600  
FXUS02 KWBC 240553  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
152 AM EDT MON APR 24 2017  
 
VALID 12Z THU APR 27 2017 - 12Z MON MAY 01 2017  
 
...LATE SEASON WINTER STORM LIKELY FOR THE FRONT RANGE OF WY/CO  
AND POSSIBLE FOR THE HIGH PLAINS THIS COMING WEEKEND...  
 
...HEAVY RAIN PROBABLE FOR THE MIDDLE TO LOWER MISSISSIPPI VALLEY  
OVER THE WEEKEND...  
   
..OVERVIEW AND GUIDANCE EVALUATION
 
 
THE UPPER PATTERN ACROSS THE LOWER 48 WILL BE DOMINATED BY A  
PERSISTENT TROUGH EXTENDING FROM THE ROCKIES ACROSS THE CENTRAL  
PLAINS AND MS VALLEY AND UPPER GREAT LAKES. THE TROUGH IS FLANKED  
ON BOTH SIDES IN THE EASTERN PACIFIC AND WESTERN ATLANTIC/EAST  
COAST WITH HIGH AMPLITUDE RIDGES.  
 
WITHIN THE CENTRAL US TROUGH...THE MODELS/ENSEMBLES THIS PERIOD  
FOCUS ON TWO CYCLONES: THE FIRST MOVES ON DAY 3 THU FROM THE MS  
VALLEY ACROSS THE UPPER LAKES INTO CANADA. THE TRAILING COLD  
FRONT CROSSES THE LOWER LAKES INTO THE NORTHEAST FRI. THE  
ECMWF/GFS MODELS AND THEIR ENSEMBLE MEANS HAVE SHIFTED SLIGHTLY  
WEST OF PRIOR CYCLES WITH THE STORM TRACK ACROSS THE UPPER MS  
VALLEY/UPPER LAKES. GIVEN GOOD OVERALL AGREEMENT A BLEND OF THESE  
FORECASTS WAS USED.  
 
THE SECOND CYCLONE DEVELOPS LATER FRI 28 APR IN THE SOUTHERN HIGH  
PLAINS AND MOVES NORTHEAST ACROSS THE SOUTHERN PLAINS TO THE MID  
MS VALLEY SUN AND THEN EITHER THE GREAT LAKES OR UPPER MS VALLEY  
MON BEFORE EXITING INTO CANADA. THE 18Z GFS/18Z GEFS MEAN/12Z  
ECMWF/00Z SUN ECMWF CLUSTER WELL...WITH THE 12Z SUN OPERATIONAL  
ECMWF FURTHER WEST WITH ITS CYCLONE TRACK. THE 00Z GFS HAS SLOWED  
ITS FORWARD PROGRESSION SEVERAL HOURS...SO IT IS FURTHER SOUTH  
THAN THE PREDOMINANT CLUSTER. A CONSENSUS OF THE MAJORITY CLUSTER  
WAS USED FOR THE DAYS 5-7 PROGS...CLOSEST TO THE 12Z ECMWF  
ENSEMBLE MEAN/18Z GEFS MEAN/18Z SUN GFS.  
 
A CLOSED LOW OFF THE MID-ATLANTIC COAST WILL WEAKEN AS IT EXITS  
INTO THE NORTHWESTERN ATLANTIC ON DAY 3/THU 27 APR. THE MODELS NOW  
CLUSTER WELL WITH THIS EVOLUTION...LENDING THE SITUATION TO A  
MULTI-MODEL/ENSEMBLE MEAN BLEND.  
 
   
..WEATHER HIGHLIGHTS
 
 
BOUTS OF SHOWERS AND WILL CONTINUE IN THE PACIFIC NORTHWEST  
THROUGH THE REST OF THE WORK WEEK BEFORE SUBSIDING OVER THE  
WEEKEND. SNOW IS EXPECTED ACROSS THE RANGES OF WA/OR AND FARTHER  
INLAND ACROSS THE MOUNTAINS OF ID/UT/MT/WY/CO. BY FRI INTO THE  
WEEKEND, THE TREND TOWARD A DEEPER/COLDER SYSTEM IN THE ROCKIES  
SUPPORTS WIDESPREAD MODERATE TO HEAVY SNOW FROM THE WY/CO FRONT  
RANGE INTO THE FOOTHILLS. THE SNOW MAY EXPAND INTO THE HIGH PLAINS  
NEXT WEEKEND AS COLD AIR IS ADVECTED SOUTH DOWN THE PLAINS ON THE  
WESTERN SIDE OF THE CIRCULATION. SNOW MAY ALSO OCCUR WED INTO  
EARLY THU IN THE ARROWHEAD OF MN INTO THE WESTERN UP OF MI.  
 
RAINFALL BECOMES WIDESPREAD ACROSS THE CENTRAL PLAINS THU AND THU  
NIGHT WITH A SHOT OF WARM ADVECTION AND AGAIN FRI AS THE SOUTHERN  
PLAINS STORMS DEVELOPS AND MOISTURE SURGES NORTH...CONTINUING INTO  
THE MID MS VALLEY AND GREAT LAKES OVER THE WEEKEND. SEE THE STORM  
PREDICTION CENTER CONVECTIVE OUTLOOKS THAT ADDRESS SEVERE WEATHER  
POTENTIAL. LOCALLY HEAVY RAIN IS POSSIBLE IN THE MID TO LOWER MS  
VALLEY TO THE SOUTHERN PLAINS LATE IN THE WEEK THROUGH NEXT  
WEEKEND AS GEFS M-CLIMATE QPF VALUES INCREASE TO THE 97 TO 99TH  
PERCENTILE FROM EASTERN CO AND AGAIN FROM EASTERN OK AND  
NORTHEASTERN TEXAS THROUGH MISSOURI TO CENTRAL/SOUTHERN IL.  
 
MUCH OF THE EASTERN THIRD OF THE CONUS WILL SEE INCREASING  
TEMPERATURES LATER THIS WEEK AFTER THE COASTAL LOW DEPARTS. AREAS  
OF RECORD WARM TEMPERATURES ARE EXPECTED FROM FRIDAY 28 APR  
THROUGH SUNDAY 30 APR FROM THE LOWER RIO GRANDE VALLEY OF TEXAS  
EASTWARD THROUGH THE SOUTHEAST INTO THE MID-ATLANTIC. BELOW  
AVERAGE TEMPERATURES WILL REMAIN ANCHORED NEAR THE UPPER TROUGH  
AXIS ACROSS THE CENTRAL ROCKIES AND PLAINS TO THE UPPER MS VALLEY  
AND UPPER GREAT LAKES. THE PACIFIC NORTHWEST SHOULD REMAIN COOLER  
THAN AVERAGE THROUGH THE WEEK BEFORE A RETURN TOWARD MORE TYPICAL  
TEMPERATURES. MUCH OF THE SOUTHWEST (SOUTHERN CA INTO NV/AZ)  
SHOULD TREND TO ABOVE NORMAL TEMPERATURES AT THE END OF THE  
WEEKEND INTO EARLY NEXT WEEK.  
 
PETERSEN/FRACASSO  
 

 
 
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