192  
FXUS21 KWNC 212024  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST DECEMBER 21 2017  
 
SYNOPSIS: AT THE START OF THE PERIOD, A COLD FRONT IS FORECAST TO BE MOVING OFF  
THE EAST COAST. SURFACE LOW PRESSURE IS EXPECTED TO MOVE NORTHEASTWARD ALONG  
THE FRONT AND BE OFF THE NEW ENGLAND COAST DEC 25. COLD SURFACE HIGH PRESSURE  
IS ANTICIPATED TO MOVE FROM THE NORTHWESTERN U.S. SOUTHEASTWARD TO THE LOWER  
MISSISSIPPI VALLEY. MOIST INFLOW ON THE REAR SIDE OF THIS AREA OF SURFACE HIGH  
PRESSURE WILL INTERACT WITH A FRONTAL SYSTEM OVER THE SOUTH-CENTRAL U.S. A  
FRONTAL SYSTEM IS FORECAST TO MOVE ACROSS THE ALEUTIANS AND ALASKA PENINSULA  
AND WEAKEN DEC 24-25. AT THE SAME TIME, ANOTHER FRONTAL SYSTEM IS ANTICIPATED  
OVER NORTHEASTERN MAINLAND ALASKA. DURING WEEK 2, UPPER-LEVEL LOW PRESSURE IS  
FORECAST TO DOMINATE MUCH OF THE CENTRAL AND EASTERN U.S. WHILE UPPER-LEVEL  
HIGH PRESSURE BUILDS OVER THE WEST.  
 
HAZARDS  
 
HIGH WINDS FOR THE NORTHEAST COAST, MON, DEC 25.  
 
HEAVY SNOW FOR PARTS OF SOUTHEASTERN NEW ENGLAND, SUN-MON, DEC 24-25.  
 
HEAVY PRECIPITATION FOR PARTS OF THE SOUTHERN AND CENTRAL PLAINS, LOWER AND  
MIDDLE MISSISSIPPI VALLEYS, OHIO AND TENNESSEE VALLEYS, AND GREAT LAKES,  
WED-THU, DEC 27-28.  
 
FROZEN PRECIPITATION FOR PARTS OF THE TENNESSEE VALLEY, SOUTHERN AND CENTRAL  
APPALACHIANS, MID-ATLANTIC, AND NORTHEAST, FRI, DEC 29.  
 
MUCH BELOW-NORMAL TEMPERATURES SPREADING EASTWARD ACROSS MUCH OF THE NORTHERN  
TIER OF THE CONUS SUN-THU, DEC 24-28.  
 
CRITICAL FIRE WEATHER FOR SOUTHERN CALIFORNIA, SUN, DEC 24.  
 
MUCH ABOVE-NORMAL TEMPERATURES FOR WESTERN AND NORTHERN MAINLAND ALASKA,  
SUN-MON, DEC 24-25.  
 
HIGH WINDS FOR PARTS OF THE ALEUTIANS, ALASKA PENINSULA, ALASKA PANHANDLE, AND  
WESTERN AND SOUTHERN COASTAL SECTIONS OF MAINLAND ALASKA, SUN, DEC 24.  
 
SIGNIFICANT WAVES FOR PARTS OF THE ALASKA PENINSULA AND THE SOUTHERN ALASKA  
COAST, SUN, DEC 24.  
 
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE NORTHERN,  
CENTRAL, AND EASTERN CONUS (EXCEPT FLORIDA), FRI-THU, DEC 29-JAN 4.  
 
MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE NORTHERN CONUS  
FRI-MON, DEC 29-JAN 1.  
 
HIGH RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN PLAINS,  
FRI-SAT, DEC 29-30.  
 
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 SUNDAY DECEMBER 24 - THURSDAY DECEMBER 28: ON DEC 24TH A COLD FRONT IS  
FORECAST TO SLOWLY MOVE OFF THE EAST COAST. LOW PRESSURE IS FORECAST TO FORM  
ALONG THE FRONT AND DEEPEN AS IT MOVES OFF THE NEW ENGLAND COAST. HEAVY SNOW  
(AMOUNTS IN EXCESS OF 4 INCHES IN 24 HOURS) IS EXPECTED FOR PARTS OF  
SOUTHEASTERN NEW ENGLAND DEC 24-25. AS THE LOW DEEPENS, STRONG WINDS (SPEEDS IN  
EXCESS OF 30 KNOTS) ARE ANTICIPATED FOR PARTS OF THE NORTHEAST COAST DEC 25.  
BLOWING AND DRIFTING SNOW IS POSSIBLE FOR PARTS OF THE REGION DURING THIS  
PERIOD.  
 
COLD HIGH PRESSURE BEHIND THE FRONT IS EXPECTED TO SHIFT FROM THE GREAT BASIN  
TO THE LOWER MISSISSIPPI VALLEY AND THEN THE EASTERN CONUS DEC 24-26. OFFSHORE  
FLOW IN COMBINATION WITH AREAS OF LOW RELATIVE HUMIDITY LEAD TO CRITICAL FIRE  
WEATHER FOR PARTS OF SOUTHERN CALIFORNIA DEC 24. MUCH BELOW TEMPERATURES  
(NEGATIVE ANOMALIES OF 20 TO AS MUCH OF 25 DEGREES F) ARE FORECAST TO SPREAD  
EASTWARD ACROSS THE NORTHERN TIER OF THE CONUS DEC 24-28.  
 
MOIST INFLOW ON THE REAR SIDE OF THE AREA OF HIGH PRESSURE ARE ANTICIPATED TO  
INTERACT WITH A FRONTAL SYSTEM LEADING TO HEAVY PRECIPITATION FOR PARTS OF THE  
SOUTHERN AND CENTRAL PLAINS, LOWER AND MIDDLE MISSISSIPPI VALLEYS, OHIO AND  
TENNESSEE VALLEYS, AND GREAT LAKES DEC 27-28. RAINFALL AMOUNT OF 1-1.5 INCHES  
ARE POSSIBLE FOR THE SOUTHERN EXTENT OF THE PRECIPITATION SHIELD, WHILE FROZEN  
PRECIPITATION IS EXPECTED ON THE NORTHWEST PORTION. SNOWFALL AMOUNTS COULD  
LOCALLY EXCEED 6 INCHES.  
 
FOR ALASKA, LOW PRESSURE AND ITS ASSOCIATED FRONTAL SYSTEM ARE EXPECTED TO  
CROSS THE ALEUTIANS AND WEAKEN AS THEY MOVE TO THE ALASKA PENINSULA. HIGH WINDS  
(SPEEDS IN EXCESS OF 35 KNOTS) AND SIGNIFICANT WAVES (WAVE HEIGHTS IN EXCESS OF  
20 FEET) ARE EXPECTED FOR PARTS OF THE ALEUTIANS, ALASKA PENINSULA, ALASKA  
PANHANDLE, AND WESTERN AND SOUTHERN COASTAL SECTIONS OF MAINLAND ALASKA DEC 24.  
SOUTHERLY FLOW AHEAD OF THE FRONTAL SYSTEM LEADS TO MUCH ABOVE NORMAL  
TEMPERATURES (POSITIVE ANOMALIES IN EXCESS OF 20 DEGREES F) FOR WESTERN AND  
NORTHERN ALASKA DEC 24-25. 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 24-25.  
 
FOR FRIDAY DECEMBER 29 - THURSDAY JANUARY 04: LOW PRESSURE IS FORECAST TO FORM  
ON THE FRONT FORECAST OVER THE SOUTH-CENTRAL CONUS AT THE END OF THE 3-7 DAY  
PERIOD. AS THE LOW MOVES NORTHEASTWARD TOWARDS THE MID-ATLANTIC COAST,  
SIGNIFICANT AMOUNTS OF FROZEN PRECIPITATION ARE POSSIBLE FOR PARTS OF THE  
TENNESSEE VALLEY, SOUTHERN AND CENTRAL APPALACHIANS, MID-ATLANTIC, AND  
NORTHEAST DEC 29.  
 
A DEEP TROUGH IS FORECAST TO DOMINATE MUCH OF THE CENTRAL AND EASTERN CONUS FOR  
MUCH OF THE PERIOD. THIS LEADS TO A SLIGHT RISK OF MUCH BELOW-NORMAL  
TEMPERATURES FOR MUCH OF THE NORTHERN, CENTRAL, AND EASTERN CONUS (EXCEPT  
FLORIDA) DEC 29- JAN 4 2018, A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES  
FOR MUCH OF THE NORTHERN CONUS DEC 29-JAN 1 2018, AND A HIGH RISK OF MUCH  
BELOW-NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN PLAINS DEC 29-30.  
TEMPERATURES ARE EXPECTED TO MODERATE OVER THE WESTERN CONUS TOWARD THE MIDDLE  
OF THE WEEK 2 PERIOD.  
 
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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