Prognostic Meteorological Discussion
Issued by NWS

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8
926
FXUS10 KWNH 230429
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1128 PM EST WED NOV 22 2017

VALID NOV 23/0000 UTC THRU NOV 26/1200 UTC

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

00Z MODEL EVALUATION...WITH PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...UPPER TROUGH EXITING THE NORTHEAST THROUGH EARLY THANKSGIVING...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE IN VERY GOOD AGREEMENT WITH THE DEPARTURE OF THE
UPPER TROUGH OVER THE NORTHEAST...SO A GENERAL MODEL BLEND WILL BE
PREFERRED.


...SLOW-MOVING UPPER LEVEL TROUGH OVER THE GULF OF MEXICO LIFTING
ACROSS THE FL PENINSULA...
...SURFACE LOWS OVER THE EASTERN GULF OF MEXICO/NEAR
FLORIDA...TRACKING NORTH OVER THE WESTERN ATLANTIC THIS WEEKEND...
...REINFORCING UPPER TROUGH OVER THE GULF OF MEXICO BY SUNDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 12Z ECMWF...12Z ECENS MEAN...18Z GEFS MEAN
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE MODELS GRADUALLY LIFT THE SOUTHERN STREAM UPPER TROUGH OVER
THE EASTERN GULF OF MEXICO OFF TO THE NORTHEAST OVER THE NEXT
COUPLE OF DAYS WITH THE ENERGY CROSSING THE FL PENINSULA AND THEN
LIFTING OFFSHORE THE SOUTHEAST COAST OUT OVER THE WESTERN
ATLANTIC. THE GUIDANCE IS IN RATHER GOOD AGREEMENT IN DEVELOPING A
PAIR OF SURFACE LOWS ALONG A FRONTAL ZONE DRAPED OVER THE
REGION...WITH ONE LOW INITIALLY OVER THE EASTERN GULF OF MEXICO
AND THEN GRADUALLY A SECONDARY LOW OFFSHORE THE SOUTHEAST COAST AS
THE HEIGHT FALLS BEGIN TO LIFT OFF TO THE NORTHEAST. THIS
SECONDARY LOW WILL BECOME THE DOMINANT LOW BY SATURDAY AND THEN
COME UNDER THE INFLUENCE OF NORTHERN STREAM TROUGHING MOVING
TOWARD THE EAST COAST BY SATURDAY NIGHT AND SUNDAY.

THE 12Z CMC OVERALL APPEARS TOO WEAK WITH ITS HEIGHT FALLS AND
ALSO WITH ITS SURFACE REFLECTION AT LEAST THROUGH FRIDAY ACROSS
THE EASTERN GULF OF MEXICO AND OFFSHORE THE SOUTHEAST.
HOWEVER...THE CMC ON SATURDAY AND SUNDAY SHOWS MUCH MORE IN THE
WAY OF INTERACTION WITH THE NORTHERN STREAM ENERGY WHICH RESULTS
IN A MUCH STRONGER SURFACE LOW LIFTING UP OFF THE EAST COAST AND
TOWARD NOVA SCOTIA. THE REMAINING GUIDANCE SHOWS BETTER CLUSTERING
THROUGH FRIDAY...BUT THEN ON SATURDAY AND SUNDAY THE 00Z GFS AND
12Z UKMET ARE WEAKER AND FASTER WITH THE EJECTING SURFACE
LOW...WITH THE 00Z NAM AND 12Z ECMWF SLOWER AND FARTHER WEST.
OVERALL THE CMC ENDS UP BEING FARTHEST WEST AND THE DEEPEST. THE
LATEST 18Z GEFS MEAN AND 12Z ECENS MEAN BOTH TEND TO SUPPORT THE
OPERATIONAL ECMWF AND SUGGEST THE GFS AND UKMET ARE TOO WEAK AND
TOO FAR EAST. REGARDING UPSTREAM ENERGY APPROACHING THE GULF COAST
ON SUNDAY WHICH RENEWS A TROUGH OVER THE GULF OF MEXICO...THE CMC
APPEARS TO BE GENERALLY TOO WEAK AS THE REMAINING GUIDANCE IS
BETTER CLUSTERED WITH THIS SYSTEM. THE ECMWF HAS THE BEST ENSEMBLE
SUPPORT ACROSS THE REGION...AND A BLEND OF THIS MODEL WITH THE
GEFS MEAN AND ECENS MEAN WILL BE PREFERRED.


...UPPER TROUGH AXIS CROSSING THE PACIFIC NORTHWEST AND REACHING
THE GREAT LAKES BY FRI NIGHT...
...ASSOCIATED SURFACE LOW CROSSING SOUTHERN CANADA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: NON-CMC BLEND
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A POSITIVELY-TILTED UPPER TROUGH CROSSING THE PACIFIC NORTHWEST ON
THANKSGIVING DAY WILL QUICKLY ADVANCE EAST ACROSS SOUTHERN CANADA
AND THEN SOUTHEAST ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST
THROUGH FRIDAY. THIS WILL DRIVE A STRONG AREA OF LOW PRESSURE
ACROSS SOUTHERN CANADA WITH A TRAILING COLD FRONT THAT WILL CROSS
THE NORTHWEST AND THEN ADVANCE RAPIDLY THROUGH THE EASTERN U.S.
THIS WEEKEND AS THE ENERGY LIFTS TOWARD SOUTHEAST CANADA THIS
WEEKEND. THE CMC TENDS TO TRACK ITS LOW CENTER FARTHER SOUTH
ACROSS SOUTHERN CANADA COMPARED TO THE OTHER GUIDANCE. A NON-CMC
BLEND WILL BE PREFERRED WITH THIS SYSTEM.


...LOW PRESSURE LIFTING UP OFF THE WEST COAST ON SATURDAY...
...DEEP UPPER TROUGH OFFSHORE THE WEST COAST THROUGH SUNDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 18Z GEFS MEAN AND 12Z ECENS MEAN
CONFIDENCE: BELOW AVERAGE

ENERGY THAT IS NEAR THE BASE OF THE POSITIVELY-TILTED UPPER TROUGH
THAT IS NEAR AND OFFSHORE THE PACIFIC NORTHWEST WILL BREAK AWAY
AND DRIFT SLOWLY SOUTH OVER THE NEXT COUPLE OF DAYS BEFORE THEN
GETTING PICKED UP BY A STRONGER INTRUSION OF NORTHERN STREAM
HEIGHT FALLS FROM THE GULF OF AK. THE SOUTHERN STREAM ENERGY WILL
GET SLINGSHOT NORTHEAST TOWARD THE WA/OR COASTAL RANGES AND
VANCOUVER ISLAND BY SATURDAY NIGHT AS AN AREA OF LOW PRESSURE
DEVELOPS AND STRENGTHENS OFFSHORE THE PACIFIC NORTHWEST. THE 12Z
UKMET AND 12Z ECMWF BOTH BECOME DEEP OUTLIERS WITH THIS LOW
CENTER...WITH THE 12Z CMC BY FAR THE WEAKEST. THE 00Z NAM AND 00Z
GFS SPLIT THE DIFFERENCE BETWEEN STRONG AND WEAK CAMPS. THE
ENSEMBLE GUIDANCE IS GENERALLY MORE SUPPORTIVE OF THE OPERATIONAL
GFS...ALTHOUGH THE GFS MAY BE A TAD TOO FAR EAST AT THE END OF THE
PERIOD. WILL STAY AWAY FROM THE DEEPER UKMET/ECMWF CAMP FOR NOW
AND LEAN TOWARD A BLEND OF THE ENSEMBLE MEANS AS PER THE 18Z GEFS
MEAN AND 12Z ECENS MEAN FOR NOW. CONFIDENCE IS HIGHLY LIMITED
GIVEN THE SPREAD IN THE AMOUNT OF DEEPENING OF THIS LOW CENTER.


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

ORRISON

$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.