714
FXUS10 KWNH 081855
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 PM EDT SAT AUG 08 2020
VALID AUG 08/1200 UTC THRU AUG 12/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
OVERALL WEATHER PATTERN ACROSS THE CONTINENTAL U.S.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND, GREATEST WEIGHT ON 12Z
GFS/ECMWF/UKMET ACROSS OHIO VALLEY AFTER SUNDAY AFTERNOON
CONFIDENCE: AVERAGE
..19Z UPDATE
THE 12Z CMC TRENDED IN THE DIRECTION OF THE 12Z NAM WITH A
STRONGER MID-LEVEL VORTICITY MAXIMUM CROSSING THE OHIO VALLEY
SUNDAY NIGHT INTO MONDAY. OTHERWISE, NO SIGNIFICANT CHANGES WERE
NOTED ACROSS THE REST OF THE COUNTRY WITH TYPICAL MINOR RUN TO RUN
CHANGES NOTED IN THE 12Z ECMWF/UKMET/CMC COMPARED TO THEIR
PREVIOUS 00Z CYCLES. THERE IS NOT ENOUGH CONFIDENCE AT THIS TIME
TO GO TOWARD THE STRONGER NAM/CMC IDEA NEAR THE OHIO VALLEY, SO
THE PREFERENCE WILL BE TO LEAN TOWARD THE CONSENSUS OF THE 12Z
GFS/ECMWF/UKMET WHICH HAS BETTER SUPPORT FROM THE ENSEMBLE
GUIDANCE.
..PREVIOUS DISCUSSION FOLLOWS
THE OVERALL WEATHER PATTERN ACROSS THE CONTINENTAL U.S. WILL BE
QUASI-ZONAL ACROSS THE NORTHERN HALF OF THE LOWER 48, WITH A SLOW,
EASTWARD MOVING (AND SOMEWHAT COMPACT) MID-LEVEL RIDGE OVER THE
SOUTH-CENTRAL U.S. THE MAIN SYNOPTIC FEATURE ON THE MAP WILL BE A
LARGE MID-LEVEL CLOSED LOW TRACKING EASTWARD ACROSS CANADA, WITH A
RELATED COLD FRONT AT THE SURFACE FORECAST TO MOVE ACROSS THE
GREAT LAKES REGION.
THE MODELS SHOW FAIRLY GOOD AGREEMENT REGARDING THE
TIMING/STRENGTH OF THE CLOSED LOW AND A SHORTWAVE SPOKE ROUNDING
THE BASE OF THE CLOSED LOW, TRACKING FROM SASKATCHEWAN ON SUNDAY
TO WESTERN ONTARIO ON MONDAY. A SECOND CLOSED LOW/SHORTWAVE IS
FORECAST TO ENTER WESTERN CANADA ON TUESDAY. THE LATEST GUIDANCE
SHOWS ONLY MINOR AMPLITUDE DIFFERENCES WITH THE SECOND CLOSED LOW,
WITH THE 12Z NAM STRONGEST.
LARGER SCALE IMPACT DIFFERENCES ARE TIED TO CONVECTIVELY
GENERATED/ENHANCED VORTICITY MAXIMA IN THE VICINITY OF THE UPPER
MIDWEST, GREAT PLAINS AND OHIO VALLEY. THE 12Z NAM WAS STRONGEST
WITH ONE MID-LEVEL VORTICITY MAXIMUM THAT TRACKS EASTWARD FROM MO
INTO IL BY SUNDAY MORNING. THE 12Z NAM MAINTAINS ROBUST STRENGTH
OF THIS FEATURE INTO TUESDAY AS IT TRACKS EASTWARD TOWARD THE
MID-ATLANTIC REGION. HOWEVER, THE 12Z NAM DOES NOT HAVE MUCH
SUPPORT FROM THE ECMWF/GEFS/CMC ENSEMBLES BY MONDAY, NOR THE
REMAINING DETERMINISTIC GUIDANCE. FOR THAT REASON, WHILE THE NAM
MAY HAVE UTILITY ELSEWHERE, LITTLE WEIGHT SHOULD BE PLACED ON THE
12Z NAM FOR THE OHIO VALLEY REGION FROM SUNDAY EVENING ONWARD.
ELSEWHERE, MODEL DIFFERENCES ARE CONSIDERED SMALL ENOUGH TO
SUPPORT A GENERAL BLEND OF THE GUIDANCE.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
THIS PRODUCT WILL TERMINATE AUGUST 15, 2020:
WWW.WEATHER.GOV/MEDIA/NOTIFICATION/PDF2/SCN20-58PMDHMD_TERMINATION.
OTTO
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