428  
FXUS10 KWNH 160745  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
345 AM EDT WED OCT 16 2019  
 
VALID OCT 16/0000 UTC THRU OCT 19/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION WITH PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
GREAT LAKES CLOSED LOW AND DEVELOPING NORTHEAST COASTAL SURFACE LOW  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM AND HIGHER WEIGHT TOWARD ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
07Z UPDATE: CONTINUED GOOD CLUSTERING WITH THE REST OF THE 00Z  
GUIDANCE NOW AVAILABLE. THE NAM REMAINS A BIT TOO DEEP INITIALLY  
AND THEN TOO SLOW AS THE LOW MOVES NORTH OF NOVA SCOTIA. A NON-NAM  
BLEND WITH HIGHER WEIGHT TOWARD THE ECMWF REMAINS THE PREFERRED  
BLEND.  
 
---PREVIOUS DISCUSSION---  
CLOSED UPPER LOW CURRENTLY OVER EASTERN WISCONSIN WILL TAKE ON  
MORE OF A NEGATIVE TILT AS IT APPROACHES THE NORTHEAST U.S. BY  
THURSDAY. THE INCREASING DIFFLUENT PATTERN ALOFT WILL SUPPORT  
RAPID SURFACE CYCLOGENESIS ALONG OR JUST OFFSHORE THE MID-ATLANTIC  
COAST AND WILL TRACK INLAND ACROSS NEW ENGLAND. THE 00Z NAM  
CONTINUES TO SHOW THE MOST VERTICALLY STACKED AND DEEPEST  
SOLUTION, WHICH MAY BE RELATED TO BETTER HIGHER RESOLUTION OF WARM  
GULF STREAM AIR, BUT THIS VERY STRONG SIGNAL DEPARTS RAPIDLY FROM  
THE OTHER GUIDANCE MEMBERS AND ENSEMBLE SUITE/TREND, LEAVING IT  
OUT OF THE PREFERENCE (THOUGH IT MAY NOT BE FULLY UNREALISTIC).  
THE REST OF THE GUIDANCE OFFERS FAIRLY GOOD CLUSTERING THROUGH 60  
HOURS AS THE LOW LIFTS NORTHEAST THROUGH MAINE AND INTO CANADA. AS  
SUCH, WILL CONTINUE TO LEAN ON PREVIOUS PREFERENCE TOWARD THE  
ECMWF AND CONTINUED LESS WEIGHTING OF THE NAM AT THIS TIME.  
 
RECORD FOR LOW PRESSURE ARE FOR NON-TROPICAL CYCLONE PRESSURES IN  
OCTOBER...POST-TROPICAL SANDY IS INCLUDED IN THIS DATABASE, SO  
RECORDS ACROSS THE LOWER HUDSON AND MID-ATLANTIC ARE AT MUCH LOWER  
RISK OF BEING BROKEN...PLEASE SEE  
WWW.WPC.NCEP.NOAA.GOV/RESEARCH/ROTH/SLPRECORDS.HTML.  
 
SHORT WAVE ENERGY AFFECTING TEXAS THROUGH MIDWEEK SHEARING THRU  
EASTERN GULF STATES BY FRI  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
07Z UPDATE: BETTER AGREEMENT NOW WITH THE WEAK SURFACE WAVE  
LIFTING FROM THE SOUTHWESTERN GULF TOWARD THE CENTRAL GULF COAST  
BY SATURDAY. THE GFS REMAINS ON THE RIGHT SIDE OF THE MODEL SPREAD  
WHILE THE ECWMF IS WEST, BUT THE OVERALL SPREAD HAS LESSENED.  
ALTHOUGH THE NAM/CMC/UKMET OFFER A FAVORABLE CONSENSUS APPROACH,  
SOME INCLUSION OF THE GFS AND ECMWF WOULD BE ACCEPTABLE AS WELL  
DESPITE SOME LOWER CONFIDENCE BY DAY 3.  
 
---PREVIOUS DISCUSSION---  
TROUGHING CURRENTLY MOVING INTO THE TEXAS PANHANDLE WILL GRADUALLY  
REACH THE GULF COAST BY LATER THIS WEEK. INTERACTION WITH AN AREA  
OF DISTURBED WEATHER IN THE SOUTHWESTERN GULF WILL EVENTUALLY LEAD  
TO A WEAK SURFACE WAVE LIFTING NORTHEAST TOWARD THE CENTRAL GULF  
COAST. THERE IS A FAIR AMOUNT OF SPREAD IN THE EVENTUAL TRACK OF  
ANY SURFACE WAVE WITH THE LATEST ECMWF SLOWER/WESTWARD COMPARED TO  
THE FASTER/EAST GFS, WHILE THE CMC LIES IN BETWEEN. THE 00Z NAM  
OFFERED A GOOD COMPROMISE/CONSENSUS APPROACH AS WELL. THERE  
REMAINS ABOVE NORMAL UNCERTAINTY IN HOW THIS EVOLVES OVER THE  
COMING DAYS AND WHAT SENSIBLE WEATHER IMPACTS THERE WILL BE, BUT A  
BLEND OF THE LATEST NAM/CMC/UKMET REPRESENTS THE CONSENSUS  
APPROACH THE BEST AT THIS TIME.  
 
WESTERN U.S. LONGWAVE TROUGH (WED-THURS) SHIFTS INTO ROCKIES WITH  
NORTHERN PLAINS CYCLOGENESIS THURS INTO FRI  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
07Z UPDATE: NO SIGNIFICANT CHANGES NOTED WITH THE REST OF THE 00Z  
GUIDANCE NOW AVAILABLE AND A GENERAL MODEL BLEND IS STILL  
PREFERRED.  
 
---PREVIOUS DISCUSSION---  
POSITIVELY TILTED TROUGH WILL CROSS INTO THE WESTERN U.S. LATE  
WEDNESDAY AND PUSH INTO THE CENTRAL U.S. BY THIS WEEKEND. MODEL  
SPREAD IS AVERAGE TO SLIGHTLY ABOVE AVERAGE AT THIS POINT, WITH  
THE LARGEST DIFFERENCES SEEN IN TIMING AS THE SHORTWAVE MOVES EAST  
OF THE ROCKIES. TYPICAL MODEL BIASES ARE NOTED, WITH THE GFS BEING  
SLIGHTLY FASTER COMPARED TO THE ECMWF/CMC/UKMET, BUT COMPARED TO  
PREVIOUS CYCLES, THE DIFFERENCES ARE NOT AS SIGNIFICANT. AS SUCH,  
A GENERAL MODEL IS PREFERRED GIVEN THE BETTER THAN AVERAGE MODEL  
AGREEMENT.  
 
PACIFIC NORTHWEST REINFORCING SHORTWAVE LATE THURS INTO FRI WITH  
BROAD/STRONG WESTERLY PACIFIC JET THEREAFTER  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
IN THE WAKE OF THE INITIAL LONGWAVE TROUGH ACROSS THE PACIFIC  
NORTHWEST, A STRONGER/COMPACT SHORTWAVE PIECE OF ENERGY PUSHES  
INTO THE REGION LATE THURSDAY INTO FRIDAY. IN THE PREVIOUS  
FORECAST CYCLE, THE 12Z UKMET WAS TOO AMPLIFIED AND WAS NOT  
CONSIDERED FOR THE PREFERRED BLEND. THE NEW 00Z IS CONSIDERABLY  
LESS AMPLIFIED AND NOW IS IN MUCH BETTER AGREEMENT WITH THE REST  
OF THE DETERMINISTIC MODELS AND WITHIN THE MODEL SPREAD. A GENERAL  
MODEL BLEND CAN BE USED HERE.  
 
MODEL TRENDS AT WWW.WPC.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
TAYLOR  
 

 
 
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