410  
FXUS21 KWNC 282144  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST NOVEMBER 28 2017  
 
SYNOPSIS: FOR THE BEGINNING OF THE FORECAST PERIOD, A LOW-PRESSURE SYSTEM  
CENTERED OVER THE PACIFIC NORTHWESTERN COAST IS PREDICTED TO PROGRESS TO THE  
CENTRAL UNITED STATES AND GREAT LAKES REGION DURING WEEK 1, WITH AN AREA OF  
HIGH PRESSURE BUILDING BEHIND IT OVER THE WEST. THE EASTERN HALF THE UNITED  
STATES IS MOST LIKELY TO BE DOMINATED BY AN AREA OF HIGH PRESSURE FOR THE  
MAJORITY OF WEEK 1. OFF THE COAST OF ALASKA, A STRONG LOW-PRESSURE SYSTEM IS  
FORECAST NORTH OF THE ALEUTIAN ISLANDS, EVENTUALLY MOVING SOUTHWARD ALONG THE  
COAST AS THE PERIOD PROGRESSES. AN UPPER-LEVEL LOW-PRESSURE SYSTEM IS PREDICTED  
TO BUILD ACROSS THE WESTERN HALF THE UNITED STATES THROUGH THE END OF WEEK 1  
AND MOVE ACROSS THE COUNTRY DURING WEEK 2.  
 
HAZARDS  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF THE PACIFIC NORTHWEST, FRI-SAT, DEC  
1-DEC 2.  
 
HEAVY SNOW ACROSS PORTIONS OF THE CASCADES, FRI-SAT, DEC 1-DEC 2.  
 
HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN ROCKIES AND THE NORTHERN GREAT  
BASIN, SAT, DEC 2.  
 
HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL ROCKIES AND THE CENTRAL GREAT BASIN,  
SUN, DEC 3.  
 
FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE PACIFIC NORTHWEST.  
 
HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, WED-THU, DEC 6-DEC  
7.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND  
ALASKA, SUN-TUE, DEC 3-DEC 5.  
 
HIGH WINDS ACROSS PORTIONS OF THE ALASKA PANHANDLE, MAINLAND ALASKA, AND THE  
ALEUTIANS, FRI, DEC 1 AND MON-TUE, DEC 4-DEC 5.  
 
HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF THE ALASKA PANHANDLE AND  
MAINLAND ALASKA, MON, DEC 4.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FROM TEXAS, ALONG THE GULF COAST,  
UP THROUGH PARTS OF THE MIDWEST AND MID-ATLANTIC, FRI-MON, DEC 8-DEC 11.  
 
SEVERE DROUGHT ACROSS 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 01 - TUESDAY DECEMBER 05: THE LOW-PRESSURE SYSTEM THAT  
BEGINS THE PERIOD IN THE PACIFIC NORTHWEST BRINGS POTENTIAL FOR HEAVY  
PRECIPITATION TO AREAS ALONG ITS PATH. WASHINGTON STATE AND NORTHERN OREGON  
WILL LIKELY SEE HEAVY RAIN ALONG THE COASTAL REGION, AS WELL AS HEAVY SNOW IN  
THE CASCADES FOR DEC 1. POSSIBILITY OF FLOODING DUE TO ADDITIONAL RAINFALL IS  
LIKELY IN THE AFFECTED REGION. THERE IS ALSO A POTENTIAL FOR PRECIPITATION IN  
NORTHERN CALIFORNIA, BUT THE MODEL GUIDANCE SHOWED UNCERTAINTY DESPITE THE  
SHORT LEAD TIME. A SMALLER TROUGH IS FORECAST TO AFFECT THE GREAT LAKES REGION,  
BRINGING PRECIPITATION DEC 1-2 WITH SOME SNOW AND WINTRY MIX OVERNIGHT,  
PROGRESSING TO RAIN DURING THE DAY WITH THE WARMER TEMPERATURES.  
 
THE FRONT FROM THE PACIFIC NORTHWEST IS FORECAST TO PROGRESS EASTWARD, LEADING  
TO POTENTIALLY HEAVY SNOWS ARE FOR INTERIOR IDAHO AND THE BITTERROOTS ON DEC 2,  
AS WELL AS WESTERN COLORADO FOR DEC 3. BY DEC 4 AND 5, THE FRONT WILL MOVE  
THROUGH THE GREAT LAKES REGION, THOUGH PRECIPITATION WILL MOST LIKELY BE RAIN  
AND ACCUMULATION IS FORECAST TO BE UNDER 1 INCH. THE EASTERN HALF THE CONUS IS  
LIKELY TO SEE A QUIET PERIOD, WITH AN AREA OF HIGH PRESSURE FORECAST OVER THE  
AREA DURING WEEK 1.  
 
THE STRONG LOW-PRESSURE SYSTEM OVER ALASKA IS FORECAST TO STAY TO THE NORTH OF  
THE ALEUTIAN ISLANDS IN THE BERING SEA, BUT STILL IMPACTING THE AREA WITH HIGH  
WINDS ON DEC 1. BY THE BEGINNING OF THE FORECAST PERIOD, MODEL GUIDANCE SHOWS  
THAT WAVE IMPACTS FOR THE AREA SHOULD BE MINIMAL. LATER IN THE PERIOD, THE LOW  
PRESSURE SYSTEM WILL LIKELY MOVE DOWN OVER THE ALEUTIANS AND INTO THE GULF OF  
ALASKA. THIS SYSTEM IS FORECAST TO BRING HIGH WINDS (30-40 KNOTS) AND HIGH  
SIGNIFICANT WAVE HEIGHTS (> 20 FEET) TO THE SOUTHERN ALASKAN GULF COAST, AND  
PARTS OF THE ALASKAN PANHANDLE FOR DEC 4-5. HEAVY PRECIPITATION IS LIKELY TO  
ACCOMPANY THIS SYSTEM, AFFECTING THE ALASKAN GULF COAST AND THE PANHANDLE.  
 
FOR WEDNESDAY DECEMBER 06 - TUESDAY DECEMBER 12: AN UPPER LEVEL TROUGH BUILDS  
INTO THE WEST AT THE END OF WEEK 1, CENTERED ON THE FOUR CORNERS REGION, AND  
PROPAGATES EASTWARD OVER WEEK 2. MODEL GUIDANCE IS NO LONGER SHOWING THE UPPER  
LEVEL TROUGH TILTED AS FAR WEST AS PREVIOUSLY FORECAST, SO THE POTENTIAL FOR  
MUCH BELOW NORMAL TEMPERATURES FOR SOUTHWESTERN UNITED STATES HAS DIMINISHED.  
 
THE ALASKAN REGION IS LIKELY TO CONTINUE TO SEE HEAVY PRECIPITATION ON THE GULF  
COAST AND PANHANDLE INTO WEEK 2, AS THE LOW PRESSURE SYSTEM FROM WEEK 1 MOVES  
ALONG THE COAST.  
 
THERE AN ELEVATED LIKELIHOOD FOR HEAVY RAINS DEC 6-8 FOR THE LOWER MISSISSIPPI  
RIVER VALLEY AS THE UPPER LEVEL TROUGH MOVES ACROSS THE COUNTRY AND A FRONT  
PASSES THROUGH THE AREA DURING DEC 6-7. THE SOUTHERLY FLOW FORECAST TO COME  
INTO THE REGION IS LIKELY TO ENHANCED CONVECTION, SO THE PRECIPITATION IS MOST  
LIKELY TO REMAIN RAIN.  
 
AS THE UPPER LEVEL TROUGH PROGRESSES TOWARD THE EASTERN HALF OF CONUS, THERE IS  
A SLIGHT RISK OF MUCH BELOW AVERAGE TEMPERATURES FOR THE SOUTHEAST, GULF COAST,  
AND PARTS OF THE MIDWEST AND MID-ATLANTIC REGIONS FOR DEC 8-11. IT IS LIKELY  
THAT TEMPERATURES WILL DROP BELOW FREEZING IN THESE AREAS, SO THERE IS A  
POTENTIAL FOR OVERNIGHT FROSTS FOR PORTIONS OF THE SOUTHEAST.  
 
THE U.S. DROUGHT MONITOR, UPDATED ON NOV 21, SHOWS SEVERE TO EXCEPTIONAL  
(D2-D4) DROUGHT COVERS 4.14% OF THE CONVENTIONAL UNITED STATES, A SLIGHT  
INCREASE OF 0.62% COVERAGE FROM THE PREVIOUS WEEK. AREAS OF SEVERE DROUGHT HAVE  
INCREASED IN ARKANSAS AND TEXAS.  
 
FORECASTER: CHRISTINA FINAN  
 

 
 
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