925  
FXUS21 KWNC 221939  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST DECEMBER 22 2017  
 
SYNOPSIS: AT THE START OF THE PERIOD, SURFACE LOW PRESSURE IS EXPECTED TO  
DEEPEN OFF THE NEW ENGLAND COAST AND MOVE NORTHEASTWARD. A COLD FRONT IS  
ANTICIPATED TO MOVE SOUTHEASTWARD FROM THE GREAT LAKES/MIDDLE MISSISSIPPI  
VALLEY/CENTRAL PLAINS AND STALL OVER FLORIDA DEC 25-27. COLD SURFACE HIGH  
PRESSURE BEHIND THE FRONT WILL DOMINATE MUCH OF THE NORTH-CENTRAL AND EASTERN  
PARTS OF THE NATION. SURFACE LOW PRESSURE IS FORECAST TO FORM OVER THE  
SOUTHEAST STATES OR OFF THE SOUTHEAST COAST DEC 29 AND MOVE NORTHEASTWARD NEAR  
THE EAST COAST DEC 30. ON DEC 25 SURFACE LOW PRESSURE OVER THE BERING SEA LEADS  
TO SOUTHERLY FLOW OVER MUCH OF WESTERN AND NORTHERN MAINLAND ALASKA, WHILE A  
FRONTAL SYSTEM OVER COASTAL SECTIONS OF NORTHEASTERN MAINLAND ALASKA PRODUCES  
LOCALLY GUSTY WINDS. DURING WEEK-2, UPPER-LEVEL LOW PRESSURE IS FORECAST TO  
DOMINATE MUCH OF THE CENTRAL AND EASTERN U.S. (ALTHOUGH IT IS EXPECTED TO  
WEAKEN LATER IN THE PERIOD), WHILE UPPER-LEVEL HIGH PRESSURE BUILDS OVER THE  
WEST. A STALLED FRONTAL SYSTEM FORECAST OVER THE SOUTHEAST LATE IN WEEK-2 MAY  
BRING UNSETTLED WEATHER TO THE REGION.  
 
HAZARDS  
 
HIGH WINDS FOR COASTAL SECTIONS OF THE MID-ATLANTIC AND NORTHEAST, MON-TUE, DEC  
25-26.  
 
HEAVY SNOW FOR PARTS OF THE SOUTHERN AND CENTRAL APPALACHIANS, MID-ATLANTIC,  
AND NORTHEAST, FRI, DEC 29.  
 
HEAVY PRECIPITATION FOR PARTS OF THE MID-ATLANTIC, FRI, DEC 29.  
 
FROZEN PRECIPITATION FOR PARTS OF THE CENTRAL APPALACHIANS, MID-ATLANTIC, AND  
NORTHEAST, SAT, DEC 30.  
 
MUCH BELOW-NORMAL TEMPERATURES SPREADING EASTWARD ACROSS MUCH OF THE NORTHERN  
TIER OF THE CONUS AND PARTS OF THE CENTRAL PLAINS, MON-FRI, DEC 25-29.  
 
MUCH ABOVE-NORMAL TEMPERATURES FOR WESTERN AND NORTHERN MAINLAND ALASKA,  
MON-TUE, DEC 25-26.  
 
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE CENTRAL AND  
EASTERN CONUS, SAT-THU, DEC 30-JAN 4 2018.  
 
MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE NORTH-CENTRAL  
AND NORTHEASTERN CONUS, AND PARTS OF THE OHIO AND TENNESSEE VALLEYS,  
APPALACHIANS, MID-ATLANTIC, AND SOUTHEAST, SAT-MON, DEC 30-JAN 1 2018.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE SOUTHEAST, WED-FRI, JAN 3-5  
2018.  
 
FLOODING POSSIBLE FOR PARTS OF THE OHIO AND TENNESSEE VALLEYS.  
 
SEVERE DROUGHT (D2 OR WORSE) IS INDICATED OVER THE MIDDLE/LOWER MISSISSIPPI  
VALLEY, SOUTHERN GREAT PLAINS, NORTHERN GREAT PLAINS, ARIZONA, UTAH AND HAWAII.  
 
DETAILED SUMMARY  
 
FOR MONDAY DECEMBER 25 - FRIDAY DECEMBER 29: ON DEC 25TH LOW PRESSURE IS  
EXPECTED TO DEEPEN OFF THE NEW ENGLAND COAST. HEAVY SNOW IS POSSIBLE FOR PARTS  
OF EASTERN NEW ENGLAND BUT MODEL UNCERTAINTY PRECLUDES THE SPECIFICATION OF A  
HAZARD SHAPE. HIGH WINDS (SPEED IN EXCESS OF 30 KNOTS) ARE ANTICIPATED FOR  
COASTAL SECTIONS OF THE MID-ATLANTIC AND NORTHEAST DEC 25-26. AS THIS AREA OF  
LOW PRESSURE MOVES NORTHEASTWARD AWAY FROM THE NEW ENGLAND COAST, ARCTIC HIGH  
PRESSURE IS FORECAST TO BUILD OVER MUCH OF THE CENTRAL AND EASTERN CONUS. MUCH  
BELOW NORMAL TEMPERATURES (NEGATIVE ANOMALIES IN EXCESS OF 20 DEGREES F) ARE  
EXPECTED TO SPREAD EASTWARD ACROSS MUCH OF THE NORTHERN TIER OF THE CONUS AND  
PARTS OF THE CENTRAL PLAINS DEC 25-29.  
 
LATE IN THE PERIOD, LOW PRESSURE IS PREDICTED TO FORM NEAR OR JUST OFF THE  
SOUTHEAST COAST AND MOVE NORTHEASTWARD ALONG OR OFF THE EASTERN SEABOARD. MODEL  
UNCERTAINTY ON THIS EVOLUTION IS HIGH BUT HEAVY SNOW IS ANTICIPATED FOR PARTS  
OF THE SOUTHERN AND CENTRAL APPALACHIANS, MID-ATLANTIC, AND NORTHEAST DEC 29,  
WHILE HEAVY PRECIPITATION (SNOW/SLEET/FREEZING RAIN) IS EXPECTED FOR PARTS OF  
THE MID-ATLANTIC THE SAME DAY.  
 
FOR ALASKA, SOUTHERLY FLOW AHEAD OF A TROUGH OF LOW PRESSURE LEADS TO MUCH  
ABOVE NORMAL TEMPERATURES (POSITIVE ANOMALIES IN EXCESS OF 20 DEGREES F) FOR  
WESTERN AND NORTHERN ALASKA DEC 25-26. ANOTHER FRONTAL SYSTEM OVER NORTHEASTERN  
ALASKA WILL LEAD TO GUSTY WINDS AND BLOWING SNOW FOR PORTIONS OF THE NORTHEAST  
ARCTIC COAST OF MAINLAND ALASKA. BLIZZARD-LIKE CONDITIONS ARE POSSIBLE FOR  
PARTS OF THE REGION DEC 25.  
 
ANTECEDENT PRECIPITATION LEADS TO POSSIBLE RIVER FLOODING FOR PARTS OF THE OHIO  
AND TENNESSEE VALLEYS.  
 
FOR SATURDAY DECEMBER 30 - FRIDAY JANUARY 05: AT THE START OF THE PERIOD, LOW  
PRESSURE IS FORECAST OFF THE NEW ENGLAND COAST. SIGNIFICANT AMOUNTS OF FROZEN  
PRECIPITATION ARE POSSIBLE FOR PARTS OF THE CENTRAL APPALACHIANS, NORTHERN  
MID-ATLANTIC, AND NORTHEAST DEC 30TH.  
 
A DEEP TROUGH IS FORECAST TO DOMINATE MUCH OF THE CENTRAL AND EASTERN CONUS FOR  
MOST OF WEEK-2, ALTHOUGH IS IS EXPECTED TO WEAKEN TOWARDS THE END OF THE  
PERIOD. THIS LEADS TO A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH  
OF THE CENTRAL AND EASTERN CONUS DEC 30- JAN 4 2018, AND A MODERATE RISK OF  
MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE NORTH-CENTRAL AND NORTHEASTERN  
CONUS DEC 29-JAN 1 2018. TEMPERATURES ARE EXPECTED TO MODERATE OVER THE WESTERN  
CONUS DURING THE PERIOD.  
 
A STALLED FRONTAL SYSTEM LEADS TO A SLIGHT RISK OF HEAVY PRECIPITATION FOR  
PARTS OF THE SOUTHEAST JAN 3-5.  
 
THE U.S. DROUGHT MONITOR, UPDATED ON DEC 19, SHOWS AN INCREASE IN AREAS OF  
EXCEPTIONAL DROUGHT (D2-D4) TO 6.97% FROM 6.49%. MOST OF THE NEWLY INDICATED  
SEVERE DROUGHT WAS OVER THE SOUTHERN PLAINS.  
 
FORECASTER: RANDY SCHECHTER  
 

 
 
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