270  
FXUS21 KWNC 261847  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT OCTOBER 26 2017  
 
SYNOPSIS: A SURFACE LOW PRESSURE SYSTEM, POTENTIALLY A TROPICAL CYCLONE, IS  
EXPECTED TO MOVE NORTH FROM THE WESTERN CARIBBEAN SEA AND MERGE WITH A COLD  
FRONT ALONG THE EAST COAST THIS WEEKEND. MULTIPLE SURFACE HIGHS, ORIGINATING  
FROM THE HIGH LATITUDES OF NORTHWEST CANADA, ARE EXPECTED TO BUILD SOUTH INTO  
THE CONTINENTAL U.S. THROUGH EARLY NOVEMBER. DURING WEEK-2, A STRONG AREA OF  
UPPER-LEVEL HIGH (LOW) PRESSURE IS FORECAST OVER ALASKA (WESTERN NORTH AMERICA).  
 
HAZARDS  
 
HEAVY RAIN FROM THE OUTER BANKS OF NORTH CAROLINA NORTH TO NEW ENGLAND, SUN,  
OCT 29.  
 
POSSIBLE FLASH FLOODING FOR NORTHERN NEW JERSEY, THE HUDSON VALLEY, AND PARTS  
OF NEW ENGLAND, SUN, OCT 29.  
 
HIGH WINDS FOR PARTS OF THE NORTHEAST, SUN-MON, OCT 29-30.  
 
MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE LOWER MISSISSIPPI VALLEY AND  
SOUTHEAST, SUN-MON, OCT 29-30.  
 
MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN AND CENTRAL ROCKIES,  
GREAT PLAINS, AND MIDWEST, MON-THU, OCT 30-NOV 2.  
 
HIGH WINDS FOR PARTS OF THE GREAT PLAINS AND UPPER MIDWEST, SUN-MON, OCT 29-30.  
 
HEAVY, LAKE-EFFECT SNOW DOWNWIND OF LAKE SUPERIOR, MON-TUE, OCT 30-31.  
 
HEAVY PRECIPITATION FOR PARTS OF SOUTHEAST MAINLAND ALASKA AND THE NORTHERN  
ALASKA PANHANDLE, SUN-MON, OCT 29-30.  
 
HIGH WINDS FOR THE ALASKA PANHANDLE, THU-FRI, NOV 2-3.  
 
HEAVY SNOW FOR THE NORTHERN ROCKIES, CASCADES, AND NORTHERN SIERRA MOUNTAINS,  
FRI-SAT, NOV 3-4.  
 
HIGH RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF MONTANA, FRI-SUN, NOV  
3-5.  
 
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN  
ROCKIES AND NORTHERN GREAT PLAINS, FRI-WED, NOV 3-8.  
 
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF EASTERN OREGON AND  
WASHINGTON, SAT-WED, NOV 4-8.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE WESTERN AND  
CENTRAL U.S., FRI-THU, NOV 3-9.  
 
FLOODING OCCURRING ALONG THE ST. JOHNS RIVER IN FLORIDA.  
 
SEVERE DROUGHT ACROSS THE NORTHERN ROCKIES, NORTHERN GREAT PLAINS, AND HAWAII.  
 
DETAILED SUMMARY  
 
FOR SUNDAY OCTOBER 29 - THURSDAY NOVEMBER 02: A BROAD AREA OF LOW PRESSURE IS  
CURRENTLY LOCATED OVER THE WESTERN CARIBBEAN SEA AND IT MAY BECOME A TROPICAL  
CYCLONE PRIOR TO THIS PERIOD. REGARDLESS OF ITS DEVELOPMENT, TROPICAL MOISTURE  
IS LIKELY TO SPREAD NORTH AND INTERACT WITH A COLD FRONT ALONG THE EAST COAST  
THIS WEEKEND. THE DETERMINISTIC 6Z GFS MODEL INDICATES A 50 TO 70 KNOT JET AT  
850-HPA AND HIGHLY ANOMALOUS MOISTURE (PRECIPITABLE WATER VALUES OF 1.5  
INCHES), AFFECTING SOUTHERN NEW ENGLAND BY SUNDAY. THE DETERMINISTIC 6Z GFS AND  
0Z ECMWF MODELS AGREE ON AN AXIS OF HEAVY RAINFALL (3 TO 7 INCHES PER 24 HOURS)  
ACROSS NORTHERN NEW JERSEY, THE HUDSON VALLEY, AND NEW ENGLAND ON OCT 29. THIS  
HEAVY RAINFALL IN SHORT PERIOD OF TIME MAY TRIGGER FLASH FLOODING. A COUPLED  
UPPER-LEVEL JET, HIGHLY ANOMALOUS LOW-LEVEL MOISTURE, AND MODEL CONSISTENCY  
RAISE FORECAST CONFIDENCE IN THIS HEAVY RAINFALL AND POSSIBLE FLOODING EVENT.  
 
THE DETERMINISTIC 0Z ECMWF MODELS INDICATES THAT THE SURFACE LOW TRACKING NORTH  
FROM NEW ENGLAND ON OCT 29 STRENGTHENS TO 972-HPA, OR DEEPER, WHEN IT REACHES  
THE ST. LAWRENCE VALLEY ON OCT 30. THEREFORE, HIGH WINDS (SUSTAINED WINDS OF 25  
TO 45 MPH) ARE LIKELY FOR LONG ISLAND AND NEW ENGLAND ON OCT 29 AND 30.  
 
SURFACE HIGH PRESSURE IS EXPECTED TO BUILD SOUTHEAST INTO THE LOWER MISSISSIPPI  
VALLEY AND SOUTHEAST ON OCT 29 AND 30. A MUCH BELOW-NORMAL TEMPERATURE HAZARD  
IS POSTED FOR AREAS WHERE MINIMUM TEMPERATURES ARE FORECAST TO AVERAGE MORE  
THAN 10 DEGREES F BELOW NORMAL AND WHERE THE FIRST WIDESPREAD FROST OR LIGHT  
FREEZE IS EXPECTED.  
 
MODEL SOLUTIONS INDICATE A STRONG COLD FRONT ADVANCING SOUTH ACROSS THE CENTRAL  
U.S. EARLY NEXT WEEK. BEHIND THIS COLD FRONT, HIGH WINDS (GUSTS ABOVE 40 MPH)  
ARE FORECAST ACROSS THE GREAT PLAINS ON OCT 29 AND 30. MUCH BELOW-NORMAL  
TEMPERATURES (DAILY NEGATIVE DEPARTURES OF 10 TO 15 DEGREES F) ARE EXPECTED TO  
EXPAND SOUTHEAST ACROSS THE NORTHERN ROCKIES, NORTHERN AND CENTRAL GREAT  
PLAINS, AND MIDWEST ON OCT 30 AND 31. MUCH BELOW-NORMAL TEMPERATURES ARE  
FORECAST TO PERSIST ACROSS THE NORTHERN GREAT PLAINS AND UPPER MISSISSIPPI  
VALLEY THROUGH NOV 2 AS ANOTHER STRONG SURFACE HIGH (1032-HPA) BUILDS SOUTH  
FROM CANADA. UNLIKE THE PREVIOUS SURFACE HIGHS DURING THE FINAL WEEK OF  
OCTOBER, THIS ONE IS NOT EXPECTED TO SHIFT SOUTH OF THE 40TH PARALLEL, LIMITING  
THE SOUTHERN EXTENT OF MUCH BELOW-NORMAL TEMPERATURES DURING EARLY NOVEMBER.  
 
STRONG COLD AIR ADVECTION IS LIKELY TO CAUSE PERIODS OF LAKE-ENHANCED RAIN AND  
SNOW NEXT WEEK DOWNWIND OF LAKES MICHIGAN AND SUPERIOR. THE HEAVIEST  
LAKE-EFFECT SNOW (6 INCHES OR MORE PER 24 HOURS) IS MOST LIKELY DOWNWIND OF  
LAKE SUPERIOR IN NORTHERN WISCONSIN AND THE UPPER PENINSULA OF MICHIGAN ON OCT  
30 AND 31. UPSLOPE FLOW IS EXPECTED TO LEAD TO PERIODS OF SNOW ACROSS THE  
NORTHERN AND CENTRAL HIGH PLAINS, BUT AMOUNTS ARE NOT ANTICIPATED TO BE HEAVY  
AT THIS TIME. AS THE WESTERN U.S. TROUGH BECOMES MORE AMPLIFIED LATER NEXT  
WEEK, HEAVY SNOW (6 INCHES OR MORE) IS EXPECTED ACROSS THE NORTHERN ROCKIES ON  
NOV 2.  
 
A LOW PRESSURE SYSTEM AND ITS ASSOCIATED ONSHORE FLOW ARE EXPECTED TO BRING  
HEAVY PRECIPITATION FROM PRINCE WILLIAM SOUND EAST TO YAKUTAT, ALASKA ON OCT 29  
AND 30. TOTAL PRECIPITATION AMOUNTS OF 2 TO 4 INCHES, LIQUID EQUIVALENT, ARE  
FORECAST FOR THIS REGION. THE DETERMINISTIC 6Z GFS AND 0Z ECMWF MODELS INDICATE  
A 1048 TO 1052-HPA SURFACE HIGH OVER THE YUKON TERRITORY WHICH IS EXPECTED TO  
RESULT IN TAKU WINDS (OFFSHORE GUSTS ABOVE 50 MPH) IN THE VICINITY OF JUNEAU,  
ALASKA, BEGINNING ON NOV 2.  
 
FOR FRIDAY NOVEMBER 03 - THURSDAY NOVEMBER 09: A LONGWAVE PATTERN CHANGE IS  
EXPECTED TO BE ONGOING AT THE BEGINNING OF NOVEMBER AS ANOMALOUS RIDGING  
(500-HPA HEIGHTS NEAR 564DM) BECOMES ESTABLISHED ACROSS WESTERN ALASKA AND AN  
UPPER-LEVEL TROUGH RETROGRADES TO WESTERN NORTH AMERICA. THIS PATTERN CHANGE IS  
CONSISTENT WITH THE ENHANCED PHASE OF THE MJO PROPAGATING EAST ACROSS THE  
WESTERN HEMISPHERE DURING THE NEXT TWO WEEKS. HIGH, OFFSHORE WINDS (GUSTS ABOVE  
50MPH) ARE EXPECTED TO CONTINUE THROUGH NOV 3 ACROSS THE ALASKA PANHANDLE, DUE  
TO SURFACE HIGH PRESSURE (1048 TO 1052-HPA) OVER WESTERN CANADA.  
 
THE EVOLVING LONGWAVE PATTERN SUPPORTS AT LEAST A SLIGHT RISK OF MUCH  
BELOW-NORMAL TEMPERATURES FOR PARTS OF THE WESTERN AND CENTRAL U.S. DURING  
WEEK-2. A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES IS POSTED FOR PARTS  
OF THE NORTHERN ROCKIES AND NORTHERN HIGH PLAINS THROUGH NOV 8. A HIGH RISK OF  
MUCH BELOW-NORMAL TEMPERATURES IS HIGHLIGHTED FOR PARTS OF MONTANA WHERE THE 6Z  
GFS ENSEMBLE MEAN INDICATES TEMPERATURES AVERAGING NEAR 12 DEGREES F BELOW  
NORMAL FROM NOV 3 TO 5. ALSO, THE 0Z ECMWF MODEL INDICATES LARGE NEGATIVE  
850-HPA TEMPERATURE DEPARTURES FROM NORMAL OVER THIS SAME AREA EARLY IN WEEK-2.  
THE MORE CONSISTENT AND PREFERRED ECMWF MODEL INDICATES MUCH COLDER  
TEMPERATURES SPREADING INTO THE INTERIOR PACIFIC NORTHWEST, BEGINNING ON NOV 4.  
THEREFORE, A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES IS ALSO IDENTIFIED  
FOR EASTERN WASHINGTON AND OREGON FROM NOV 4 TO 8.  
 
THE AMPLIFYING UPPER-LEVEL TROUGH ALOFT FAVORS MODERATE TO HEAVY SNOW ACROSS  
THE NORTHERN ROCKIES, CASCADES, AND NORTHERN SIERRA MOUNTAINS EARLY IN WEEK-2.  
THE GFS AND ECMWF ENSEMBLE MEANS INDICATE 0.25 TO 0.5 INCHES, OR MORE OF LIQUID  
EQUIVALENT PER 24 HOURS, ACROSS THESE AREAS ON NOV 3 AND 4. SHALLOW,  
SUB-FREEZING TEMPERATURES MAY LEAD TO FREEZING RAIN ACROSS THE COLUMBIA RIVER  
GORGE.  
 
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 HAWAII.  
 
FORECASTER: BRAD PUGH  
 

 
 
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