415
FXUS10 KWNH 221921
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
321 PM EDT WED APR 22 2020
VALID APR 22/1200 UTC THRU APR 26/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...SOUTHERN STREAM TROUGH EXITING THE SOUTHERN PLAINS, CROSSING
THE OH VALLEY THURSDAY AND MID-ATLANTIC FRIDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z UKMET/ECMWF/ECENS WITH SOME 12Z GEFS/CMC BLEND
CONFIDENCE: AVERAGE
A POSITIVELY TILTED SOUTHERN STREAM TROUGH AND ASSOCIATED SURFACE
LOW OVER THE SOUTHERN PLAINS THIS AFTERNOON REACHES THE MIDDLE MS
VALLEY TONIGHT. THIS LOW PRESSURE SYSTEM WILL ADVANCE NORTHEAST
AND CROSS THE OH VALLEY THURSDAY AND PUSH OFF THE NORTHERN
MID-ATLANTIC COAST FRIDAY AS AN ATTENDANT COLD FRONT SWEEPS ACROSS
THE SOUTH. THE 12Z GFS DRAMATICALLY SLOWED THIS SYSTEM AND WENT
FROM BEING ONE OF THE FASTEST SOLUTIONS TO THE SLOWEST WHILE IT
ALSO REMAINS FARTHER NORTH WITH ITS SURFACE LOW TRACK OVER THE OH
VALLEY/MID-ATLANTIC AND IS THUS NOT PREFERRED. THE 12Z NAM REMAINS
THE FASTEST SOLUTION WITH THE TROUGH AND SURFACE LOW AND IS THUS
ALSO NOT PREFERRED. THE 12Z CMC IS NEARLY IDENTICAL TO ITS
PREVIOUS RUN, REMAINING THE WEAKEST WITH THE SURFACE LOW, BUT
REMAINS IN LINE WITH THE 12Z ECMWF AND UKMET FOR LOW TRACK.
REGARDING TIMING AND DEPTH OF THE SYSTEM, THE 12Z UKMET/ECMWF HAVE
BETTER ENSEMBLE SUPPORT (12Z GEFS/00Z ECENS MEANS). SO, WILL FAVOR
A BLEND OF THE UKMET/ECMWF SOLUTIONS AND ALONG WITH A PREFERENCE
FOR THE 00Z ECENS ENSEMBLE MEAN ALONG WITH SOME INCLUSION OF THE
12Z GEFS AND 12Z CMC.
...NORTHERN STREAM SHORTWAVE/LOW CENTER ACROSS THE NORTHERN PLAINS
TONIGHT/THURSDAY AND MIDWEST FRIDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GENERAL MODEL BLEND
CONFIDENCE: AVERAGE
GUIDANCE BRINGS A NORTHERN STREAM SHORTWAVE AND ASSOCIATED LOW
CENTER DOWN FROM CANADA AND ACROSS THE EASTERN DAKOTAS TONIGHT
INTO THURSDAY. MOST 12Z GUIDANCE THEN WEAKENS THE SURFACE LOW BY
FRIDAY IN FAVOR OF THE SOUTHERN STREAM LOW OVER THE TN VALLEY. THE
12Z CMC AND NAM HOLD ONTO THE SURFACE LOW THE LONGEST OVER THE
MIDWEST INTO FRIDAY, BUT GIVEN THE FOCUS OF THE
FORCING/ENERGY/MOISTURE TO THE SYSTEM TO THE SOUTH CONSISTENT
AMONG THE MODELS, NONE ARE REMOVED AND A GENERAL MODEL BLEND IS
PREFERRED.
..SHORTWAVE TROUGH DIGGING ACROSS THE INTERMOUNTAIN WEST
..ENERGY AMPLIFYING INTO THE LOWER MS VALLEY FRIDAY NIGHT
..ASSOCIATED DEEPENING SURFACE LOW
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z CMC/ECMWF AND 00Z ECENS MEAN
CONFIDENCE: SLIGHTLY BELOW AVERAGE
A SHORTWAVE TROUGH CURRENTLY SHIFTING EAST TO THE PACIFIC
NORTHWEST COAST IS FORECAST TO TAKE A SOUTHEAST TURN AS IT CROSSES
THE NORTHERN ROCKIES THURSDAY NIGHT AND AMPLIFY ACROSS THE
SOUTHERN PLAINS ON FRIDAY BEFORE CROSSING THE LOWER MS VALLEY BY
FRIDAY NIGHT AND PUSHING INTO THE MIDWEST SATURDAY. GUIDANCE IS IN
AGREEMENT ON THE TROUGH BECOMING NEGATIVELY TILTED FRIDAY NIGHT,
DRIVING ANOTHER DEEPENING SURFACE LOW CENTER. DESPITE THE 12Z GFS
SLOWING FROM THE 06Z RUN, IT STILL BECOMES A FAST OUTLIER BY
FRIDAY NIGHT AND PROBABLY TAKES ITS ENERGY A BIT TOO FAR NORTH AND
IS THE EASIEST TO REMOVE FROM PREFERENCE. THE 12Z NAM AND UKMET
ARE CLOSER TO THE FARTHER SOUTH AND SLOWER SURFACE LOW TRACK OF
THE CMC/ECMWF THAN BEFORE, BUT ARE STILL DISTINCT ENOUGH TO NOT BE
PREFERRED. THE CMC/ECMWF CAMP IS SUPPORTED BY THE 00Z ECENS MEAN
AND SOMEWHAT BY THE 06Z GEFS. THE PREFERENCE WILL REMAIN A BLEND
OF THE SLOWER CMC/ECMWF AND ECENS MEAN. HOWEVER, GIVEN SOME OF THE
UNCERTAINTIES OVER HOW STRONG THE NEARBY NORTHERN STREAM ENERGY
AND RELATED INTERACTION WILL BE, CONFIDENCE IS A BIT LIMITED IN
THE FRIDAY/SATURDAY TIME FRAME.
..TROUGH REACHING BRITISH COLUMBIA ON SATURDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-NAM BLEND
CONFIDENCE: AVERAGE
A TROUGH ROUNDING A GULF OF ALASKA LOW AND ASSOCIATED COLD FRONT
REACHES THE BC/PACIFIC NORTHWEST COAST ON SATURDAY. THERE IS GOOD
AGREEMENT ON DEPTH AND TIMING OF THE TROUGH EXCEPT FOR THE 12Z NAM
WHICH IS FASTER AND A BIT FARTHER NORTH. THEREFORE A NON-NAM
GENERAL MODEL BLEND IS PREFERRED.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
JACKSON
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