872
FXUS10 KWNH 171642
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1240 PM EDT WED JUN 17 2020
VALID JUN 17/1200 UTC THRU JUN 21/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING INITIAL PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
EASTERN U.S. CLOSED LOW AND COASTAL FRONT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND THROUGH 00Z SATURDAY, THEN
NAM/ECMWF/UKMET
CONFIDENCE: MODERATE-HIGH
THE CUT-OFF UPPER LOW THAT IS CURRENTLY PARKED OVER WESTERN NORTH
CAROLINA IS EXPECTED TO GRADUALLY LIFT NORTH ACROSS THE
APPALACHIANS AND EVENTUALLY REACH THE NORTHEAST U.S. BY THIS
WEEKEND AS IT SLOWLY EVOLVES INTO AN OPEN WAVE ALOFT. THIS IS
SUPPORTING A SURFACE LOW OVER EASTERN NORTH CAROLINA THAT IS
FUELING CONVECTION AND HEAVY RAIN FOR PORTIONS OF THE SOUTHEAST
AND MID-ATLANTIC REGION. THE MODELS ARE INDICATING VERY GOOD
SYNOPTIC SCALE AGREEMENT ON THE PROGRESS OF THE UPPER LEVEL SYSTEM
THROUGH FRIDAY EVENING, AFTER WHICH THE GFS AND ITS GEFS MEAN ARE
A LITTLE QUICKER WITH THE WESTERLIES ABSORBING THE TROUGH. IN
CONTRAST, THE CMC TENDS TO KEEP THE CLOSED LOW INTACT AND FARTHER
SOUTH ON SATURDAY. AT THE SURFACE, THE 00Z UKMET IS SLIGHTLY
STRONGER WITH THE LOW, BUT STILL WITHIN THE REALM OF
POSSIBILITIES. THEREFORE, BLENDING THE ECMWF/UKMET/NAM SHOULD
WORK WELL AFTER 00Z SATURDAY.
CLOSED LOW MOVING INTO THE NORTHWEST TUESDAY INTO THE NORTHERN
HIGH PLAINS BY THURSDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND THROUGH 12Z FRIDAY, THEN 00Z
UKMET/ECMWF/EC MEAN BLEND
CONFIDENCE: MODERATE
THE UPPER LEVEL LOW OVER THE NORTHERN ROCKIES IS EXPECTED TO
BECOME ABSORBED BY A SECOND EVOLVING UPPER LOW OVER SOUTH-CENTRAL
CANADA BY THURSDAY MORNING. THIS WILL SUSTAIN AN OCCLUDED SURFACE
LOW AND A SLOW MOVING COLD FRONT ACROSS THE CENTRAL AND NORTHERN
PLAINS THROUGH THE END OF THE WEEK. THE TWO MAIN DIFFERENCES
NOTED IN THE GUIDANCE IS A MORE AMPLIFIED SOLUTION WITH THE 12Z
GFS ACROSS THE PLAINS REGARDING HEIGHT FALLS, AND THIS ALSO HOLDS
TRUE FOR THE NAM BY SATURDAY MORNING. THE 00Z CMC BECOMES
DISPLACED TO THE WEST OF THE MODEL CONSENSUS BY 12Z FRIDAY WITH
THE CLOSED LOW OVER SOUTH-CENTRAL CANADA, BUT IT DOES NOT APPEAR
TO AFFECT QPF TOO MUCH ACROSS THE PLAINS. THEREFORE A BLEND OF
THE 00Z ECMWF/UKMET/EC MEAN SHOULD SUFFICE AS A STARTING POINT IN
THE FORECAST PROCESS.
TROUGH APPROACHING THE PACIFIC NORTHWEST BY FRIDAY NIGHT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/12Z NAM/GFS
CONFIDENCE: MODERATE
A SHORTWAVE TROUGH PIVOTING AROUND A BROAD UPPER LEVEL GYRE OVER
THE GULF OF ALASKA IS EXPECTED TO REACH THE OFFSHORE WATERS OF THE
PACIFIC NORTHWEST AND VANCOUVER ISLAND BY FRIDAY EVENING,
ACCOMPANIED BY A SLOW MOVING COLD FRONT. THE 00Z UKMET IS SLOWEST
IN BRINGING THIS TROUGH TOWARDS THE BRITISH COLUMBIA COAST, AND
THIS IS MORE EVIDENT WITH ITS SURFACE LOW BEING MUCH SLOWER THAN
THE MODEL CONSENSUS BY 12Z FRIDAY. BY THE END OF THE FORECAST
PERIOD SATURDAY EVENING, THE CMC IS MORE AMPLIFIED WITH THE SECOND
SHORTWAVE TROUGH TO PIVOT TROUGH THE REGION. THERE IS ENOUGH
MODEL AGREEMENT AMONG THE NCEP GUIDANCE AND THE ECMWF TO MERIT A
BLEND OF THOSE MODELS WITH AVERAGE CONFIDENCE.
HAMRICK
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
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