614  
FXUS21 KWNC 072202  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST DECEMBER 07 2017  
 
SYNOPSIS: AN AMPLIFIED RIDGE AND TROUGH PATTERN OVER NORTH AMERICA IS LIKELY TO  
PERSIST FOR THE FORECAST PERIOD. WITH THE TROUGH IN THE EASTERN HALF THE U.S.,  
A SERIES OF FRONTS ARE FORECAST TO MOVE OVER THE GREAT LAKES SOUTHEAST TO THE  
EASTERN SEABOARD DURING WEEK-1 AND INTO WEEK-2. A PERSISTENT SURFACE HIGH  
PRESSURE SYSTEM WILL CONTINUE IN THE WESTERN U.S., WITH A POSSIBLE WEAKENING  
LATER IN WEEK-2. SURFACE LOW-PRESSURE SYSTEMS ARE LIKELY TO CONTRIBUTE TO  
ANOMALOUS SOUTHERLY FLOW AFFECTING ALASKA OVER MUCH OF THE NEXT TWO WEEKS.  
 
HAZARDS  
 
HEAVY SNOW ACROSS PORTIONS OF THE GREAT LAKES AND THE UPPER MISSISSIPPI VALLEY,  
SUN-WED, DEC 10-DEC 13.  
 
HEAVY SNOW ACROSS PORTIONS OF THE EASTERN GREAT LAKES, MON-WED, DEC 11-DEC 13.  
 
HIGH WINDS ACROSS PORTIONS OF CALIFORNIA, SUN-TUE, DEC 10-DEC 12.  
 
MUCH BELOW NORMAL TEMPERATURES ACROSS THE EASTERN HALF THE U.S., SUN-THU, DEC  
10-DEC 14.  
 
ENHANCED WILDFIRE RISK ACROSS PORTIONS OF CALIFORNIA, SUN, DEC 10.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND  
ALASKA, SUN-MON, DEC 10-DEC 11.  
 
HIGH WINDS ACROSS PORTIONS OF MAINLAND ALASKA, MON, DEC 11.  
 
HIGH WINDS ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND ALASKA, SUN,  
DEC 10.  
 
MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF MAINLAND ALASKA, SUN-THU, DEC  
10-DEC 14.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHEAST,  
THE MID-ATLANTIC, THE GREAT LAKES, AND THE OHIO VALLEY, FRI-THU, DEC 15-DEC 21.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE SOUTHEAST,  
THE MID-ATLANTIC, THE SOUTHERN APPALACHIANS, THE OHIO VALLEY, AND THE TENNESSEE  
VALLEY, FRI-SAT, DEC 15-DEC 16.  
 
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHEAST  
AND GREAT LAKES, FRI-SUN, DEC 15-DEC 17.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE ALASKA PANHANDLE AND  
MAINLAND ALASKA, FRI-TUE, DEC 15-DEC 19.  
 
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 SUNDAY DECEMBER 10 - THURSDAY DECEMBER 14: THE FORECAST PERIOD BEGINS WITH  
AN AMPLIFIED UPPER-LEVEL TROUGH ANTICIPATED TO BE DOMINATING THE EASTERN HALF  
OF THE CONTINENTAL US AND RIDGING IN THE WEST. SEVERAL COLD FRONTS WILL MOVE  
DOWN FROM CANADA DURING THE PERIOD OVER THE MIDWEST AND GREAT LAKES REGION AND  
INTO THE EASTERN US. HEAVY LAKE EFFECT SNOW MAY PERSIST OVER THE GREAT LAKES  
REGION WITH THE FRONTAL PASSAGES DEC 10 - 14. THESE SAME FRONTS ARE FORECAST TO  
ALSO BRING HEAVY SNOW TO THE APPALACHIANS, FROM WEST VIRGINIA DOWN THROUGH  
NORTH CAROLINA ON DEC 12 - 13.  
 
THE THREAT FOR MUCH-BELOW NORMAL TEMPERATURES REMAINS EAST OF THE MISSISSIPPI  
RIVER VALLEY TO THE EAST COAST, THOUGH THE MINIMUMS OUTPUT BY THE MODEL  
GUIDANCE ARE LESS EXTREME THAN PREVIOUSLY FORECAST. COLD TEMPERATURES WILL BE  
MORE LIKELY IN THE SOUTHEAST FOR THE BEGINNING OF THE PERIOD, WITH THE COLD  
CONCENTRATING IN THE GREAT LAKES REGION AND NORTHEAST FOR THE LATTER HALF OF  
WEEK-1. NORTHERN MAINE COULD SEE SOME SNOW FROM THESE FRONTAL SYSTEMS TOWARD  
THE END OF THE PERIOD, DEC 13-14, BUT THE ACCUMULATIONS ARE LIKELY TO REMAIN  
BELOW HAZARDOUS CRITERIA.  
 
A FIRE WEATHER THREAT IS FORECAST FOR SOUTHERN CALIFORNIA IN THE BEGINNING OF  
THE PERIOD. LOW RELATIVE HUMIDITY, OFFSHORE FLOW AND ABOVE-NORMAL TEMPERATURES  
ARE EXPECTED TO PERSIST DUE TO THE AREAS OF HIGH PRESSURE SETTLED INTO THE  
WESTERN US. THE UPPER-LEVEL GRADIENT IS EXPECTED TO WEAKEN ON DEC 10 WITH A  
FORMATION OF A TROUGH OFF THE SOUTHWESTERN COAST, WHICH WILL HOPEFULLY BRING  
SOME RELIEF TO THE CRITICAL AREAS OF FIRE WEATHER. THE REGION WILL CONTINUE TO  
BE DRY AND COOL THOUGH THROUGH WEEK-1, SO THERE REMAINS A CONTINUED POSSIBILITY  
FOR FIRE WEATHER IN THE AREA.  
 
ALASKA IS EXPECTED TO CONTINUE EXPERIENCING ABOVE-NORMAL TEMPERATURES IN THE  
INTERIOR BASIN AND PARTS OF THE WESTERN REGION THROUGH WEEK-1 DUE TO  
UPPER-LEVEL RIDGING. A LOW-PRESSURE SYSTEM IS FORECAST TO MOVE OVER THE  
ALEUTIAN ISLANDS AND INTO THE ALASKAN GULF, CAUSING ANOMALOUS SOUTHERLY FLOW  
OVER THE KENAI PENINSULA. THIS IS LIKELY TO BRING HIGH WINDS FOR DEC 10 AND  
HEAVY PRECIPITATION FOR DEC 10-11 TO THE ALASKAN GULF COAST AND PARTS OF THE  
PANHANDLE.  
 
FOR FRIDAY DECEMBER 15 - THURSDAY DECEMBER 21: INTO MID-DECEMBER, THE  
UPPER-LEVEL RIDGE-TROUGH PATTERN OVER THE CONTINENTAL US IS FORECAST TO WEAKEN.  
THE UPPER-LEVEL TROUGH OVER THE EASTERN US APPEARS LIKELY TO MOVE INTO THE  
NORTHEAST, AS THE ANOMALOUS RIDGING IN THE WEST FLATTENS. MODEL GUIDANCE FROM  
THE GFS SHOWS THAT FLOW FROM CANADA INTO THE EASTERN U.S. WILL CONTINUE, BUT  
WILL SHIFT WESTWARD TO AFFECT THE NORTHERN PLAINS.  
 
THE COLD AIR PERSISTING OVER THE EASTERN HALF THE US IS FORECAST TO RETREAT AS  
THE UPPER-LEVEL TROUGH MOVES NORTHEAST. A SLIGHT RISK FOR MUCH BELOW NORMAL  
TEMPERATURES EXISTS FOR MOST OF THE EASTERN SEABOARD AND MIDWEST FROM DEC 15  
-16. THE RISK WILL CONTINUE FOR THE MID-ATLANTIC, NORTHEAST AND GREAT LAKES  
REGION FOR DEC 17-21. A MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES IS  
FORECAST FOR THE GREAT LAKES REGION FOR DEC 15-17. LAKE EFFECT SNOW IS LIKELY  
TO CONTINUE FOR THE GREAT LAKES REGION IN THE BEGINNING OF WEEK-2, FROM DEC  
15-16.  
 
 
 
AN UPPER-LEVEL LOW-PRESSURE SYSTEM IS FORECAST MOVING OVER SOUTHERN ALASKA AND  
THE ALEUTIANS INTO WEEK-2. THE CONTINUED SOUTHERLY FLOW FROM THIS SYSTEM  
SUPPORTS SLIGHT RISK FOR HEAVY PRECIPITATION ALONG THE COAST, FROM THE KENAI  
PENINSULA TO THE PANHANDLE FROM DEC 15-19.  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page