864
FXUS10 KWNH 201859
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT FRI MAR 20 2020
VALID MAR 20/1200 UTC THRU MAR 24/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z MODEL EVALUATION WITH LATEST PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..EXITING NORTHEAST LOW PRESSURE AND ASSOCIATED FRONT TODAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
THE SURFACE LOW AND ATTENDANT COLD FRONT PROGRESSING THROUGH THE
LOWER GREAT LAKES CONTINUES TO PROGRESS EASTWARD WITH HIGH MODEL
AGREEMENT AND SOLID RUN TO RUN CONTINUITY TO HAVE ABOVE AVERAGE
CONFIDENCE IN A GENERAL MODEL BLEND INCLUDING THE LINGERING
FRONTAL ZONE THROUGH THE CAROLINAS.
...PHASING STREAMS ACROSS PLAINS SUNDAY,BROADENS FROM GREAT LAKES
TO SOUTH SUN-MON; EAST COAST LATE MON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND (WEIGHT TO 12Z GFS/00Z ECMWF AND
ECENS/GEFS MEANS)
CONFIDENCE: SLIGHTLY BELOW AVERAGE
A COMPLEX EVOLUTION IS STARTING TO TAKE SHAPE WITH SHORTWAVE
ENERGY FROM NORTHERN AND SOUTHERN STREAMS AS WELL AS MULTIPLE
STREAMS OF MOISTURE FROM THE SUBTROPICAL PACIFIC AND THE GULF OF
MEXICO WILL GENERALLY PHASE FROM THE GREAT LAKES TO THE SOUTH.
HOWEVER, THESE ARE THE LOW CONFIDENCE EVOLUTION SITUATIONS WHERE
SMALL DIFFERENCES IN TIMING, STRENGTH OF EITHER STREAM OR
INCREASED LATENT HEAT RELEASE SUPPORTING UNDER-FORECAST UPSCALE
ENHANCEMENT TO THE UPPER JET STRUCTURE/PATTERN LEADS TO SMALL BUT
SIGNIFICANT RUN TO RUN ADJUSTMENTS. CYCLES OF THE ECMWF HAVE BEEN
TRENDING A BIT FASTER WITH THE SOUTHERN STREAM SHORTWAVE EMERGING
FROM THE SOUTHWEST SUNDAY, BUT STILL GENERALLY LAGS THE BULK OF
ECENS MEMBERS AND THEREFORE THE ECENS MEAN. HOWEVER, IT IS PAIRED
WITH THE 00Z CMC SUGGESTING THE STRENGTH OF THE SOUTHERN STREAM
WAVE IS ASSOCIATED WITH THE GREAT BASIN CLOSED LOW INNER CORE,
RATHER THAN THE FAST MOVING UNDERCUTTING SHORTWAVE CURRENTLY WELL
SW OF CENTRAL CA (PER GOES-W). THE GFS/NAM AND UKMET ALL SUGGEST
THE UNDERCUTTING WAVE IS THE DOMINANT AND IS FASTER. THIS ALLOWS
FOR GREATER PHASING WITH THE NORTHERN STREAM AS IT AMPLIFIES
THROUGH THE GREAT LAKES MONDAY; THOUGH THE UKMET IS SLIGHTLY
FASTER IN TO BE LESS PHASED WITH INCREASED BINARY INTERACTION AND
NORTHWARD DRIFT TO THE DEVELOPING COASTAL LOW AT 00Z TUESDAY
(AGAIN RELATIVE TO OTHER GUIDANCE). THE 12Z NAM UNLIKE THE
GFS/UKMET SHOWS TYPICAL LATE DAY 3 OVER-AMPLIFICATION BIAS, WITH
INCREASED QPF/LATENT HEAT RELEASE BUILDING A STRONGER
ANTICYCLONICALLY CURVED 250MB JET AND STRONGER NORTHWARD SURFACE
DEVELOPMENT. GIVEN ALIGNMENT WITH TYPICAL BIAS, BELIEVE THE NAM
IS UNTENABLE IN THE BLEND EVEN AS EARLY AS 22/18Z. SO WILL
SUPPORT A NON-NAM BLEND AT THIS TIME, TRENDING TOWARD HIGHER
WEIGHTING OF THE CENTRAL SOLUTIONS OF THE 12Z GFS AND 00Z ECENS
MEAN BY 00Z TUESDAY ALONG THE EAST COAST. AS STATED BEFORE, ALL
GUIDANCE WILL HAVE A TENDENCY TO STRUGGLE WITH PHASING/UPSCALE
ENHANCEMENT IN TRANSITION SEASON...SO WHILE THE CLUSTERING IS
FAIRLY TIGHT CONFIDENCE IS SLIGHTLY BELOW AVERAGE IN A NON-NAM
BLEND.
...CLOSED MID LEVEL LOW APPROACHING CENTRAL CALIFORNIA SUNDAY,
SHEARING INTO FOUR CORNERS LATE MON...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND THROUGH 23.00Z; NON-CMC THEREAFTER
CONFIDENCE: SLIGHTLY ABOVE AVERAGE BECOMING AVERAGE
STRONG NORTHERN STREAM CLOSED LOW BETWEEN 130-140W WILL CONTINUE
TO DIG SOUTHWARD UNDER INFLUENCE OF THE LARGER SCALE GYRE CENTERED
OFF THE CENTRAL CA COAST AT THIS TIME. AS THE GREAT BASIN AND
FASTER PRECEDING SHORTWAVE EITHER SHEAR OR ACCELERATE EASTWARD,
RESPECTFULLY, THIS CLOSED LOW WILL CONTINUE TO START TO PRESS
EASTWARD EARLY SUNDAY PROMOTING INCREASED MOISTURE FLUX INTO
SOUTHERN CA EVENTUALLY OVERSPREADING INTO THE GREAT BASIN MONDAY,
WITH TYPICAL TIMING DIFFERENCES STARTING TO MANIFEST: GFS/NAM AND
UKMET SHEARING QUICKER AND ECMWF/CMC SLOWER. WHILE THERE BECOMES
GREATER SPREAD ON LATE MONDAY, ONLY THE CMC LOOKS TOO SLOW TO THE
OVERALL MASS FIELD SPREAD... SO WILL SUGGEST A GENERAL MODEL BLEND
THROUGH 23.00Z AND NON-CMC THEREAFTER WITH CONFIDENCE SLIGHTLY
ABOVE AVERAGE BECOMING AVERAGE.
...AMPLIFYING NORTHERN STREAM SHORTWAVE INTO CLOSED LOW ENTERING
PAC NW MONDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND
CONFIDENCE: ABOVE AVERAGE
NEXT WELL DEFINE COMPACT CLOSED LOW ROLLS DOWN THE BC COAST SUN
INTO MONDAY, EVENTUALLY SPREADING MOISTURE ACROSS THE PACIFIC NW
BY MONDAY. THE EVOLUTION WITHIN THE OVERALL MODEL SUITE LOOKS
FAIRLY STRONG/WELL AGREED UPON, THOUGH MONDAY. THOUGH THE 12Z NAM
STARTS INCREASING DEPTH RELATIVE TO THE REMAINING SUITE BUT
ATYPICAL OF THIS EVOLUTION, SLIDES A BIT EAST OF THE OTHERWISE
WELL CLUSTERED SOLUTIONS. AS SUCH A NON-NAM BLEND IS SUPPORTED AT
ABOVE AVERAGE CONFIDENCE FOR DAY 3 MASS FIELD SOLUTION.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
GALLINA
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page