713  
FXUS21 KWNC 051935  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST JANUARY 05 2018  
 
SYNOPSIS: ARCTIC HIGH PRESSURE IS FORECAST TO WEAKEN ALONG THE EAST COAST ON  
JAN 8, WHILE A SURFACE LOW PRESSURE SYSTEM PROGRESSES EAST FROM THE CENTRAL  
U.S. A VIGOROUS MID-LEVEL LOW IS FORECAST TO MOVE INLAND OVER CALIFORNIA AND  
THE SOUTHWESTERN U.S. EARLY IN THE PERIOD. DURING MID-JANUARY, A MAJOR PATTERN  
CHANGE IS LIKELY AS A STRONG AREA OF MID-LEVEL LOW PRESSURE BECOMES ESTABLISHED  
OVER THE NORTHEAST PACIFIC. A TRANSITION TO ABOVE-NORMAL TEMPERATURES IS  
FAVORED ACROSS MUCH OF THE CONTINENTAL U.S. DURING WEEK-2 AS INCREASING PACIFIC  
FLOW PREVAILS.  
 
HAZARDS  
 
FREEZING RAIN FOR PARTS OF THE 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 ACROSS SOUTHERN CALIFORNIA AND THE SOUTHWESTERN U.S.,  
TUE-WED, JAN 9-10.  
 
MUCH BELOW-NORMAL TEMPERATURES SHIFTING EAST FROM THE NORTHERN GREAT PLAINS TO  
THE UPPER MISSISSIPPI VALLEY, WED-FRI, JAN 10-12.  
 
HEAVY PRECIPITATION FOR THE PACIFIC NORTHWEST, THU-FRI, JAN 11-12.  
 
HIGH WINDS EXPANDING FROM THE ALEUTIANS TO THE ALASKA PENINSULA AND PARTS OF  
SOUTHWEST MAINLAND ALASKA, MON-TUE, JAN 8-9.  
 
HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF THE ALEUTIANS AND ALASKA  
PENINSULA, MON-TUE, JAN 8-9.  
 
A MODERATE RISK OF HEAVY PRECIPITATION (RAIN AND HIGH-ELEVATION SNOW) FOR PARTS  
OF THE PACIFIC NORTHWEST AND NORTHERN SIERRA NEVADA MOUNTAINS, SAT-FRI, JAN  
13-19.  
 
A SLIGHT RISK OF HEAVY PRECIPITATION (RAIN AND HIGH-ELEVATION SNOW) FOR THE  
PACIFIC NORTHWEST, NORTHERN GREAT BASIN, AND NORTHERN CALIFORNIA, SAT-FRI, JAN  
13-19.  
 
SEVERE DROUGHT ACROSS THE GREAT PLAINS, THE SOUTHWEST, THE MIDDLE AND LOWER  
MISSISSIPPI VALLEY, AND HAWAII.  
 
DETAILED SUMMARY  
 
FOR MONDAY JANUARY 08 - FRIDAY JANUARY 12: DETERMINISTIC MODEL SOLUTIONS ON JAN  
5 FEATURE A SHORTWAVE TROUGH PROGRESSING RAPIDLY EAST FROM THE CENTRAL U.S. AS  
LIGHT PRECIPITATION SPREADS INTO THE RETREATING ARCTIC AIR, FREEZING RAIN  
REMAINS A RISK FOR THE CENTRAL APPALACHIANS AND MID-ATLANTIC ON JAN 8. RECENT  
MODEL RUNS CONTINUE TO TREND TOWARDS A MORE SUPPRESSED TRACK OF THE SHORTWAVE  
TROUGH WITH LOWER PRECIPITATION AMOUNTS ACROSS THE EASTERN U.S. THEREFORE,  
MAXIMUM ICE ACCUMULATIONS ARE ANTICIPATED TO BE AROUND 0.10 INCH.  
 
A POTENT SHORTWAVE TROUGH, WITH SUBTROPICAL MOISTURE, IS FORECAST TO MOVE  
INLAND FROM THE EAST PACIFIC EARLY IN THIS PERIOD. HEAVY RAIN IS EXPECTED  
ACROSS SOUTHERN CALIFORNIA, INCLUDING THE THOMAS FIRE BURN AREA, ON JAN 8 AND  
9. RAINFALL AMOUNTS ARE EXPECTED TO RANGE FROM 1 TO 2 INCHES ALONG THE COAST  
AND VALLEY WITH 2 TO 4 INCHES POSSIBLE ALONG THE SOUTH FACING SLOPES IN THE  
MOUNTAINS. A HIGH RISK OF FLASH FLOODING AND DEBRIS FLOWS EXISTS ACROSS RECENT  
BURN AREAS WHERE HEAVY RAINFALL OCCURS. A FEW FEET OF SNOW ARE FORECAST ACROSS  
THE SIERRA NEVADA MOUNTAINS ON JAN 8 AND 9. HIGH WINDS (GUSTS ABOVE 40 MPH) ARE  
EXPECTED TO ACCOMPANY THE SHORTWAVE TROUGH AS IT PROGRESSES ACROSS SOUTHERN  
CALIFORNIA AND THE SOUTHWESTERN U.S.  
 
A RISK OF HEAVY SNOW EXISTS FROM THE CENTRAL HIGH PLAINS NORTHEAST TO THE  
MIDWEST DURING MID-WEEK, IF A SURFACE LOW DEVELOPS IN THE LEE OF THE ROCKIES  
WITH A SUBSEQUENT TRACK TO THE NORTHEAST. HOWEVER, DUE TO CONTINUED LARGE  
SPREAD AMONG ENSEMBLE MEMBERS AND POOR MODEL CONTINUITY, A HEAVY SNOW HAZARD IS  
NOT POSTED.  
 
AN UPPER-LEVEL TROUGH APPROACHING FROM THE CENTRAL U.S. ALONG WITH RETURN FLOW  
FROM THE GULF OF MEXICO INCREASES CHANCES FOR HEAVY PRECIPITATION, WITH SNOW ON  
THE NORTHWEST PERIPHERY, ACROSS THE EASTERN U.S. LATE IN THIS PERIOD. LARGE  
UNCERTAINTY EXISTS ON THE TIMING AND STRENGTH OF ANY WINTER STORM THAT  
POTENTIALLY AFFECTS THE UPPER OHIO VALLEY, NORTHERN MID-ATLANTIC, AND NORTHEAST  
BY THE FOLLOWING WEEKEND. ALSO, MODEL SOLUTIONS ARE EXPECTED TO VARY AND REMAIN  
INCONSISTENT DURING THIS UPCOMING PATTERN CHANGE. THEREFORE, NO CATEGORICAL  
HEAVY PRECIPITATION HAZARD IS POSTED AT THIS TIME.  
 
ALTHOUGH THE OVERALL PATTERN IS LIKELY TO RESULT IN A WARMING TREND ACROSS THE  
CENTRAL AND EASTERN U.S. WITH TIME, MODEL SOLUTIONS ARE IN GOOD AGREEMENT THAT  
AN ARCTIC SURFACE HIGH BRIEFLY SHIFTS SOUTH INTO THE NORTH-CENTRAL U.S. NEXT  
WEEK. THEREFORE, MUCH BELOW-NORMAL TEMPERATURES ARE EXPECTED TO SHIFT EAST FROM  
THE NORTHERN GREAT PLAINS TO THE UPPER MISSISSIPPI VALLEY FROM JAN 10 TO 12.  
MINIMUM TEMPERATURES ARE EXPECTED TO FALL BELOW -10 DEGREES F ACROSS THESE  
AREAS. THIS OUTBREAK OF ARCTIC IS LIKELY TO BE SHORT-LIVED WITH A RAPID WARMING  
TREND BY MID-JANUARY.  
 
ENHANCED ONSHORE FLOW ACROSS THE PACIFIC NORTHWEST, ASSOCIATED WITH AN  
AMPLIFYING 500-HPA TROUGH OVER THE NORTH PACIFIC, IS EXPECTED TO BEGIN AS EARLY  
AS JAN 11. THEREFORE, A HEAVY PRECIPITATION HAZARD IS POSTED FOR PARTS OF THE  
PACIFIC NORTHWEST ON JAN 11 AND 12.  
 
THE UPPER-LEVEL PATTERN OVER THE NORTH PACIFIC FAVORS AN INTENSE LOW PRESSURE  
SYSTEM TRACKING ACROSS THE ALEUTIANS ON JAN 8 AND 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 SATURDAY JANUARY 13 - FRIDAY JANUARY 19: MERIDIONAL FLOW IS LIKELY TO EASE  
OVER NORTH AMERICA BY MID-JANUARY AS AN AMPLIFIED 500-HPA TROUGH BECOMES  
ESTABLISHED OVER THE NORTHEAST 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, ABOVE-NORMAL TEMPERATURES ARE LIKELY TO  
EXPAND FROM WEST TO EAST ACROSS THE CONTINENTAL U.S. LATE IN WEEK-2, THE GFS  
ENSEMBLE MEAN ON JAN 5 INDICATES DAILY TEMPERATURES AVERAGING MORE THAN 12  
DEGREES F ABOVE NORMAL ACROSS THE GREAT PLAINS.  
 
THE ANOMALOUS 500-HPA TROUGH OVER THE NORTHEAST PACIFIC AND INCREASING ONSHORE  
FLOW SUPPORT A SLIGHT TO MODERATE RISK OF HEAVY PRECIPITATION ACROSS THE  
NORTHWESTERN U.S. A MODERATE RISK OF HEAVY PRECIPITATION IS POSTED FOR COASTAL  
WASHINGTON AND OREGON WHERE THE EVOLVING PATTERN MAY EVENTUALLY LEAD TO  
EXCESSIVE RAINFALL AND FLOODING. A MODERATE RISK IS ALSO POSTED FOR THE  
CASCADES AND NORTHERN SIERRA NEVADA MOUNTAINS WHERE PERIODS OF HEAVY SNOW ARE  
MOST LIKELY.  
 
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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