005  
FXUS02 KWBC 270557  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
156 AM EDT FRI OCT 27 2017  
 
VALID 12Z MON OCT 30 2017 - 12Z FRI NOV 03 2017  
   
..POWERFUL STORM TO EXIT THE NORTHEAST MONDAY
 
 
   
..OVERVIEW
 
 
A STRONG SURFACE LOW WILL LIFT OUT OF THE NORTHEAST ON MONDAY  
WHILE A COUPLE WEAKER SYSTEMS FOLLOW IN ITS WAKE ACROSS THE  
NORTHERN TIER. FARTHER UPSTREAM, IMPRESSIVELY STRONG UPPER RIDGING  
OVER THE GULF OF ALASKA WILL MIGRATE NORTHWARD INTO WESTERN ALASKA  
MID WEEK WHICH WILL FAVOR TROUGHING INTO THE PACIFIC NORTHWEST.  
BROAD CYCLONIC FLOW AROUND AN UPPER LOW IN NUNAVUT WILL BE IN  
PLACE ACROSS THE CENTRAL/EASTERN CONUS FOR MUCH OF THE WEEK.  
 
   
..GUIDANCE/UNCERTAINTY ASSESSMENT AND PREFERENCES
 
 
12Z GFS/ECMWF AND THEIR ENSEMBLE MEANS SHOWED REASONABLE  
CLUSTERING THROUGH THE ENTIRE MEDIUM RANGE PERIOD AND A BLEND OF  
THEIR SOLUTIONS SERVED AS THE STARTING POINT. THE 18Z GFS DEPARTED  
FROM THE GOOD 12Z GUIDANCE CLUSTERING IN THE NORTHEAST TO START  
THE FORECAST AND CONCURRENTLY SEEMED TO MISHANDLE THE HIGH  
LATITUDE FLOW THROUGH ALASKA WHICH TRANSLATED INTO CANADA AND THE  
LOWER 48 THEREAFTER. DIFFERENCES BETWEEN THE 12Z GFS/ECMWF NOTED  
OVER THE HIGH PLAINS/UPPER MIDWEST EARLY TUESDAY AND OVER S CA/AZ  
WITH THE TRACK/DEPTH OF AN UPPER LOW MID/LATE WEEK. TREND BY THE  
END OF THE PERIOD HAS BEEN TOWARD STRONGER RIDGING INTO W ALASKA  
WHICH SHOULD DIG HEIGHTS NEARLY DUE SOUTH ALONG 130W NEXT THU/FRI.  
SURFACE FRONTAL BOUNDARY WILL LIKELY GET HUNG UP ON THE DIVIDE AS  
THE PARENT LOW AND EASTERN COLD FRONT RACE EASTWARD IN RELATIVELY  
QUICK WESTERLY FLOW.  
 
   
..WEATHER THREATS/HIGHLIGHTS
 
 
MULTI-HAZARD THREAT WITH THE CYCLONE WILL SLOWLY WIND DOWN IN THE  
NORTHEAST ON MONDAY AS IT CONTINUES TO DEEPEN INTO CANADA. NEXT  
SYSTEM ON ITS HEELS WILL BRING MUCH COLDER AIR TO THE ROCKIES AND  
SOUTHERN PLAINS AS THE COLD FRONT SPILLS OVER THE DIVIDE. SNOW IS  
LIKELY OVER SOUTHERN COLORADO MON-TUE THANKS TO UPSLOPE FLOW AS  
THE SFC HIGH SLIDES OUT OF MONTANA INTO NE/KS. FINAL SYSTEM DURING  
THIS BUSY WEEK WILL DROP SOUTHEASTWARD OUT OF CANADA INTO THE  
UPPER MIDWEST WED/THU AND OFF THE NORTHEAST COAST BY FRIDAY. TAIL  
END OF THIS FRONT WILL HAVE A HARDER TIME CRESTING THE DIVIDE FROM  
ID/MT INTO WY AS THE HEIGHT FALLS WILL BE OFFSHORE THE WEST COAST.  
THIS SHOULD INCREASE THE RAIN/SNOW CHANCES FOR WASHINGTON AND NW  
MONTANA WITH MUCH COLDER TEMPERATURES LIKELY FOR NORTHERN MONTANA  
(10-20F BELOW AVERAGE) BY NEXT FRIDAY.  
 
FRACASSO  
 

 
 
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