340  
FXUS02 KWBC 290659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 AM EDT SAT SEP 29 2018  
 
VALID 12Z TUE OCT 02 2018 - 12Z SAT OCT 06 2018  
 
...HEAVY RAINS EARLY WEEK FOR THE SOUTHWEST AND CENTRAL GREAT  
BASIN/ROCKIES WITH ROSA...  
...HEAVY RAINS MID-LATER WEEK FROM THE MID-UPPER MISSISSIPPI  
VALLEY TO GREAT LAKES...  
...EARLY SEASON SNOWS FROM THE NORTHERN CASCADES TO THE NORTHERN  
ROCKIES/PLAINS...  
 
   
..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/UTAH EARLY NEXT WEEK, BUT WILL BRING SIGNIFICANT MOISTURE  
TO THE SOUTHWEST. COMBINED WITH A PRE-ROSA SURGE THROUGH THE GULF  
OF CALIFORNIA AND AN INCOMING PACIFIC FRONT INTO CALIFORNIA, THIS  
SETS THE STAGE FOR A LOCALLY HEAVY MULTI-DAY RAINFALL EVENT FOR  
PORTIONS OF SOUTHERN CALIFORNIA EASTWARD ACROSS THE SOUTHWEST AND  
NORTHEASTWARD TO THE CENTRAL GREAT BASIN/ROCKIES. THIS SYSTEM HAS  
THE POTENTIAL FOR SIGNIFICANT HYDROLOGICAL IMPACTS INCLUDING HEAVY  
RAINFALL 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 OFF/ALONG THE U.S. WEST COAST AS WELL AS  
HUDSON BAY, AND PERSISTENT SUBTROPICAL RIDGING ANCHORED OVER THE  
SOUTHEAST. ADDITIONALLY, THE EXTRATROPICAL TRANSITION OF TYPHOON  
TRAMI NEAR EASTERN ASIA THIS WEEKEND 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 TO THE  
SOUTHWEST 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 THEN  
NORTHEAST AND MORE SUMMER-LIKE CONDITIONS FROM THE GULF COAST TO  
THE SOUTHEAST. 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 ARE 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 VALLLEY. EJECTING MOISTURE/ENERGY FROM THE  
REMNANTS OF ROSA MAY ACT TO ENHANCE RAINFALL RATHER EFFICIENCY  
ALONG THE FRONT. SUFFICIENTLY COLD AIR IN PLACE NORTH OF THE  
FRONTAL BOUNDARY MAY 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 GEFS/NAEFS/ECMWF  
ENSEMBLE MEANS GIVEN MODEL RUN TO RUN UNCERTAINTIES. THE BLEND WAS  
MANUALLY ADJUSTED TO THEN BETTER FIT THE LATEST NATIONAL HURRICANE  
CENTER TRACK AND STRENGTH FORECAST FOR ROSA AND DOWNSTREAM  
MOISTURE INFLUX.  
 
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  
 

 
 
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