Prognostic Meteorological Discussion
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FXUS10 KWNH 221850
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
150 PM 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 FINAL 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 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.  THE CMC HAS TRENDED CLOSER TO THE MODEL CONSENSUS
REGARDING THE SPEED OF THE TROUGH AXIS, AND CAN BE CONSIDERED PART
OF THE BLEND.  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, BUT IS OTHERWISE IN VERY
GOOD AGREEMENT MASS FIELD WISE.


...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
GFS/ECMWF COMPROMISE
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 AND ROCKY
MOUNTAINS.  THE MODELS ARE IN GOOD AGREEMENT WITH THEIR MASS FIELD
TIMING AND DEPTH THROUGH ABOUT 12Z WEDNESDAY. THEREAFTER, THE
UKMET AND CMC BECOME LESS AMPLIFIED THAN THE MODEL CONSENSUS AND
THE CMC IS SLIGHTLY FASTER.  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 ENHANCE 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

A LARGE LOW PRESSURE GYRE IS FORECAST TO DEVELOP ABOUT 500 MILES
WEST OF 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 SMALLER DETAIL DIFFERENCES WITH THE
STRENGTH AND POSITION OF SHORTWAVE ENERGY ROTATING AROUND IT .
THE GFS INITIALLY 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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