EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 139 AM EDT MON APR 23 2018 VALID 12Z THU APR 26 2018 - 12Z MON APR 30 2018 ...OVERVIEW AND GUIDANCE PREFERENCES... RELOADING TROUGHING IN THE EAST MAY RELENT BY NEXT WEEK AS AN UPPER LOW OFF THE CALIFORNIA COAST SLOWLY BUT SURELY MEANDERS INLAND BY THE WEEKEND. THE ENSEMBLES REMAIN RATHER STEADY IN THIS LONGWAVE EVOLUTION BUT RECENT GFS (12Z/18Z) RUNS WERE STILL QUICKER THAN MOST OR EVEN ALL OF THE ENSEMBLES THROUGHOUT THE PERIOD. OPTED TO RELY ON THE SLOWER AND LARGER CONSENSUS OF THE 12Z ECMWF/UKMET/CANADIAN WITH SUPPORT FROM THE 12Z ECMWF ENSEMBLE MEAN WHILE THE 18Z GEFS MEAN WAS QUICKER BUT NOT AS QUICK AS THE GFS. BY THE WEEKEND, THE ECMWF/CANADIAN MAY BE TOO DEEP/SLOW WITH THE EASTERN TROUGH LIFTING OUT AND AS SUCH TRENDED TOWARD THE ECMWF ENSEMBLE MEAN WHICH WAS JUST A BIT SLOWER THAN THE GEFS MEAN. IN THE WEST, STILL PREFERRED TO TAKE THE UPPER LOW INTO SE OREGON THEN EASTWARD INTO ID AND SW MT BY NEXT MONDAY BUT WITH LOW CONFIDENCE GIVEN THE ENSEMBLE SPREAD. UPSTREAM FLOW OUT OF THE NORTH EAST PACIFIC BECOMES QUITE UNCERTAIN BY THE WEEKEND AS THE GFS/GEFS ALLOW NORTHERN STREAM ENERGY TO SLIDE EAST-SOUTHEASTWARD TOWARD THE PAC NW OR AT LEAST BRITISH COLUMBIA WHILE THE OTHER ENSEMBLES KEEP IT FARTHER NORTH. PREFER TO LET THE UPPER RIDGE OVER IDAHO AND BRITISH COLUMBIA STAY DOMINANT ENOUGH (HAND-IN-HAND WITH A SLOWER UPPER LOW) TO PREVENT SIGNIFICANT HEIGHT FALLS PER THE GEFS. ...WEATHER/THREATS HIGHLIGHTS... UNSETTLED WEATHER DUE TO THE EASTERN TROUGH WILL MAINTAIN A PERSISTENT BUT NON-CONTINUOUS CHANCE OF LIGHT TO MODERATE RAIN IN THE EAST FROM THURSDAY INTO THE WEEKEND BEFORE THE FRONT EXITS THE NORTHEAST BY SUNDAY. TEMPERATURES WILL GENERALLY BE BELOW AVERAGE BUT TRENDING BACK TO MORE SEASONABLE VALUES NEXT WEEK. IN THE WEST, UPPER RIDGING WILL ENSURE WELL ABOVE AVERAGE TEMPERATURES (10 TO 20F ABOVE CLIMO) WITH SOME RECORDS POSSIBLE UNTIL THE CLOSED LOW FINALLY PUSHES INLAND. PRECIPITATION WILL GRADUALLY INCREASE ALONG THE COAST OF NORTHERN CALIFORNIA INTO OREGON LATE FRIDAY INTO SATURDAY THEN THROUGH THE REST OF THE PAC NW INTO THE NORTHERN ROCKIES. SNOW LEVELS WILL BE HIGH TO START BUT GRADUALLY LOWER AS THE UPPER LOW MOVES THROUGH. RAIN AMOUNTS SHOULD GENERALLY BE LIGHT TO MODERATE. ENOUGH OF A RETURN FLOW FROM THE W GULF SHOULD ALLOW FOR GENERALLY LIGHT/SCATTERED RAIN OVER NEW MEXICO INTO COLORADO AHEAD OF THE WESTERN SYSTEM, EVENTUALLY EXPANDING INTO THE PLAINS LATE NEXT MONDAY AND BEYOND. ASSOCIATED WPC MEDIUM RANGE FORECASTS OF 500 MB HEIGHTS...SURFACE SYSTEMS...WEATHER GRIDS...QUANTITATIVE PRECIPITATION FORECASTS (QPF)...AND WINTER WEATHER OUTLOOK SNOW/SLEET PROBABILITIES CAN BE FOUND AT... http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 FRACASSO