NWS HPC Extended Forecast Discussion - 93L still the one to watch long term
Posted by DTB_2009 on 8/13/2011, 4:01 pm
| Scroll down to bottom for Cliff's Notes version... EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 213 PM EDT SAT AUG 13 2011 VALID 12Z TUE AUG 16 2011 - 12Z SAT AUG 20 2011 LATEST GUIDANCE FOR THE MEDIUM RANGE PERIOD STILL DISPLAYS SIGNIFICANT DIFFS WITH FLOW PROGRESSING FROM THE NRN PACIFIC INTO WRN-CNTRL NOAM. IN CONTRAST TO SOLNS YDAY THAT SEEMED TO BE RATHER RANDOM IN THEIR SPREAD... THERE ARE NOW TWO GENERAL CLUSTERS WITH THEIR CHARACTERISTICS APPEARING TO ARISE FROM HOW FLOW IS HANDLED JUST S/W OF THE ALASKA MAINLAND EARLY IN THE PERIOD. ONE CLUSTER COMPOSED OF THE 00Z GFS AND TO A SOMEWHAT LESSER EXTENT GEFS MEAN/12Z CANADIAN ENSEMBLE MEAN BUILD A RIDGE INTO WRN CANADA BY DAYS 5-6 THU-FRI... WHILE 12Z-00Z ECMWF RUNS/12Z ECMWF MEAN/00Z CANADIAN BRING A DECENT TROF INTO WRN CANADA AND NWRN CONUS IN THAT TIME FRAME. BY DAY 7 SAT THE 00Z ECMWF AND LESS AMPLIFIED ECMWF MEAN/CANADIAN ALL SHOW FASTER PROGRESSION OF THIS TROF COMPARED TO THE 12Z ECMWF RUN. THE STRONG WRN CANADA RIDGE IN THE GFS ULTIMATELY LEADS TO A DEEPER DOWNSTREAM TROF THAN FCST BY OTHER GUIDANCE INCLUDING THE GEFS/12Z CANADIAN MEANS AS WELL AS PREVIOUS GFS RUNS OVER THE PAST 24 HRS. AS A RESULT THE GFS WILL BE CONSIDERED THE LEAST LIKELY SOLN BY DAYS 5-7 THU-SAT. OTHERWISE LACK OF CONTINUITY AS WELL AS LACK OF SUFFICIENTLY AGREEABLE ANOMALY CENTERS FOR DETERMINING TELECONNECTION FAVORED FLOW RECOMMEND A COMPROMISE BETWEEN ENSEMBLE MEANS UNTIL BETTER AGREEMENT EMERGES. AHEAD OF THIS EVOLUTION THERE IS FAIR CLUSTERING WITH LOW PRESSURE TRACKING ACROSS CANADA AND TRAILING COLD FRONT THAT SHOULD WEAKEN AS IT APPROACHES THE APLCHNS LATE NEXT WEEK. THE GFS MAY BE A TAD SLOW WITH THE MID LVL SYSTEM AT SOME HRS IN THE FIRST HALF OF THE PERIOD BUT THE SFC EVOLUTION IS SUFFICIENTLY CLOSE TO CONSENSUS TO INCLUDE AS PART OF A BLEND. THE GEFS MEAN IS A FAST EXTREME WITH THE SFC LOW OVER CANADA. MEANWHILE THE 00Z ECMWF TRENDS FASTER THAN MOST GUIDANCE ASIDE FROM THE UKMET WITH THE WAVY FRONT NEAR THE EAST COAST. THE DAYS 3-4 TUE-WED FCST STARTS WITH A BLEND OF 00Z ECMWF/00Z GFS/12Z ECMWF ENSEMBLE MEAN TO EMPHASIZE THE MOST AGREEABLE ASPECTS OF GUIDANCE WITH THE TWO PRIMARY FEATURES EARLY IN THE PERIOD... WITH ADDITIONAL SLIGHT ADJUSTMENTS TOWARD THE ENSEMBLE MEANS OFF THE EAST COAST. DAYS 5-7 THU-SAT USE A 60/40 WEIGHTING OF THE 12Z ECMWF MEAN/00Z GEFS MEAN TO YIELD THE DESIRED COMPROMISE FOR WRN NOAM FLOW MID-LATE PERIOD. WITH ADDITIONAL INPUT FROM NAEFS/06Z GFS/00Z ECMWF ENS MEANS AND LAGGED AVERAGE FORECAST OF GFS AND ECMWF SOME CHANGES ARE IN ORDER FROM EARLIER PRELIMS BUT OVERALL RESULT IN THE SAME SCENARIO AND THINKING..WITH AN OVERALL SIMPLIFICATION WHICH IS USUALLY THE BEST SOLUTION. UPDATED MORNING BLENDS USE A 50/50 MIX OF GFS AND ECMWF ENS MEANS TO RESOLVE THE DIFFERENCES BETWEEN THE OPERATIONAL SOLUTIONS DESCRIBED ABOVE UNTIL ONE OR THE OTHER BECOMES DOMINANT OR THEY YIELD TO THIS PRESCRIBED MIXTURE. NO CHANGES TO AFTN FINALS FROM EARLIER PRELIMS. LATEST GFS TRENDING TOWARDS THE ENS MEANS USED PREVIOUSLY OF GFS/ECMWF AND NAEFS. ONLY ADDITIONAL FEATURE ADDED IS TROPICAL DEPICTION OF AL93 ENTERING THE CARRIBEAN WITH SEVERAL MODELS INTENSIFYING THE SYSTEM LATE PERIOD AND BEYOND AS IT ENCOUNTERS A MORE FAVORABLE ENVIRONMENT. SEE NHC/TPC DISCUSSIONS AND OUTLOOKS. RAUSCH/ROSENSTEIN They are currently going with the Caribbean route...  |
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