751
FXUS10 KWNH 201905
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
305 PM EDT SAT JUN 20 2020
VALID JUN 20/1200 UTC THRU JUN 24/0000 UTC
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z FINAL MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
CLOSED LOW OVER MANITOBA/ONTARIO AND ASSOCIATED PARADE OF
SHORTWAVES ACROSS THE GREAT PLAINS TO MIDWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z ECMWF/GFS BLEND
CONFIDENCE: SLIGHTLY BELOW AVERAGE
19Z UPDATE: THE 12Z GLOBAL CONSENSUS ON THE ONTARIO LOW IS NOW TO
DO SOMETHING SIMILAR TO THE 00Z ECMWF WITH EJECTING MUCH OF THE
ENERGY FROM THE LOW CURRENTLY NEAR THE SOUTH-CENTRAL
MANITOBA/ONTARIO BORDER NORTHEAST TO JAMES BAY BY MONDAY AND ALLOW
LOW REDEVELOPMENT JUST NORTH OF LAKE SUPERIOR ON TUESDAY. MULTIPLE
IMPULSES STILL ROUND THE TROUGH OVER THE NORTH-CENTRAL CONUS
THROUGH THIS TIME WITH DIFFERENCES AMONG THE GUIDANCE. FELT THE
12Z GFS AND ECMWF ARE SIMILAR ENOUGH TO WARRANT A BLEND OF THEM
FOR THE PREFERENCE. THE 12Z UKMET IS FARTHER SOUTH WITH THE
RESULTANT LOW (OVER LAKE SUPERIOR NOT NORTH OF) ON DAY 3 WHILE THE
12Z CMC IS MORE OPEN AND FARTHER EAST ON DAY 3. THE 12Z NAM HAS
THE SHORTWAVE TROUGH STRENGTH ISSUE, SO IT IS STILL RULED OUT.
PREVIOUS DISCUSSION...
THE MAIN WEATHER FEATURE FOR THE CONUS FOR THE NEXT THREE DAYS IS
THE CLOSED LOW CURRENTLY CENTERED OVER MANITOBA WHICH IS ON THE
EAST SIDE OF AN OMEGA HIGH CENTERED OVER ALBERTA. SHORTWAVE ENERGY
ROUNDS THIS LOW AS WELL AS SHORTWAVE TROUGHS/IMPULSES ROUNDING THE
TROUGH EXTENDING DOWN THE GREAT PLAINS WHICH MERELY DRIFTS EAST
THROUGH TUESDAY. THESE IMPULSES CROSSING EXISTING SURFACE FRONTS
PROVIDE MUCH OF THE FOCUS FOR CONVECTIVE STORMS ACROSS THE CENTRAL
US THROUGH EARLY NEXT WEEK.
FIRST, WITH THE LOW CENTER ITSELF THE 00Z ECMWF IS MOST UNIQUE IN
THAT A MORE AMPLIFIED SHORTWAVE ROUNDING THE BASE OF THE LOW
TONIGHT DISLODGES MUCH OF THE ENERGY AND EJECTS IT NORTHEAST TO
JAMES BAY, LEAVING BEHIND AN OPEN TROUGH OVER NORTHWESTERN ONTARIO
EXTENDING TO THE EASTERN DAKOTAS BY LATE MONDAY. ALL OTHER
DETERMINISTIC GLOBAL GUIDANCE MAINTAINS A CLOSED LOW OVER WESTERN
ONTARIO. HOWEVER, THE RESULTANT TROUGH POSITIONS ARE SIMILAR, SO
THIS DOES NOT RULE OUT THE 00Z ECMWF.
SECOND, THERE ARE A NUMBER OF SHORTWAVE TROUGHS/IMPULSES THAT
ROUND THIS TROUGH THROUGH EARLY NEXT WEEK. GLOBAL GUIDANCE
STRUGGLES WITH THE RESULTANT CONVECTIVE PROCESSES FROM THESE
IMPULSES WHICH IS SEEN ACROSS THE BOARD IN THE LATEST AVAILABLE
GUIDANCE AND MAKES SPECIFIC SENSIBLE WEATHER FORECASTS
PARTICULARLY DIFFICULT. WELCOME TO SUMMER (LITERALLY, ASTRONOMICAL
SUMMER BEGINS THIS AFTERNOON). THE ONLY MODEL TO GREATLY DIVERGE
WITH SHORTWAVE TROUGH/IMPULSE ADVECTION IS THE 12Z NAM WHICH IS
MORE AMPLIFIED WITH A SHORTWAVE TROUGH REACHING VANCOUVER ISLAND
LATER TODAY AND EJECTING SOUTHEAST FROM BC EARLY SUNDAY AND
ROUNDING THE TROUGH, CROSSING NEBRASKA LATE MONDAY. THEREFORE, THE
12Z NAM IS NOT PREFERRED. OTHERWISE THE SYNOPTIC PATTERNS ARE
SIMILAR AMONG THE OTHER GLOBAL GUIDANCE WITH THE CAVEAT OF CAUTION
WITH CONVECTIVE PROCESSES.
TROUGHS APPROACHING THE PACIFIC NORTHWEST TUESDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE
A DEEP GULF OF ALASKA LOW PERSISTS NEAR KODIAK ISLAND THROUGH
TUESDAY. TROUGHS ROUNDING THIS LOW CROSS THE WA COAST LATER TODAY
AND APPROACH ON TUESDAY. THE 12Z NAM DOES STAND OUT FOR AMPLITUDE
WITH THE TROUGH AXIS REACHING VANCOUVER ISLAND LATER TODAY, BUT
THE EFFECT ON QPF IS MINIMAL. THE WAVE APPROACHING TUESDAY REMAINS
FAR ENOUGH OFFSHORE TO NOT RESULT IN QPF OVER WA BY 24/00Z, THE
END OF THIS FORECAST PERIOD. THEREFORE A GENERAL MODEL BLEND
SHOULD BE SUFFICIENT.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
JACKSON
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page