535  
FXUS21 KWNC 192052  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT OCTOBER 19 2017  
 
SYNOPSIS: A COLD FRONT IS ANTICIPATED TO SWEEP ACROSS THE EASTERN HALF OF THE  
CONTIGUOUS U.S. THROUGHOUT THE DAY 3 TO 7 PERIOD. SURFACE HIGH PRESSURE IS  
FORECAST ACROSS MUCH OF THE CONTIGUOUS U.S., ONE EAST OF THE COLD FRONT AND ONE  
WEST OF THE FRONT. MEANWHILE, A SURFACE LOW PRESSURE SYSTEM IS PREDICTED TO  
DEVELOP OVER THE GULF OF ALASKA, BRINGING STRONG ONSHORE FLOW TO THE PACIFIC  
NORTHWEST AT THE BEGINNING OF THE PERIOD. A SERIES OF STORMS ARE EXPECTED TO  
FORM OVER THE ALEUTIANS AND THE GULF OF ALASKA THROUGHOUT WEEK-1 AND WEEK-2.  
SOME MODELS FAVOR AMPLIFIED MID-LEVEL TROUGHING THROUGHOUT WEEK-2 ACROSS THE  
EASTERN HALF OF THE U.S. FROM THE BEGINNING TO MIDDLE OF WEEK-2, TRANSITIONING  
TO A LOW AMPLITUDE FLOW THROUGHOUT THE CONUS.  
 
HAZARDS  
 
HEAVY RAIN ACROSS PORTIONS OF THE PACIFIC NORTHWEST, SUN, OCT 22.  
 
HEAVY RAIN FROM THE GULF COAST TO THE LOWER GREAT LAKES, SUN-MON, OCT 22-OCT  
23.  
 
HEAVY RAIN ACROSS PORTIONS OF THE MID-ATLANTIC AND THE NORTHEAST, TUE-WED, OCT  
24-OCT 25.  
 
HEAVY SNOW ACROSS PORTIONS OF THE PACIFIC NORTHWEST AND THE NORTHERN ROCKIES,  
SUN, OCT 22.  
 
FLOODING POSSIBLE ACROSS PORTIONS OF THE PACIFIC NORTHWEST.  
 
FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF FLORIDA.  
 
HIGH WINDS ACROSS PORTIONS OF CALIFORNIA AND THE PACIFIC NORTHWEST, SUN, OCT 22.  
 
HIGH WINDS ACROSS PORTIONS OF THE CENTRAL AND NORTHERN PLAINS, THE CENTRAL AND  
NORTHERN ROCKIES, AND THE UPPER AND MIDDLE MISSISSIPPI VALLEYS, OCT 22-OCT 23.  
 
HIGH WINDS ACROSS PORTIONS OF SOUTHERN CALIFORNIA, SUN-MON, OCT 22-OCT 23.  
 
ENHANCED WILDFIRE RISK ACROSS PORTIONS OF THE CALIFORNIA, SUN-MON, OCT 22-OCT  
23.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF THE ALASKA PANHANDLE AND SOUTHERN  
MAINLAND ALASKA, MON-TUE, OCT 23-OCT 24.  
 
HIGH WINDS ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND ALASKA,  
MON-TUE, OCT 23-OCT 24.  
 
HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF THE ALASKA PANHANDLE AND  
MAINLAND ALASKA, MON, OCT 23.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF SOUTHERN MAINLAND ALASKA AND THE  
ALEUTIANS, TUE-THU, OCT 24-OCT 26.  
 
HIGH WINDS ACROSS PORTIONS OF SOUTHERN MAINLAND ALASKA AND THE ALEUTIANS,  
TUE-THU, OCT 24-OCT 26.  
 
HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF MAINLAND ALASKA AND THE  
ALEUTIANS, TUE-THU, OCT 24-OCT 26.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND  
ALASKA, FRI, OCT 27.  
 
HIGH WINDS ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND ALASKA, FRI,  
OCT 27.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FROM THE GREAT LAKES TO GULF  
COAST, AS FAR WEST AS THE MISSISSIPPI VALLEY, FRI-SUN, OCT 27-OCT 29.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR NORTHERN PORTIONS OF MAINLAND  
ALASKA, FRI-SAT, OCT 27-OCT 28.  
 
SLIGHT RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR PORTIONS OF SOUTHERN  
CALIFORNIA AND THE SOUTHWEST, FRI-SAT, OCT 27-OCT 28.  
 
SEVERE DROUGHT ACROSS THE MIDDLE MISSISSIPPI VALLEY, THE NORTHERN PLAINS, THE  
NORTHERN ROCKIES, AND HAWAII.  
 
DETAILED SUMMARY  
 
FOR SUNDAY OCTOBER 22 - THURSDAY OCTOBER 26: A LOW-PRESSURE SYSTEM IS FORECAST  
TO IMPACT THE PACIFIC NORTHWEST. HEAVY RAINS (GREATER THAN 2 INCHES IN 24  
HOURS) AND HEAVY SNOWS (LIQUID EQUIVALENT OF UP TO 2.5 INCHES AND ABOVE 4000FT)  
ARE LIKELY OVER THE CASCADES AND NORTHERN ROCKIES DURING OCT 23. ALONG THE  
COAST, HIGH WINDS ARE ALSO LIKELY FROM NORTHERN CALIFORNIA TO THE PACIFIC  
NORTHWEST.  
 
A COLD FRONT IS FORECAST TO PUSH ACROSS THE EASTERN CONUS DURING NEXT WEEK,  
WITH A WAVE OF LOW-PRESSURE MOVING FROM SOUTH TO NORTH ALONG THE FRONT. THIS  
WAVE OF LOW-PRESSURE IS EXPECTED TO SUPPORT HEAVY RAINS (UP TO 2.5 INCHES IN 48  
HOURS) ACROSS PORTIONS OF THE TENNESSEE VALLEY. SOME ISOLATED SEVERE WEATHER IS  
POSSIBLE FROM THE SOUTHERN GREAT PLAINS TO THE LOWER MISSISSIPPI VALLEY, LIKELY  
IN THE FORM OF A SQUALL LINE, ON SUNDAY.  
 
AS THE LOW-PRESSURE SYSTEM MOVES NORTHWARD, HEAVY RAINS ARE FORECAST TO SPREAD  
TO THE MID-ATLANTIC AND NORTHEAST. SOME MODELS INDICATE WIND SPEEDS APPROACHING  
30 MPH NEAR THE NORTHEAST COAST, LATER ON TUESDAY AND INTO WEDNESDAY, OCT 25,  
THOUGH MODEL UNCERTAINTY IN THE WIND SPEEDS IS TOO HIGH TO DEPICT A HAZARD.  
 
HIGH PRESSURE IS LIKELY TO BUILD OVER THE ROCKIES, IN A POSITION WHERE A HIGH  
PRESSURE SYSTEM CAN SUPPORT HIGH WINDS OVER CALIFORNIA. THE HIGH WINDS ARE  
LIKELY TO CONTRIBUTE TO CRITICAL FIRE WEATHER CONDITIONS OVER SOUTHERN  
CALIFORNIA ON OCT 22-23, WITH MARGINAL FIRE WEATHER CONDITIONS EXTENDING TO THE  
24TH. DURING SUN-TUE, OCT 22-24, HIGH WINDS (GREATER THAN 35 MPH) ARE ALSO  
FORECAST OVER THE NORTHERN AND CENTRAL PLAINS ON THE NORTHERN PERIPHERY OF THE  
HIGH PRESSURE SYSTEM.  
 
MULTIPLE LOW-PRESSURE SYSTEMS ARE FORECAST TO IMPACT ALASKA. HIGH WINDS  
(EXCEEDING 40 MPH), HIGH SIGNIFICANT WAVE HEIGHTS, AND HEAVY PRECIPITATION ARE  
LIKELY FOR SOUTHEAST ALASKA AND THE ALASKA PANHANDLE EARLY NEXT WEEK, WITH THE  
FIRST SYSTEM. A SUBSEQUENT LOW-PRESSURE SYSTEM IS FORECAST TO DEVELOP NEAR THE  
ALEUTIANS, AND TRACK EASTWARD TOWARD SOUTHERN COASTAL ALASKA, SPREADING HEAVY  
PRECIPITATION (EXCEEDING 3 INCHES IN 24 HOURS), HIGH WINDS (LIKELY IN EXCESS OF  
50 MPH IN SOME LOCATIONS), AND HIGH SIGNIFICANT WAVE HEIGHTS. THESE IMPACTS ARE  
LIKELY TO BEGIN ON OCT 24, AND SPREAD EASTWARD, WHILE LASTING THROUGH OCT 27.  
 
FOR FRIDAY OCTOBER 27 - THURSDAY NOVEMBER 02: THERE IS GOOD AGREEMENT BETWEEN  
THE 6Z GEFS AND 0Z ECMWF ENSEMBLE REGARDING THE  
 
DEVELOPMENT OF A MID-LEVEL TROUGH ACROSS THE EASTERN HALF OF THE CONUS  
THROUGHOUT  
 
THE BEGINNING TO MIDDLE OF WEEK-2. THIS PATTERN MAY TRANSLATE TO MUCH BELOW  
NORMAL  
 
TEMPERATURES ACROSS THE EASTERN HALF OF THE CONUS OCT 27 TO 29. MODELS INDICATE  
A  
 
TRANSITION TO MORE ZONAL FLOW FOR THE REST OF WEEK-2. THE GEFS REFORECAST TOOL  
 
INDICATES A 20 PERCENT CHANCE OF TEMPERATURES FOR HIGHLIGHTED AREAS REACHING  
THE  
 
LOWEST 15TH PERCENTILE, WITH THE MINIMUM TEMPERATURES OF SOME AREAS REACHING  
SUB-  
 
FREEZING TEMPERATURES. THIS COLD EVENT COULD BE THE FIRST FREEZE FOR PORTIONS  
OF THE OHIO VALLEY AND CORN BELT.  
 
AN AMPLIFIED MID-LEVEL RIDGE IS PREDICTED TO BUILD ACROSS THE WESTERN HALF OF  
THE  
 
CONUS AT THE BEGINNING OF WEEK-2. THIS PATTERN FAVORS A SLIGHT CHANCE OF MUCH  
ABOVE  
 
NORMAL TEMPERATURES ACROSS PARTS OF SOUTHERN CALIFORNIA AND THE SOUTHWEST, OCT  
27  
 
TO 28. THE GEFS REFORECAST TOOL INDICATES A 20 PERCENT CHANCE OR GREATER OF  
MAXIMUM  
 
TEMPERATURES IN THE HIGHLIGHTED AREAS REACHING THE 85TH PERCENTILE AND  
LOCALIZED  
 
AREAS REACHING UP TO 90 DEG F.  
 
SURFACE HIGH PRESSURE IS ANTICIPATED TO DEVELOP OVER THE BEAUFORT SEA AT THE  
 
BEGINNING OF WEEK-2. THIS PATTERN MAY SUPPORT A SLIGHT CHANCE OF MUCH BELOW  
NORMAL  
 
TEMPERATURES ACROSS NORTHERN PARTS OF MAINLAND ALASKA OCT 27 TO 28. THE GEFS  
 
REFORECAST TOOL INDICATES A SLIGHT CHANCE OF MINIMUM TEMPERATURES IN THIS  
REGION  
 
REACHING THE LOWEST 15TH PERCENTILE, WITH TEMPERATURES REACHING 0 DEG F.  
 
THE U.S. DROUGHT MONITOR, VALID ON OCTOBER 10, INDICATES THAT SEVERE TO  
EXCEPTIONAL  
 
(D2-D4) DROUGHT COVERS 2.98 PERCENT OF THE CONTINENTAL U.S., DOWN FROM 4.03  
PERCENT OF THE CONUS. THE LARGEST CHANGES WERE OVER THE NORTHERN PLAINS AND  
MIDWEST.  
 
FORECASTER: MATTHEW ROSENCRANS  
 

 
 
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