Prognostic Meteorological Discussion
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FXUS10 KWNH 221650
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1149 AM EST MON JAN 22 2018

VALID JAN 22/1200 UTC THRU JAN 26/0000 UTC

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

12Z INITIAL MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...DEEP LAYER CYCLONE OVER THE MIDWEST REGION TODAY...
...SURFACE LOW CROSSING THE GREAT LAKES REGION THROUGH TUESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND THROUGH 6Z WEDNESDAY, THEN
ECMWF/GFS COMPROMISE
CONFIDENCE: ABOVE AVERAGE

THE MODELS ARE OVERALL IN VERY GOOD AGREEMENT WITH THE DETAILS OF
THE DEEP CLOSED LOW AND ITS ACCOMPANYING SURFACE LOW OVER THE
UPPER MIDWEST AND THE GREAT LAKES REGION THROUGH 6Z WEDNESDAY.
THERE IS A GOOD SIGNAL IN THE PMSL GUIDANCE THAT A TRIPLE POINT
LOW COULD FORM ONCE THE STORM SYSTEM APPROACHES NEW ENGLAND
TUESDAY NIGHT.  BY 12Z WEDNESDAY, THE CMC APPEARS TO BE SLIGHTLY
SLOWER IN LIFTING OUT THE UPPER TROUGH OVER NEW ENGLAND AND MORE
PRONOUNCED WITH THE SURFACE COLD FRONT AS IT EXITS THE EAST COAST.
 THE NAM IS INDICATING A DUAL 700MB LOW STRUCTURE OVER SOUTHERN
QUEBEC AT 12Z WEDNESDAY THAT THE OTHER GUIDANCE IS NOT ON BOARD
WITH AT THE PRESENT TIME.


...SHORTWAVE ENERGY DIGGING ACROSS THE NORTHERN PLAINS BY
TUESDAY...
...EASTERN U.S UPPER LEVEL TROUGH BY WEDNESDAY NIGHT...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND THROUGH 12Z WEDNESDAY, THEN
NON-UKMET CONSENSUS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A NORTHERN STREAM UPPER LEVEL TROUGH INITIALLY OVER ALBERTA TODAY
IS FORECAST TO DIG TOWARDS THE SOUTHEAST THROUGH THE MIDDLE OF THE
WEEK ACROSS THE NORTHERN PLAINS AND MIDWEST STATES, IN RESPONSE TO
THE UPSTREAM RIDGING OVER THE INTERMOUNTAIN WEST.  THE MODELS ARE
IN GOOD AGREEMENT WITH THEIR MASS FIELD TIMING AND DEPTH THROUGH
ABOUT 12Z WEDNESDAY. THEREAFTER, THE UKMET BECOMES LESS AMPLIFIED
THAN THE MODEL CONSENSUS AND IS SLIGHTLY SLOWER.  THE GFS IS NOW
CLOSER TO THE MODEL CONSENSUS AND NOT AS PROGRESSIVE AS EARLIER
MODEL RUNS.


...SHORTWAVE IMPACTING THE PACIFIC NORTHWEST ON TUESDAY...
...ATTENDANT SURFACE LOW LIFTING UP OFFSHORE BRITISH COLUMBIA...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE

THE MODELS SHOW A SHORTWAVE ARRIVING ACROSS WESTERN WASHINGTON AND
OREGON ON TUESDAY WITH THE SYSTEM THEN WEAKENING AS IT ENCOUNTERS
A DEVELOPING RIDGE OVER THE GREAT BASIN AND CANADIAN ROCKIES. THIS
WILL DRIVE A FOCUS OF STRONGER SOUTH/SOUTHWEST FLOW UP ALONG THE
COASTAL RANGES OUT AHEAD OF A STRONG AREA OF LOW PRESSURE THAT
LIFTS UP OFFSHORE BRITISH COLUMBIA. THE MODELS ARE IN GOOD
AGREEMENT WITH THIS SYSTEM AS IT ARRIVES AND SO A GENERAL MODEL
BLEND WILL BE PREFERRED.


...DEEP UPPER TROUGH AND SURFACE LOW OFFSHORE THE WEST COAST BY
WEDNESDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MODELS ALLOW A LOW PRESSURE GYRE TO DEVELOP OFFSHORE THE
BRITISH COLUMBIA AND PACIFIC NORTHWEST COAST FOR THE MIDDLE OF THE
WEEK WITH STRONG SOUTHWEST ONSHORE FLOW SETTING UP ACROSS THE
PACIFIC NORTHWEST.  THIS WOULD BE SOUTH OF AN APPROACHING SURFACE
LOW WHICH WILL BE NEAR VANCOUVER ISLAND BY THURSDAY MORNING.
ALTHOUGH THERE IS GOOD OVERALL SYNOPTIC SCALE AGREEMENT, THERE ARE
SOME DETAIL DIFFERENCES WITH THE STRENGTH AND POSITION OF THE
UPPER LOW. THE GFS KEEPS THE LOW MORE TO THE NORTHWEST, WHEREAS
THE ECMWF IS FARTHER SOUTH.  BY THE END OF THE FORECAST PERIOD,
THE GFS PIVOTS THE SURFACE LOW SOUTH OF THE MODEL CONSENSUS.


MODEL TRENDS AT www.wpc.ncep.noaa.gov/html/model2.shtml
500 MB FORECASTS AT www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

HAMRICK

$$





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