982  
FXUS21 KWNC 162016  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT OCTOBER 16 2017  
 
SYNOPSIS: A SURFACE LOW IS EXPECTED TO TRACK FROM WESTERN TO EASTERN CANADA  
OVER WEEK-1. ITS TRAILING COLD FRONT IS ANTICIPATED TO SWEEP ACROSS THE LOWER  
48 STATES THROUGHOUT THE DAY 3 TO 7 PERIOD INTO THE BEGINNING OF WEEK-2.  
SURFACE HIGH PRESSURE IS FORECAST TO BUILD ACROSS MUCH OF THE CONTIGUOUS U.S.  
AHEAD OF AND IN THE WAKE OF THE COLD FRONT. A SERIES OF SURFACE LOW PRESSURE  
SYSTEMS ARE PREDICTED TO DEVELOP OVER PARTS OF MAINLAND ALASKA AS WELL AS THE  
GULF OF ALASKA DURING THE 3 TO 7 DAY PERIOD. SOME MODELS FAVOR AMPLIFIED  
MID-LEVEL TROUGHING THROUGHOUT WEEK-2 ACROSS THE EASTERN HALF OF THE U.S. WITH  
THE POTENTIAL FOR A STORM APPROACHING THE ALEUTIANS, SOUTH COAST OF ALASKA, AND  
THE ALASKA PANHANDLE.  
 
HAZARDS  
 
HEAVY RAIN ACROSS PORTIONS OF NORTHERN CALIFORNIA AND THE PACIFIC NORTHWEST,  
THU, OCT 19.  
 
HEAVY RAIN ACROSS PORTIONS OF THE PACIFIC NORTHWEST, SAT-SUN, OCT 21-OCT 22.  
 
EPISODES OF HEAVY SNOW ACROSS HIGH ELEVATION AREAS OF THE CASCADES, THU-SUN,  
OCT 19-OCT 22.  
 
HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN ROCKIES, FRI-SAT, OCT 20-OCT 21.  
 
HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE SOUTHERN PLAINS, AND THE  
MISSISSIPPI VALLEY, SAT, OCT 21.  
 
HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST, THE LOWER MISSISSIPPI VALLEY, THE  
SOUTHERN PLAINS, AND THE TENNESSEE VALLEY, SUN, OCT 22.  
 
FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHEAST, THE GREAT  
LAKES, THE MIDDLE MISSISSIPPI VALLEY, AND THE SOUTHERN PLAINS.  
 
HIGH WINDS ACROSS COASTAL PORTIONS OF THE PACIFIC NORTHWEST, THU, OCT 19.  
 
HEAVY SNOW ACROSS PORTIONS OF THE KENAI PENINSULA, SUN, OCT 22.  
 
HIGH WINDS ACROSS PARTS OF SOUTHERN CALIFORNIA, SAT-SUN, OCT 21-OCT 22.  
 
SEVERE DROUGHT ACROSS THE MIDDLE MISSISSIPPI VALLEY, THE NORTHERN PLAINS, THE  
NORTHERN ROCKIES, AND HAWAII.  
 
DETAILED SUMMARY  
 
FOR THURSDAY OCTOBER 19 - MONDAY OCTOBER 23: A SURFACE LOW IS PREDICTED TO FORM  
OVER ALBERTA, CANADA AT THE START OF THE PERIOD AND TRACK EASTWARD ACROSS  
CANADA THROUGHOUT THE 3 TO 7 DAY PERIOD. ITS TRAILING COLD FRONT OVER THE CONUS  
IS EXPECTED TO SWEEP ACROSS THE LOWER 48 STATES THROUGHOUT WEEK-1, BRINGING  
HEAVY PRECIPITATION TO PARTS OF THE COUNTRY. AT THE BEGINNING OF THE PERIOD, AS  
THE COLD FRONT STRETCHES ACROSS THE PACIFIC NORTHWEST, PARTS OF NORTHERN  
CALIFORNIA AND THE PACIFIC NORTHWEST MAY RECEIVE HEAVY RAIN ON OCT 19 AND THE  
PACIFIC NORTHWEST OCT 21 TO 22. HIGHER ELEVATION AREAS IN THE CASCADES MAY  
RECEIVE EPISODES OF HEAVY SNOW OCT 19 TO 22. SOME MODELS INDICATE THE  
POSSIBILITY OF LOCALIZED AREAS RECEIVING 3 TO 4 INCHES OR GREATER OF LIQUID  
EQUIVALENT IN A 24-HOUR PERIOD. ADDITIONALLY, PARTS OF THE NORTHERN ROCKIES IN  
IDAHO MAY RECEIVE HEAVY SNOW OCT 20 TO 21. SEVERAL INCHES OF SNOW IS POSSIBLE  
ACROSS HIGH ELEVATION AREAS. ANOTHER SURFACE LOW PRESSURE IS FORECAST TO  
DEVELOP OFF THE WEST COAST OF CANADA. THIS FEATURE SUPPORTS HIGH WINDS (40  
KNOTS OR GREATER) ACROSS COASTAL PARTS OF THE PACIFIC NORTHWEST OCT 19.  
 
S  
 
STRONG SURFACE HIGH PRESSURE IS FORECAST TO BUILD ACROSS THE WESTERN CONUS  
BEHIND THE COLD FRONT BY OCT 21. THIS PATTERN MAY SUPPORT A PROLONGED PERIOD OF  
MODERATE TO STRONG OFFSHORE WINDS ACROSS PARTS OF SOUTHERN CALIFORNIA. THESE  
ELEVATED WIND SPEEDS MAY LEAD TO INCREASED CHANCES FOR WILDFIRE RISK THROUGHOUT  
THE WEEKEND. SUSTAINED WIND SPEEDS MAY REACH 30 KNOTS OR GREATER.  
 
AS THE AFOREMENTIONED COLD FRONT TRAVERSES THE CONUS, PARTS OF THE CENTRAL  
PLAINS, THE SOUTHERN PLAINS, AND THE MISSISSIPPI VALLEY MAY RECEIVE HEAVY  
RAINFALL ON OCT 21, FOLLOWED BY THE SOUTHEAST, THE LOWER MISSISSIPPI VALLEY,  
THE SOUTHERN PLAINS, AND THE TENNESSEE VALLEY ON OCT 22. LOCALIZED AREAS MAY  
RECEIVE UP TO 2 INCHES OR GREATER OF RAINFALL IN A 24-HOUR PERIOD.  
 
A SURFACE LOW IS PREDICTED TO FORM OVER THE SOUTH COAST OF ALASKA BY OCT 22.  
THIS STORM MAY BRING HEAVY SNOW TO PARTS OF THE KENAI PENINSULA (LIQUID  
EQUIVALENT TOTALS OF 2 INCHES OR GREATER IN A 24-HOUR PERIOD).  
 
FOR TUESDAY OCTOBER 24 - MONDAY OCTOBER 30: IN GENERAL, SOME MODELS ARE  
INDICATING THE DEVELOPMENT OF A MID-LEVEL TROUGH ACROSS THE EASTERN HALF OF THE  
CONUS THROUGHOUT WEEK-2. THIS PATTERN MAY TRANSLATE TO MUCH BELOW NORMAL  
TEMPERATURES ACROSS THE SOUTHEASTERN QUARTER OF THE CONUS OCT 27 TO 29. THE 6Z  
GEFS SHOWS A MORE AMPLIFIED TROUGH THAN THE 0Z ECMWF ENSEMBLE, LEADING TO  
SIGNIFICANT FORECAST UNCERTAINTY. THE GEFS REFORECAST TOOL INDICATES A 20  
PERCENT CHANCE OF TEMPERATURES IN THE SOUTHEASTERN QUADRANT OF THE CONUS BEING  
IN THE LOWEST 15TH PERCENTILE, WITH THE MINIMUM TEMPERATURES OF SOME AREAS  
DIPPING INTO THE 40S (DEG F). THE GEFS REFORECAST TOOL ALSO INDICATES INCREASED  
CHANCES FOR HEAVY RAIN ACROSS PARTS OF TEXAS, LOUISIANA, THE LOWER MISSISSIPPI  
AND TENNESSEE VALLEY OCT 24 TO 26. THIS IS ATTRIBUTED TO THE PLACEMENT OF THE  
SUBTROPICAL HIGH PRESSURE FAVORING STRONG SOUTHERLY FLOW FROM THE GULF OF  
MEXICO INTO THE CONUS, IN ADDITION TO SURFACE LOW PRESSURE NORTH OF THE YUCATAN  
PENINSULA. HOWEVER, DUE TO THE 0Z ECMWF ENSEMBLE HAVING A LESS AMPLIFIED  
TROUGH, IT DOES NOT INDICATE PRECIPITATION AMOUNTS AS HIGH AS THE GEFS. DUE TO  
THESE SIGNIFICANT MODEL DIFFERENCES, SPECIFIC HAZARDS AREAS ARE NOT HIGHLIGHTED  
AT THIS TIME FOR WEEK-2.  
 
A STRONG STORM SYSTEM MAY APPROACH THE ALEUTIANS AT THE BEGINNING OF WEEK-2,  
TRACKING ALONG THE GULF OF ALASKA THROUGHOUT WEEK-2. THIS STORM MAY BRING HEAVY  
PRECIPITATION TO SOUTHWESTERN MAINLAND ALASKA, THE SOUTH COAST OF ALASKA, AND  
THE ALASKA PANHANDLE THROUGHOUT WEEK-2. THE GEFS REFORECAST TOOL SHOWS BROAD  
AREAS OF 20 PERCENT, LOCALIZED AREAS OF 40 PERCENT OF HEAVY PRECIPITATION. THE  
0Z ECMWF ENSEMBLE FAVORS A LESS INTENSE STORM, LEADING TO LOWER EXPECTED  
PRECIPITATION AMOUNTS. THIS SIGNIFICANT MODEL DIFFERENCE PRECLUDES A RELATED  
HAZARDS AREA FROM BEING DETERMINED AT THIS TIME BUT WILL BE MONITORED IN THE  
UPCOMING DAYS.  
 
FORECASTER: MELISSA OU  
 

 
 
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