409
FXUS10 KWNH 121848
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
247 PM EDT WED AUG 12 2020
VALID AUG 12/1200 UTC THRU AUG 16/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
LONGWAVE TROUGH OVER THE NORTHWEST TO THE NORTHERN PLAINS THROUGH
FRIDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NAM/CMC/ECMWF BLEND
CONFIDENCE: AVERAGE
A BROAD UPPER LEVEL TROUGH, IN CONJUNCTION WITH A CLOSED LOW OVER
SOUTHWESTERN CANADA AND A CLOSED MID- AND UPPER-LEVEL HIGH ALONG
155W, WILL BE IN PLACE ACROSS THE NORTHWESTERN U.S. THROUGH THE
MIDDLE OF THE WEEK. OVERALL, THE MODELS ARE IN AGREEMENT WITH THE
IDEA THAT THE TROUGH GRADUALLY SHIFTS EASTWARD AND BE IN PLACE
ACROSS THE NORTHERN PLAINS BY THE WEEKEND. THIS WILL SUSTAIN A
COLD FRONT TRACKING FROM THE NORTHERN ROCKIES TO THE DAKOTAS. THE
12/12Z GFS BECOMES FASTER AND MORE AMPLIFIED WITH THIS TROUGH BY
12Z FRIDAY ACROSS THE DAKOTAS THAN THE 12/12Z RUNS OF THE UKMET
AND ECMWF. THIS FAST GFS SOLUTION TENDS TO BE A KNOWN BIAS...SO
WILL CONTINUE TO FAVOR A BLEND OF THE 12/12Z NAM/CMC/ECMWF
PREFERENCE.
NORTHEASTERN U.S. UPPER TROUGH
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: ECMWF/CMC/GFS BLEND INTO SATURDAY MORNING...GFS/CMC BY
SATURDAY AFTERNOON
CONFIDENCE: AVERAGE
AN UPPER LEVEL TROUGH AXIS GRADUALLY BUILDS IN ACROSS NEW ENGLAND
AND EASTERN CANADA BY THE END OF THE WEEK, DOWNSTREAM OF A
BUILDING RIDGE AXIS ACROSS ONTARIO AND WESTERN QUEBEC. THE LATEST
NAM WAS THE STRONGEST WITH THE TROUGH, WHILE THE GFS WAS SLIGHTLY
EAST OF THE MODEL CONSENSUS. BLENDING THE ECMWF AND CMC STILL
YIELDS A SUITABLE STARTING POINT IN THE PROCESS INTO SATURDAY
MORNING. HOWEVER, THE 12/12Z ECMWF CLOSES OFF A MID- AND
UPPER-LEVEL HIGH OVER MAINE BY SATURDAY AFTERNOON/EVENING WHILE
THE GFS CONTINUES TO MOVE AN OPEN WAVE EASTWARD...RESULTING IN 500
MB HEIGHTS BEING NEARLY 80 METERS LOWER IN THE GFS OVER DOWN EAST
MAINE COMPARED WITH THE GFS. PREFER TO GIVE LITTLE WEIGHT TO THE
ECMWF IDEA BY SATURDAY AFTERNOON.
SOUTHEASTERN U.S. UPPER TROUGH
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12/12Z GFS/NAM/CMC
CONFIDENCE: BELOW AVERAGE
A WEAK CLOSED LOW CURRENTLY OVER MISSOURI WILL SLOWLY TRACK
EASTWARD AND EVOLVE INTO AN OPEN TROUGH AS IT REACHES THE OHIO
VALLEY AND SOUTHERN APPALACHIANS BY THIS WEEKEND. THE MODELS HAVE
A BETTER HANDLE ON THE EVOLUTION OF THE FLOW PATTERN ALOFT BUT
SOME RATHER LARGE DIFFERENCES DEVELOP AT 850 MB AND...TO A LESSER
EXTENT...AT 700 MB WITH RESPECT TO WHERE A CLOSED LOW FORMS. THE
12/12Z ECMWF PLACED ITS LOW LEVEL LOW IN TENNESSEE ON SATURDAY
MORNING...A NORTHWARD SHIFT COMPARED WITH ITS 12/00Z RUN...WHILE
THE NCEP GUIDANCE AND CMC FAVORED LOW PRESSURE NORTH OF THE OHIO
RIVER. THE APPROACH OF A MID-LEVEL WAVE FROM THE UPPER MIDWEST
AND THE WESTERN GREAT LAKES REGION APPEARS TO FAVOR THE MORE
NORTHERLY SOLUTION...PROMPTING A SHIFT IN OUR PREFERENCE TO THE
NAM/GFS/CMC SOLUTION. THIS DOES NOT PRECLUDE THERE BEING A
SECONDARY AREA OF LOW PRESSURE OVER THE TENNESSEE VALLEY GIVEN ITS
POSITION DOWNSTREAM OF A CLOSED MID- AND UPPER-LEVEL HIGH OVER THE
SOUTHWEST. CONFIDENCE REMAINED BELOW AVERAGE.
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.
BANN
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