713  
FXUS10 KWNH 011612  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1212 PM EDT FRI MAY 01 2020  
 
VALID MAY 01/1200 UTC THRU MAY 05/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...DEEP TROUGH/CLOSED LOW IMPACTING THE EAST THROUGH FRIDAY AND  
EARLY SATURDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET BLEND OR GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE TO ABOVE AVERAGE  
 
HIGH AMPLITUDE TROF ALONG THE EAST COAST IS A NORTH-SOUTH STACK OF  
TWO SMALLER SCALE FEATURES, THE BROADER/SOUTHERN OF WHICH WILL  
CONTINUE TO NARROW AND WEAKEN, WHILE THE NORTHERN WILL ELONGATE  
BUT STRENGTHEN ACROSS SW QUEBEC INTO THE NORTHEAST EARLY SATURDAY.  
THE MODEL SPREAD IS FAIRLY SMALL AND AGREEABLE WITH THE OVERALL  
EVOLUTION INCLUDING THE NEWER SURFACE CYCLONE THAT DEVELOPS ALONG  
40N EAST OF 70W EARLY SAT. THE UKMET IS A TAD SLOW WITH THE  
SURFACE WAVE ALONG EAST COAST TODAY AND SHIFTS THE DEVELOPMENT OF  
THE 2ND SURFACE WAVE FURTHER NORTH. SO FOR A TIGHTER BLEND A  
NON-UKMET BLEND IS SUPPORTED BUT A GENERAL MODEL BLEND MAY BE  
VIABLE, TO HANDLE SOME OF THE UNCERTAINTY IF DESIRED. CONFIDENCE  
IS SLIGHTLY TO ABOVE AVERAGE  
 
...SHORTWAVE/SURFACE LOW TRACKING NEAR THE U.S./CANADIAN BORDER  
THROUGH SUNDAY, FRONTAL ZONE THROUGH OHIO VALLEY; NORTHEAST  
REINFORCEMENT/SURFACE REDEVELOPMENT SUNDAY TO MONDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
FAVORING: 00Z UKMET CANADA/GREAT LAKES/NORTHEAST  
12Z NAM/GFS AND ECMWF ACROSS OHIO VALLEY TO MID-ATLANTIC  
CONFIDENCE: AVERAGE TO SLIGHTLY BELOW AVERAGE (BY END OF D3)  
 
IN THE WAKE OF LARGER SCALE TROUGH ALONG THE EAST COAST, GENERALLY  
FLATTER FLOW EXISTS ACROSS THE WEST INTO THE NORTHERN PLAINS.  
SMALLER SCALE SHORTWAVE FEATURES INITIALLY IN THE NORTHERN ROCKIES  
AND CANADIAN ROCKIES WILL BE START TO EXPAND AND INTERACT ACROSS  
THE SOUTHERN PRAIRIES OF CANADA INTO THE NORTHERN PLAINS AND UPPER  
GREAT LAKES BY SAT MORNING. THIS ELONGATION AND MAGNITUDE OF  
INTERACTION BETWEEN THE FEATURES ALONG WITH INFLUENCE OF  
CONVECTIVE UPSCALE/LATENT HEAT INTO THE SYSTEM LEADS TO LOWER  
PREDICTABILITY SCENARIO UNFOLDING ACROSS THE GREAT LAKE INTO THE  
NORTHEAST THE THE END OF THE WEEKEND, ESPECIALLY AS A SUBTLE  
SHORTWAVE/SPEED MAX EMERGES OUT OF THE CENTRAL ROCKIES AND RACES  
ACROSS THE OHIO VALLEY SAT INTO SUNDAY.  
 
INITIALLY, HOWEVER, THE MERGER OF THE WAVES ACROSS SW ONTARIO BY  
LATE SAT/SUN IS IN MODERATE AGREEMENT THOUGH WITH TYPICAL TIMING  
ISSUES. THE GFS/GEFS ARE FAST AND THE 12Z NAM SHIFTED FASTER TO  
JOIN ITS NCEP BRETHREN, WHILE THE ECMWF IS SLOWER. THE CMC IS  
ALREADY WELL NORTH AND OFFSET TO REMAIN OUT OF PHASE AND THEREFORE  
OUT OF PREFERENCE THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD.  
 
THE UKMET IS BETWEEN THE TWO CAMPS, BUT FAVORS THE NAM/GFS JUST  
GENERALLY WEAKER THROUGH EARLY SUNDAY. AS THE NAM/GFS RAPIDLY  
DEVELOP THE SURFACE LOW AND STARTS THE OCCLUSION PROCESS EARLIER  
AS IT PROGRESSES THROUGH THE GREAT LAKES ON SUNDAY, THE UPSTREAM  
(NORTHERN CANADIAN ROCKIES) WAVE SWINGS THROUGH THE BASE AND  
PRESSES THE FRONTAL ZONE ACROSS THE OHIO VALLEY. GIVEN THE ECMWF  
WAS WEAKER/SLOWER WITH THE INITIAL WAVE THE INITIAL SURFACE WAVE  
IS WEAKER AND SOUTH, BUT THE UPSTREAM KICKER IS STRONGER AND  
FASTER SUPPORTING A TRIPLE-POINT LOW TO FORM OVER THE NORTHEAST BY  
LATE SUNDAY, PRESSING THE FRONTAL ZONE FURTHER EAST WITH TIME,  
EVEN MORE AGGRESSIVELY THAN THE BULK OF ECENS MEMBERS. SO THERE  
IS LARGE SPREAD BY 60HRS IN THE NORTHEAST WITH THE FOCUS OF  
STRONGER SURFACE CYCLONE THEREFOR WIND FIELDS. THE UKMET IS  
MIDDLE GROUND, AND FRANKLY IDEAL IN PLACEMENT OF THE CANADIAN  
WAVE, BUT BEING WEAKER/ELONGATED INITIALLY...DID NOT PRESS THE  
FRONTAL ZONE SOUTH THROUGH THE OHIO VALLEY. BY DAY 3, THERE IS NO  
IDEAL SOLUTION/PREFERENCE BUT A COMPROMISE SOMETHING CLOSER TO THE  
UKMET NORTH IN CANADA/NORTHEAST BUT SOMETHING CLOSER TO THE  
TIMING/ORIENTATION OF THE FRONTAL ZONE ACROSS THE OHIO  
VALLEY/MID-ATLANTIC MONDAY BY A NAM/GFS/ECMWF BLEND.  
 
CONFIDENCE IS AVERAGE INITIALLY BECOMING SLIGHTLY BELOW AVERAGE BY  
DAY 3.  
 
...DEEP TROUGH OFFSHORE THE WEST COAST TODAY AND SATURDAY WITH  
REMNANT SHORTWAVE ENERGY MOVING THROUGH THE NORTHERN ROCKIES  
SUNDAY MORNING, NORTHERN HIGH PLAINS SURFACE LOW...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND THRU 03.12Z  
NON-CMC COMPROMISE AFTERWARD  
CONFIDENCE: ABOVE AVERAGE THRU 03.12Z  
AVERAGE TO SLIGHTLY BELOW AVERAGE AFTERWARD  
 
DEVELOPING GULF OF ALASKA CYCLONIC GYRE WILL BE SHIFTING SOUTHEAST  
WITH AN INITIAL SHORTWAVE THAT IS LIFTING NORTH ALONG 135W TODAY.  
QUICK ON ITS HEALS, ANOTHER POTENT SHORTWAVE FURTHER SHIFTS THE  
GYRE EASTWARD, WITH THE LEADING SHORTWAVE ENERGY DEEPENING INTO A  
STACKED DEEP SURFACE WAVE WITH A FRONTAL ZONE THAT WILL PRESS  
THROUGH THE PACIFIC NW BY MIDDAY SATURDAY WITH LITTLE MODEL  
DIFFERENCE TO SUPPORT A GENERAL MODEL BLEND THROUGH THE PACIFIC NW.  
 
THE BASE OF THE TROF WILL ACCELERATE EASTWARD INTO THE NORTHERN US  
ROCKIES WITHIN THE LEFT EXIT OF A WEAKLY CYCLONICALLY CURVED UPPER  
LEVEL JET. WITH VERY STRONG 130-150KT UPSTREAM ENERGY, THERE  
COULD BE POTENTIAL FOR VIGOROUS DEVELOPMENT AS IT DETACHES FROM  
THE GYRE AND MOVES INTO THE NORTHERN HIGH PLAINS LATE SUNDAY. BY  
THIS TIME, TYPICAL TIMING DIFFERENCES START TO MANIFEST, WITH THE  
GFS/NAM AND UKMET SHIFTING FASTER THAN THE ECMWF/CMC. IN  
COMBINATION OF TIMING OF THE EXITING SHORTWAVE AND RETURN OF  
SHORTWAVE RIDGING DOWNSTREAM, AS WELL AS SOME VORTICITY STRETCH IN  
THE LEE OF THE MT ROCKIES, THE GFS/NAM BOTH RAPIDLY DEEPEN THE  
SHORTWAVE INTO A COMPACT CLOSED LOW THAT LIFTS NORTH INTO  
ALBERTA/SASKATCHEWAN BY MONDAY; WITH THE UKMET INITIALLY A BIT  
SLOWER IN DEVELOPMENT AND THEREFORE HAVING THE OPPORTUNITY TO  
PRESS FURTHER EAST BY 00Z TUESDAY. THE SLOWER CMC IS VERY WEAK  
AND MOVES OUTSIDE OF THE ENSEMBLE SUITE AND IS QUICKLY DISMISSED.  
THE ECMWF IS SLOWER AND THEREFORE WEAKER REMAINING SOUTH AS IT  
CLOSES OFF MONDAY, THIS WILL HELP WITH STRONGER UPSLOPE FLOW AND  
CLOSER PROXIMITY TO BETTER INSTABILITY AND MOISTURE ACROSS THE  
CENTRAL PLAINS.  
 
ADDITIONALLY AND POTENTIALLY MORE IMPORTANT FOR THE DOWNSTREAM  
EVOLUTION (AS WELL AS UPSTREAM SEE SECTION BELOW) IN THE NORTHERN  
AND CENTRAL PLAINS, THE NAM/GFS AND LESSER EXTENT SO UKMET SHOW A  
STRONG TRAILING SHORTWAVE ENTERING N CA AT 04.00Z. THE  
ECMWF/ECENS SOLUTIONS DEPICT THIS FEATURE MUCH WEAKER IF AT ALL,  
WHICH ONLY INCREASES THE SPREAD AND UNCERTAINTY 72-84HRS, AS THE  
NAM/GFS BOTH SHOW A STRONG SURFACE RESPONSE WITH A NEW SURFACE  
WAVE ALONG THE FRONT CROSSING INTO SD BY 84HRS. THIS FALLS INTO  
LINE WITH BOTH THE NAM/GFS FAST BIASES AS WELL AS THE ECMWF SLOWER  
SOLUTION BIAS; ENSEMBLE SUITE ARE VERY SIMILAR TO THEIR PARENT  
OPERATIONAL MODEL, PROVIDING LITTLE HELP ONE SIDE OR THE OTHER.  
SO A COMPROMISE OF NON-CMC SOLUTIONS SEEMS PRUDENT AFTER A GENERAL  
MODEL BLEND THROUGH 60HRS. CONFIDENCE IS ABOVE AVERAGE THROUGH  
60HRS, BUT RAPIDLY SHIFTS TO AVERAGE OR SLIGHTLY BELOW AVERAGE IN  
THE COMPROMISE THEREAFTER WITH LIKELY SIZABLE RUN TO RUN VARIATION  
EXPECTED WITH UPCOMING MODEL CYCLES.  
 
...NEXT EMBEDDED SHORTWAVE IN GULF OF AK GYRE, CLIPPING NW  
MONDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: AVERAGE  
 
THE NEXT PACIFIC SHORTWAVE WITHIN THE PARADE ALONG THE SOUTHERN  
EDGE OF THE ALASKAN GYRE, WILL PRESS EASTWARD BY SUNDAY. THE  
UNCERTAINTY HERE, IS HOW MUCH OF THE INITIAL SHORTWAVE WILL BE  
SHED INTO THE ZONE FLOW BEFORE THE WAVE DEEPENS SUNDAY OUT WEST OF  
140W. THE GFS/NAM BEING FASTER, SHED MORE BEFORE THE WAVE BUCKLES  
THE FLOW (SEE LAST PARAGRAPH OF SECTION ABOVE), RELATIVE TO THE  
SLOWER ECMWF. IN RETAINING MORE ENERGY, THIS ALLOWS FOR THE ECMWF  
TO BE STRONGER AND THEREFORE DOMINATE THE BINARY INTERACTION WITH  
THE LARGER SCALE GYRE...AND SHIFT IT EASTWARD TO THE PACIFIC COAST  
LATE MONDAY INTO TUESDAY. WHILE THE GFS/NAM BEING A BIT WEAKER,  
RELATIVE TO THE EC LIFTS NORTHWARD TOWARD THE CENTER OF THE GYRE  
AND THEREFORE SLOWS RELATIVE TO PRIOR RUNS, WITH BARELY AND QPF  
REACHING THE WEST COAST BY THE END OF THE FORECAST PERIOD. THE  
00Z UKMET, TYPICAL OF ITS BIAS, WHILE FAST, IS ALSO STRONG IN ITS  
EVOLUTION AND SPLITS THE DIFFERENCE, BETWEEN THE ECWMF AND  
NAM/GFS. THE CMC REMAINS OUT OF PHASE, WELL EAST OF THE ENSEMBLE  
SOLUTIONS AND WITH DOWNSTREAM ISSUES ELSEWHERE THAT ARE IMPORTANT  
TO THIS SYSTEM'S EVOLUTION...IT IS DISCARDED. SO A NON-CMC BLEND  
IS SUPPORTED AND WITH MILDER SPREAD, CONFIDENCE IS AVERAGE.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
GALLINA  
 

 
 
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