499
FXUS10 KWNH 181821
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 PM EDT THU JUN 18 2020
VALID JUN 18/1200 UTC THRU JUN 22/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
EASTERN U.S. CLOSED LOW AND COASTAL FRONT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: MODERATE-HIGH
THE CLOSED UPPER LOW CURRENTLY OVER THE CENTRAL APPALACHIANS WILL
GRADUALLY WEAKEN AND REMAIN NEARLY STATIONARY THROUGH SATURDAY
MORNING, AND THEN IS EXPECTED TO SLOWLY EVOLVE INTO AN OPEN WAVE
AND EVENTUALLY BECOME ABSORBED BY THE WESTERLIES BY THE END OF THE
FORECAST PERIOD. THERE IS EXCELLENT AGREEMENT IN THE LATEST MODEL
GUIDANCE WITH THIS EVOLUTION THROUGH SATURDAY EVENING. AFTERWARD,
AS THE OPEN WAVE BEGINS TO BECOME ABSORBED BY THE APPROACHING
TROUGH FROM THE GREAT LAKES REGION, THE GFS AND ITS ENSEMBLE MEAN
BECOME A LITTLE FASTER AS THE WAVE TRACKS TOWARDS THE NORTHEAST.
IT IS STILL CLOSE ENOUGH TO THE MODEL CONSENSUS TO INCLUDE AS PART
OF A GENERAL MODEL BLEND.
CLOSED LOW DEVELOPING OVER NORTHERN HIGH PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z UKMET/ECMWF/00Z ECENS BLEND
CONFIDENCE: MODERATE
A CLOSED UPPER LOW OVER SASKATCHEWAN AND MANITOBA IS EXPECTED TO
REMAIN NEARLY ANCHORED IN PLACE OVER THE NEXT FEW DAYS AS IT
GRADUALLY DEEPENS WITH ASSOCIATED SHORTWAVE ENERGY CROSSING THE
NORTH-CENTRAL U.S. THIS WEEKEND, SUSTAINING A SLOW MOVING COLD
FRONT WITH MULTIPLE WAVES OF LOW PRESSURE ALONG IT. MODEL
DIFFERENCES BECOME APPARENT BY 12Z SATURDAY WITH THE 12Z GFS MORE
AMPLIFIED WITH THE TROUGH CROSSING THE CENTRAL AND NORTHERN
PLAINS, MAINTAINING CONTINUITY FROM ITS EARLIER RUNS, BUT STRONGER
THAN THE GEFS MEAN. MULTIPLE CMC RUNS HAD BEEN WEST OF THE MODEL
CONSENSUS REGARDING THE MAIN UPPER LOW OVER SOUTH-CENTRAL CANADA,
BUT THE 12Z CMC IS NOW MUCH CLOSER TO THE CONSENSUS AND CAN BE
PART OF THE BLEND. THE NAM REMAINS ON THE STRONGER SIDE OF THE
GUIDANCE. A BLEND OF THE UKMET/ECMWF/CMC SHOULD SERVE WELL AS A
STARTING POINT IN THE FORECAST PROCESS.
TROUGHS APPROACHING THE PACIFIC NORTHWEST THROUGH SUNDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NAM/UKMET BLEND
CONFIDENCE: LIMITED-MODERATE
SHORTWAVES ROTATING AROUND THE BROAD GULF OF ALASKA GYRE WILL KEEP
AN ACTIVE WEATHER PATTERN IN PLACE GOING INTO THE WEEKEND OFF THE
PACIFIC NORTHWEST COAST. THE FIRST PERTURBATION TO MOVE THROUGH
IS EXPECTED TO REACH THE BRITISH COLUMBIA COAST FRIDAY NIGHT,
ALONG WITH A WELL DEFINED SURFACE LOW AND TRAILING COLD FRONT.
EXCEPT FOR A SLIGHTLY SLOWER COLD FRONT WITH THE 12Z UKMET, THE
MODELS ARE IN DECENT AGREEMENT ON THIS SYSTEM. THE SECOND STORM
SYSTEM BEGINS APPROACHING THE REGION BY SUNDAY NIGHT, AND THERE
ARE MORE NOTEWORTHY DIFFERENCES IN THE TIMING AND EVOLUTION OF
THIS EVENT. THE GFS IS FASTER WITH THE SURFACE LOW AND A LITTLE
AHEAD OF THE GEFS MEAN, WHEREAS THE ECMWF IS MUCH SLOWER AND WELL
TO THE WEST. THE CMC IS SUGGESTING THE LOW TRACK FARTHER SOUTH
AND CONSIDERABLY WEAKER WITH LITTLE ENSEMBLE SUPPORT. THERE IS
REASONABLY GOOD AGREEMENT AMONG THE NAM AND UKMET WITH THIS LOW,
AND BETWEEN THE GFS AND ECMWF SOLUTIONS. THIS BLEND SHOULD SERVE
WELL AS A STARTING POINT, ALONG WITH SOME OF THE 12Z GEFS MEAN.
HAMRICK
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