665  
FXUS10 KWNH 261844  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
242 PM EDT SUN APR 26 2020  
 
VALID APR 26/1200 UTC THRU APR 30/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
DEVELOPING NORTHEAST COASTAL LOW TODAY THROUGH MONDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND WITH LOW GFS WEIGHTING OR NON-GFS  
BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
19Z UPDATE: THE 12Z NON-NCEP SOLUTIONS SHIFTED TOWARD THE 12Z NCEP  
SOLUTIONS OF THE NAM/GFS. WHILE THE GFS REMAINS TOO WARM RELATIVE  
TO THE SUITE ON DAY 1 INTO DAY 2; AND IS STILL THE FASTEST  
SOLUTION IN TIMING AND THEREFORE SLIGHTLY EAST; WILL SUPPORT A  
GENERAL MODEL BLEND WITH LOWER WEIGHTING TO THE GFS OR REMOVE THE  
GFS OUTRIGHT BASED ON HIGHLY LOCALIZED NEEDS.  
 
---PRIOR DISCUSSION---  
THE MILLER-B COASTAL CYCLOGENESIS IS ALREADY WELL ON ITS WAY ALONG  
THE EAST COAST/LOWER CHESAPEAKE AS THE OHIO VALLEY SURFACE WAVE  
WEAKENS UNDER INCREASINGLY SHEARED MID TO UPPER LEVEL PATTERN (AS  
EVIDENCED BY GOES-E WV SUITE). THE GFS CONTINUES TO BULGE  
SLIGHTLY WARMER 850MB TEMPS ACROSS THE CATSKILLS/POCONOS AND NJ IN  
EXITING MAKING IT LESS FAVORABLE WITHIN INCREASINGLY STRONGER  
SW-NE GRADIENT IN THE REMAINDER OF THE GUIDANCE SUITE. OTHERWISE,  
A MORE TRADITIONAL ALIGNMENT OF GUIDANCE MEMBERS WILL OCCUR WITH  
THE WAVE LIFTING NORTH. THE GFS IS FASTEST AND GENERALLY WEAKER  
THAN THE SLOWER BUT STRONGER UKMET, AND EVEN DEEPER 12Z NAM. THE  
00Z CMC/ECMWF LAG A LITTLE SLOWER; BUT ALLOWS FOR A MORE  
TRADITIONAL BLENDING SCENARIO. THE TRAILING SOUTHERN STREAM  
SHORTWAVE ENERGY WILL ENHANCE SOUTH OF THE 40N70W BENCHMARK LATE  
MONDAY INTO EARLY TUESDAY, UNDER THE INFLUENCE OF THE UPSTREAM  
(SEE SECTION BELOW) 'KICKER' WAVE. THE GFS REMAINS FAST/LIKELY  
TOO FAST, BUT THE UKMET/NAM DEPICT A SLOWER, MORE REASONABLE  
SIMILARITY. THE 00Z CMC/ECMWF ARE TOO SLOW, ALLOWING FOR THE  
SURFACE OCCLUSION TO LINGER LIKELY TOO LONG. THIS ALLOWS FOR THE  
ECMWF TO SHIFT WELL NORTH OF THE OTHER CONSENSUS SOLUTIONS. WHILE  
NEITHER CAMP LOOKS IDEAL, A COMPROMISE OF THE NAM/UKMET AND THE  
ECMWF/CMC SEEMS PRUDENT AFTER 28.12Z (48HRS); AS SUCH A NON-GFS  
BLEND IS SUPPORTED AT SLIGHTLY ABOVE CONFIDENCE.  
 
TROUGH AXIS CROSSING CANADIAN PRAIRIES, CLIPPING UPPER  
MIDWEST/GREAT LAKES THROUGH MONDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
GOES-WV SUITE DENOTES MATURING CYCLONE ACROSS CENTRAL  
ALBERTA/SASKATCHEWAN, THIS WILL DROP A FRONTAL ZONE THAT CROSSES  
THE NORTHERN PLAINS LATER TODAY INTO MONDAY. WHILE THE BULK OF  
THE SHORTWAVE ENERGY WILL LIFT NORTH OVER THE DOWNSTREAM BLOCKING  
RIDGE IN ONTARIO, THE BASE OF THE SHORTWAVE WILL SLIDE UNDERNEATH  
ACROSS THE GREAT LAKES EVENTUALLY ACTING AS A KICKER TO THE LARGER  
COASTAL CYCLONE (SEE SECTION ABOVE). UNTIL THE WAVE IS  
UNDER-CUTTING THE RIDGE ON MONDAY, THERE IS SOLID MODEL AGREEMENT.  
THE GFS STARTS TO ACCELERATE EAST-SOUTHEAST THEREAFTER BUT THAT  
IS DRIVEN MORE BY THE DOWNSTREAM FASTER EXIT. ADDITIONALLY, THE  
FRONTAL ZONE WILL DRAPE ACROSS THE NORTHERN PLAINS AND ACT AS A  
SEEDING OF THE APPROACHING SHORTWAVE (SEE SECTION BELOW) MONDAY.  
HERE THE GUIDANCE IS TIGHTLY AGREED UPON TO AT LEAST START THE  
NEXT SYSTEM ON SIMILAR FOOTING. SO A GENERAL MODEL BLEND CAN BE  
AFFORDED AT ABOVE AVERAGE CONFIDENCE  
 
PACIFIC NORTHWEST SHORTWAVE ON MONDAY DIGGING ACROSS NORTHERN  
PLAINS TUES AND INTO A CLOSED LOW OVER MIDWEST BY  
WED...ACCOMPANYING FRONT THRU SOUTHERN PLAINS (TUES) AND MID-MS TO  
TN VALLEYS (WED)  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
19Z UPDATE: THE 12Z ECMWF TRENDED A LITTLE STRONGER INITIALLY WITH  
THE LEAD WAVE, AND THE CMC/UKMET SHIFTED TIGHTER TO THE GFS/NAM  
SOLUTION AS WELL THROUGH LATE TUESDAY TO BUILD MUCH HIGHER  
CONFIDENCE. SO AS THE MAIN SHORTWAVE DIGS ACROSS THE PLAINS AND  
BOTTOMS OUT ACROSS THE MIDWEST BY WED, THE MASS FIELDS REMAIN IN  
GOOD AGREEMENT. THE NAM IS A BIT STRONGER/BASE HEAVY; THE GFS  
SHIFTS A BIT FASTER THROUGH MI AND THE UKMET IS A LITTLE TOO  
STRONG WITH THE OLD OCCLUDED LOW CENTER ACROSS N IL/S WI BY LATE  
WED; BUT GENERALLY BLENDING ALL THE GUIDANCE WITH THEIR  
BIAS/ISSUES SEEMS TO PRESENT A SOLID FORECAST. SO WILL SUPPORT A  
GENERAL MODEL BLEND WITH INCREASED CONFIDENCE (SLIGHTLY ABOVE  
AVERAGE) AS WE ARE SEEING SOME CONTINUITY TOWARD A COMMON SOLUTION  
EVEN IN A LOWER PREDICTABILITY REGIME.  
 
---PRIOR DISCUSSION---  
STRONG GULF OF AK GYRE, WILL EJECT THE BASE OF SHORTWAVE AND  
STRONG ANTI-CYCLONIC UPPER LEVEL JET FEATURES ACROSS BRITISH  
COLUMBIA THE END OF MONDAY INTO TUESDAY. PRECEDING THE MAIN  
WAVE, THE LEFT EXIT OF THE JET PROGRESSES THROUGH THE NORTHERN  
ROCKIES. THIS FEATURE LINKS UP WITH THE FRONTAL ZONE FROM THE  
PRIOR SHORTWAVE (SEE SECTION ABOVE) AND PROGRESSES THROUGH S MT  
INTO THE NORTHERN PLAINS AT THE SAME TIME. SOLID MOISTURE FROM  
THE PACIFIC STREAM WILL REMAIN AND INTERSECT WITH RETURN MOISTURE  
ACROSS THE PLAINS. THIS WILL SPARK SOME CONVECTION AND SPUR  
SURFACE CYCLOGENESIS. GUIDANCE HAS BEEN FLIP-FLOPPING ON WHICH  
SOLUTION WILL BE OVER-AGGRESSIVE WITH THE CONVECTION. YESTERDAY'S  
RUNS WERE THE ECMWF FOLLOWED BY THE UKMET. THE LAST FEW CYCLES  
HAS BEEN THE GFS. THIS IS STILL THE CASE WITH THE 12Z RUN, BUT  
HAS TEMPERED A BIT BUT STILL SHOWING STRONGER MOISTURE FLUX  
CONVERGENCE ON THE ELEVATED BOUNDARY VERSUS MORE SURFACE ROOTED  
CELLS, WHICH TENDS TO BE A WEAKNESS OF THE GFS.  
 
AS THE MAIN WAVE EXITS THE TERRAIN EARLY TUESDAY, IT WILL DIG AND  
LEAD TO A BINARY INTERACTION WITH THE INITIAL SHORTWAVE...THE  
STRONGER THE INITIAL WAVE THE FURTHER NORTH AND BROADER THE TROF  
WILL BE. WHILE, MOISTURE IS THERE, IT IS MEAGER AND LATENT HEAT  
RELEASE TO BUILD THIS NORTHWARD SOLUTION IS LOOKING LESS LIKELY.  
THE 12Z GFS/NAM AND 00Z UKMET ARE STRONGER WITH THIS THAN THE  
ECMWF SO ARE A TAD NORTH INITIALLY. HOWEVER, THE 00Z CMC IS MUCH  
SLOWER OVERALL AND QUICKLY MOVES OUT OF PREFERENCE BY 29.00Z. AS  
THE UPSTREAM WAVE DIGS BY WED, THE STRONG 12Z NAM, TIGHTENS EVEN  
FURTHER SHOWING SOME TYPICAL DAY 3 OVER-AMPLIFICATION BIAS...THAT  
SLOWS ITS OVERALL PROGRESSION. OTHERWISE, THE WEAKER/SOUTH ECMWF  
IS NOT TOO FAR FROM THE STRONGER/NORTH UKMET/GFS AND THE  
GEFS/ECENS SOLUTIONS TO SUPPORT A BLEND OF THE THREE BY THE END OF  
DAY 3. THERE ARE NUMEROUS INTERNAL INTERACTIONS AND IMPORTANCE OF  
CONVECTIVE UPSCALE ENHANCEMENT VIA LATENT HEAT RELEASE TO HAVE  
TREMENDOUS CONFIDENCE IN A LOWER THAN NORMAL PREDICTABILITY  
FORECAST. HOWEVER THE AGREEMENT IS SOLID TO SUPPORT AVERAGE  
CONFIDENCE AT THIS POINT IN A 12Z GFS AND 00Z UKMET/ECMWF BLEND.  
 
GLANCING EFFECTS(FRONT) OF LEAD SHORTWAVE LATE TUES/WED IN  
PACNW...FULL BODIED SHORTWAVE REACHING PACNW BY 00Z THURS...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND THROUGH 29.00Z  
12Z GFS/UKMET/CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE THROUGH 29.00Z  
AVERAGE AFTERWARD  
 
19Z UPDATE: THE 12Z GEFS MEAN MEMBERS PRESENT A TIGHTER OVERALL  
CLUSTERING AND JUST A BIT NORTH OF THE OPERATIONAL GFS (BUT THE  
TIMING OF THE TROF APPEARS ON TARGET), AND OVERALL REMAINS  
CENTRAL/GREATEST CLUSTER IN THE 00Z ECENS MEMBERS. THE 12Z UKMET  
TRENDED SOUTH TOWARD THE OPERATIONAL GFS AND THE CMC SHIFTED MUCH  
QUICKER; WITH BOTH PRESENTING THE STRONGEST SOLUTIONS AND A CLOSED  
SURFACE WAVE. THIS LEAVES THE ECMWF SLOW, WELL SOUTHWEST AND  
THEREFORE A BIT TOO WEAK TOO, THIS REMAINS ON THE SLOW SIDE OF THE  
ECENS SUITE. AS SUCH, WILL FAVOR A 12Z GFS/UKMET/CMC BLEND  
SUPPORTED BY THE GEFS/ECENS SOLUTIONS AFTER 29.00Z WITH AVERAGE  
CONFIDENCE.  
 
---PRIOR DISCUSSION---  
THE NEXT PACIFIC SHORTWAVE HAS TRENDED A BIT NORTH, SLOWER AND  
THEREFORE A BIT FLATTER. GIVEN THE OLDER GULF OF AK BINARY GYRE  
WILL BE ERODING LATE MONDAY INT TUESDAY, THE UPSTREAM WAVE'S  
ARRIVAL LATE TUESDAY WILL RESET THE LARGER SCALE TROUGH BUT SHIFT  
IT EASTWARD. THIS WILL ALLOW FOR SOLID SOUTHWESTERLY MOISTURE  
TRANSPORT MAINLY INTO SOUTHWEST BRITISH COLUMBIA BUT IS EXPECTED  
TO CLIP THE OLYMPIC PENINSULA BY LATE TUESDAY/EARLY WED. ANOTHER  
TRAILING PACIFIC WAVE WILL QUICKLY APPROACH ON WED AND WITH THE  
LINGERING FRONTAL ZONE DIRECTED TOWARD THE WA COAST...STRONGER  
MOISTURE FLUX WILL ENTER W WA BY 00Z ON THURS. THERE IS SOLID  
AGREEMENT IN TIMING/DEPTH AND POSITION OF THE INITIAL WAVE/FRONTAL  
ZONE THROUGH WED, WITH PERHAPS THE 12Z NAM A TAD TOO STRONG  
(TYPICAL BY D3). THIS LIKELY LEADS THE NAM TO BE A TAD TOO  
FAST/SOUTH WITH THE SECONDARY PUSH. HOWEVER, THE 12Z GFS AND 00Z  
UKMET ARE QUICK ON THE HEELS, WITH THE ECMWF/CMC BOTH LAGGING IN  
TYPICAL FORMATION. BEING A BIT FASTER, THE UKMET/GFS ARE A BIT  
DEEPER AND MORE MATURE IN THE CYCLOGENESIS PROCESS, ALSO TYPICAL.  
THE ENSEMBLE SUITE SHOWS MODERATE TO HIGH SPREAD ACROSS THE TIMING  
OF THIS WAVE, TO NOT REALLY HELP DETERMINE WHICH SIDE TO GO  
TOWARD...AS SUCH WILL SPLIT IN A NON-NAM COMPROMISE. CONFIDENCE  
IS SLIGHTLY ABOVE AVERAGE THROUGH THE FIRST WAVE 29.12Z BUT  
BECOMING SLIGHTLY BELOW AVERAGE GIVEN THE SPREAD FOR THE LAST FEW  
TIME-STEPS OF THE SHORT-TERM FORECAST.  
 
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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