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FXUS10 KWNH 011642
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1242 PM EDT WED APR 01 2020
VALID APR 01/1200 UTC THRU APR 05/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z PRELIMINARY MODEL EVALUATION
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...WESTERN ATLANTIC CLOSED LOW AND OFFSHORE SURFACE LOW THROUGH
FRIDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: ANY OF THE OPERATIONAL MODELS
A MATURING LARGE SCALE CLOSED TROUGH, WITH INTENSE SURFACE LOW
PRESSURE DIPPING DOWN TO NEAR OR BELOW 980 MB, WILL AFFECT THE
EAST COAST AND WESTERN ATLANTIC WITH STRONG WINDS. THE GENERAL
CIRCULATION PATTERN NOW FEATURES THIS AND ANOTHER DEVELOPING HIGH
AMPLITUDE, CLOSED TROUGH OVER THE INTERMOUNTAIN WEST / NORTHERN
PLAINS. SO THE PATTERN IS SLOWING DOWN, AND THE INTENSE CYCLONE
OFF THE COAST WILL BE SLOW TO EXIT. THE GLOBAL MODELS ARE IN
STRONG AGREEMENT IN THEIR HANDLING OF THIS SYSTEM.
..INTERMOUNTAIN WEST / GREAT PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z GFS / 00Z ECMWF...EMPHASIS ON THE
ECMWF AFTER 04/00Z
AS A LARGE SCALE CLOSED TROUGH DEVELOPS OVER THE MOUNTAINS AND
PARTS OF THE PLAINS, ELONGATED LOW PRESSURE WILL SLIP OUT THROUGH
THE PLAINS AND UPPER MIDWEST ALONG A COLD FRONT, WITH WINTRY
WEATHER IMPACTS FELT ACROSS THE NORTHERN ROCKIES TO THE UPPER
MIDWEST. THERE HAS BEEN QUITE A BIT OF TRENDING OF MESOSCALE
DETAILS, AND IT DOES NOT YET APPEAR THAT ANY PARTICULAR MODEL HAS
THIS EVENT NAILED DOWN. EARLIER THE 00Z ECMWF/UKMET LOOKED LIKE A
GOOD STARTING POINT, BUT THE 12Z GFS HAS BECOME MORE VIABLE AND
NOW REPLACES THE UKMET - WHICH APPEARS TOO SLOW, ESPECIALLY ALOFT
OVER THE NORTHERN PLAINS ON DAY 2. THE GFS AND ECMWF DO LOOK QUITE
SIMILAR THROUGH THE DURATION, AS THE LOW ALONG THE FONT EVENTUALLY
BECOMES MORE CONSOLIDATED AND SETTLES IN BENEATH A RIDGE IN CANADA
ON DAY 3. IN BROADER TERMS, HOWEVER, WE WOULD RECOMMEND LESS
WEIGHT ON THE GFS OVER THE MOUNTAIN REGION AND CENTRAL U.S. ON DAY
3, AS THE GFS UPPER AIR PATTERN TURNS A LITTLE OUT OF PHASE GIVEN
SOME UPSTREAM PROBLEMS OVER THE EASTERN PACIFIC.
REGARDING THE NAM... ITS SOLUTION OVER THE NORTHERN PLAINS IS
MOSTLY IN STEP WITH THE ECMWF/GFS UNTIL ABOUT 03/12Z, SO ONLY 48
HOURS INTO THE FORECAST. BUT EVEN THEN THE SOLUTION IS SLIGHTLY
FAST AND WITH A WEAKER PRESSURE GRADIENT ALONG THE FRONT. IT THEN
BECOMES MORE UNREALISTIC IN HOW IT SIGNIFICANTLY ERODES THE
SOUTHERN FLANK OF THE CANADIAN RIDGE. WE ALSO NOTE THAT QPF
INTENSITY DROPS OFF WITH SOUTHERN EXTENT. IN FACT, ON DAY 3 THE
SYNOPTICS LOOK FAVORABLE FOR RETURN MOISTURE TO ENCOUNTER A FAIR
AMOUNT OF DEEP LAYER FORCING OVER TEXAS, SO THE VERY DRY NAM
SOLUTIONS THERE IS NOT RECOMMENDED.
..WEST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z ECMWF/UKMET
CHALLENGING PATTERN ON THE BACK SIDE OF THE DEVELOPING LARGER
SCALE TROUGH OVER THE INTERMOUNTAIN WEST. TWO NOTEWORTHY SHORTWAVE
TROUGHS COME INTO PLAY ALONG THE WEST COAST. THE FIRST INTO
CALIFORNIA SHOWS THE TELLTALE SIGNS OF A REMARKABLY FAST GFS
SOLUTION THAT STANDS OUT AS AN OUTLIER. THE SECOND, LARGER WAVE
SHOWS A TENDENCY TO FORM A CLOSED CIRCULATION AND EXPAND ITS
INFLUENCE AS IT APPROACHES WASHINGTON/OREGON ON DAY 3. THE NCEP
GUIDANCE IS MORE BULLISH IN STRENGTHENING THIS FEATURE AND DRIVING
IT FARTHER SOUTH AND WEST OFFSHORE. THIS IS ESPECIALLY TRUE OF THE
NAM. SPAGHETTI PLOT SHOW THAT THIS FARTHER SOUTH AND WEST POSITION
HAS LOST FAVOR IN THE ENSEMBLES OVER TIME. CONSENSUS DEFINITELY
POINTS TOWARD THE ECMWF/UKMET SOLUTIONS, ALTHOUGH SOME FURTHER
DEEPENING, MORE THE FLAVOR OF THE GFS RATHER THAN NAM, IS WITHIN
REASON. OVERALL THE GFS PROBLEMS WITH THE LEAD WAVE INTO
CALIFORNIA MAKE IT LESS DESIRABLE ALONG THE WEST COAST, AND OUR
PREFERENCE REMAINS WITH THE EC/UK, PENDING THE 12Z RUNS. BUT IF
ONE WANTED TO INCLUDE THE NAM FOR THE CALIFORNIA WAVE AND GFS FOR
THE WA/OR WAVE, THEY MAY HAVE SOME UTILITY.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
BURKE
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