984  
FXUS10 KWNH 021715  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1214 PM EST MON MAR 02 2020  
 
VALID MAR 02/1200 UTC THRU MAR 06/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z EVALUATION INCLUDING MODEL PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
AMPLIFYING SHORTWAVE OVER THE NORTHERN PLAINS/UPPER MIDWEST BY  
TUESDAY WITH SURFACE LOW DRAWING WEAK SURFACE WAVE CROSSING THE OH  
VALLEY AND DEEPENING OVER NORTHERN NEW ENGLAND BY WEDNESDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND HEDGING TOWARD UKMET  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
GOES-E WV DEPICTS LEADING SHORTWAVE ENERGY CURRENTLY OVER SE  
SASKATCHEWAN MOVING INTO MANITOBA, INCREASING IN SHARPNESS AT THE  
LEFT EXIT OF STRONG BUT FAIRLY ZONAL (FROM NNW TO SSE) UPPER JET,  
BUT ALSO AT THE LEFT ENTRANCE TO STRONG CONFLUENT 150KT+ OVER THE  
OHIO VALLEY. THE NORTHERN STREAM WILL SUPPORT A STRONG SURFACE  
WAVE TO RUN ALONG 50N THROUGH MORNING WED. CONCURRENTLY, THE  
BROAD UPGLIDE FROM THE SUBTROPICAL EASTERN PACIFIC STREAM PROVIDES  
ASCENT IN THE WARM CONVEYOR PROVIDES MOISTURE AND INSTABILITY TO  
ENHANCE A WEAKER SURFACE WAVE OUT OF OK/MO TODAY THROUGH THE OHIO  
VALLEY TONIGHT. EVENTUALLY, THE COMBINATION OF STREAMS SUPPORTS  
THE OHIO VALLEY WAVE TO DEEPEN ACROSS THE LOWER GREAT LAKES AND  
BECOME THE DOMINANT LOW OVER THE CANADIAN MARITIMES BY LATER WED,  
AS THE UPPER LEVEL SHORTWAVE SHARPENS NEGATIVE TILT. THERE HAS  
BEEN SIGNIFICANT MODEL ALIGNMENT OVER THE LAST FEW CYCLES HERE, TO  
HAVE INCREASED CONFIDENCE IN A GENERALLY LOWER PREDICTABLE REGIME  
(COMBINATION OF STREAMS). THE 12Z GFS HAS TEMPERED BUT REMAINS  
THE SHARPEST, FASTEST WITH THE NEGATIVE TILTING AS SO APPEARS TO  
SHIFT THE WAVE A TAD FASTER, BUT NOT SIGNIFICANTLY SO.  
 
INFLUENCE OF THE NEXT SHORTWAVE/JET STREAK EXIT IS THE GREATEST  
FACTOR TOWARD MODEL SPREAD AFTER WED, THIS SUGGESTS A GENERAL  
MODEL BLEND WILL SUFFICE FOR THIS SYSTEM UNTIL THE NEXT WAVE'S  
INFLUENCE TAKES GRIP, BUT THIS IS ALSO GENERALLY INTO CANADA AND  
ONLY AFFECTS ME/GULF OF MAINE WITH MORE UNCERTAINTY. SO OVERALL,  
THE UKMET IS FAVORED A BIT HEAVIER IN A GENERAL MODEL BLEND, AS IT  
IS MORE CENTRAL/REASONABLE WITHIN THE OVERALL SUITE WITH THE  
APPROACH OF THIS NEXT WAVE. CONFIDENCE IS INCREASED TO SLIGHTLY  
ABOVE AVERAGE DUE TO THE OVERALL MASS FIELD ALIGNMENT THROUGH WED,  
THOUGH GIVEN SIZABLE BUT STILL NOT STABLE MODEL TRENDS OVER THE  
LAST FEW DAYS CYCLES IN A LOWER THAN NORMAL PREDICTABLE PATTERN.  
 
SHORTWAVE APPROACHING BRITISH COLUMBIA ON TUESDAY, SIGNIFICANTLY  
AMPLIFYING ACROSS THE NORTHERN PLAINS/UPPER MIDWEST BY EARLY  
THURSDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND; REDUCE WEIGHT OF UKMET AT 84HRS.  
CONFIDENCE: AVERAGE  
 
PROGRESSIVE NORTHERN STREAM FLOW OUT OF THE GULF OF AK CONTINUES  
THROUGH LATE TUESDAY INTO WED, THE TIMING, STRENGTH OF THE SUBTLE  
UPSTREAM WAVE CROSSING THE MIDWEST/GREAT LAKES ON WED, LEADS TO  
SOME UNCERTAINTY IN INCREASED RIDGING ACROSS THE NORTHERN PLAINS.  
HERE THE CMC IS CLEARLY SOUTH/DEEPER MORE AMPLIFIED LEADING TO  
STALLED FLOW AND A FURTHER SOUTHWARD DIGGING OF THIS TROF IN THE  
NORTHERN PLAINS/MIDWEST; WHILE EVEN THE SLIGHTLY SLOWER ECMWF,  
DEEPENS/AMPLIFIES A BIT FURTHER NORTH AND EAST, EVEN FURTHER NORTH  
THAN THE SLIGHTLY FASTER GFS/NAM. THE UKMET IS A BIT STRONGER BUT  
ALSO FASTER, SHOWING SOME TYPICAL LATE DAY 3 NEGATIVE BIAS, BUT  
COULD BE KEPT IN THE PREFERENCE THROUGH THE SHORT-TERM (84HRS) BUT  
SHOULD START TO BE WEIGHTED A BIT LOWER. ALL CONSIDERED AT  
NON-CMC BLEND IS PREFERRED BUT WILL WEIGHT A TOWARD THE  
GFS/NAM/ECMWF AFTER 72 INTO 84HRS. WITH THE GOOD MASS AGREEMENT,  
BUT HARDER TO PREDICT FLOW REGIME (AND EVENTUAL BINARY INTERACTION  
WITH THE SOUTHERN STREAM WAVE), CONFIDENCE IS CONSIDERED AVERAGE  
IN THIS BLEND.  
 
SOUTHERN STREAM CLOSED LOW SYSTEM MOVING FROM NORTHERN MEXICO  
THROUGH THE SOUTHERN PLAINS INTO SOUTH WED INTO THURS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
SIZABLE MODEL DIFFERENCE OVER THE LAST WEEK CONTINUE WITH THIS  
CLOSED LOW AND HAS GONE FROM NEARLY EQUALLY PHASED WITH THE  
NORTHERN STREAM TO BARELY CONNECTED WITH THIS CURRENT SUITE. THE  
12Z GFS CONTINUES TO SUGGEST FURTHER SLOWING AND LESS INFLUENCE OF  
THE NORTHERN STREAM AND IS IN AN USUAL PLACE WITHIN THE OVERALL  
SUITE: SLOWEST AND THEREFORE STRONGEST COMING THROUGH THE  
TENNESSEE VALLEY LATE THURSDAY. THIS IS OPPOSED BY THE ECWMF,  
WHICH HAD SHOWN THE FIRST INCLINATIONS TO A SLOWER TREND BUT HAS  
STOPPED THE TREND AND IS NOW VACILLATING RUN TO RUN, WITH LARGER  
JUMPS OVER THE LAST HALF-WEEK, THOUGH SEEMS TO HAVE STABILIZED  
AROUND A COMMON SOLUTION OVER THE LAST FEW CYCLES INCLUDING A  
FAIRLY TIGHT ENSEMBLE SUITE. CURRENTLY THE CLOSED LOW HAS SETTLED  
IN THE CALIFORNIA BIGHT WITH SOME UPSTREAM SUBTROPICAL KICKING  
INFLUENCES, SUGGESTING SLIGHTLY FASTER PROGRESSION MAY START  
SOONER THAN LATER, TIPPING TOWARD THE ECMWF SOLUTION. THE 12Z NAM  
IS SLOW/STRONG AND NORTH OVERALL IN THE SUITE, AND GIVEN THIS IS  
IN LINE WITH ITS TYPICAL NEGATIVE BIAS, WILL DISCARD ITS SOLUTION  
AT THIS TIME. THE ECMWF/CMC ALSO BEING FURTHER SOUTH, SHIFTING  
TOWARD THE INSTABILITY PROVIDES SOME ADDITIONAL CONFIDENCE. BUT  
INFLUENCES OUT OF THE NORTHERN STREAM (PARTICULARLY ON DAY 3 IN  
THE SOUTHEAST) PROVIDE VERY LOW CONFIDENCE OVERALL. SO WILL FAVOR  
THE ECMWF/CMC A BIT MORE IN A NON-NAM BLEND PREFERENCE BUT CANNOT  
FULLY DISCOUNT THE GFS/UKMET GIVEN THE INFLUENCES IN THE NORTHERN  
STREAM THAT SEEM TO FAVOR THEM OVER THE ECMWF/CMC AT THIS TIME.  
 
CLOSED LOW IN NORTHERN GULF OF AK WITH DEEP LATITUDE TROF ALONG  
THE PACIFIC NW BY THURSDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z ECMWF/CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
TOWARD THE END OF THE FORECAST PERIOD, FINALLY A LARGER SCALE,  
CLOSED LOW DEVELOPS ACROSS THE NORTHERN GULF OF AK LATE WED. A  
STRONG UPSTREAM SHORTWAVE WILL SWING AROUND ITS BASE LEADING TO  
FURTHER SOUTHWARD BUILDING AND BROADENING OF THE TROF OVER THE  
ENTIRE GULF OF AK BY THURS. THE 12Z GFS IS FASTER TO DO SO IN LINE  
WITH TYPICAL NEGATIVE BIAS, BUT THE EVENTUAL LOCATION/CENTER OF  
THE CLOSED LOW SOLIDIFIES NW OF HAIDA GWAII BY 06.00Z AND IS  
SUPPORTED BY THE OTHER GUIDANCE MEMBERS. THIS WILL DIRECT STRONG  
SOUTHWESTERLY, MOIST FLOW REGIME INTO BC AND THE PACIFIC NW BY THE  
END OF THE FORECAST PERIOD. HOWEVER, THE STRONGER/COMPACT BUT  
SLOWER SOLUTIONS OF THE NAM/UKMET FAVOR A DEEPER SURFACE LOW  
FURTHER NORTH, DELAYING THE COLD FRONT. THE ENSEMBLES SUPPORT  
THE ECMWF/CMC TIMING PLACEMENT OF THE MASS FIELDS AND GIVEN THE  
AFOREMENTIONED ISSUES IN THE GFS/NAM/UKMET, WILL SUPPORT AN  
ECMWF/CMC BLEND FOR MASS FIELDS AT SLIGHTLY ABOVE AVERAGE  
CONFIDENCE.  
 
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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