331  
FXUS21 KWNC 131952  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST NOVEMBER 13 2017  
 
SYNOPSIS: MID-LEVEL LOW PRESSURE IS FORECAST TO SHIFT FROM THE PACIFIC  
NORTHWEST THROUGH THE GREAT LAKES DURING WEEK-1, WHILE A SECOND REGION OF LOW  
PRESSURE BUILDS OVER THE NORTHEAST PACIFIC. IN ASSOCIATION WITH THE FIRST  
MID-LEVEL LOW PRESSURE, A SURFACE DISTURBANCE IS ANTICIPATED TO TRACK FROM THE  
PLAINS TOWARDS THE GREAT LAKES, WITH A TRAILING COLD FRONT EXTENDING WELL INTO  
THE SOUTH. SURFACE HIGH PRESSURE IS FORECAST TO BUILD ACROSS THE ROCKIES IN THE  
WAKE OF THIS FEATURE. THE WEEK-2 OUTLOOK FAVORS MID-LEVEL HIGH PRESSURE OVER  
THE WESTERN U.S., WITH LOW PRESSURE OVER THE EAST. ALASKA IS FORECAST TO  
EXPERIENCE PERIODIC SURFACE LOW PRESSURE SYSTEMS IN THE BERING SEA AND GULF OF  
ALASKA THROUGHOUT THE FORECAST PERIOD.  
 
HAZARDS  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF THE WEST COAST THROUGH THE SIERRA  
NEVADAS AND CASCADES, THU-MON, NOV 16-20.  
 
HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE CENTRAL GREAT BASIN, AND  
THE NORTHERN ROCKIES, THU, NOV 16.  
 
SEVERE WEATHER ACROSS PORTIONS OF THE MISSISSIPPI VALLEY, THE TENNESSEE VALLEY,  
THE GREAT LAKES, THE SOUTHERN PLAINS, AND THE OHIO VALLEY, FRI, NOV 17.  
 
HEAVY LAKE-EFFECT SNOW ACROSS PORTIONS OF NEW YORK, SUN-MON, NOV 19-20.  
 
MUCH BELOW-NORMAL TEMPERATURES ACROSS PORTIONS OF NORTH DAKOTA AND MINNESOTA,  
SUN, NOV 19.  
 
HIGH WINDS ACROSS PORTIONS OF THE GREAT BASIN, ROCKIES, AND PLAINS, THU-FRI,  
NOV 16-17.  
 
HIGH WINDS ACROSS PORTIONS OF THE ALASKA PENINSULA AND THE ALEUTIANS, SUN, NOV  
19.  
 
MUCH BELOW-NORMAL TEMPERATURES ACROSS PORTIONS OF THE ALASKA PANHANDLE AND  
MAINLAND ALASKA, SUN-MON, NOV 19-20.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF THE WEST COAST THROUGH THE SIERRA  
NEVADAS AND CASCADES, TUE, NOV 21.  
 
HEAVY LAKE-EFFECT SNOW ACROSS PORTIONS OF NEW YORK, TUE, NOV 21.  
 
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE EAST, TUE-SAT,  
NOV 21-NOV 25.  
 
MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE ALASKA  
PANHANDLE AND SOUTHEASTERN MAINLAND ALASKA, TUE-WED, NOV 21-NOV 22.  
 
SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF SOUTHERN AND EASTERN  
ALASKA, TUE-SAT, NOV 21-NOV 25.  
 
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 THURSDAY NOVEMBER 16 - MONDAY NOVEMBER 20: THE HIGHLY-AMPLIFIED, BLOCKY  
PATTERN IS FORECAST TO PERSIST THROUGHOUT THE OUTLOOK PERIOD, WITH A HIGHLY  
ANOMALOUS RIDGE SITUATED OVER THE BERING SEA. DOWNSTREAM TROUGHING IS FORECAST  
TO INITIALLY EXIST OVER THE NORTHEAST PACIFIC, BEFORE PROGRESSING TOWARDS THE  
GREAT LAKES DURING WEEK-1, WHILE A SECONDARY TROUGH BUILDS NORTH OF HAWAII. THE  
TROUGHING IN THE PACIFIC THROUGHOUT WEEK-1 FAVORS PERIODIC SHOTS OF HEAVY  
PRECIPITATION (24 HOUR LIQUID EQUIVALENT VALUES OF 2 INCHES OR GREATER, WITH  
MOUNTAIN SNOWS AND RAIN ELSEWHERE) EXTENDING ACROSS MUCH OF THE WEST COAST  
THROUGH THE CASCADES AND SIERRA NEVADAS THROUGHOUT WEEK-1. SOME OF THIS  
MOISTURE WILL MAKE IT FURTHER INLAND, AND RESULT IN HEAVY UPSLOPE SNOWS  
(EXCEEDING 8" IN 24 HOURS) FOR PORTIONS OF THE BITTERROOTS, UINTA MOUNTAINS,  
AND PARK RANGE ON THE 16TH. AS THE MID-LEVEL TROUGH IS FORECAST TO PUSH INLAND,  
HIGH WINDS (EXCEEDING 35 KNOTS) ARE POSSIBLE ACROSS MUCH OF THE GREAT BASIN,  
ROCKIES, AND PLAINS ON THE 16TH AND 17TH. THESE HIGH WINDS COULD ALSO  
MARGINALLY ELEVATE FIRE WEATHER CONCERNS FOR PORTIONS OF THE CENTRAL AND  
SOUTHERN PLAINS ON THE 17TH.  
 
A SURFACE LOW PRESSURE SYSTEM IS FORECAST TO DEVELOP IN THE LEE OF THE ROCKIES,  
DOWNSTREAM OF THE AFOREMENTIONED TROUGH, AND TO SHIFT TOWARDS THE GREAT LAKES  
BY THE END OF WEEK-1. THIS LOW PRESSURE AND ITS TRAILING COLD FRONT MAY BRING  
THE POTENTIAL FOR SEVERE WEATHER FROM THE ARKLATEX REGION THROUGH THE MIDWEST  
ON THE 17TH. STRONG, UNIDIRECTIONAL SHEAR IS FORECAST TO BE PRESENT WITH THIS  
SYSTEM, WHICH DESPITE MARGINAL INSTABILITY, SUGGESTS THE POTENTIAL FOR  
WIDESPREAD HIGH WINDS IN ASSOCIATION WITH A SQUALL LINE AT THE FRONTAL  
BOUNDARY. MORE WIDESPREAD, PROLONGED HIGH WINDS ARE POSSIBLE IN THE VICINITY OF  
THE GREAT LAKES IN THE WAKE OF THE SYSTEM'S PASSAGE, ALTHOUGH CURRENT MODEL  
GUIDANCE SUGGESTS THE ASSOCIATED SPEEDS TO BE MARGINALLY HAZARDOUS. FURTHER  
EAST, COOLER AIR AND STRONG WESTERLY WINDS ARE FORECAST, WHICH WOULD SUPPORT  
THE POTENTIAL FOR HEAVY LAKE-EFFECT SNOW DOWNWIND OF LAKE ONTARIO ON THE 19TH  
AND 20TH. FURTHER WEST, MUCH ABOVE-NORMAL TEMPERATURES ARE POSSIBLE FOR  
PORTIONS OF EASTERN NORTH DAKOTA AND NORTHWESTERN MINNESOTA ON THE 19TH AS COLD  
AIR SPILLS OUT OF CANADA INTO THE REGION AND COULD PUSH MINIMUM TEMPERATURES TO  
NEAR 0 DEGREES F (ANOMALIES OF -12 TO -16 DEGREES F).  
 
ALASKA WILL NOT BE SPARED FROM POTENTIAL HAZARDOUS WEATHER, AS PERIODIC SURFACE  
CYCLONES ARE FORECAST IN BOTH THE BERING SEA AND GULF OF ALASKA DURING WEEK-1.  
THE MOST POTENT OF THESE IS FORECAST TO BRING HIGH WINDS (EXCEEDING 50 MPH) TO  
PORTIONS OF THE ALASKA PENINSULA AND ALEUTIANS ON THE 19TH DUE TO THE  
SIGNIFICANT FETCH FOR THE NORTH-NORTHWESTERLY WINDS. MUCH BELOW-NORMAL  
TEMPERATURES ARE FORECAST IN ASSOCIATION WITH BITTERLY COLD AIR SPILLING OUT OF  
THE YUKON INTO EASTERN AND INTERIOR PORTIONS OF THE STATE FOR THE 19TH AND  
20TH. THE 0Z DETERMINISTIC ECMWF MODEL FORECASTS MINIMUM TEMPERATURE ANOMALIES  
OF -20 DEGREES F OR GREATER FOR HIGHLIGHTED AREAS DURING THIS EVENT.  
 
FOR TUESDAY NOVEMBER 21 - MONDAY NOVEMBER 27: FOR WEEK-2, THE BLOCK IN THE  
NORTH PACIFIC IS ANTICIPATED TO CONTINUE BEING A MAJOR FACTOR FOR THE U.S.,  
WITH ANOMALOUS DOWNSTREAM TROUGHING FOR THE NORTHEAST PACIFIC, RIDGING OVER THE  
WEST, AND TROUGHING IN THE EAST. THIS SETUP FAVORS A BRIEF CONTINUATION OF  
FORECAST HAZARDS FROM LATE IN WEEK-1, WITH HEAVY PRECIPITATION CONTINUING TO BE  
FAVORED THROUGH THE SIERRA NEVADAS AND CASCADES ON THE 21ST, WHILE LAKE-EFFECT  
SNOWFALL CONTINUES IN NEW YORK STATE FOR AREAS DOWNWIND OF LAKE ONTARIO. BEYOND  
THE 21ST MODEL GUIDANCE BEGINS TO DIVERGE IN TERMS OF SHORTWAVE FEATURES AND  
THE RESULTING LOW-LEVEL FLOW WHICH PRECLUDES EXTENSION OF THESE HAZARDS FURTHER  
INTO THE OUTLOOK PERIOD. WITH ANOMALOUS TROUGHING FORECAST ACROSS THE EAST IN  
WEEK-2, A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES IS FORECAST FROM THE  
21ST THROUGH THE 25TH FROM THE TENNESSEE AND OHIO VALLEYS AND AREAS TO THE  
EAST. HERE THE GEFS PROBABILISTIC EXTREMES TOOL FORECASTS A 20-30% CHANCE OF  
MINIMUM TEMPERATURES BEING BELOW THE 15TH CLIMATOLOGICAL PERCENTILE, WHILE  
ECMWF REFORECAST GUIDANCE ALSO TILTS COLD IN THIS REGION THROUGHOUT WEEK-2.  
 
ALASKA IS FORECAST TO CONTINUE TO EXPERIENCE ANOMALOUSLY COLD AIR DURING THE  
EARLY PORTION OF WEEK-2. A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES IS  
FORECAST FOR THE 21ST AND 22ND FOR MUCH OF SOUTHEASTERN MAINLAND ALASKA AND A  
SMALL PORTION OF THE ALASKA PANHANDLE. A SLIGHT RISK OF MUCH BELOW-NORMAL  
TEMPERATURES IS FORECAST ACROSS MUCH OF SOUTHERN AND EASTERN ALASKA FOR THE  
21ST THROUGH 25TH. THESE AREAS APPROXIMATELY CORRESPOND WITH THE 40% AND 20%  
PROBABILITIES OF MINIMUM TEMPERATURES BEING BELOW THE 15TH CLIMATOLOGICAL  
PERCENTILE BY THE GEFS PROBABILISTIC EXTREMES TOOL. ECMWF REFORECAST GUIDANCE  
ALSO PROJECTS COLDER THAN NORMAL TEMPERATURES ACROSS THE SOUTHERN HALF OF  
ALASKA THROUGHOUT WEEK-2.  
 
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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