Prognostic Meteorological Discussion
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654
FXUS10 KWNH 211737
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
137 PM EDT MON AUG 21 2017

VALID AUG 21/1200 UTC THRU AUG 25/0000 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...

...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY
PREFERENCES/FORECAST CONFIDENCE...


...TUTT CELL DRIFTING ACROSS THE NORTHERN GULF OF MX...
...TROPICAL DISTURBANCE MOVING TOWARD THE BAY OF CAMPECHE BY
MID-WEEK...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF/UKMET
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

WATER VAPOR/RADAR IMAGERY SHOW A WELL-DEFINED TUTT CELL TRACKING
WESTWARD ACROSS THE CENTRAL GULF OF MX CONTINUES TO BE A FOCUS FOR
CONVECTION ON THE EASTERN SIDE OF THE CIRCULATION. DURING THE NEXT
24 TO 36 HOURS...MODELS SHOW A GREAT DEAL OF SHEARING TAKING PLACE
ALTHOUGH THE PRIMARY AXIS OF VORTICITY SHOULD CONGREGATE AROUND
THE UPPER TX COAST. SOME RESIDUAL SHORTWAVE ENERGY LINGERS INTO
THE MIDDLE OF THE WEEK ALTHOUGH IT GETS COMPLICATED WITH A
TROPICAL DISTURBANCE PUSHING TOWARD THE BAY OF CAMPECHE. A COUPLE
OF NOTABLE OUTLIERS ARE THE 12Z NAM WHICH IS WELL TO THE NORTHEAST
OF THE GENERAL CONSENSUS WHILE THE 00Z CMC SIGNIFICANTLY DEEPENS
THE SYSTEM AS TENDS TO BE ITS BIAS. WHILE DIFFERENT FROM ONE
ANOTHER...THE 12Z GFS AND 00Z ECMWF/UKMET AT LEAST SITUATE CLOSE
TO ONE ANOTHER WHILE ALSO RESIDING WITHIN THE PATH OF TROPICAL
DEVELOPMENT NOTED IN THE NHC OUTLOOK.


...COMPLEX OF VORTICITY CENTERS EJECTING OUT OF THE
SOUTHERN/CENTRAL ROCKIES...
...SHEARING FEATURES EVENTUALLY ABSORBED IN EASTERN U.S. LONGWAVE
TROUGH...

PRELIMINARY PREFERENCE: 12Z GFS
FORECAST CONFIDENCE: AVERAGE

MULTIPLE VORTICITY CENTERS SPINNING ACROSS THE FOUR CORNERS REGION
WILL GRADUALLY SHIFT THEIR FOCUS TOWARD THE NORTHEAST. ONE SUCH
IMPULSE HAS ALREADY MOVED INTO SOUTHWESTERN KS WHICH HAS SHIFTED
INTO A VERY MOIST/UNSTABLE ENVIRONMENT...THUS SPREADING CONVECTION
INTO THE CENTRAL PLAINS. BASED ON THE CURRENT POSITION OF THE
VORTICITY CENTER...THE 12Z GFS/00Z ECMWF ARE CLOSEST BASED ON
SATELLITE IMAGERY AND SHORT-TERM RAP FORECASTS. MEANWHILE...THE
00Z CMC SITS WELL TO THE WEST BACK IN EASTERN CO. LOOKING TOWARD
TUESDAY MORNING...THE 00Z ECMWF SLOWS DOWN A BIT AS THE SHEARING
SHORTWAVE ACCELERATES TOWARD THE LOWER OH VALLEY. THIS BRINGS IT
CLOSER TO THE MORE WESTWARD DISPLACED 00Z CMC/UKMET. WILL STICK
WITH THE 12Z GFS GIVEN IT IS HANDLING THE CURRENT ACTIVITY MORE
ACCURATELY.


...LONGWAVE TROUGH AFFECTING CENTRAL TO EASTERN NORTH AMERICA...
...ASSOCIATED DEEP SURFACE LOW/COLD FRONT...
...TRAILING SHORTWAVE PUSHING THROUGH THE UPPER MIDWEST 24/0000Z...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF
FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE

AMPLIFIED FLOW WITHIN THE ACTIVE NORTHERN STREAM WILL USHER IN A
RATHER PRONOUNCED BAND OF HEIGHT FALLS INITIALLY THROUGH THE UPPER
MIDWEST/GREAT LAKES REGION. THE SYSTEM SHOULD CONTINUE TO DIG AS
IT PROGRESSES DOWNSTREAM TOWARD THE LOWER GREAT LAKES/NEW ENGLAND
THE FOLLOWING COUPLE OF DAYS. WHILE THERE IS GENERAL
SYNOPTIC-SCALE AGREEMENT WITH THE TRACK OF THIS SYSTEM...MUCH OF
THE UNCERTAINTY LIES WITH THE SOUTHWESTERN EXTENT OF THE FRONTAL
ZONE ACROSS THE RED RIVER. OF NOTE...BY 23/1200Z...THE 00Z ECMWF
DEPICTS THE BOUNDARY ACROSS CENTRAL TX TOWARD THE BIG BEND WHILE
THE WHILE THE 12Z GFS FAVORS THE TAIL END CLOSER TO THE TX
PANHANDLE. SUCH DIFFERENCES CONTINUE THROUGH THE END OF THE
FORECAST PERIOD. FARTHER NORTH...THERE ARE TIMING ISSUES WITH THE
TRAILING SHORTWAVE PUSHING THROUGH THE UPPER MIDWEST WITH THE 00Z
UKMET BEING QUITE THE SLOW OUTLIER. GIVEN THE UNCERTAINTY IN THE
FORECAST ACROSS THE SOUTHERN PLAINS...WILL SPLIT THE DIFFERENCE
BETWEEN THE 12Z GFS/00Z ECMWF


...QUASI-STATIONARY UPPER LOW IN THE VICINITY OF CA/DESERT
SOUTHWEST...

PRELIMINARY PREFERENCE: BLEND OF THE 12Z NAM/GFS WITH THE 00Z UKMET
FORECAST CONFIDENCE: AVERAGE

A BROAD CIRCULATION ACROSS THE EASTERN PACIFIC INTO THE
SOUTHWESTERN U.S. WILL CONTINUE TO AFFECT THE REGION THROUGH
THURSDAY. DURING THE FIRST 24 HOURS OR SO...THE SYSTEM SHOULD
RETROGRADE BACK TOWARD THE OFFSHORE WATERS BEFORE EVENTUALLY
ACCELERATING EASTWARD IN TIME BACK TOWARD THE DESERT SOUTHWEST. IT
APPEARS THE 00Z CMC IS OUT OF THE PHASE FROM THE CONSENSUS
SOLUTION BEING A BIT QUICKER BY MID-WEEK. TOWARD DAY
3/THURSDAY...THE 00Z UKMET DOES NOT DEPICT MUCH EASTWARD
PROGRESSION AS ADVERTISED AMONG MOST OF THE ENSEMBLE MEMBERS. WILL
FAVOR A COMBINATION OF THE 12Z NAM/GFS AND 00Z ECMWF HERE.


...STRONG HEIGHT FALLS MOVING INTO WESTERN CANADA/PACIFIC
NORTHWEST BY THURSDAY...

PRELIMINARY PREFERENCE: MODEL COMPROMISE BETWEEN THE 12Z GFS AND
00Z ECMWF/CMC
FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE

LATE IN THE FORECAST PERIOD...A PRONOUNCED LONGWAVE TROUGH BEGINS
TO PUSH THROUGH BRITISH COLUMBIA DOWN INTO THE PACIFIC NORTHWEST.
COMPARED TO THE WELL CLUSTERED ENSEMBLE MEMBERS VIA THE SPAGHETTI
PLOT...THE 00Z UKMET IS FLATTER AND QUICKER. EVENTUALLY THE 12Z
NAM JOINS THIS MORE PROGRESSIVE SOLUTION BY LATE WEDNESDAY/EARLY
THURSDAY. GIVEN SOLID AGREEMENT BETWEEN THE 12Z GFS AND 00Z
ECMWF/CMC...WILL FAVOR A MODEL COMPROMISE AMONG THESE SOLUTIONS.



www.wpc.ncep.noaa.gov/html/model2.shtml
www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

RUBIN-OSTER

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