLE AND UPPER MISSISSIPPI VALLEY, CALIFORNIA,  
THE PACIFIC NORTHWEST, AND THE SOUTHWEST, SAT-MON, DEC 23-DEC 25.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF THE SOUTH COAST OF ALASKA AND KODIAK  
ISLAND, FRI-SAT, DEC 22-DEC 23.  
 
HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF THE SOUTH COAST OF ALASKA  
AND KODIAK ISLAND, FRI-SUN, DEC 22-DEC 24.  
 
HIGH WINDS ACROSS PORTIONS OF THE WESTERN COASTAL MAINLAND ALASKA, THE SOUTH  
COAST OF ALASKA, AND THE ALEUTIANS, FRI-SUN, DEC 22-DEC 24.  
 
HIGH WINDS ACROSS PORTIONS OF THE ALASKA PANHANDLE, SAT, DEC 23.  
 
MUCH ABOVE NORMAL TEMPERATURES ACROSS MANY PARTS OF MAINLAND ALASKA, FRI-MON,  
DEC 22-DEC 25.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR MANY PARTS OF THE CONUS,  
EXCLUDING THE SOUTHWESTERN QUARTER OF THE CONUS AND SOUTHERN FLORIDA, WED-SUN,  
DEC 27-DEC 31.  
 
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHERN  
PLAINS, THE NORTHERN ROCKIES, AND THE NORTHERN GREAT BASIN, WED-TUE, DEC 27-JAN  
2.  
 
SLIGHT RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR NORTHERN PORTIONS OF MAINLAND  
ALASKA, WED-TUE, DEC 27-JAN 2.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE LOWER MISSISSIPPI  
VALLEY, THE TENNESSEE VALLEY, THE SOUTHERN APPALACHIANS, THE SOUTHEAST, AND THE  
SOUTHERN PLAINS, FRI-SUN, DEC 29-DEC 31.  
 
MODERATE RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE LOWER MISSISSIPPI  
VALLEY AND ALABAMA, FRI-SUN, DEC 29-DEC 31.  
 
SEVERE DROUGHT ACROSS THE CENTRAL PLAINS, THE LOWER MISSISSIPPI VALLEY, THE  
NORTHERN PLAINS, HAWAII, THE NORTHERN ROCKIES, THE MIDDLE MISSISSIPPI VALLEY,  
THE SOUTHERN PLAINS, AND THE SOUTHWEST.  
 
DETAILED SUMMARY  
 
FOR FRIDAY DECEMBER 22 - TUESDAY DECEMBER 26: ARCTIC HIGH PRESSURE IS EXPECTED  
EXERT ITS INFLUENCE OVER MUCH OF THE NORTHERN CONUS, PUSHING SOUTH AND EAST  
WITH TIME. MUCH BELOW NORMAL TEMPERATURES ARE DEPICTED FOR MOST OF THE  
WEST-CENTRAL CONUS, WHERE MINIMUM TEMPERATURE ANOMALIES RANGING FROM 12 TO 24  
DEGREES F BELOW NORMAL ARE FORECAST.  
 
LATE THIS WEEKEND AND EARLY NEXT WEEK A FRONT IS EXPECTED TO STALL OVER THE  
EASTERN CONUS. THIS FRONT IS EXPECTED TO BRING HEAVY RAINFALL TO PARTS OF THE  
LOWER MISSISSIPPI VALLEY, THE TENNESSEE VALLEY, THE SOUTHERN APPALACHIANS, THE  
SOUTHERN PLAINS, AND THE OHIO VALLEY DEC 23. WINTRY WEATHER IS LIKELY TO OCCUR  
ON THE COLD SIDE OF THIS STALLED FRONT OVER THE EASTERN CONUS. GIVEN THE  
INCREASED VISIBILITY ASSOCIATED WITH THE CHRISTMAS DAY HOLIDAY, A BROAD SHAPE  
FOR DEC 24-25 IS DEPICTED FOR THOSE REGIONS WHERE SNOW, SLEET, OR FREEZING RAIN  
COULD IMPACT TRAVEL. HEAVY RAINFALL IS ALSO POSSIBLE ACROSS PARTS OF THE  
SOUTHEAST AND THE MID-ATLANTIC DEC 24. MODELS INDICATE HIGHLIGHTED AREAS  
RECEIVING ANYWHERE FROM AN INCH TO 3 INCHES OR GREATER OF LIQUID EQUIVALENT IN  
A 24-HOUR PERIOD. AS THE SURFACE LOW ALONG THIS FRONT EXITS THE NORTHEAST BY  
THE WEEKEND, COASTAL PARTS OF THE NORTHEAST AND NEW JERSEY MAY EXPERIENCE HIGH  
WINDS (30 KNOTS OR GREATER).  
 
AN ACTIVE PATTERN IS FORECAST FOR SOUTHERN ALASKA, WITH HIGH WINDS (IN EXCESS  
OF 45 MPH) FOR SOUTHERN AND WESTERN ALASKA, HIGH SIGNIFICANT WAVE HEIGHTS  
(EXCEEDING 20 FEET) FOR SOUTHERN ALASKA, AND HEAVY PRECIPITATION (3 INCHES OF  
LIQUID EQUIVALENT IN A 24-HOUR PERIOD) FOR PARTS OF THE SOUTH COAST OF ALASKA  
AND KODIAK ISLAND LATE THIS WEEK THROUGH THE WEEKEND. MEANWHILE, SURFACE  
RIDGING IS FORECAST TO BUILD ACROSS INTERIOR MAINLAND ALASKA, LIKELY SUPPORTING  
TEMPERATURES MUCH ABOVE NORMAL (DAILY TEMPERATURES 28 TO 32 DEGREES F ABOVE  
NORMAL) THROUGHOUT MOST OF THIS PERIOD.  
 
FOR WEDNESDAY DECEMBER 27 - TUESDAY JANUARY 02: WEEK-2 IS LIKELY TO FEATURE A  
CONTINUATION OF THE WARMTH OVER ALASKA, THOUGH THIS IS EXPECTED TO TIME OFF  
QUICKLY AS THE MEAN RIDGE POSITION RETROGRADES. MUCH ABOVE NORMAL TEMPERATURES  
FOR WEEK-2 ARE EXPECTED TO BE LIMITED TO MAINLY THE NORTHERN PORTION OF ALASKA.  
DOWNSTREAM OVER CENTRAL NORTH AMERICA, THE COLDEST AIR MASS OF THE SEASON THUS  
FAR IS FORECAST TO AFFECT THE NORTHERN PLAINS, EXTENDING SOUTHWARD AND EASTWARD  
AT TIMES. A BROAD AREA OF SLIGHT RISK FOR MUCH BELOW NORMAL TEMPERATURES IS  
DEPICTED FOR THE WEEK UNDER ARCTIC HIGH PRESSURE. THIS REGION HIGHLIGHTS WHERE  
THERE IS A 20 PERCENT CHANCE OF MINIMUM TEMPERATURES BEING IN THE LOWEST 15TH  
PERCENTILE.  
 
SURFACE TROUGHING IS POSSIBLE DURING WEEK 2 ACROSS THE CENTRAL CONUS. THIS  
PATTERN FAVORS SOUTHERLY FLOW AND INCREASED CHANCES FOR HEAVY RAINFALL EAST OF  
THIS REGION. A SLIGHT CHANCE OF HEAVY PRECIPITATION IS HIGHLIGHTED ACROSS PARTS  
OF THE LOWER MISSISSIPPI VALLEY, THE TENNESSEE VALLEY, THE SOUTHERN  
APPALACHIANS, THE SOUTHEAST, AND THE SOUTHERN PLAINS FOR DEC 29 TO 31 AND A  
MODERATE AREA IS HIGHLIGHTED ACROSS PARTS OF THE LOWER MISSISSIPPI VALLEY AND  
ALABAMA DEC 29 TO 31. 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: MELISSA OU  
 

 
 
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