Prognostic Meteorological Discussion
Issued by NWS

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000 FXUS02 KWBC 301600 PMDEPD EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1200 PM EDT SAT APR 30 2016 VALID 12Z TUE MAY 03 2016 - 12Z SAT MAY 07 2016 ...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES... MODEL/ENSEMBLE SOLNS CONTINUE TO DEPICT AN INCREASINGLY AMPLIFIED/BLOCKY PATTERN NEXT WEEK. OVERALL GUIDANCE HAS BEEN BETTER BEHAVED WITH THE UPR LOW FCST TO CLOSE OFF NEAR THE WEST COAST AROUND THU AND PUSH INLAND THEREAFTER VERSUS THE DETAILS OF THE DEEPENING ERN NOAM TROUGH ALOFT AND CORRESPONDING SFC EVOLUTION. FROM THE ERN PAC INTO WRN U.S. THE PRIMARY ISSUE OVER RECENT DAYS HAS BEEN WITH TIMING OF THE UPR TROUGH NEARING THE WEST COAST AND LOW THAT CLOSES OFF WITHIN THIS TROUGH. THE 00Z/06Z CYCLE HAS ADJUSTED SOMEWHAT FASTER IN WHAT APPEARS TO HAVE BECOME AN ONGOING DAILY OSCILLATION FOR TIMING. AT THE VERY LEAST... GENERALLY SLOW EVOLUTION OF THE PATTERN SHOULD FAVOR LEANING AWAY FROM THE 06Z GFS/00Z CMC THAT BECOME SOMEWHAT FASTER THAN REMAINING SOLNS BY THE LATTER HALF OF THE PERIOD. FARTHER EWD... A SIGNIFICANT KEY TO THE FCST WILL BE WHAT HAPPENS TO SHRTWV ENERGY TO THE W OF HUDSON BAY AS OF EARLY SUN. AFTER THAT TIME AND INTO THE MEDIUM RANGE PERIOD INDIVIDUAL MODEL RUNS DIVERGE GREATLY AMONG EACH OTHER AND FROM PREVIOUS RUNS WITH THE HANDLING OF THIS ENERGY AND TO A MEANINGFUL DEGREE WITH UPSTREAM AMPLIFYING ENERGY THAT MAY FORM A CLOSED LOW... ULTIMATELY LEADING TO SIGNIFICANT DIFFS IN STRENGTH/TRACK OF SFC LOW PRES ALONG THE EAST COAST AFTER 12Z WED. IN PRINCIPLE GUIDANCE CONSENSUS WOULD SUGGEST THAT BY TUE THERE SHOULD BE MORE PLAINS/MS VLY ENERGY PRESENT THAN DEPICTED IN 00Z/06Z GFS AND PARALLEL GFS RUNS. HOWEVER WOULD BE HESITANT TO GIVE ANY MORE THAN PERHAPS 20 PCT CONFIDENCE IN ANY SPECIFIC SCENARIO AT THIS TIME. THUS PREFER TO STAY CLOSER TO A SLIGHTLY DEEPER VERSION OF THE ENSEMBLE MEANS WHICH HAVE PROVIDED BETTER RUN TO RUN STABILITY IN KEEPING LOW PRES JUST OFF THE EAST COAST. ANOTHER SOURCE OF UNCERTAINTY FOR FEATURES ALONG BOTH COASTS WILL BE HOW NERN PAC ENERGY HEADING TOWARD ALASKA PANHANDLE ULTIMATELY CONTINUES INLAND. THE PAST COUPLE ECMWF RUNS HAVE BEEN ON THE QUICK SIDE OF GUIDANCE WITH BRINGING THIS ENERGY INLAND AND THE 00Z ECMWF BECOMES INCREASINGLY OUT OF SYNC WITH CONSENSUS ACROSS THE NERN PAC/NWRN NOAM BY DAY 7 SAT. ABOVE CONSIDERATIONS LEAD TO FAVORING THE 00Z GEFS/ECMWF MEANS AS THE MAJORITY BASIS FOR THE DAYS 3-7 TUE-SAT FCST. THE BLEND INCLUDES A MINORITY WEIGHT OF 00Z GFS/ECMWF FOR A PORTION OF THE PERIOD ESPECIALLY CONSIDERING THE RELATIVE CLUSTERING WITH THE WEST COAST TROUGH/UPR LOW... BUT NOT ENOUGH TO HAVE UNDUE INFLUENCE ON THE EAST COAST EVOLUTION. ...WEATHER HIGHLIGHTS/THREATS... UPR TROUGH/CLOSED LOW HEADING INTO THE WEST WILL SPREAD A BROAD AREA OF PCPN... MOSTLY RAIN... FROM THE WEST COAST INTO THE ROCKIES AND PSBLY AS FAR EAST AS THE PLAINS BY NEXT WEEKEND. BEST POTENTIAL FOR HIGHEST TOTALS OVER THE FCST PERIOD SHOULD EXTEND OVER FAVORED TERRAIN INLAND FROM THE CNTRL WEST COAST AND EWD INTO THE N-CNTRL/CNTRL ROCKIES. NRN AREAS SHOULD SEE TEMPS REMAIN 5-15F ABOVE NORMAL MOST OF NEXT WEEK WITH THIS WARMTH EXTENDING INTO THE NRN PLAINS. CNTRL-SRN LOCATIONS OVER THE WEST WILL TREND STEADILY COOLER WITH SOME HIGHS MORE THAN 10F BELOW NORMAL BY NEXT SAT. THE MOST CONFIDENT ASPECT OF THE FCST OVER THE EAST WILL BE THE TREND TOWARD A COOL AND UNSETTLED PATTERN WITH BEST RNFL POTENTIAL FROM THE ERN GRTLKS/OH VLY/APLCHNS TO EAST COAST. AREAS OF RELATIVELY HEAVIER RNFL ARE PSBL IN ASSOC WITH FRONTAL WAVINESS OVER THE SOUTHEAST/SRN MID ATLC DURING THE FIRST HALF OF THE PERIOD. AFTER MIDWEEK POTENTIAL IMPACTS VARY CONSIDERABLY... WITH VARIOUS SCENARIOS INCLUDING A MULTI-DAY WRN ATLC SYSTEM THAT WOULD KEEP THE MOST SIGNIFICANT WINDS/RNFL ALONG OR OFF THE COAST OR A DEEPER/MORE PROGRESSIVE SYSTEM TRACKING INTO THE NORTHEAST WHICH WOULD SEE GREATER WIND/RNFL EFFECTS. UPR LOW MAY ALSO PROVIDE ANOTHER FOCUS FOR RNFL AT SOME LOCATIONS. RAUSCH $$

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