381  
FXUS21 KWNC 311827  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT OCTOBER 31 2017  
 
SYNOPSIS: A SURGE OF PACIFIC MOISTURE IS FORECAST INTO THE WESTERN U.S. DURING  
THE FIRST HALF OF WEEK-1, IN ASSOCIATION WITH MID-LEVEL LOW PRESSURE FORECAST  
ACROSS THE PACIFIC NORTHWEST. MID-LEVEL HIGH PRESSURE IS FORECAST TO BUILD  
ACROSS TEXAS AND THE SOUTHEAST OVER THE COURSE OF WEEK-1. ANOTHER DISTURBANCE  
IS ANTICIPATED TO APPROACH THE PACIFIC NORTHWEST LATE IN WEEK-1. HIGH PRESSURE  
IS FORECAST ACROSS ALASKA DURING BOTH FORECAST WEEKS. ACROSS THE LOWER-48  
STATES DURING WEEK-2 THERE IS A TENDENCY TOWARDS LOW PRESSURE FAVORED OVER THE  
PACIFIC NORTHWEST WITH HIGH PRESSURE ACROSS THE REST OF THE COUNTRY.  
 
HAZARDS  
 
HEAVY SNOW ACROSS PORTIONS OF THE CASCADES OF OREGON, FRI, NOV 3.  
 
HEAVY SNOW ACROSS PORTIONS OF THE SIERRA NEVADAS, FRI-SAT, NOV 3-4.  
 
HEAVY RAIN ACROSS PORTIONS OF CALIFORNIA AND OREGON, FRI-SAT, NOV 3-4.  
 
HEAVY SNOW ACROSS PORTIONS OF THE GREAT BASIN AND NORTHERN ROCKIES, FRI-SAT,  
NOV 3-4.  
 
HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN AND CENTRAL ROCKIES, FRI-SUN, NOV  
3-5.  
 
HEAVY SNOW ACROSS PORTIONS OF THE UINTA MOUNTAINS, SUN, NOV 5.  
 
MUCH BELOW-NORMAL TEMPERATURES ACROSS PORTIONS OF THE NORTHERN PLAINS, THE  
NORTHERN ROCKIES, AND THE NORTHERN GREAT BASIN, SUN-TUE, NOV 5-7.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF WASHINGTON STATE, TUE, NOV 7.  
 
FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF FLORIDA AND THE NORTHEAST.  
 
MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF WASHINGTON  
STATE THROUGH NORTH DAKOTA, WED-FRI, NOV 8-10.  
 
MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PORTIONS OF NORTHERN  
CALIFORNIA, WED, NOV 8.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF GREAT BASIN, THE  
NORTHERN PLAINS, THE NORTHERN AND CENTRAL ROCKIES, CALIFORNIA, AND THE PACIFIC  
NORTHWEST, WED-SUN, NOV 8-12.  
 
SEVERE DROUGHT ACROSS THE NORTHERN PLAINS, THE NORTHERN ROCKIES, AND HAWAII.  
 
DETAILED SUMMARY  
 
FOR FRIDAY NOVEMBER 03 - TUESDAY NOVEMBER 07: A TRICKY FORECAST IS IN STORE FOR  
THE WEST, ALTHOUGH SNOW-LOVERS AND SKI RESORTS MAY SEE THINGS AS MORE OF A  
TREAT. ANOMALOUS MID-LEVEL TROUGHING IS FORECAST TO BE ESTABLISHED OVER THE  
PACIFIC NORTHWEST AT THE OUTSET OF THE FORECAST PERIOD. SURFACE LOW PRESSURE IS  
FORECAST DOWNSTREAM OF THE TROUGH AND TO PUSH EASTWARD INTO THE NORTHERN PLAINS  
BY THE WEEKEND BEFORE LIFTING TOWARDS HUDSON BAY. THIS SETUP FAVORS AN ENHANCED  
FLOW OF MOISTURE OFF THE PACIFIC AND INTO THE WEST. THE MOST WIDESPREAD HAZARD  
IS CURRENTLY FORECAST TO BE HEAVY RAIN (EXCEEDING 1 INCH IN 24 HOURS) AND HEAVY  
SNOW (EXCEEDING (6 INCHES IN 24 HOURS) FOR PORTIONS OF NORTHERN CALIFORNIA AND  
OREGON AND THE SIERRA NEVADAS RESPECTIVELY. OTHER PERIODS OF HEAVY SNOW ARE  
FORECAST FOR WINDWARD SLOPES AND HIGHER ELEVATIONS OF THE: OREGON CASCADES  
(NOVEMBER 3RD), BITTERROOTS AND PORTIONS OF CENTRAL IDAHO (NOVEMBER 3-4),  
TETONS AND YELLOWSTONE (NOVEMBER 3-5), AND UINTA MOUNTAINS (NOVEMBER 5). AS THE  
SURFACE LOW PRESSURE SYSTEM ASSOCIATED WITH THIS TROUGH LIFTS NORTHWARD INTO  
CANADA IT IS FORECAST TO PULL DOWN ANOMALOUSLY COLD AIR FROM CANADA AND INTO  
THE NORTHERN ROCKIES AND HIGH PLAINS THAT COULD SEND A CHILL UP YOUR SPINE.  
MUCH BELOW-NORMAL TEMPERATURES ARE FORECAST FOR THIS REGION FROM THE 5TH  
THROUGH 7TH WHERE MINIMUM TEMPERATURE ANOMALIES COULD BE 16 TO 20 DEGREES F  
BELOW NORMAL.  
 
A WEAKER DISTURBANCE IS FORECAST TO APPROACH THE PACIFIC NORTHWEST AT THE TAIL  
END OF WEEK-1. MODEL GUIDANCE BRINGS MOST OF THE PRECIPITATION ON NOVEMBER 7TH  
INTO BRITISH COLUMBIA, WITH A PLUME OF LESSER ACCUMULATIONS RUNNING PARALLEL TO  
THE PACIFIC COASTLINE OVER WASHINGTON STATE. HEAVY PRECIPITATION IS POSSIBLE  
WITH THIS EVENT ON THE 7TH WHERE 6 INCHES OR MORE OF SNOW IN THE HIGHER TERRAIN  
OF THE CASCADES IS POSSIBLE, WHILE RAINFALL AT LOWER ELEVATIONS COULD BE IN THE  
1-2 INCH RANGE AS DYNAMICAL MODEL ENSEMBLE MEAN 24-HOUR TOTALS FOR THE OLYMPIC  
PENINSULA ARE AROUND AN INCH OF LIQUID.  
 
ANOMALOUS RIDGING IS FORECAST TO BUILD ACROSS TEXAS AND THE GULF STATES  
THROUGHOUT WEEK-1, WITH THE WEATHER PREDICTION CENTER FORECASTING DAILY HIGH  
TEMPERATURE ANOMALIES EXCEEDING 20 DEGREES F ABOVE NORMAL FOR PORTIONS OF THE  
CENTRAL AND SOUTHERN PLAINS. WHILE THIS WOULD ONLY BRING DAILY HIGH  
TEMPERATURES INTO THE MID- TO UPPER-80S, AND THUS NOT BE HAZARDOUS, SOME HIGH  
TEMPERATURE RECORDS COULD FALL FOR PLACES SUCH AS ABILENE, TEXAS, WHERE RECORD  
VALUES ARE ONLY IN THE MID-80S.  
 
ANTECEDENT RAINS LEAD TO ONGOING FLOODING ACROSS PORTIONS OF THE NORTHEAST FROM  
THE SYSTEM THAT IMPACTED THE REGION OVER THE PAST WEEKEND. PROLONGED FLOODING  
CONTINUES ALONG THE ST. JOHNS RIVER IN FLORIDA.  
 
ALASKA IS FORECAST TO BE IMPACTED BY SURFACE HIGH PRESSURE ACROSS THE STATE  
THROUGHOUT WEEK-1, LEAVING WEATHER NOWHERE TO BE FOUND. THIS SCENARIO SUPPORTS  
WARMER THAN USUAL CONDITIONS AND GENERALLY MOIST WEATHER, BUT THERE ARE NO  
SIGNS OF ANY SUBSTANTIVE DISTURBANCES APPROACHING THE STATE THAT WOULD BRING  
HEAVY PRECIPITATION. AS SUCH, NO HAZARDS ARE FORECAST FOR ALASKA.  
 
FOR WEDNESDAY NOVEMBER 08 - TUESDAY NOVEMBER 14: DURING WEEK-2, WICKED  
ANOMALOUS 500-HPA TROUGHING IS INITIALLY FORECAST TO EXTEND FROM THE WESTERN  
U.S. THROUGH THE NORTHERN PLAINS BEFORE BECOMING CONFINED TO THE PACIFIC  
NORTHWEST LATER IN THE WEEK. THIS IS ANTICIPATED TO GIVE RISE TO A SLIGHT RISK  
OF MUCH BELOW-NORMAL TEMPERATURES DURING NOVEMBER 8-12 FOR MUCH OF THE WESTERN  
U.S. THROUGH THE NORTHERN PLAINS, ALTHOUGH THE HAZARD IS EXPECTED TO BE  
CONFINED TO THE NORTHERN TIER BEYOND THE 8TH. THE GEFS PROBABILISTIC EXTREMES  
TOOL INDICATES AT LEAST A 40% CHANCE OF MINIMUM TEMPERATURES BEING BELOW THE  
15TH CLIMATOLOGICAL PERCENTILE FOR PORTIONS OF NORTHERN CALIFORNIA ON THE 8TH  
AND FROM WASHINGTON THROUGH WESTERN NORTH DAKOTA FROM THE 8TH THROUGH 10TH,  
RESPECTIVELY. ELSEWHERE, ANOMALOUS RIDGING IS FORECAST WITH A HIGHER AMPLITUDE  
DURING WEEK-2 ACROSS THE REMAINDER OF THE CONUS RELATIVE TO YESTERDAY'S MODEL  
GUIDANCE.  
 
THE U.S. DROUGHT MONITOR, VALID ON OCTOBER 24, INDICATES THAT SEVERE TO  
EXCEPTIONAL (D2-D4) DROUGHT COVERS 2.58 PERCENT OF THE CONTINENTAL U.S., WHICH  
IS THE LOWEST COVERAGE SINCE JUNE. DUE TO RECENT RAINFALL, SEVERE TO  
EXCEPTIONAL DROUGHT IS LIMITED TO THE NORTHERN GREAT PLAINS, AND NORTHERN  
ROCKIES AND HAWAII.  
 
FORECASTER: CPC FORECASTER  
 

 
 
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