850  
FXUS02 KWBC 280646  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
245 AM EDT FRI SEP 28 2018  
 
VALID 12Z MON OCT 01 2018 - 12Z FRI OCT 05 2018  
 
...EXCESSIVE RAINS EARLY NEXT WEEK FOR THE SOUTHWEST ASSOCIATED  
WITH HURRICANE ROSA...  
 
...BELOW AVERAGE TEMPERATURES FROM THE NORTHERN ROCKIES TO THE  
UPPER MIDWEST...  
 
   
..PATTERN OVERVIEW AND WEATHER HIGHLIGHTS/THREATS
 
 
A HIGHLY AMPLIFIED FLOW PATTERN IS EXPECTED TO PERSIST FROM THE  
NORTH PACIFIC ACROSS NORTH AMERICA THROUGH MEDIUM RANGE TIME  
SCALES, WITH A BLOCKING RIDGE CENTERED OVER ALASKA, MEAN TROUGHING  
OFF/ALONG THE U.S. WEST COAST AND 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.  
 
IN THIS PATTERN, AMPLE TROUGHING NEAR THE WEST COAST SHOULD ACT TO  
STEER HURRICANE ROSA NORTHEASTWARD TOWARD BAJA CALIFORNIA EARLY  
NEXT WEEK PER THE LATEST NATIONAL HURRICANE CENTER TRACK, WITH A  
WEAKENING ROSA THEN LIFTING INTO THE SOUTHWEST. THERE REMAINS A  
SIGNIFICANT THREAT FOR DEEPENED TROPICAL MOISTURE TO WORK INTO THE  
SOUTHWEST AND SOUTH-CENTRAL GREAT BASIN/ROCKIES BY EARLY NEXT  
WEEK. DESPITE A WEAKENING TROPICAL SYSTEM, POTENTIAL EXISTS FOR  
HEAVY RAINFALL AND LOCAL RUNOFF ISSUES AS ENHANCED BY TERRAIN.  
 
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 PREVAIL FROM THE  
NORTHERN ROCKIES TO THE UPPER MIDWEST 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 INTO EARLY-MID NEXT WEEK. EJECTING  
MOISTURE/ENERGY FROM THE REMNANTS OF ROSA MAY ACT TO ENHANCE  
RAINFALL EFFICIENCY. SUFFICIENTLY COLD AIR IN PLACE NORTH OF THE  
FRONTAL BOUNDARY MAY ALSO SUPPORT SOME NORTHERN ROCKIES TO THE  
NORTHERN HIGH PLAINS SNOWS.  
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED FROM AN  
ENSEMBLE MEAN COMPOSITE BLEND AFTER CONSIDERATION OF RECENT RUN TO  
RUN MODEL VARIANCE. LEANED WPC BLEND WEIGHTING IN FAVOR OF THE  
18/00 UTC GEFS MEANS THAT OFFER A ROSA AND DRIVING UPSTREAM  
PATTERN SOLUTION MOST IN LINE WITH LATEST NHC TRACK GUIDANCE. THE  
MOST RECENT NHC TRACK FORECAST TRENDED PROGRESSIVE DAYS 3-5.  
OTHERWISE ACROSS THE ENTIRE DOMAIN AND THROUGH LONGER TIME FRAMES,  
THE REASONABLY WELL CLUSTERED ENSEMBLE MEANS BLEND ALSO SEEMS TO  
MITIGATE MODEL TO MODEL TIMING/EMPHASIS ISSUES WITH ROSA'S  
EJECTING EXTRATROPICAL REMNANTS, NORTHERN STREAM EMBEDDED  
SYSTEMS/FRONTS RUNNING OVERTOP AND UNCERTAIN STREAM INTERACTIONS.  
THIS OVERALL FORECAST STRATEGY ACTS TO MAINTAIN GOOD WPC  
CONTINUITY.  
 
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