894
FXUS10 KWNH 040718
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
317 AM EDT WED SEP 04 2019
VALID SEP 04/0000 UTC THRU SEP 07/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z FINAL MODEL EVALUATION, CONFIDENCE, AND PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
..OVERALL PATTERN ACROSS THE CONUS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 00Z ECMWF/GEFS AND 12Z ECENS
CONFIDENCE: SIGHTLY BELOW AVERAGE
07Z UPDATE: THE SPREAD AMONGST THE FULL 00Z SUITE NOW INCLUDING
THE NON-NCEP MODELS HAS INCREASED LATE ON DAY2 AND DAY3 ACROSS THE
WEST/NORTHWEST. THE CMC IS COMPLETELY OUT OF PHASE WITH MOST OF
THE OTHER MODELS, WHILE THE UKMET BECOMES A FAST OUTLIER AT THE
EDGE OF THE ENSEMBLE ENVELOPE. DUE TO LOW PREDICTABILITY AND
INCREASING SPREAD, WILL UPDATE THE TIMES FOR THE NEWER GUIDANCE,
BUT KEEP THE PREFERENCES UNCHANGED.
PREVIOUS DISCUSSION:
BROAD TROUGH ACROSS THE EAST AND RIDGING IN THE WEST WILL PERSIST
THROUGH THE PERIOD, ALTHOUGH SLOW BREAK DOWN OF THE RIDGE AND
DECREASE IN MID-LEVEL THICKNESSES IS LIKELY TO PRODUCE A MORE
ZONAL FLOW ON DAY 3. NO LESS THAN THREE SHORTWAVES WILL TRAVERSE
FROM THE PACIFIC NW THROUGH CONFLUENT FLOW ACROSS THE NORTHERN
TIER AND TOWARDS THE ATLANTIC COAST. THE FIRST OF THESE
DEAMPLIFIES QUICKLY TONIGHT WHILE RACING TOWARDS THE GREAT LAKES.
ALTHOUGH FOR MOST OF THE LIFESPAN OF THIS FEATURE THE SPREAD IS
MINIMAL, THE NAM IS A CLEAR DEEP OUTLIER AS IT MOVES TOWARDS THE
MID-ATLANTIC. THE EVOLUTION OF THIS SHORTWAVE TROUGH WILL THEN
IMPACT THE SPEED AND POSITION OF HURRICANE DORIAN, BUT THOSE
PREFERENCES ARE HANDLED BELOW.
TWO OTHER SHORTWAVES ADVECTING INTO THE PACIFIC NORTHWEST AND THEN
RACE EASTWARD. THE FIRST OF THESE WILL QUICKLY DEAMPLIFY FROM A
CLOSED FEATURE OFF THE COAST THURSDAY TO A SHORT-WAVELENGTH
RIDGE/TROUGH ACROSS THE ROCKIES AND INTO THE PLAINS BY DAY 3.
IMMEDIATELY FOLLOWING THIS, YET ANOTHER PIECE OF ENERGY WILL DROP
DOWN THE PACIFIC COAST TO BE A LONGER WAVE TROUGH MOVING TOWARDS
CALIFORNIA LATE IN THE FORECAST PERIOD. THERE IS CONSIDERABLE
SPREAD IN THE POSITION AND DEPTH OF THIS LAST TROUGH, LEADING TO
LOWER THAN AVERAGE CONFIDENCE ACROSS THE NORTHWEST BY LATE FRIDAY.
WHILE MUCH OF THE COUNTRY FEATURES ABOVE AVERAGE CONFIDENCE DUE TO
LOWER SPREAD, THE DIFFICULTY OF THE NORTHWEST LEADS TO AVERAGE
OVERALL CONFIDENCE AND SUGGESTS TRENDING TOWARDS THE MEANS IS
LIKELY BEST UNTIL SOME MORE DETAIL AND AGREEMENT CAN BE IRONED OUT.
..HURRICANE DORIAN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PLEASE REFER TO THE OFFICIAL NATIONAL HURRICANE CENTER FORECAST
TRACK
FOR THE FIRST 12-24 HOURS, MUCH OF THE GUIDANCE IS WELL CLUSTERED
AROUND THE 03Z NHC ADVISORY TRACK. THEREAFTER, SPREAD BEGINS TO
INCREASE WITH THE NAM OUTRACING EVERYTHING AS DORIAN BENDS TO THE
NORTHEAST TOWARDS NC, WHILE THE ECMWF BEGINS TO LAG THE TRACK. THE
UKMET, AS IT HAS BEEN MANY OF THE PAST FEW DAYS, REMAINS THE
CLOSEST PROXY TO THE NHC TRACK AND SHOULD BE GIVEN THE HIGHEST
WEIGHT, WITH THE GEFS/ECENS MEAN ALSO INCLUDED TO MAINTAIN THE
BEST TRACK INTEGRITY. THERE HAS BEEN A SUBTLE SHIFT SW AND SLOWING
OF DORIAN IN THE NON-NCEP GUIDANCE, WHICH MAKES THE BEST PROXY A
LITTLE LESS DEFINED THAN EARLIER. STILL, THE UKMET/ECMWF/GEFS ARE
THE CLOSEST, BUT IF NHC SHOULD SLOW/SHIFT AT 09Z, THE UKMET WOULD
AGAIN BE THE GUIDANCE UPON WHICH THE HEAVIEST WEIGHT CREATES THE
BEST PROXY.
..TROPICAL STORM FERNAND.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PLEASE REFER TO THE OFFICIAL NATIONAL HURRICANE CENTER FORECAST
TRACK
THE GFS IS CLOSEST TO THE 03Z NHC TRACK, BUT MOST GUIDANCE IS
REASONABLE WITH DIFFUSE AND WEAKENING SURFACE LOW PRESSURE MOVING
SUBTLY NORTH OF WEST INTO NORTHEAST MEXICO. A BLEND OF ALL BUT THE
CMC, WHICH IS FAR TOO SLOW, SHOULD SUFFICE, BUT THE GFS IS CLOSEST
OVERALL, WHILE THE NAM FEATURES THE BEST PROXY FOR QPF.
MODEL TRENDS AT WWW.WPC.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NOAA.GOV/H5PREF/H5PREF.SHTML
WEISS
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