046  
FXUS21 KWNC 101912  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST NOVEMBER 10 2017  
 
SYNOPSIS: THE NEXT TWO WEEKS APPEAR ACTIVE IN TERMS OF HAZARDS ACROSS BOTH THE  
LOWER-48 STATES AND ALASKA. PERSISTENT ON-SHORE FLOW IS FORECAST TO AFFECT THE  
WEST IN ASSOCIATION WITH MID-LEVEL LOW PRESSURE OVER THE NORTHEAST PACIFIC. A  
SURFACE LOW PRESSURE SYSTEM IS FORECAST TO LOOP AROUND THIS MID-LEVEL FEATURE  
AND DEEPEN ACROSS THE NORTHERN U.S. WHILE APPROACHING THE GREAT LAKES BY LATE  
IN WEEK-1. ARCTIC HIGH PRESSURE IS FORECAST ACROSS ALASKA THROUGHOUT BOTH  
WEEKS, WITH SURFACE LOW PRESSURES IN THE GULF OF ALASKA DURING WEEK-1 AND AN  
INTENSE SYSTEM IN THE BERING SEA BY EARLY IN WEEK-2. ACROSS THE LOWER-48 DURING  
WEEK-2, MID-LEVEL HIGH PRESSURE IS FORECAST TO BUILD ACROSS THE WESTERN U.S.  
WHILE LOW PRESSURE SETTLES EAST OF THE MISSISSIPPI RIVER.  
 
HAZARDS  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF CALIFORNIA, OREGON, WASHINGTON, AND  
NORTHERN IDAHO, MON-FRI, NOV 13-17.  
 
HIGH WINDS ACROSS COASTAL PORTIONS OF CALIFORNIA AND THE PACIFIC NORTHWEST,  
MON-TUE, NOV 13-14.  
 
HIGH WINDS ACROSS PORTIONS OF THE GREAT BASIN, MON, NOV 13.  
 
HEAVY SNOW ACROSS PORTIONS OF THE BITTERROOTS, WED-FRI, NOV 15-17.  
 
HEAVY SNOW ACROSS PORTIONS OF THE TETONS, WED, NOV 15.  
 
HEAVY SNOW ACROSS PORTIONS OF THE WESTERN GREAT LAKES AND THE UPPER MISSISSIPPI  
VALLEY, THU-FRI, NOV 16-17.  
 
HIGH WINDS ACROSS MUCH OF THE ROCKIES, GREAT PLAINS, UPPER AND MIDDLE  
MISSISSIPPI VALLEY, AND GREAT LAKES, THU-FRI, NOV 16-17.  
 
MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE ALASKA PANHANDLE AND  
SOUTHEASTERN ALASKA, WED-FRI, NOV 15-17.  
 
HIGH WINDS ACROSS DOWNSLOPE AREAS OF THE ALASKA PANHANDLE AND SOUTHEASTERN  
ALASKA, WED-FRI, NOV 15-17.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF CALIFORNIA, OREGON, AND WASHINGTON,  
SAT-SUN, NOV 18-19.  
 
HEAVY SNOW ACROSS PORTIONS OF THE BITTERROOTS, SAT-SUN, NOV 18-19.  
 
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE GREAT LAKES,  
NORTHEAST, THE APPALACHIANS, THE TENNESSEE AND OHIO VALLEY, THE MID-ATLANTIC,  
THE SOUTHEAST, AND THE GREAT LAKES, WED-FRI, NOV 22-24.  
 
MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE ALASKA  
PANHANDLE, SAT, NOV 18.  
 
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE ALASKA  
PANHANDLE AND MAINLAND ALASKA, SAT-WED, NOV 18-22.  
 
SEVERE DROUGHT ACROSS PARTS OF THE THE LOWER AND MIDDLE MISSISSIPPI VALLEY, THE  
NORTHERN AND SOUTHERN PLAINS, THE NORTHERN ROCKIES, ARIZONA, AND HAWAII.  
 
DETAILED SUMMARY  
 
FOR MONDAY NOVEMBER 13 - FRIDAY NOVEMBER 17: A HIGH-AMPLITUDE 500-HPA PATTERN  
IS ANTICIPATED TO BE IN PLACE BY THE TIME THE FORECAST PERIOD BEGINS, WITH A  
SUBSTANTIAL BLOCK OVER THE BERING SEA THAT IS FORECAST TO LAST THROUGH WEEK-2.  
DOWNSTREAM, ANOMALOUS TROUGHING IS FAVORED OVER THE NORTHEAST PACIFIC, WHICH  
SUGGESTS A PERSISTENT WET PATTERN FOR THE PACIFIC NORTHWEST AS PERIODIC SURFACE  
SHORTWAVES DIG THROUGH THIS FEATURE. PERIODIC HEAVY PRECIPITATION (MOUNTAIN  
SNOWS, WITH RAIN AT LOWER ELEVATIONS, AND DAILY LIQUID EQUIVALENT ACCUMULATIONS  
OF 2 INCHES OR MORE) IS FORECAST FOR THE ENTIRETY OF WEEK-1 FROM NORTHERN  
CALIFORNIA THROUGH THE CASCADES AND EASTWARD ALONG THE CANADIAN BORDER INTO  
IDAHO. UP TO 10 INCHES OF LIQUID EQUIVALENT PRECIPITATION ARE POSSIBLE OVER THE  
COURSE OF THE WEEK. HIGH WINDS (EXCEEDING 35 KNOTS) ARE POSSIBLE ALONG THE  
PACIFIC COASTLINE FROM NORTHERN CALIFORNIA THROUGH THE OLYMPIC PENINSULA ON THE  
13TH AND 14TH IN ASSOCIATION WITH AN EARLY SURGE OF PACIFIC MOISTURE. THERE IS  
ALSO POTENTIAL FOR DOWNSLOPE-ENHANCED HIGH WINDS OUT OF THE SOUTH FURTHER  
INLAND ACROSS PORTIONS OF THE GREAT BASIN ON THE 13TH. AS THIS PACIFIC MOISTURE  
PUSHES FURTHER INLAND, HEAVY SNOW (DAILY TOTALS EXCEEDING 8 INCHES) ARE  
FORECAST ACROSS THE BITTERROOTS DURING THE 15TH-17TH AND TETONS ON THE 15TH.  
 
BY THE MIDDLE OF WEEK-1 THE MID-LEVEL FLOW OVER THE WEST IS FORECAST TO  
DEAMPLIFY SOMEWHAT, BUT SURFACE LOW PRESSURE IS ANTICIPATED TO DEVELOP AND  
INTENSIFY DOWNSTREAM OVER THE NORTHERN ROCKIES. THIS LOW IS THEN FORECAST TO  
TRACK TOWARDS THE GREAT LAKES BY LATE IN WEEK-1. INITIALLY, HIGH WINDS IN THE  
LEE OF THE ROCKIES ARE ANTICIPATED TO BE THE INITIAL THREAT ON THE 16TH, THEN  
SHIFTING TOWARDS THE NORTHERN PLAINS AND GREAT LAKES ON THE 17TH AS THE SURFACE  
LOW DEEPENS. DETERMINISTIC MODELS ARE GENERALLY LESS PROGRESSIVE WITH THIS  
FEATURE THAN THE ENSEMBLES, BUT BOTH THE DETERMINISTIC GFS AND ECMWF HAVE  
SUB-980 HPA LOWS OVER THE GREAT LAKES NEAR THE END OF WEEK-1. HEAVY SNOW (4  
INCHES OR MORE IN 24 HOURS) IS POSSIBLE WITH THIS SYSTEM ACROSS THE UPPER  
MISSISSIPPI VALLEY AND WESTERN GREAT LAKES ON THE 16TH AND 17TH, WITH  
LAKE-EFFECT SNOWFALL SETTING UP ACROSS THE UPPER PENINSULA OF MICHIGAN OFF OF  
LAKE SUPERIOR ON THE 17TH.  
 
ACTIVE WEATHER IN TERMS OF HAZARDOUS POTENTIAL ALSO LOOKS TO LOOM FOR ALASKA  
DURING WEEK-1 AS ARCTIC HIGH PRESSURE BUILDS ACROSS THE STATE. AS THE COLD AIR  
BUILDS, MUCH BELOW-NORMAL TEMPERATURES (MINIMUM TEMPERATURE ANOMALIES OF AT  
LEAST -20 DEGREES F) ARE FORECAST ACROSS SOUTHEASTERN PORTIONS OF THE STATE AND  
THE PANHANDLE ON THE 15TH THROUGH 17TH. FURHTER NORTH, SOME AREAS IN THE  
VICINITY OF THE NORTH SLOPE COULD SEE TEMPERATURES OF -40 DEGREES F FOR THE  
FIRST TIME OF THE SEASON, EARLIER THAN CLIMATOLOGY WOULD SUGGEST. HOWEVER, NO  
HAZARDS ARE INDICATED THIS FAR NORTH DUE TO TEMPERATURE ANOMALIES BEING  
RELATIVELY MODEST. THE ANTICIPATED COLD AIR SETTLING ACROSS THE HIGHER TERRAIN  
OF THE KENAI, CHUGACH, AND ST. ELIAS MOUNTAINS DOES LEAD TO THE POTENTIAL FOR  
STRONG KATABATIC (GAP) WINDS THAT COULD YIELD GUSTS TO 100 MPH FOR PORTIONS OF  
SOUTHEASTERN ALASKA AND THE PANHANDLE ON THE 15TH THROUGH 17TH.  
 
FOR SATURDAY NOVEMBER 18 - FRIDAY NOVEMBER 24: THE PERSISTENT WET PATTERN FOR  
THE PACIFIC NORTHWEST LOOKS TO CONTINUE INTO EARLY WEEK-2 AS ANOMALOUS 500-HPA  
TROUGHING IS FORECAST TO CONTINUE FROM HAWAII THROUGH THE YUKON. AS SUCH,  
CONTINUED HEAVY PRECIPITATION (MOUNTAIN SNOWS WITH RAIN ELSEWHERE) ON THE 18TH  
AND 19TH IS FORECAST FOR COASTAL REGIONS THROUGH THE CASCADES AND SIERRA  
NEVADAS FROM WASHINGTON STATE THROUGH NORTHERN CALIFORNIA. FURTHER INLAND,  
HEAVY SNOW IS ALSO FAVORED TO CONTINUE FROM WEEK-1 THROUGH THE 19TH OVER THE  
BITTERROOTS, WHERE ANOTHER 6 INCHES OF SNOW COULD ACCUMULATE EACH DAY.  
 
FURTHER EAST, TROUGHING IS FORECAST TO BUILD TO THE EAST OF THE MISSISSIPPI  
RIVER OVER THE COURSE OF WEEK-2. THIS WOULD SUPPORT THE POTENTIAL FOR  
BELOW-NORMAL TEMPERATURES BY THE END OF THE WEEK FOR MANY PARTS OF THE EASTERN  
CONUS, WITH A SLIGHT-RISK FORECAST HERE FROM THE 22ND THROUGH 24TH. THIS  
LOW-LEVEL FLOW SETUP ALSO SUPPORTS THE POTENTIAL FOR LAKE-EFFECT SNOWS TO THE  
SOUTHEAST OF THE GREAT LAKES DURING MUCH OF WEEK-2, BUT FORECAST FLOW APPEARS  
LARGELY PERPENDICULAR TO THE LAKES WITH LIMITED FETCH, WHICH COULD KEEP  
ACCUMULATIONS DOWN.  
 
BOTH THE GFS AND ECMWF MODELS SUPPORT A SURFACE CYCLONE IN THE BERING SEA NEAR  
THE START OF WEEK-1. THE GFS IS FURTHER NORTH AND DEEPER WITH THIS SYSTEM THAN  
THE ECMWF, WITH A 967-HPA LOW OVER SOUTHWESTERN ALASKA BY 0Z ON THE 19TH.  
CONVERSELY, THE DETERMINISTIC ECMWF HAS THIS SYSTEM APPROACHING THE ALEUTIANS  
AS A WEAKER, 991-HPA LOW AT THE SAME TIME. EACH MODEL THEN TRACKS THE SYSTEM  
TOWARDS THE BERING SEA DURING THE NEXT TWO DAYS, WHICH WOULD SHIFT THE FOCUS  
FOR ANY ASSOCIATED HAZARDS TOWARDS THE SOUTHERN COASTS. NO HAZARDS ARE  
PRESENTLY INDICATED IN ASSOCIATION WITH THIS SYSTEM GIVEN THE UNCERTAINTY AMONG  
DYNAMICAL GUIDANCE.  
 
ANOMALOUSLY COLD AIR IS ALSO FORECAST TO LINGER ACROSS MUCH OF ALASKA IN  
WEEK-2. A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES CONTINUES FOR THE  
ALASKA PANHANDLE ON THE 18TH, WHERE THE GEFS PROBABILISTIC EXTREMES TOOL  
SUPPORTS A BETTER THAN 40% CHANCE OF OBSERVED MINIMUM TEMPERATURES BEING BELOW  
THE 15TH CLIMATOLOGICAL PERCENTILE. A SLIGHT RISK OF MUCH BELOW-NORMAL  
TEMPERATURES IS FORECAST FOR MUCH OF THE REMAINDER OF THE STATE FOR THE 18TH  
THROUGH 22ND WHERE THE GEFS GIVES AT LEAST A 20% CHANCE OF MINIMUM TEMPERATURES  
BEING BELOW THE 15TH CLIMATOLOGICAL PERCENTILE.  
 
THE U.S. DROUGHT MONITOR, VALID ON NOV 7, INDICATES THAT SEVERE TO EXCEPTIONAL  
(D2-D4) DROUGHT COVERS 2.90 PERCENT OF THE CONTINENTAL U.S., WHICH IS A SLIGHT  
INCREASE FROM 2.67 PERCENT LAST WEEK. THE MOST WIDESPREAD IMPROVEMENTS MADE TO  
THE DROUGHT DEPICTION THIS WEEK WERE OVER THE NORTHWESTERN CONUS. AREAS ACROSS  
THE SOUTHERN AND CENTRAL PLAINS AND THE LOWER AND MIDDLE MISSISSIPPI VALLEY HAD  
THE MOST WIDESPREAD DROUGHT CLASS DEGRADATION.  
 
FORECASTER: CPC FORECASTER  
 

 
 
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