Prognostic Meteorological Discussion
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FXUS10 KWNH 181857
PMDHMD

MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
156 PM EST THU JAN 18 2018

VALID JAN 18/1200 UTC THRU JAN 22/0000 UTC

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

12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

...SOUTHERN STREAM WAVE EJECTING NORTHEAST FROM THE GULF OF
MEXICO...

PREFERENCE: NON GFS SOLN WEIGHTED SOMEWHAT FASTER THAN THE ECMWF
OR NAM
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE NUMERICAL GUIDANCE GENERALLY HANDLED THIS SYSTEM COMPARABLY AS
IT SLOWLY MAKES ITS WAY EAST AND NORTH FROM THE WESTERN GULF OF
MEXICO AND STRADDLES THE GULF COAST STATES THROUGH DAY 2.  THE
REAL DIFFERENCES BEGIN TO OPEN UP BETWEEN THE GFS AND THE OTHER
MODELS ON DAY 3...SATURDAY.  THE PAST FEW RUNS OF THE DEEPENED THE
MID LEVEL SYSTEM AND BEGAN TO SHOW REFLECTIONS OF THE WAVE CLOSER
TO THE SURFACE.  IT DOES THIS IN A REGION WHERE MID/UPPER LEVEL
HEIGHTS TO ITS NORTH AND EAST ARE RISING...NOT GENERALLY A
FAVORABLE ENVIRONMENT FOR A SYSTEM TO BECOME REINVIGORATED. THAT
IS NOT TO SAY THAT THERE WILL NOT BE SOME FLUCTATIONS IN
STRENGTH...BUT SUSPECT THAT THE GFS WAS STRENGTHENING THINGS TOO
MUCH.  THE 18/12Z ECMWF REMAINED ON THE SLOWER/WEAKER
SIDE...ALTHOUGH IT APPEARS TO DEVELOP SOME CONVECTIVE FEEDBACK OR
GRID SCALE FEDBACK BY THE END OF DAY 3 OVER THE CAROLINAS.  STILL
PREFER A SOLN BETWEEN THE GFS AND ECMWF...WITH THE STRENGTH MORE
CLOSELY ALIGNED TO THE ECMWF/NAM.


...SHORTWAVE INITIALLY OVER UPPER MIDWEST MOVING ACROSS NEW
ENGLAND FRIDAY AFTERNOON...

PREFERENCE: GENERAL MODEL COMPROMISE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

A WAVE MAKING ITS WAY ALONG THE INTERNATIONAL BORDER THIS MORNING
WILL CROSS THE GREAT LAKES AND THEN CLIP PARTS OF THE NORTHEASTERN
U.S. STATES BY FRIDAY AFTERNOON.  THE NUMERICAL GUIDANCE TENDED TO
HANDLE THIS FEATURE IN A SIMILAR FASHION...BOTH IN TERMS OF
STRENGTH AND FORWARD SPEED.  A GENERAL MODEL COMPROMISE SHOULD
TAKE CARE OF ANY SMALL DIFFERENCES WHICH LINGER.


...SLOW MOVING MID/UPPER LEVEL SYSTEM MOVING OFF THE MID ATLANTIC
REGION DAY 1...

PREFERENCE: 18/12Z ECMWF/NAM/GFS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE

THE MID/UPPER LEVEL CIRCULATION OF A SYSTEM WHICH IMPACTED THE
EASTERN STATES STILL LINGERED OVER THE CAROLINAS AND FAR SOUTHEAST
VA EARLY THIS MORNING...WHILE THE SURFACE REFLECTION WAS LOCATED
OUT AT SEA.  THE 18/12Z ECMWF AND THE 18/12Z NAM/GFS HANDLED THE
DEPARTURE OF THE SYSTEM IN A SIMILAR WAY.


...DEEPENING TROUGH MOVING INLAND...WITH SOUTHERN STREAM ENERGY
EMERGING OVER THE PLAINS SUNDAY...

PREFERENCE: 18/12Z ECMWF/UKMET BLEND
CONFIDENCE: ABOVE AVERAGE ON DAYS 1/2...AVERAGE AT BEST ON DAY 3

THE MODELS TEND TO BE IN PRETTY GOOD AGREEMENT WITH A CLOSED LOW
INITIALLY OFF THE COAST OF BRITISH COLUMBIA THIS MORNING AS IT
WEAKENS THROUGH FRIDAY MORNING.  EVEN THE DETAILS WITH THE LARGER
SCALE TROUGH WERE IN PRETTY GOOD AGREEMENT AS A SHORTWAVE HELPS
CARVE OUT A SOUTHERN STREAM THAT COMES ONSHORE OVER CA LATE FRIDAY
AND THEN PROGRESSES ACROSS THE SOUTHERN INTERMOUNTAIN REGION BY
SATURDAY AFTERNOON/EVENING.

THE REAL DIFFERENCES OPEN UP STARTING ABOUT 21/00Z AND PERSIST
BEYOND THE END OF THE DAY 3 PERIOD AT 22/00Z.  THE 12Z NCEP
GUIDANCE HAS SHIFTED TO A STRONGER...MORE DEVELOPED SOLUTION AS A
MID/UPPER LEVEL LOW DEVELOPS OVER THE WESTERN HIGH PLAINS.  THE
18/00Z ECMWF WAS SLOWER AND WEAKER BY THE END OF DAY 3.  THE
SUBSEQUENT RUN AT 12Z STRONGLY MOVED TOWARDS THE GFS/NAM/UKMET BY
THE END OF DAY 3 ESPECIALLY AT THE SURFACE.  THE ECMWF UPPER
TROUGH ALSO SPED UP WHEN COMPARED WITH THE 18/00Z RUN AND
CLUSTERED WELL WITH THE 12Z NAM.  THE 12Z UKMET ALSO MOVED TOWARDS
THIS CAMP...ALTHOUGH ITS RUN TO RUN MOVE WAS NOT AS GREAT AS THE
MOVE MADE BY THE ECMWF.  AT THIS POINT...THINK AN ECMWF/UKMET/

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

BANN



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