721  
FXUS21 KWNC 241859  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT OCTOBER 24 2017  
 
SYNOPSIS: A SURFACE LOW AND A TRAILING COLD FRONT ARE FORECAST TO ADVANCE  
ACROSS THE EASTERN U.S. FROM OCT 27 TO 29. A LOW PRESSURE SYSTEM, POTENTIALLY A  
TROPICAL CYCLONE, IS EXPECTED TO EMERGE FROM THE NORTHWEST CARIBBEAN SEA AND  
AFFECT THE FLORIDA KEYS AND SOUTH FLORIDA THIS WEEKEND. A STRONG AREA OF  
UPPER-LEVEL HIGH PRESSURE IS FORECAST TO PERSIST OVER ALASKA DURING THE FIRST  
WEEK OF NOVEMBER, WHILE AN AREA OF UPPER-LEVEL LOW PRESSURE DEVELOPS ACROSS THE  
WESTERN U.S.  
 
HAZARDS  
 
HEAVY RAIN FOR THE FLORIDA KEYS ALONG WITH PARTS OF CENTRAL AND SOUTH FLORIDA,  
SAT-SUN, OCT 28-29.  
 
HEAVY RAIN FROM THE OUTER BANKS NORTH TO NEW ENGLAND, SUN, OCT 29.  
 
HIGH WINDS FOR THE UPPER MISSISSIPPI VALLEY AND NORTHERN TO CENTRAL GREAT  
PLAINS, FRI, OCT 27.  
 
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-TUE, OCT 30-31.  
 
HEAVY PRECIPITATION FOR PARTS OF SOUTHEAST MAINLAND ALASKA AND THE NORTHERN  
ALASKA PANHANDLE, FRI, OCT 27.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR THE ROCKIES, NORTHERN AND  
CENTRAL GREAT PLAINS, AND UPPER MISSISSIPPI VALLEY, WED-TUE, NOV 1-7.  
 
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR THE NORTHERN GREAT PLAINS,  
WED-FRI, NOV 1-3.  
 
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 FRIDAY OCTOBER 27 - TUESDAY OCTOBER 31: A BROAD AREA OF LOW PRESSURE IS  
LOCATED OVER THE WESTERN CARIBBEAN SEA. LIMITED DEVELOPMENT IS EXPECTED DURING  
THE NEXT 24 HOURS DUE TO ITS CLOSE PROXIMITY TO CENTRAL AMERICA. LATER THIS  
WEEK, ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE CONDUCIVE FOR SLOW TROPICAL  
CYCLONE DEVELOPMENT AS IT EMERGES FROM THE NORTHWEST CARIBBEAN SEA. 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.  
 
A COLD FRONT IS FORECAST TO PROGRESS EAST FROM THE MISSISSIPPI VALLEY ON OCT 27  
TO THE EAST COAST ON OCT 29. AS THE UPPER-LEVEL TROUGH AMPLIFIES OVER THE  
EASTERN U.S., TROPICAL MOISTURE IS EXPECTED TO BE DRAWN NORTHWARD WHICH IS  
LIKELY TO RESULT IN HEAVY RAINFALL (MORE THAN 1 INCH) FROM THE OUTER BANKS  
NORTH TO NEW ENGLAND ON OCT 29. ACCUMULATING SNOW IS EXPECTED AT THE HIGHEST  
ELEVATIONS OF THE CENTRAL AND SOUTHERN APPALACHIANS BY OCT 30, BUT HEAVY  
AMOUNTS ARE NOT ANTICIPATED. PERIODS OF COLD AIR ADVECTION ARE FORECAST TO  
RESULT IN OCCASIONAL LAKE-ENHANCED RAIN AND SNOW, BUT ANY SNOWFALL  
ACCUMULATIONS ARE GENERALLY EXPECTED TO BE LIGHT ACROSS THE GREAT LAKES.  
 
A TIGHT PRESSURE GRADIENT IS FORECAST TO RESULT IN HIGH WINDS (GUSTS ABOVE  
40MPH) ACROSS THE UPPER MISSISSIPPI VALLEY ALONG WITH THE NORTHERN AND CENTRAL  
GREAT PLAINS ON OCT 27. BEHIND A COLD FRONT, THE COLDEST TEMPERATURES SO FAR  
THIS FALL ARE LIKELY TO AFFECT THE SOUTHERN GREAT PLAINS, OZARKS, LOWER  
MISSISSIPPI VALLEY, AND SOUTHWEST FROM OCT 28 TO 31. 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.  
 
ONSHORE FLOW, ASSOCIATED WITH A LOW PRESSURE SYSTEM OVER WESTERN ALASKA, IS  
FORECAST TO BRING HEAVY PRECIPITATION (WIDESPREAD 2 INCHES, WITH LOCALLY MORE  
THAN 4 INCHES LIQUID EQUIVALENT) TO SOUTHEAST MAINLAND ALASKA AND THE NORTHERN  
ALASKA PANHANDLE ON OCT 27. EARLY NEXT WEEK, ANOTHER LOW PRESSURE SYSTEM IS  
EXPECTED TO BRING ADDITIONAL RAIN TO SOUTHERN MAINLAND ALASKA BUT THE LATEST  
MODEL SOLUTIONS INDICATE RAINFALL AMOUNTS REMAINING BELOW HAZARDS CRITERIA.  
 
FOR WEDNESDAY NOVEMBER 01 - TUESDAY NOVEMBER 07: A LONGWAVE PATTERN CHANGE IS  
EXPECTED TO BE ONGOING BY THE BEGINNING OF NOVEMBER AS ANOMALOUS RIDGING  
(500-HPA HEIGHTS OF 564DM OR GREATER) BUILDS ACROSS ALASKA AND A DOWNSTREAM  
TROUGH AMPLIFIES OVER THE WESTERN AND CENTRAL U.S. THIS LONGWAVE PATTERN CHANGE  
OVER NORTH AMERICA IS CONSISTENT WITH THE ENHANCED PHASE OF THE MJO PROPAGATING  
EAST ACROSS THE WESTERN HEMISPHERE DURING THE NEXT TWO WEEKS. THE AMPLIFYING  
UPPER-LEVEL TROUGH OVER THE WESTERN U.S. SUPPORTS AT LEAST A SLIGHT RISK OF  
MUCH BELOW-NORMAL TEMPERATURES ACROSS THE NORTHERN ROCKIES, NORTHERN AND  
CENTRAL GREAT PLAINS, AND UPPER MISSISSIPPI VALLEY DURING WEEK-2. THE PREFERRED  
ECMWF MODEL INDICATES A STRONG COLD FRONT PUSHING SOUTH ACROSS THE GREAT PLAINS  
EARLY IN WEEK-2. BASED THIS MODEL SOLUTION, WHICH INCLUDES LARGE NEGATIVE  
850-HPA TEMPERATURE ANOMALIES, AND STATISTICAL TEMPERATURE TOOLS, A MODERATE  
RISK OF MUCH BELOW-NORMAL TEMPERATURES IS POSTED FOR THE NORTHERN GREAT PLAINS  
AND ROCKIES FROM NOV 1 TO 3.  
 
UPSLOPE FLOW AND THE AMPLIFYING TROUGH ALOFT MAY BRING HEAVY SNOW TO THE  
NORTHERN AND CENTRAL HIGH PLAINS EARLY IN WEEK-2, BUT MODEL DIFFERENCES ON  
SNOWFALL AMOUNTS PRECLUDE DESIGNATION OF A HEAVY SNOW HAZARD AT THIS TIME.  
 
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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