150
FXUS10 KWNH 020451
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1249 AM EDT THU APR 02 2020
VALID APR 02/0000 UTC THRU APR 05/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..WESTERN ATLANTIC CLOSED LOW AND OFFSHORE SURFACE LOW
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
AN ELONGATED TROUGH WILL MOVE OFF THE MID-ATLANTIC/NORTHEAST COAST
THROUGH THE PERIOD, EVENTUALLY CONSOLIDATING INTO A STRONG DEEPLY
STACKED OCEAN CYCLONE NW OF BERMUDA. THERE IS A HIGHLY AMPLIFIED
SYNOPTIC BLOCKING PATTERN THAT WILL SET UP OVER THE HIGHER
LATITUDES RESULTING IN A DEEP AND SLOW MOVING 500MB TROUGH OVER
THE WESTERN ATLANTIC OCEAN. A SURFACE LOW WILL DEVELOP OFFSHORE
AND RETROGRADE AS STRONG MID LEVEL VORTICITY ROUNDS THE STACKED
LOW. THE SURFACE LOW WILL MAKE ITS CLOSEST APPROACH TO LAND ON
FRIDAY. MODEL DIFFERENCES ARE FAIRLY MINOR OVERALL WITH THE 12Z
GFS A BIT FARTHER WEST WITH ITS SURFACE LOW FEATURE AS COMPARED TO
THE REST OF THE DETERMINISTIC MODELS. HOWEVER, THE LATEST 00Z GFS
HAS COME MORE IN LINE AND COULD BE USED WITHIN THE BLEND. THERE IS
SOME VARIABILITY WITH RESPECT TO QPF, BUT THIS IS LARGELY A RESULT
OF A WARM FRONTAL PLACEMENT, LOW LEVEL JET INFLUENCES AND
MID-LEVEL IMPULSE PROPAGATION.
..UPPER MIDWEST/GREAT PLAINS/MISSISSIPPI VALLEY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z EC/ECENSMEAN/GEFSMEAN
CONFIDENCE: AVERAGE
A LARGE SCALE TROUGH ACROSS THE WESTERN US ASSOCIATED WITH A GYRE
ANCHORED IN ALBERTA WILL HELP TO EJECT MULTIPLE IMPULSES ACROSS
THE NORTHERN ROCKIES/PLAINS AND INTO THE UPPER MIDWEST/GREAT LAKES
REGION. THE FIRST IMPULSE WILL SHIFT FROM THE NORTHERN
ROCKIES/PLAINS INTO THE UPPER MIDWEST THROUGH EARLY SUNDAY AND THE
SECOND IMPACTING THE NORTHERN ROCKIES SATURDAY INTO SUNDAY.
WITHIN THIS SECTION WE WILL DISCUSS THE FIRST IMPULSE THAT WILL
HELP TO DEVELOP A WEAK SURFACE LOW IN THE UPPER MIDWEST REGION
WITH A TRAILING COLD FRONT THROUGH THE PLAINS EDGING EAST INTO THE
MS VALLEY REGION FRIDAY THROUGH SUNDAY. THE 00Z NAM/GFS IS A BIT
TOO FAST WITH BOTH THE IMPULSE AND THUS SURFACE FEATURES.
ADDITIONALLY, THE AXIS OF VORTICITY FROM THE 00Z GFS IS MORE
LONGITUDINAL IN NATURE WHICH RESULTS IN THE ENERGY PROPAGATING TOO
QUICKLY BY THE END OF THE PERIOD. MEANWHILE THE 12Z UKMET/CMC ARE
TOO SLOW. THEREFORE, THE EC/ECENSMEAN/GEFSMEAN SEEMS LIKE A
REASONABLE MIDDLE GROUND AND IS THE SUGGESTED MODEL BLEND OF
CHOICE. THERE ARE DIFFERENCES AMONG THE MODELS IN TERMS OF
MESOSCALE FEATURES THAT WILL RESULT IN VARIABILITY WITH RESPECT TO
QPF.
ANOTHER ASPECT OF THIS BROAD SCALE TROUGH IS THE INCREASING GULF
MOISTURE INTERACTING WITH A FRONT AND SEASONABLY STRONG WESTERLY
FLOW/SOUTHERN STREAM JET WHICH WILL YIELD THUNDERSTORMS IN THE
SOUTHERN PLAINS. THE 00Z NAM QPF INTENSITY CONTINUES TO DROP OFF
WITH SOUTHWARD EXTENT. THE OTHER MODELS DO DISPLAY SOME SPATIAL
SPREAD WHICH IS A PRODUCT OF THE SURFACE BOUNDARY PLACEMENT AND
MID-LEVEL ENERGY INTERACTION, BUT ALL ARE MORE INDICATIVE OF
ROBUST PRECIPITATION, SO THE NAM APPEARS TO BE A DRY OUTLIER,
ESPECIALLY ACROSS SOUTH TEXAS. SO WHILE THE 00Z NAM SHOULD BE
REMOVED FROM ANY BLEND WITHIN THIS REGION, THE REMAINING QPF
DIFFERENCES WILL BE IMPROVED BY HIGHER RESOLUTION GUIDANCE THAT
CAN HANDLE THESE MESOSCALE FEATURES. FOR NOW, THE EC SEEMS A BIT
TOO FAR SOUTH THE THE HIGHER QPF AMOUNTS, THUS, IN TERMS OF A
MODEL BLEND FOR QPF, THE 00Z GFS/12Z UKMET/12Z CMC SEEMS LIKE A
LOGICAL CHOICE.
..NORTHERN ROCKIES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-00Z GFS BLEND
CONFIDENCE: AVERAGE
WITH RESPECT TO THE LARGE SCALE SYNOPTIC TROUGH PATTERN SITUATED
ACROSS THE WESTERN US AS DISCUSSED ABOVE, THE SECOND IMPULSE
ROUNDING THE TROUGH WILL SWING THROUGH THE NORTHERN ROCKIES/PLAINS
SATURDAY INTO SUNDAY. MODELS ARE IN FAIRLY GOOD AGREEMENT WITH
THIS FEATURE. HOWEVER, THE 00Z GFS IS SLIGHTLY FARTHER SOUTH AND
IS THUS PRODUCING MORE PRECIPITATION SOUTH INTO THE RANGES OF NW
WY. THEREFORE, WITH REGARD TO THIS FEATURES MOVING THROUGH, WOULD
OPT FOR A NON-00Z GFS BLEND.
..WEST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z ECMWF/ECENSMEAN AND 00Z GFE/GEFSMEAN
CONFIDENCE: AVERAGE
ANOTHER STRONG IMPULSE WILL DROP SOUTH AND EAST TOWARD THE WEST
COAST AROUND THE AFOREMENTIONED TROUGH ANCHORED OVER THE WESTERN
HALF OF THE COUNTRY. ALL MODELS DEPICT THIS FEATURE WELL, BUT
THERE ARE DIFFERENCES WITH RESPECT TO INTENSITY AND OVERALL
PLACEMENT. THE 12Z UKMET IS TOO SLOW AND WEAK WITH THIS ENERGY.
MEANWHILE, THE 12Z CMC IS TOO FAR SOUTH, ESPECIALLY WITH RESPECT
TO ENERGY EJECTING WEST INTO CA. WHILE THE 00Z NAM SEEMS TO BE
WITHIN THE MODEL CLUSTER, THE LOOK OF THE LARGE SCALE SYNOPTIC
PATTERN BY THIS POINT IS A BIT QUESTIONABLE WITH THE ENERGY ON THE
SOUTHERN PERIPHERY OF THE CONSENSUS. THUS, THIS LEAVES THE 12Z
EC/00Z GFS AND THEIR RESPECTIVE MEANS FOR THE MODEL BLEND OF
CHOICE. THERE ARE SUBTLE HINTS THE GFS IS STARTING TO BECOME TOO
FAST WITH THIS FEATURE, WHICH IS A KNOWN BIAS AMONG THE MODEL.
BUT IT IS WITHIN TOLERANCE. THEREFORE, THESE MODELS ARE A GOOD
MIDDLE GROUND FOR NOW.
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500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
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