899  
FXUS21 KWNC 041942  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST JANUARY 04 2018  
 
SYNOPSIS: ARCTIC HIGH PRESSURE IS FORECAST TO BECOME CENTERED OVER THE EASTERN  
U.S. THIS WEEKEND. AS THIS SURFACE HIGH SHIFTS OFF OF THE EAST COAST, A SURFACE  
LOW PRESSURE SYSTEM IS ANTICIPATED TO PROGRESS EAST FROM THE CENTRAL U.S. ON  
JAN 8. DURING THE MIDDLE PART OF NEXT WEEK, A VIGOROUS MID-LEVEL LOW IS  
FORECAST TO MOVE INLAND OVER CALIFORNIA AND THE SOUTHWESTERN U.S. ANOTHER  
STRONG AREA OF MID-LEVEL LOW PRESSURE IS FORECAST TO DEVELOP OVER THE NORTH  
PACIFIC BY THE BEGINNING OF WEEK-2.  
 
HAZARDS  
 
MUCH BELOW-NORMAL TEMPERATURES FOR THE EASTERN U.S., SUN, JAN 7.  
 
FREEZING RAIN FOR PARTS OF THE OHIO VALLEY, CENTRAL APPALACHIANS, AND  
MID-ATLANTIC, MON, JAN 8.  
 
HEAVY SNOW FOR THE SIERRA NEVADA MOUNTAINS, MON-TUE, JAN 8-9.  
 
HEAVY RAIN FOR PARTS OF SOUTHERN CALIFORNIA, MON-TUE, JAN 8-9.  
 
HIGH WINDS SHIFTING EAST FROM THE SOUTHWESTERN U.S. TO THE CENTRAL AND SOUTHERN  
HIGH PLAINS, TUE-WED, JAN 9-10.  
 
HIGH WINDS EXPANDING FROM THE ALEUTIANS TO THE ALASKA PENINSULA AND PARTS OF  
SOUTHWEST MAINLAND ALASKA, SUN-TUE, JAN 7-9.  
 
HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF THE ALEUTIANS AND ALASKA  
PENINSULA, SUN-TUE, JAN 7-9.  
 
A SLIGHT RISK OF HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST, SUN-THU, JAN  
14-18.  
 
SEVERE DROUGHT ACROSS THE GREAT PLAINS, THE SOUTHWEST, THE MIDDLE AND LOWER  
MISSISSIPPI VALLEY, AND HAWAII.  
 
DETAILED SUMMARY  
 
FOR SUNDAY JANUARY 07 - THURSDAY JANUARY 11: THE COLDEST MORNING THIS WEEK  
ACROSS THE MID-ATLANTIC AND NORTHEAST IS LIKELY TO OCCUR ON JAN 7 AS ARCTIC  
HIGH PRESSURE BECOMES CENTERED OVER THESE AREAS. SUBZERO MINIMUM TEMPERATURES  
ARE EXPECTED AS FAR SOUTH AS THE CENTRAL APPALACHIANS AND NORTHERN  
MID-ATLANTIC, WHILE MINIMUM TEMPERATURES COULD FALL TO -20 DEGREES F IN  
NORTHERN NEW ENGLAND.  
 
DETERMINISTIC MODEL SOLUTIONS CONTINUE TO FEATURE A SHORTWAVE TROUGH  
PROGRESSING RAPIDLY EAST AND REACHING THE LOWER MISSISSIPPI VALLEY BY EARLY  
NEXT WEEK. AS PRECIPITATION SPREADS INTO THE RETREATING ARCTIC AIR, FREEZING  
RAIN MAY DEVELOP ACROSS PARTS OF THE OHIO VALLEY, CENTRAL APPALACHIANS, AND  
MID-ATLANTIC ON SUNDAY NIGHT INTO MONDAY MORNING. RECENT MODEL RUNS HAVE  
TRENDED TOWARDS A MORE SUPPRESSED LOW TRACK AND LOWER PRECIPITATION AMOUNTS  
WHICH WOULD HELP LIMIT ICE ACCUMULATIONS.  
 
ALTHOUGH THERE REMAINS SLIGHT TIMING DIFFERENCES ON WHEN A POTENT SHORTWAVE  
TROUGH MOVES INLAND FROM THE EAST PACIFIC, MODEL SOLUTIONS AGREE THAT THIS  
SYSTEM IS LIKELY TO TAP INTO SUBTROPICAL MOISTURE. THEREFORE, HEAVY RAIN  
(ISOLATED AMOUNTS NEAR 2 INCHES) IS EXPECTED ACROSS PARTS OF SOUTHERN  
CALIFORNIA WHICH INCLUDES THE THOMAS FIRE BURN AREA. THE DETERMINISTIC 0Z ECMWF  
MODEL INDICATES MORE THAN 2 INCHES, LIQUID EQUIVALENT, TO FALL OVER THE SIERRA  
MOUNTAINS WHERE TOTAL SNOWFALL AMOUNTS COULD EXCEED 2 FEET ON JAN 8 AND 9.  
 
A SHORTWAVE TROUGH IS FORECAST TO MOVE RAPIDLY EAST ACROSS THE SOUTHWESTERN  
U.S. AND RESULT IN HIGH WINDS (GUSTS ABOVE 40 MPH) FROM THE DESERT SOUTHWEST  
EAST TO THE CENTRAL AND SOUTHERN HIGH PLAINS. A RISK OF HEAVY SNOW EXISTS FROM  
THE CENTRAL HIGH PLAINS NORTHEAST TO THE MIDWEST LATER NEXT WEEK, IF A SURFACE  
LOW DEVELOPS IN THE LEE OF THE ROCKIES WITH A SUBSEQUENT TRACK TO THE  
NORTHEAST. HOWEVER, DUE TO LARGE SPREAD AMONG ENSEMBLE MEMBERS AND POOR MODEL  
CONTINUITY, A HEAVY SNOW HAZARD IS NOT POSTED AT THIS TIME.  
 
THE UPPER-LEVEL PATTERN OVER THE NORTH PACIFIC FAVORS AN INTENSE LOW PRESSURE  
SYSTEM TRACKING FROM THE WESTERN ALEUTIANS TO THE ALASKA PENINSULA FROM JAN 7  
TO 9. THIS LOW PRESSURE SYSTEM IS EXPECTED TO CAUSE HIGH WINDS (SPEEDS ABOVE 50  
MPH) AND HIGH WAVE HEIGHTS (POTENTIALLY IN EXCESS OF 36 FEET) ACROSS THE  
ALEUTIANS, ALASKA PENINSULA, AND SOUTHWEST MAINLAND ALASKA.  
 
FOR FRIDAY JANUARY 12 - THURSDAY JANUARY 18: MERIDIONAL FLOW IS LIKELY TO EASE  
OVER NORTH AMERICA BY MID-JANUARY AS AN AMPLIFIED 500-HPA TROUGH BECOMES  
ESTABLISHED OVER THE NORTH PACIFIC. THIS MAJOR PATTERN CHANGE IS CONSISTENT  
WITH THE ENHANCED PHASE OF THE MADDEN-JULIAN OSCILLATION (MJO) PROPAGATING EAST  
ACROSS THE INDIAN OCEAN. DURING WEEK-2, NEAR- TO ABOVE-NORMAL TEMPERATURES ARE  
FORECAST FOR A MAJORITY OF THE CONTINENTAL U.S. AS ZONAL FLOW FROM THE PACIFIC  
IS LIKELY TO PREVAIL. THE ANOMALOUS 500-HPA TROUGH UPSTREAM OVER THE NORTH  
PACIFIC AND INCREASING ONSHORE FLOW SUPPORT A SLIGHT RISK OF HEAVY  
PRECIPITATION ACROSS THE PACIFIC NORTHWEST, BEGINNING ON JAN 14 AND LASTING  
THROUGH THE END OF THE OUTLOOK PERIOD.  
 
THE U.S. DROUGHT MONITOR, VALID ON JANUARY 2, 2018 INDICATES AN INCREASE IN THE  
COVERAGE OF SEVERE TO EXCEPTIONAL DROUGHT (D2-D4) FROM 4.95% LAST WEEK TO 7.46%  
THIS WEEK. THE INCREASE PRIMARILY OCCURRED ACROSS THE SOUTHERN GREAT PLAINS AND  
THE SOUTHWESTERN U.S.  
 
FORECASTER: BRAD PUGH  
 

 
 
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