424
FXUS10 KWNH 230649
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 AM EDT THU APR 23 2020
VALID APR 23/0000 UTC THRU APR 26/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z MODEL EVALUATION WITH INITIAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
OVERALL PATTERN ACROSS THE CONTINENTAL U.S.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND THROUGH 12Z SATURDAY, THEN 00Z
ECMWF/12Z EC MEAN BLEND FOR MOST AREAS
CONFIDENCE: MODERATE
7Z UPDATE: THE 00Z ECMWF TRENDED NORTHWARD WITH THE SURFACE LOW
CROSSING THE OHIO VALLEY THIS WEEKEND WITH A SLIGHTLY LESS
AMPLIFIED 500MB TROUGH ACROSS THE DEEP SOUTH COMPARED TO ITS 12Z
RUN. THE UKMET TRENDED A LITTLE LESS AMPLIFIED WITH THE SHORTWAVE
EXITING THE EAST COAST FRIDAY EVENING, A LITTLE STRONGER AND
FARTHER SOUTH WITH THE NEXT STORM SYSTEM ACROSS THE MIDWEST, AND
FASTER WITH THE PACIFIC SYSTEM APPROACHING BRITISH COLUMBIA. THE
CMC IS NOW A LITTLE SLOWER WITH THE TROUGH CROSSING THE SOUTHERN
U.S. ON SATURDAY. OVERALL, THERE ARE STILL SIGNIFICANT MODEL
DIFFERENCES WITH THE WEEKEND STORM SYSTEM ACROSS THE OHIO VALLEY,
AND GIVEN THE MODEL FLUCTUATIONS OVER THE PAST 24 HOURS, IT IS
STILL PRUDENT TO INCORPORATE SOME OF THE EC ENSEMBLE MEAN TO
MITIGATE THESE DIFFERENCES.
------------------
A SPLIT FLOW PATTERN WILL INITIALLY BE OVER THE CENTRAL AND
EASTERN PORTIONS OF THE U.S. WITH A STRONG SOUTHERN STREAM
SHORTWAVE TRACKING EASTWARD ACROSS THE DEEP SOUTH AND THEN EXITING
THE EAST COAST BY FRIDAY EVENING. THIS WILL SUSTAIN A SURFACE LOW
THAT WILL TRACK FROM THE OZARKS TO THE NORTHERN MID-ATLANTIC
REGION, AND THE CMC BECOMES SLIGHTLY WEAKER WITH THIS DISTURBANCE
BY FRIDAY, BUT NOT OUT OF THE REALM OF POSSIBILITY, SO A GENERAL
MODEL BLEND SHOULD SUFFICE FOR THIS STORM SYSTEM GIVEN THE OVERALL
DECENT MODEL AGREEMENT.
THE NEXT SYSTEM ARRIVES ACROSS THE MIDWEST BY FRIDAY NIGHT AS A
SHORTWAVE AMPLIFIES IN A NORTHWEST FLOW TYPE PATTERN. THIS WILL
SUPPORT A SURFACE LOW AND COLD FRONT CROSSING THE CENTRAL PLAINS
AND MIDWEST STATES, AND THEN THE LOW CROSSES THE OHIO VALLEY AND
EVENTUALLY THE NORTHEAST STATES. THIS IS WHERE THE MODELS ARE
DIFFERING THE MOST, WITH THE GFS BECOMING MORE AMPLIFIED BY FRIDAY
MORNING WITH THE SHORTWAVE ACROSS THE WESTERN HIGH PLAINS, AND
CONTINUES GOING INTO THE WEEKEND. THE NAM BECOMES SLOWER THAN THE
MODEL CONSENSUS BY LATE FRIDAY AND THE CMC IS STRONGER WITH THE
SOUTHERN PORTION OF THE TROUGH ACROSS THE MID-SOUTH BY SATURDAY
MORNING. BY THE END OF THE FORECAST PERIOD, THE UKMET IS BETWEEN
THE GEFS AND EC MEANS, AND WOULD BE A GOOD DETERMINISTIC MODEL TO
USE ALONG WITH THE EC MEAN.
ACROSS THE WESTERN U.S., AN UPPER LEVEL RIDGE AXIS BRIEFLY BUILDS
IN ACROSS THE REGION THROUGH FRIDAY AHEAD OF THE NEXT SYSTEM
ARRIVING FROM THE NORTH PACIFIC. THE MAIN SURFACE LOW WILL LIKELY
IMPACT THE BRITISH COLUMBIA COAST, WITH A COLD FRONT REACHING
WASHINGTON AND OREGON ON SATURDAY. THE GFS IS SLIGHTLY SLOWER
WITH THE ARRIVAL OF THIS FRONT, AND THE CMC IS SLIGHTLY MORE
AMPLIFIED. THERE IS ENOUGH AGREEMENT AMONG THE NAM, ECMWF, AND
UKMET TO MERIT A BLEND OF THOSE MODELS.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
HAMRICK
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