363  
FXUS21 KWNC 251913  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT OCTOBER 25 2017  
 
SYNOPSIS: A SURFACE LOW AND A TRAILING COLD FRONT ARE FORECAST TO ADVANCE  
ACROSS THE EASTERN U.S. ON OCT 28 AND 29. A SURFACE LOW PRESSURE SYSTEM,  
POTENTIALLY A TROPICAL CYCLONE, IS EXPECTED TO MOVE NORTH FROM THE WESTERN  
CARIBBEAN SEA AND MERGE WITH THE COLD FRONT. A STRONG AREA OF UPPER-LEVEL HIGH  
PRESSURE IS FORECAST TO PERSIST OVER ALASKA DURING EARLY NOVEMBER, WHILE AN  
AREA OF UPPER-LEVEL LOW PRESSURE BECOMES ESTABLISHED ACROSS THE WESTERN U.S.  
 
HAZARDS  
 
HEAVY RAIN FOR THE FLORIDA KEYS ALONG WITH PARTS OF CENTRAL AND SOUTH FLORIDA,  
SAT, OCT 28.  
 
HEAVY RAIN FROM THE OUTER BANKS OF NORTH CAROLINA NORTH TO 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 CENTRAL AND SOUTHERN GREAT  
PLAINS, OZARKS, AND LOWER MISSISSIPPI VALLEY, SAT-SUN, OCT 28-29.  
 
MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE SOUTHEAST, MON, OCT 30.  
 
MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN AND CENTRAL ROCKIES,  
GREAT PLAINS, AND MIDWEST, MON-WED, OCT 30-NOV 1.  
 
HEAVY SNOW FOR PARTS OF THE NORTHERN ROCKIES AND NORTHERN HIGH PLAINS, TUE-WED,  
OCT 31-NOV 1.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE WESTERN AND  
CENTRAL U.S., THU-WED, NOV 2-8.  
 
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN  
ROCKIES AND NORTHERN GREAT PLAINS, THU-WED, NOV 2-8.  
 
HIGH RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF MONTANA, SAT-MON, NOV  
4-6.  
 
FLOODING OCCURRING ALONG THE ST. JOHNS RIVER IN FLORIDA.  
 
SEVERE DROUGHT ACROSS THE MIDDLE MISSISSIPPI VALLEY, THE NORTHERN PLAINS, THE  
NORTHERN ROCKIES, AND HAWAII.  
 
DETAILED SUMMARY  
 
FOR SATURDAY OCTOBER 28 - WEDNESDAY NOVEMBER 01: A BROAD AREA OF LOW PRESSURE  
IS LOCATED OVER THE WESTERN CARIBBEAN SEA. ITS CLOSE PROXIMITY TO LAND AND  
INCREASING UPPER-LEVEL WINDS LATER THIS WEEK ARE EXPECTED TO LIMIT DEVELOPMENT  
OF THIS SYSTEM. PLEASE REFER TO THE NATIONAL HURRICANE CENTER AT:  
WWW.NHC.NOAA.GOV FOR THE LATEST UPDATES AND FORECASTS. REGARDLESS OF  
DEVELOPMENT, HEAVY RAIN (1 TO 3 INCHES, LOCALLY MORE) IS EXPECTED TO AFFECT THE  
FLORIDA KEYS AND PARTS OF THE CENTRAL AND FLORIDA PENINSULA ON OCT 28.  
 
A COLD FRONT AND ASSOCIATED AMPLIFYING UPPER-LEVEL TROUGH THAT BECOMES  
NEGATIVELY-TILTED ARE FORECAST TO AFFECT THE EASTERN U.S. THIS WEEKEND. A  
STRONG LOW-LEVEL JET IS LIKELY TO TRANSPORT HIGHLY ANOMALOUS MOISTURE  
(PRECIPITABLE WATER VALUES UP TO 1.5 INCHES) SPREADING FROM THE TROPICS TO  
NORTH OF THE 40TH PARALLEL THIS WEEKEND. THE EVOLVING PATTERN SIGNALS A HIGH  
RISK OF HEAVY RAINFALL (1 TO 3 INCHES, LOCALLY MORE) FROM THE MID-ATLANTIC  
NORTH TO NEW ENGLAND ON OCT 29.  
 
THE DETERMINISTIC 0/6Z GFS AND 0Z ECMWF MODELS INDICATE, THAT THE SURFACE LOW  
TRACKING NORTH FROM NEW ENGLAND ON OCT 29, STRENGTHENS TO 976-HPA, OR DEEPER,  
WHEN IT REACHES THE ST. LAWRENCE VALLEY ON OCT 30. THEREFORE, HIGH WINDS  
(SUSTAINED WINDS OF 25 TO 45 MPH) ARE BECOMING MORE LIKELY FOR LONG ISLAND AND  
NEW ENGLAND ON OCT 29 AND 30.  
 
SURFACE HIGH PRESSURE IS EXPECTED TO BUILD SOUTHEAST INTO THE SOUTHERN GREAT  
PLAINS, LOWER MISSISSIPPI VALLEY, AND SOUTHEAST FROM OCT 28 TO 30. MUCH  
BELOW-NORMAL TEMPERATURE HAZARDS ARE 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  
HAVE COME INTO BETTER AGREEMENT WITH ANOTHER STRONG SURFACE HIGH (1036-HPA)  
SHIFTING SOUTH FROM WESTERN CANADA INTO THE NORTH-CENTRAL U.S. EARLY NEXT WEEK.  
THIS SURFACE HIGH IS EXPECTED TO RESULT IN MUCH BELOW-NORMAL TEMPERATURES  
(DAILY NEGATIVE DEPARTURES OF 10 TO 15 DEGREES F) EXPANDING 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 ON NOV 1 ACROSS  
THE NORTHERN ROCKIES AND NORTHERN HIGH PLAINS AS ANOTHER STRONG SURFACE HIGH  
BUILDS SOUTH INTO THESE AREAS.  
 
ALTHOUGH THE STRONGEST COLD AIR ADVECTION SO FAR THIS FALL SEASON IS LIKELY TO  
CAUSE PERIODS OF LAKE-ENHANCED RAIN AND SNOW NEXT WEEK DOWNWIND OF THE GREAT  
LAKES, SNOWFALL AMOUNTS ARE NOT EXPECTED TO BE HEAVY AT THIS TIME. THE  
AMPLIFYING TROUGH ALOFT AND UPSLOPE FLOW ARE EXPECTED TO LEAD TO AN INCREASING  
CHANCE OF HEAVY SNOW (6 INCHES OR MORE PER 24 HOURS) ACROSS PARTS OF THE  
NORTHERN ROCKIES AND ADJACENT HIGH PLAINS ON OCT 31 AND NOV 1.  
 
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  
30. LATER NEXT WEEK, A DRIER PATTERN IS LIKELY ACROSS ALASKA AS RIDGING AT THE  
SURFACE AND ALOFT STRENGTHENS.  
 
FOR THURSDAY NOVEMBER 02 - WEDNESDAY NOVEMBER 08: A LONGWAVE PATTERN CHANGE IS  
EXPECTED TO BE ONGOING BY THE BEGINNING OF NOVEMBER AS ANOMALOUS RIDGING  
(500-HPA HEIGHTS OF NEAR 570DM) BUILDS ACROSS WESTERN ALASKA AND A DOWNSTREAM  
TROUGH AMPLIFIES OVER THE WESTERN U.S. THE GFS AND ECMWF ENSEMBLE MEANS ARE IN  
EXCELLENT AGREEMENT WITH THIS PATTERN CHANGE WHICH IS CONSISTENT WITH THE  
ENHANCED PHASE OF THE MJO PROPAGATING EAST ACROSS THE WESTERN HEMISPHERE DURING  
THE NEXT TWO WEEKS. THE DETERMINISTIC 6Z GFS AND 0Z ECMWF MODELS INDICATE A  
1048 TO 1052-HPA SURFACE HIGH OVER THE YUKON TERRITORY ON NOV 2. ALTHOUGH IT IS  
UNCERTAIN HOW FAR SOUTH THE ARCTIC AIR WILL EVENTUALLY SPREAD INTO THE LOWER  
48, 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 THROUGHOUT WEEK-2, BASED ON  
THE LONGWAVE PATTERN AND MODEL GUIDANCE. A HIGH RISK OF MUCH BELOW-NORMAL  
TEMPERATURES IS POSTED FOR PARTS OF MONTANA FROM NOV 4-6, WHERE THE 6Z GFS  
ENSEMBLE MEAN INDICATES TEMPERATURES AVERAGING NEAR 12 DEGREES F BELOW NORMAL.  
THE GEFS TEMPERATURE TOOL INDICATES THAT MINIMUM TEMPERATURES HAVE A 30 PERCENT  
CHANCE OF FALLING BELOW THE LOWEST 5TH PERCENTILE FOR THE HIGH RISK AREA ON NOV  
6.  
 
THE UPPER-LEVEL TROUGH ALOFT FAVORS PERIODS OF ADDITIONAL SNOW ACROSS THE  
NORTHERN AND CENTRAL ROCKIES, BUT UNCERTAINTY ON TIMING AND AMOUNTS PRECLUDES  
DESIGNATION OF A HEAVY SNOW HAZARD AT THIS TIME. ALSO, THE PREDICTED PATTERN  
INCREASES THE CHANCES OF AN EARLY FREEZING RAIN EVENT IN THE COLUMBIA RIVER  
GORGE. THE STRONG SURFACE HIGH OVER THE YUKON TERRITORY COULD LEAD TO TAKU  
WINDS (OFFSHORE GUSTS ABOVE 50 MPH) IN THE VICINITY OF JUNEAU, ALASKA DURING  
WEEK-2.  
 
THE U.S. DROUGHT MONITOR, VALID ON OCTOBER 17, INDICATES THAT SEVERE TO  
EXCEPTIONAL (D2-D4) DROUGHT COVERS 2.98 PERCENT OF THE CONTINENTAL U.S., WHICH  
DECREASED FROM 4.03 FROM THE PREVIOUS WEEK. THE LARGEST CHANGES WERE OVER THE  
NORTHERN PLAINS AND MIDWEST.  
 
FORECASTER: BRAD PUGH  
 

 
 
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