287  
FXUS02 KWBC 291526  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1125 AM EDT SAT SEP 29 2018  
 
VALID 12Z TUE OCT 02 2018 - 12Z SAT OCT 06 2018  
 
...HEAVY RAINS ASSOCIATED WITH ROSA WILL EXIT THE SOUTHWEST AND  
ROCKIES NEXT TUESDAY...  
 
...ADDITIONAL HEAVY RAIN THREAT FROM THE MID/UPPER MISSISSIPPI  
VALLEY TO GREAT LAKES LATER IN THE WEEK...  
 
   
..HURRICANE ROSA
 
 
PLEASE REFER TO THE NATIONAL HURRICANE CENTER ADVISORY FOR THE  
LATEST INFORMATION ON ROSA AND YOUR LOCAL NWS OFFICE FOR LOCAL  
WATCHES AND WARNINGS. ROSA IS EXPECTED TO RAPIDLY WEAKEN AS IT  
LIFTS INLAND ACROSS THE BAJA CALIFORNIA PENINSULA THEN ARIZONA  
EARLY NEXT WEEK, BUT WILL BRING SIGNIFICANT MOISTURE TO THE  
SOUTHWEST. COMBINED WITH AN INCOMING PACIFIC FRONT INTO  
CALIFORNIA, A LOCALLY HEAVY MULTI-DAY RAINFALL EVENT STRADDLING  
THE SHORT TERM INTO THE MEDIUM RANGE PERIOD IS LIKELY FOR PORTIONS  
OF SOUTHERN CALIFORNIA EASTWARD ACROSS THE SOUTHWEST AND  
NORTHEASTWARD TO THE CENTRAL GREAT BASIN/ROCKIES. THE POTENTIAL  
EXISTS FOR SIGNIFICANT/LIFE-THREATENING HYDROLOGICAL IMPACTS  
INCLUDING HEAVY RAINFALL AND FLASH FLOODING, DEBRIS FLOW IN THE  
DESERTS, AND LOCAL RUNOFF ISSUES AS ENHANCED BY TERRAIN.  
 
   
..PATTERN OVERVIEW AND WEATHER HIGHLIGHTS
 
 
IT REMAINS THE CASE THAT A HIGHLY AMPLIFIED FLOW PATTERN SHOULD  
PERSIST FROM THE NORTH PACIFIC ACROSS NORTH AMERICA WITH A  
BLOCKING RIDGE CENTERED OVER ALASKA DRIFTING NORTHWARD INTO THE  
ARCTIC, MEAN TROUGHING PUSHING INTO THE U.S. WEST COAST AS WELL AS  
THROUGH HUDSON BAY, AND PERSISTENT/RESILIENT SUBTROPICAL RIDGING  
ANCHORED OVER THE SOUTHEAST. ADDITIONALLY, THE EXTRATROPICAL  
TRANSITION OF TYPHOON TRAMI OFF JAPAN IN THE SHORT TERM SHOULD  
SUPPORT CONTINUED UPPER FLOW AMPLIFICATION DOWNSTREAM OVER THE  
NORTH PACIFIC AND ALASKA, SUGGESTING A CONTINUATION OF THE HIGHLY  
AMPLIFIED/BLOCKED NORTH AMERICAN FLOW REGIME INTO THE END OF NEXT  
WEEK.  
 
IN THIS PATTERN, AMPLE TROUGHING NEAR THE WEST COAST WILL ACT TO  
STEER HURRICANE ROSA NORTHEASTWARD TOWARD THE BAJA CALIFORNIA  
PENINSULA BEFORE FURTHER WEAKENING OCCURS WHILE LIFTING TOWARD THE  
SOUTHWEST STATES AND CENTRAL GREAT BASIN AS PER THE LATEST NHC  
TRACK. THE OVERALL FLOW PATTERN ALSO FAVORS SOUTHWARD TRANSPORT OF  
POLAR AIR FROM THE NORTHERN ROCKIES EAST TO THE GREAT LAKES VIA  
EMBEDDED UPPER LEVEL SHORTWAVES AND MORE SUMMER-LIKE CONDITIONS  
FROM THE GULF COAST TO THE SOUTHEAST AND MID-ATLANTIC STATES.  
EXPECT LINGERING RAINS FOR THE GULF COAST AND SOUTHEAST INTO  
MIDWEEK WITHIN A MOISTENED EASTERLY LOW-LEVEL FETCH. A PERSISTENT  
STRONG FRONTAL ZONE IN BETWEEN THESE AIR MASSES WILL FOCUS PERIODS  
OF ENHANCED PRECIPITATION PER DEEPENED MOISTURE. COLDER THAN  
AVERAGE TEMPERATURES WILL SPREAD/DIG FROM THE NORTHERN ROCKIES TO  
THE PLAINS AND UPPER MIDWEST/GREAT LAKES NEXT WEEK WITH MAXIMUM  
TEMPERATURES AS COLD AS 10-25 DEG F BELOW AVERAGE POSSIBLE (40S  
AND 50S). WAVES ALONG A STRONG AND REINFORCING NORTH-CENTRAL U.S.  
FRONTAL BOUNDARY MAY PRODUCE HEAVY RAINFALL FOR THE UPPER  
MIDWEST/GREAT LAKES DOWN INTO THE S-CENTRAL PLAINS AND MID-MS  
VALLEY. EJECTING MOISTURE/ENERGY FROM THE REMNANTS OF ROSA MAY ACT  
TO ENHANCE RAINFALL RATHER EFFICIENTLY ALONG THE FRONT, CONTINUING  
THE HEAVY RAINFALL THREAT THROUGH THE WEEK. SUFFICIENTLY COLD AIR  
IN PLACE NORTH OF THE FRONTAL BOUNDARY WILL ALSO SUPPORT SOME  
NORTHERN ROCKIES TO THE NORTHERN PLAINS SNOWS AS REINFORCING  
TROUGHING DIVES SOUTHWARD THROUGH WESTERN CANADA TO THE EAST OF  
THE ALASKAN UPPER RIDGE.  
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A  
BLEND OF THE REASONABLY WELL-CLUSTERED LATEST GFS/GEFS MEAN AND  
ECMWF/EC-ENS MEAN GIVEN TIMING DIFFERENCES IN THE WEST WITH THE  
LEAD AND TRAILING TROUGH. BY LATER NEXT WEEK, THE TREND HAS BEEN  
FOR MUCH MORE RIDGING IN THE EAST WHICH SUPPORTS THE CONTINUATION  
OF ABOVE AVERAGE TEMPERATURES AND A SLOWER SOUTHWARD PROGRESSION  
OF THE SURFACE FRONT.  
 
FRACASSO/SCHICHTEL  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page