Prognostic Meteorological Discussion
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000 FXUS10 KWNH 271934 PMDHMD MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 233 PM EST THU NOV 27 2014 VALID NOV 27/1200 UTC THRU DEC 01/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... =============================================== 12Z MODEL EVALUATION AND PREFERENCES =============================================== THE NAM INITIALIZED WITH 500 MB HEIGHTS ROUGHLY 10 TO 20 METERS TOO LOW/COLD ACROSS MUCH OF THE WESTERN U.S. =============================================== ...CORRECTED THE TIME STAMPS ON MODEL PREFERENCES... ...THE 12Z UKMET WAS UNAVAILABLE... ...THE 12Z CANADIAN WAS AVAILABLE ONLINE... BROAD TROUGH / JET AFFECTING THE NORTHERN AND EASTERN U.S. WITH ASSOCIATED ARCTIC FRONT AND MODEST GULF RETURN FLOW ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF 12Z ECMWF/CANADIAN MODEL TRENDS AND PATTERN RECOGNITION SUGGEST THAT THROUGH SATURDAY FLOW SHOULD AMPLIFY IN BOTH THE NORTHERN AND SOUTHERN STREAMS ACROSS THE EASTERN PACIFIC AND WESTERN NORTH AMERICA. IN THE NORTHERN STREAM THIS MEANS A TROUGH SHARPENING OVER THE PACIFIC NORTHWEST AND THEN EXPANDING EASTWARD. AN ARCTIC COLD FRONT WILL ACCOMPANY THE TROUGH. THE MODELS AGREE TO THESE SIMPLE CONCEPTS...BUT VARY IN AMPLITUDE AND TIMING. GENERALLY...THE ECMWF HAS BEEN A LITTLE SLOWER THAN CONSENSUS...BUT THE 12Z RUN TRENDED SLIGHTLY FASTER. THIS PLACES ALL THE MODELS IN GOOD AGREEMENT THROUGH DAY 2...AFTER WHICH THE NAM BECOMES DEEPER ALOFT AND THE GFS RACES OUT AHEAD OF THE PACK. THE UKMET IS A LITTLE WEAK WITH THE ARCTIC FRONT...WHEREAS THE ECMWF DEPICTS WHAT SEEMS LIKE A MORE REALISTIC SURGE THROUGH THE HIGH PLAINS ON WESTERN KANSAS SUNDAY. THE NAM ALSO DEPICTS THIS SURGE...BUT IS LESS PREFERRED ALOFT. OVERALL...THE ECMWF/CANADIAN CONTINUE TO BEST REPRESENT THE CONSENSUS AND THE TRENDS...KEEPING WITH THE OVERNIGHT PREFERENCE. SHORTWAVE APPROACHING CALIFORNIA SAT NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF 12Z ECMWF/CANADIAN WITH 00Z UKMET THE GLOBAL MODELS ARE QUITE SIMILAR OFFSHORE OF CALIFORNIA IN THE SHORT TERM. THEY ALL BRING A LOW AMPLITUDE SHORTWAVE TROUGH OUT AHEAD OF THE DEEP LOW THAT WILL FORM SOME 800 MILES WEST OF CALIFORNIA. THE GFS DISSIPATES THE STRENGTH OF THE LEAD SHORTWAVE RATHER ABRUPTLY AS IT COMES ONSHORE SATURDAY NIGHT. MORE GENERALLY THE GFS MOVES OUT OF PHASE WITH THE OTHER MODELS...IN PART DUE TO A QUICKER/LESS AMPLIFIED SOLUTION FOR THE DEEP LOW...AND LESSER GRADIENTS IN PLACE OVER THE PACIFIC NORTHWEST. GIVEN THAT THESE DIFFERENCES RESULT IN SOME SIGNIFICANT PRECIPITATION DIFFERENCES...WE PREFER THE ECMWF/UKMET/CANADIAN...WHICH ARE MORE IN LINE WITH PREVIOUS FORECASTS AND WITH THE OVERALL CONSENSUS. WE WERE QUICKER TO DISCOUNT THE NAM...AS IT QUICKLY MOVES OUT OF PHASE WITH CONSENSUS REGARDING EACH INDIVIDUAL SHORTWAVE IN THE EASTERN PACIFIC. UPPER LEVEL TROUGH MOVING THROUGH NORTHERN MEXICO TROUGH MOVING THROUGH AND LIFTING OUT OF THE EAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: ANY OF THE OPERATIONAL MODELS THE GUIDANCE IS IN VERY GOOD AGREEMENT WITH THE CONSOLIDATING NEGATIVELY TILTED TROUGH MOVING THROUGH THE NORTHEAST AND GOOD AGREEMENT WITH THE SHORTWAVE MOVING THROUGH NORTHERN MEXICO. ...MODEL TREND GRAPHICS AT www.wpc.ncep.noaa.gov/html/model2.shtml... ...500 MB FORECASTS AT www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BURKE $$

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