902  
FXUS21 KWNC 082028  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST DECEMBER 08 2017  
 
SYNOPSIS: AS WE MOVE INTO MID-DECEMBER, THE UPPER-LEVEL TROUGH (RIDGE) THAT HAS  
BEEN PERSISTENT OVER THE EASTERN (WESTERN) U.S. IS ANTICIPATED TO WEAKEN. THE  
PERIOD IS EXPECTED TO BEGIN WITH A SERIES OF LOW-PRESSURE SYSTEMS ADVANCING  
ACROSS THE GREAT LAKES REGION TOWARD THE EAST COAST THROUGH WEEK-1, WHILE THE  
WESTERN U.S WILL LIKELY TO CONTINUE TO EXPERIENCE SURFACE HIGH PRESSURE. IN  
WEEK-2, THE UPPER-LEVEL TROUGH IN THE EASTERN U.S. IS LIKELY TO WEAKEN AND  
RETREAT NORTHWARD, AS THE RIDGING IN THE WESTERN U.S. SHIFTS EAST. ENHANCED  
SOUTHERLY SURFACE FLOW IS LIKELY TO CONTINUE OVER ALASKA FOR BOTH WEEK-1 AND  
WEEK-2.  
 
HAZARDS  
 
HEAVY SNOW ACROSS PORTIONS OF THE GREAT LAKES, MON-THU, DEC 11-DEC 14.  
 
HEAVY SNOW ACROSS PORTIONS OF THE NORTHEAST, TUE, DEC 12.  
 
HIGH WINDS ACROSS PORTIONS OF CALIFORNIA, MON-TUE, DEC 11-DEC 12.  
 
MUCH BELOW NORMAL TEMPERATURES ACROSS THE GREAT LAKES, MON-FRI, DEC 11-DEC 15.  
 
MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE NORTHEAST AND  
MID-ATLANTIC, WED-FRI, DEC 13-DEC 15.  
 
MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF FLORIDA AND THE SOUTHEAST,  
MON, DEC 11.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND  
ALASKA, MON-FRI, DEC 11-DEC 15.  
 
HIGH WINDS ACROSS PORTIONS OF MAINLAND ALASKA, MON, DEC 11.  
 
HIGH WINDS ACROSS PORTIONS OF MAINLAND ALASKA AND THE ALEUTIANS, FRI, DEC 15.  
 
MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF MAINLAND ALASKA, MON-FRI, DEC  
11-DEC 15.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE GREAT LAKES  
AND THE NORTHERN PLAINS, FRI, DEC 22.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE SOUTHEAST,  
THE MID-ATLANTIC, AND THE GREAT LAKES, SAT-SUN, DEC 16-DEC 17.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHEAST,  
SAT-FRI, DEC 16-DEC 22.  
 
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHEAST,  
SAT-SUN, DEC 16-DEC 17.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE CENTRAL GULF COAST, SUN-MON, DEC  
17-DEC 18.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE ALASKA PANHANDLE AND  
MAINLAND ALASKA, SAT-WED, DEC 16-DEC 20.  
 
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 MONDAY DECEMBER 11 - FRIDAY DECEMBER 15: ANOMALOUS RIDGING IN THE WEST AND  
A DEEPENING UPPER-LEVEL TROUGH IN THE EASTERN U.S. WILL PROGRESS EASTWARD  
WEEK-1. THE CURRENT CRITICAL FIRE WEATHER FOR SOUTHERN CALIFORNIA ENDS BEFORE  
THE BEGINNING OF THE FORECAST PERIOD. HOWEVER, WITH THE CONTINUED PRESENCE OF  
THE SURFACE HIGH-PRESSURE SYSTEMS IN THE WESTERN U.S., THE LOW RELATIVE  
HUMIDITY AND HIGH WIND CONDITIONS ARE LIKELY TO PERSIST THROUGH DEC 11 12.  
 
MUCH BELOW NORMAL TEMPERATURES OVER THE GREAT LAKES ARE FORECAST FOR WEEK-1 DUE  
TO SEVERAL LOW-PRESSURE SYSTEMS MOVING SOUTH FROM CANADA OVER THE REGION AND  
THE UPPER-LEVEL TROUGH. FLORIDA AND PARTS OF THE SOUTHEAST WILL LIKELY  
EXPERIENCE MUCH BELOW NORMAL TEMPERATURES FOR DEC 11 WITH THE PASSING OF A COLD  
FRONT FROM THE GREAT LAKES REGION. AS THE UPPER-LEVEL TROUGH AND AN ENHANCED  
SURFACE LOW-PRESSURE SYSTEM SHIFT NORTH, THE MUCH BELOW NORMAL TEMPERATURES ARE  
ANTICIPATED TO MOVE INTO THE NORTHEAST AND PARTS OF THE MID-ATLANTIC FOR DEC 13  
15.  
 
THE FORECAST FOR HEAVY LAKE EFFECT SNOW IN THE GREAT LAKES REGION CONTINUES  
FROM DEC 11 14. THE FIRST SURFACE LOW IS EXPECTED TO MOVE THROUGH THE REGION  
ON DEC 11, WITH A SECOND FOLLOWING ON DEC 13 14, LIKELY BRINGING A FEW  
CHANCES FOR SNOW FOR BOTH THE UPPER AND LOWER GREAT LAKES. NEW ENGLAND AND  
PARTS OF UPSTATE NEW YORK ARE ANTICIPATED TO RECEIVE HEAVY SNOW DEC 12, AS THE  
UPPER-LEVEL TROUGH MOVES OVER THE REGION. AREAS OF ELEVATION IN WEST VIRGINIA  
MAY TO SEE SNOW ON DEC 12; HOWEVER, SNOW ACCUMULATIONS ARE EXPECTED TO REMAIN  
BELOW HAZARDOUS CRITERIA.  
 
PERSISTENT SURFACE LOW-PRESSURE AND AN UPPER-LEVEL TROUGH DURING WEEK-1 WILL  
CONTINUE ANOMALOUS SOUTHERLY FLOW AND MOISTURE INTO ALASKA, MAINLY SOUTHEASTERN  
MAINLAND ALASKA. HEAVY PRECIPITATION IS EXPECTED FROM KODIAK ISLAND AND THE  
KENAI PENINSULA DOWN TO PARTS OF THE PANHANDLE FROM DEC 11 15. AS A SURFACE  
LOW MOVES OVER THE ALEUTIANS AT THE END OF WEEK-1, HIGH WINDS ARE LIKELY FOR  
THE ALEUTIANS AND PARTS OF THE SOUTH COAST FOR DEC 15. ON DEC 11, WIDESPREAD  
CHINOOK WINDS (GUSTS GREATER THAN 50 KNOTS) ARE EXPECTED IN THE ALASKAN RANGE.  
FOR THE INTERIOR BASIN AND PARTS OF WESTERN ALASKA, MUCH ABOVE NORMAL  
TEMPERATURES ARE FORECAST TO PERSIST THROUGH WEEK-1.  
 
FOR SATURDAY DECEMBER 16 - FRIDAY DECEMBER 22: COLD IS PROJECTED TO CONTINUE  
FOR THE EASTERN HALF OF THE U.S. INTO WEEK-2 AND RETREAT BY THE MIDDLE OF THE  
PERIOD. A DEEP UPPER-LEVEL TROUGH WILL LIKELY BRING A SLIGHT RISK FOR MUCH  
BELOW NORMAL TEMPERATURES ALONG THE EAST COAST THROUGH FLORIDA FOR DEC 16 17.  
AS THE UPPER-LEVEL TROUGH RETREATS NORTHWARD, THE NORTHEAST MAY EXPERIENCE MUCH  
BELOW NORMAL TEMPERATURES THROUGH DEC 15-19, AND AGAIN DEC 21-22 AS A SECOND  
UPPER-LEVEL TROUGH MOVES THROUGH THE REGION. A MODERATE RISK FOR MUCH BELOW  
NORMAL TEMPERATURES IS FORECAST OVER NEW YORK, CONNECTICUT AND WESTERN  
MASSACHUSETTS FOR DEC 16-17. THE WESTERN AND CENTRAL GREAT LAKES REGIONS HAVE A  
SLIGHT RISK FOR MUCH BELOW NORMAL TEMPERATURES FOR DEC 22 ASSOCIATED WITH AN  
UPPER-LEVEL TROUGH.  
 
RETURN FLOW FROM A SURFACE HIGH PRESSURE OFF THE EASTERN U.S. COAST COULD BRING  
A SLIGHT RISK FOR HEAVY PRECIPITATION ALONG THE CENTRAL GULF COAST FOR DEC  
17-18, BRINGING MOISTURE UP FROM THE GULF.  
 
ANOMALOUS UPPER-LEVEL RIDGING IS EXPECTED FOR ALASKA DURING WEEK-2. THERE IS A  
SLIGHT RISK FOR HEAVY PRECIPITATION FROM DEC 16 21 ALONG THE SOUTHERN COAST  
OF ALASKA AND THE PANHANDLE AS AN ANOMALOUSLY STRONG LOW-PRESSURE SYSTEM MOVES  
INTO THE BERING SEA AT THE BEGINNING OF WEEK-2 AND ANOTHER LOW-PRESSURE SYSTEM  
MOVES INTO THE GULF OF ALASKA MID-WEEK.  
 
THE U.S. DROUGHT MONITOR, UPDATED ON DEC 5, SHOWS AN INCREASE IN AREAS OF  
EXCEPTIONAL DROUGHT (D2-D4) FROM 4.88% TO 5.99%, A CHANGE OF 1.11% OVER THE  
CONTINENTAL U.S. FROM THE PREVIOUS WEEK.  
 
FORECASTER: CHRISTINA FINAN  
 

 
 
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