970   
FXUS10 KWNH 300753  
PMDHMD  
  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
353 AM EDT MON SEP 30 2019  
  
VALID SEP 30/0000 UTC THRU OCT 03/1200 UTC  
  
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
  
00Z FINAL MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..OVERALL PATTERN ACROSS THE CONUS  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND THROUGH 48 HOURS,  
ECMWF/ECENS/UKMET/GEFS 48-84 HOURS  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
  
07Z UPDATE:  
AS SEEMS TO HAVE BEEN THE CASE THE PAST SEVERAL DAYS, THE 00Z CMC  
COMES INTO MUCH BETTER AGREEMENT WITH THE GLOBAL CONSENSUS, BUT  
ITS LACK OF CONSISTENCY RUN-TO-RUN KEEPS IT OUT OF THE PREFERRED  
BLEND AT THIS TIME. DIFFERENCES IN THE MASS FIELDS BECOME QUITE  
SIGNIFICANT BY D3 ACROSS THE WEST AS A LONGWAVE TROUGH  
RE-AMPLIFIES BEHIND THE D1-2 SYSTEM LIFTING OFF TOWARDS THE GREAT  
LAKES. FOR CONSISTENCY WILL MAINTAIN THE PREVIOUS BLEND, BUT  
DIFFERENCES IN THE SPEED AND AMPLITUDE OF THIS SECOND TROUGH WILL  
BE IMPORTANT TO TIMING A COLD FRONT AND QPF MOVING ONSHORE LATE IN  
THE PERIOD.  
  
PREVIOUS DISCUSSION:  
GUIDANCE CONTINUES TO FEATURE LITTLE SPREAD THROUGH 48 HOURS IN  
ITS EVOLUTION OF A LARGE SCALE TROUGH IN THE WEST AND DOWNSTREAM  
AMPLIFIED RIDGE IN THE EAST. THEREAFTER, SPREAD INCREASES QUICKLY,  
AND THE FORECAST CONFIDENCE BEYOND D2 DECREASES RAPIDLY.  
  
THE DIVERGENCE IN THE MASS FIELDS BEGINS WITH THE DEAMPLIFICATION  
OF THE LONGWAVE TROUGH IN THE WEST. AS THIS FEATURES BEGINS TO  
FILL, IT LIFTS NORTHEAST AND WEAKENS, BUT AT THE SAME TIME TILTS  
NEUTRALLY AND EVENTUALLY NEGATIVELY. THE SPEED AND LATITUDE AT  
WHICH THIS OCCURS MAKES CONSIDERABLE DIFFERENCE IN THE SENSIBLE  
WEATHER, ESPECIALLY ACROSS THE MIDDLE OF THE CONUS. THE CMC LAGS  
ALL THE OTHER GUIDANCE AND THE CONSENSUS MEAN IN FILLING THE UPPER  
LOW, IN SOME INSTANCES AS MUCH AS 18-24 HOURS, AND THEREFORE ITS  
DOWNSTREAM EVOLUTION IS OUT OF PHASE WITH THE GLOBAL SUITE. ON THE  
OTHER END OF THE SPECTRUM, THE OPERATIONAL 00Z/30 GFS IS MUCH  
FASTER THAN THE GLOBAL MEAN, AND BEGINS TO TILT ITS 500MB TROUGH  
NEGATIVELY INTO THE WESTERN GREAT LAKES D3. THIS IS FAST AND  
SOUTHEAST OF THE CONSENSUS, BUT IS NOT TOO FAR REMOVED FROM THE  
00Z/30 NAM. THIS APPEARS TO BE IN RESPONSE TO SLIGHTLY LOWER  
THICKNESSES WITHIN THE RIDGE ALLOWING FOR A FASTER AND MORE  
SOUTHERN PROGRESSION OF THIS TROUGH. THE GFS IS ALSO FAR OUTPACING  
ITS ENSEMBLE MEAN, WHICH IS BETTER IN LINE WITH THE  
UKMET/ECMWF/ECENS TO CREATE THE PREFERRED BLEND.  
  
A HEAVY RAIN EVENT STILL LOOKS LIKELY ACROSS THE MIDDLE OF THE  
COUNTRY THE NEXT 3 DAYS. THERE ARE SOME TIMING AND SPATIAL  
DIFFERENCES IN THE GUIDANCE ASSOCIATED WITH THE DISCREPANCIES  
NOTED ABOVE, BUT IN GENERAL THERE IS INCREASING CONFIDENCE IN  
SIGNIFICANT QPF FROM NEW MEXICO INTO THE GREAT LAKES THE NEXT FEW  
DAYS.  
  
MODEL TRENDS AT WWW.WPC.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NOAA.GOV/H5PREF/H5PREF.SHTML  
  
WEISS  
  
  
 
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