Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4
000
FXUS10 KWNH 210636
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
235 AM EDT SAT OCT 21 2017

VALID OCT 21/0000 UTC THRU OCT 24/1200 UTC

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

00Z MODEL EVALUATION ALONG WITH LATEST MODEL PREFERENCES/CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...LONGWAVE TROUGH EVOLUTION THROUGH WESTERN U.S...
...EJECTING OUT INTO THE PLAINS ON SAT ALONG WITH COLD FRONT...
...SURFACE LOW DEEPENING OVER SOUTHERN CANADA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL CONSENSUS
CONFIDENCE: ABOVE AVERAGE

THE MODELS HAVE COME INTO GOOD AGREEMENT WITH THE TIMING AND DEPTH
OF THIS UPPER TROUGH AS IT EJECTS ACROSS THE WESTERN U.S.
OVERNIGHT AND THEN OUT ACROSS THE CENTRAL/NORTHERN PLAINS ON
SATURDAY. A COLD FRONT ASSOCIATED WITH THIS TROUGH WILL ALSO EJECT
OUT ACROSS THE PLAINS AS LOW PRESSURE DEEPENS ACROSS SOUTHERN
CANADA. A GENERAL MODEL CONSENSUS WILL BE PREFERRED AT THIS TIME
GIVEN THE GOOD MASS FIELD AGREEMENT.


...SOUTHERN STREAM LOWER MS VALLEY CLOSED LOW DEVELOPMENT BY MON...
...SURFACE COLD FRONT SWEEPING ACROSS THE MS/TN VALLEYS...
...SURFACE LOW DEVELOPMENT OVER THE TN VALLEY...
...DEEP PHASED CYCLONE OVER THE GREAT LAKES REGION BY TUES...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF THE 00Z UKMET/CMC AND 12Z ECMWF
CONFIDENCE: SLIGHTLY BELOW AVERAGE

THE MODELS BREAK AWAY THE SOUTHERN PORTION OF THE LONGER WAVE
TROUGH EJECTING OUT OF THE WEST AND INTO THE PLAINS STATES ON
SUNDAY...WITH THIS ENERGY DIGGING SOUTHEAST INTO THE LOWER MS
VALLEY SUNDAY NIGHT AND RESULTING IN A CLOSED LOW FORMATION BY
MONDAY. THIS WILL STILL BE INTERACTING WITH THE SOUTHERN PORTION
OF A N/S ORIENTED FRONTAL ZONE AND THE MODELS SUGGEST A WAVE OF
LOW PRESSURE WILL DEVELOP ALONG THE BOUNDARY ACROSS THE TN VALLEY
ON MONDAY.

BY MONDAY NIGHT...THE LOW CENTER WILL LIKELY BEGIN TO DEEPEN MORE
AGGRESSIVELY AND BEGIN LIFTING NORTH TOWARD THE OH VALLEY IN
RESPONSE TO A STRONG INTRUSION OF NORTHERN STREAM SHORTWAVE ENERGY
WHICH WILL BE AMPLIFYING SOUTHEAST ACROSS THE MIDWEST. THE
NORTHERN STREAM TROUGH WILL AMPLIFY INTO THE OH VALLEY AND GREAT
LAKES REGION AND SHOULD GRADUALLY PHASE WITH THE SOUTHERN STREAM
CLOSED LOW AS IT  AND BEGINS TO INTERACT AND GRADUALLY PHASE WITH
THE CLOSED LOW ADVANCING EAST ACROSS THE GULF COAST STATES AND THE
SOUTHERN APPALACHIANS. THE RESULT IS EXPECTED TO BE A DEEP
LONGWAVE TROUGH MOVING INTO THE EASTERN HALF OF THE NATION ON
TUESDAY WITH A STRONG COLD FRONT MOVING TOWARD THE APPALACHIANS
AND A DEEPENING CYCLONE OVER THE GREAT LAKES REGION. THE 00Z NAM
BECOMES A SLOW OUTLIER WITH THE SOUTHERN STREAM EVOLUTION OF THE
CLOSED LOW AND WILL BE DISMISSED. THE 00Z CMC AND 12Z ECMWF
SOLUTIONS ARE FASTER TO LIFT THE SOUTHERN STREAM ENERGY NORTHEAST
ACROSS THE TN/OH VALLEYS ALONG WITH THEIR RESPECTIVE SURFACE LOWS.
THE 00Z GFS AND 12Z UKMET ARE SLOWER TO DO THIS AND KEEP MORE
SOUTHERN ENERGY SUPPRESSED ACROSS THE SOUTH. CONSEQUENTLY...THE
CMC AND ECMWF ARE FAVORING FASTER PHASING OF STREAMS...WITH THE
GFS SLOWER.

UPDATE: THE 00Z UKMET HAS TRENDED VERY SHARPLY TOWARD THE 00Z
CMC/12Z ECMWF CAMP AND AWAY FROM THE SLOWER GFS. THE 00Z ECMWF
THOUGH HAS TRENDED MORE PROGRESSIVE IN LIFTING ENERGY NORTH FROM
THE TN VALLEY AND ACROSS THE OH VALLEY AND GREAT LAKES REGION AND
HAS A FASTER SURFACE LOW AS A RESULT. THIS IS A BIT MORE OUT OF
TOLERANCE RELATIVE TO THE MODEL CONSENSUS AND THE SUITE OF EURO
AND CANADIAN ENSEMBLE MEMBERS. GENERALLY THERE HAS BEEN A
MULTI-DAY TREND TOWARD QUICKER PHASING AND WITH A STRONGER
INTRUSION OF NORTHERN STREAM ENERGY TO FACILITATE A MORE AMPLIFIED
SOLUTION...BUT THE 00Z ECMWF IS PROBABLY A BIT TOO PROGRESSIVE.
GIVEN THE MANY EURO/CANADIAN ENSEMBLE MEMBERS AND SOME GEFS
MEMBERS THAT WERE MORE STRONGLY FAVORING THE PRIOR 12Z ECMWF
RUN...THE PREFERENCE WILL BE TO INCORPORATE THE LATEST UKMET/CMC
AND PRIOR ECMWF RUN AS A CONSENSUS.


...SHORTWAVE REACHING B.C./PAC NORTHWEST ON SAT WITH WARM FRONT...
...ATMOSPHERIC RIVER ARRIVING OVER THE PACIFIC NORTHWEST SAT...
...UPPER TROUGH SWEEPING ACROSS THE NORTHERN PLAINS/MIDWEST MON...
...WEST COAST RIDGE/SANTA ANA WIND DEVELOPMENT MON/TUES...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL CONSENSUS
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE IN GOOD AGREEMENT THROUGH EARLY SATURDAY WITH THE
ARRIVAL OF AN UPPER SPEED MAX/SHORTWAVE AND ATTENDANT WARM FRONT
ACROSS THE PACIFIC NORTHWEST AND SOUTHWEST BRITISH COLUMBIA. THIS
ENERGY WILL ADVANCE RAPIDLY NORTHEAST INTO SOUTHWEST CANADA AND
LEAD THE WAY FOR A LONG-FETCH ATMOSPHERIC RIVER TRAVERSING THE
PACIFIC BASIN TO COME CRASHING INTO THE COASTAL RANGES AND
CASCADES OF THE PACIFIC NORTHWEST THROUGH SATURDAY NIGHT AND EARLY
SUNDAY. THE ONSHORE FLOW SHOULD THEN BEGIN TO SLACKEN BY LATER
SUNDAY AS LARGER SCALE RIDGING BEGINS TO BUILD ALONG THE WEST
COAST. MEANWHILE...THE INITIAL ARRIVAL OF SHORTWAVE ENERGY WILL
THEN AMPLIFY DOWNSTREAM ACROSS THE MIDWEST AND TOWARD THE EASTERN
U.S. LEADING THE WAY FOR A RATHER HIGH AMPLIFIED LONGWAVE PATTERN
ACROSS THE U.S. BY TUESDAY. UNFORTUNATELY...THE DEVELOPING UPPER
LEVEL RIDGE OVER THE WEST BY MONDAY AND TUESDAY WILL ALLOW
STRONGER SURFACE HIGH PRESSURE TO SETTLE OVER THE GREAT BASIN AND
LEAD TO THE DEVELOPMENT OF RATHER STRONG SANTA ANA WINDS OVER
CALIFORNIA. WILL PREFER A GENERAL MODEL CONSENSUS THROUGH THE
PERIOD GIVEN GOOD LARGE SCALE MASS FIELD AGREEMENT.


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.