EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1158 AM EDT MON MAY 19 2014 VALID 12Z THU MAY 22 2014 - 12Z MON MAY 26 2014 ...OVERVIEW AND PREFERENCES... OVER MOST AREAS THE FLOW ALOFT WILL EVOLVE AT A MODERATE TO SLOW PACE DURING THE PERIOD. ONE OR TWO PIECES OF ENERGY MAY EJECT FROM A NERN PAC MEAN TROUGH INTO THE NWRN CONUS/WRN CANADA. MEANWHILE AN UPR LOW OVER SRN CA WILL EVENTUALLY REACH THE ROCKIES/HIGH PLAINS... AND AN UPR LOW CROSSING NEW ENGLAND AND THE CANADIAN MARITIMES WILL ANCHOR A TROUGH REACHING THE EAST COAST FRI-SAT AND WRN ATLC THEREAFTER. A CLOSED HIGH INITIALLY OVER THE LWR MS VLY/CNTRL GULF COAST WILL SINK SWD INTO THE GULF OF MEXICO BUT CNTRL CONUS RIDGING WILL PERSIST AS IT DRIFTS INTO THE MS VLY. A MODEL/ENSEMBLE MEAN BLEND WEIGHTED 70 PCT TOWARD THE 00Z ECMWF/GFS REPRESENTS CONSENSUS WELL DAYS 3-4 THU-FRI WHEN DIFFS ARE FAIRLY SMALL. DAY 5 HAS EQUAL WEIGHTING OF THE GFS/ECMWF AND THEIR 00Z ENSMEANS AS A TRANSITION TO A 40/30/30 BLEND OF THE 00Z ECMWF/GEFS/NAEFS MEANS FOR DAYS 6-7 SUN-MON GIVEN INCREASING UNCERTAINTY AND OPPOSING TRENDS FOR ERN PAC/WRN NOAM DETAILS AND DECENT ENSEMBLE MEAN AGREEMENT ELSEWHERE. ...GUIDANCE EVALUATION... THE GUIDANCE DIVERGENCE APPROACHING/REACHING THE WEST COAST BY MID-LATE PERIOD STEMS FROM SUBTLE DETAIL DIFFS WITHIN THE MEAN TROUGH ALOFT FROM JUST S OF ALASKA TO NW OF HAWAII. THE 00Z/06Z GFS AND THEIR ENSEMBLE MEANS PLUS THE 00Z UKMET COMPRISE ONE CLUSTER THAT SHOWS A LITTLE LESS WWD ELONGATION OF NRN STREAM ENERGY TO THE S OF AK THUS LEADING TO STRONGER HGT FALLS EVENTUALLY REACHING THE PAC NW/BC. THE 06Z GFS/GEFS MEAN ARE A LITTLE MORE AMPLIFIED THAN THE 00Z RUN. IN CONTRAST THE 00Z ECMWF/CMC AND THEIR MEANS ARE NOTICEABLY SLOWER TO BRING NERN PAC ENERGY TOWARD THE PAC NW. THE PAST COUPLE DAYS OF GFS/ECMWF AND ENSMEAN RUNS REVEAL OPPOSING TRENDS WITH THE GFS/GEFS MEAN GENERALLY BRINGING LOWER HGTS INTO THE NORTHWEST VERSUS THE ECMWF/ECMWF MEAN THAT ARE ADJUSTING SLOWER WITH THE ARRIVAL OF NERN PAC ENERGY. SENSITIVITY OF THE DAYS 6-7 PATTERN TO SUBTLE DIFFS THAT CAN BE DIFFICULT FOR GUIDANCE TO RESOLVE EVEN 3-4 DAYS OUT IN TIME... PLUS CONFLICTING TRENDS... FAVOR A COMPROMISE APPROACH BETWEEN THE ENSEMBLE MEANS BY LATE IN THE PERIOD. IN SPITE OF THE ISSUES UPSTREAM THERE IS BETTER THAN EXPECTED CLUSTERING FOR THE UPR LOW TRACKING OUT OF SRN CA. THE PREFERRED COMPROMISE FOR ERN PAC/WRN NOAM FLOW LEADS TO A SIMILAR INTERMEDIATE SOLN FOR CLOSED LOW PROGRESSION. STILL IT WOULD NOT BE SURPRISING FOR GUIDANCE TO DISPLAY GREATER SPREAD WITH TIMING OF THE UPR LOW AT SOME POINT IN THE NEAR FUTURE. MOST SOLNS AGREE WELL WITH ERN NOAM/WRN ATLC EVOLUTION THROUGH THE PERIOD. THE 06Z GFS OFFERS THE ONE SUSPECT RUN AS IT DEVIATES FROM CONSENSUS OVER HUDSON BAY BY FRI-SAT... LEADING TO MUCH MORE TROUGHING OVER THE EAST THEREAFTER. A COMPROMISE BETWEEN THE 00Z GFS/ECMWF IS NOT FAR FROM THE MIDDLE OF THE FULL 00Z ENSEMBLE SPREAD FOR LOW PRESSURE OFF THE NEW ENGLAND COAST LATE THIS WEEK. ...SENSIBLE WEATHER HIGHLIGHTS... NRN PARTS OF THE WEST MAY SEE ONE OR MORE PERIODS OF MOSTLY SCT/LGT PCPN BUT WITH MORE UNCERTAINTY WHETHER PCPN WILL OCCUR LATE IN THE PERIOD GIVEN SPREAD IN DETAILS OF FLOW ALOFT. THE UPR LOW DRIFTING FROM SRN CA INTO THE ROCKIES SHOULD GENERATE MULTIPLE DAYS OF RNFL CHANCES OVER THE SRN HALF OF THE ROCKIES/HIGH PLAINS. MDT-HVY POCKETS OF RNFL COULD CAUSE LOCALIZED RUNOFF ISSUES BUT THIS ACTIVITY SHOULD HELP TO REDUCE THE SEVERITY OF DROUGHT CONDS SOMEWHAT. WARMEST TEMPS RELATIVE TO NORMAL OVER THE WEST SHOULD BE IN CALIFORNIA WITH SOME LOCATIONS SEEING HIGHS AT LEAST 10F ABOVE NORMAL. EXPECT AREAS OF RNFL TO ACCOMPANY THE SYSTEM AFFECTING THE NORTHEAST DURING THE FIRST HALF OF THE FCST... WITH SOME ACTIVITY ALSO EXTENDING ALONG THE TRAILING COLD FRONT THAT SHOULD PUSH INTO THE SRN MID ATLC/SOUTHEAST BUT BECOME STNRY FARTHER WWD INTO THE CNTRL PLAINS. DEPENDING ON SPECIFICS OF UPSTREAM FLOW AN AREA OF RNFL MAY REACH NRN TIER AREAS BY THIS WEEKEND/EARLY NEXT WEEK. COOL TEMPS OVER THE NERN QUADRANT OF THE CONUS LATE THIS WEEK SHOULD TREND WARMER DURING THE WEEKEND AS AN AXIS OF ABOVE NORMAL TEMPS FROM THE NRN PLAINS INTO THE SOUTHEAST EXPANDS EWD. HIGHEST ANOMALIES FOR MAX TEMPS WITHIN THIS WARMER AREA... PLUS 10-15F... SHOULD BE OVER THE NRN PLAINS LATE THIS WEEK. RAUSCH