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