379
FXUS10 KWNH 291839
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
238 PM EDT SUN MAR 29 2020
VALID MAR 29/1200 UTC THRU APR 2/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
CLOSED LOW OVER GREAT LAKES AND NEW ENGLAND WITH SURFACE
CYCLOGENESIS NEAR THE COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: ABOVE AVERAGE
18Z UPDATE: THE 12Z UKMET MADE A VERY MINOR SOUTHWARD ADJUSTMENT
WITH THE SURFACE LOW NEAR THE NEW ENGLAND COAST AND IS SOLIDLY
WITHIN THE MODEL CONSENSUS, AND A GENERAL MODEL BLEND OF THE 12Z
GUIDANCE REMAINS BEST.
THERE IS VERY GOOD SYNOPTIC SCALE AGREEMENT ON THE EVOLUTION OF
THE PARENT UPPER LOW OVER THE UPPER GREAT LAKES THAT PROGRESSES
EASTWARD TO NEW ENGLAND BY MONDAY NIGHT. THIS WILL SUPPORT THE
DEVELOPMENT OF A COASTAL LOW NEAR SOUTHEAST NEW ENGLAND THAT IS
FORECAST TO TRACK SLOWLY EASTWARD ROUGHLY NEAR 40 DEGREES NORTH.
IN REGARD TO THE DEVELOPING SURFACE LOW, THERE ARE MINOR PLACEMENT
DIFFERENCES THAT DEVELOP, WITH THE 00Z UKMET SLIGHTLY CLOSER TO
THE COAST AND THE CMC A TAD FARTHER TO THE SOUTH, BUT STILL CLOSE
ENOUGH TO MERIT A DETERMINISTIC MULTI-MODEL BLEND.
SOUTHWEST SHORTWAVE AND SOUTHERN TIER SURFACE LOW REACHING THE
EAST COAST BY TUESDAY EVENING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z NAM/GFS/ECMWF
CONFIDENCE: AVERAGE
18Z UPDATE: THERE WAS A SLIGHTLY FASTER TREND WITH THE 12Z
NON-NCEP GUIDANCE WITH THE LOW TRACK ACROSS THE SOUTHERN TIER OF
THE NATION. THE 12Z CMC HAS TRENDED SLIGHTLY LESS AMPLIFIED WITH
THE SHORTWAVE TROUGH, ALTHOUGH STILL SLIGHTLY STRONGER AND SLOWER
THAN THE OTHER MODELS. BY WEDNESDAY MORNING, THE 12Z UKMET
BECOMES CONSIDERABLY FASTER AND LOSES ENSEMBLE SUPPORT. THE
PREVIOUS MODEL PREFERENCE HOLDS, EXCEPT TO SUBSTITUTE THE 12Z
ECMWF.
SHORTWAVE CURRENTLY ALONG THE CA COAST WILL PROGRESS EASTWARD
ACROSS THE SOUTHERN TIER STATES THROUGH EARLY WEEK. THE 00Z CMC
IS ALREADY OUT OF PHASE, A BIT SOUTH, AND MORE COMPACT THAN OTHER
GUIDANCE AND IS QUICKLY DISMISSED FROM PREFERENCE. THE REMAINING
DIFFERENCE INITIALLY THROUGH TUESDAY ACROSS THE SOUTHERN PLAINS
AND INTO THE SOUTHERN MS VALLEY IS IN DEPTH AND TIMING, WITH THE
UKMET AND GFS A TAD WEAKER THAN THE ECMWF/NAM; WHICH LEADS TO
SLIGHTLY DIFFERENT PLACEMENT OF THE DEEPER MOISTURE/UNSTABLE
ENVIRONMENT AHEAD OF IT. THE WEAKER/FASTER SOLUTIONS SUGGEST A
SLOWER TRANSPORT NORTH AND STRONGER CONVECTIVE RESPONSE FARTHER
SOUTH NEAR THE GULF. THIS SEEMS LOGICAL AT THIS TIME OF YEAR, BUT
CONTINUITY AND OVERALL FORCING/MASS FIELDS SUGGEST NORTHWARD
SHIFT. THE 00Z UKMET IS MUCH FLATTER THAN THE ENSEMBLE/CONTINUITY
AND IS MORE DRAMATICALLY SO ON DAY 3 ACROSS THE SOUTHEAST. WHILE
THIS IS PLAUSIBLE, IT IS MORE DRAMATIC THAN THE GFS/GEFS WHICH
WILL REPRESENT THE UNCERTAINTY WITH ITS INCORPORATION OVER THE
UKMET IN A PREFERRED BLEND. STILL, THE UNCERTAINTY HERE IS GOING
TO BE MESOSCALE CONVECTIVE PLACEMENT AND ITS UPSCALE INFLUENCE.
SO THE PREFERENCE WILL BE NEAR A 12Z GFS/NAM AND 00Z ECMWF BLEND
AT AVERAGE CONFIDENCE.
CLOSED UPPER LOW/TROUGH APPROACHING PACIFIC NORTHWEST THROUGH
MONDAY THEN REACHING WESTERN HIGH PLAINS BY MIDWEEK
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: 12Z GFS/12Z UKMET WITH SOME 12Z ECMWF/CMC AT LOWER
WEIGHT
CONFIDENCE: AVERAGE
18Z UPDATE: THE 12Z NAM REMAINS QUICKER TO BRING MID-LEVEL HEIGHT
FALLS TO THE REGION COMPARED TO THE MODEL CONSENSUS. THE ECMWF
TRENDED DEEPER WITH THE UPPER LOW OVER SOUTHWEST CANADA BY THE END
OF THE FORECAST PERIOD, AND THE CMC TRENDED SLIGHTLY SLOWER WITH
THE FRONT AND SURFACE LOW ACROSS THE NORTHERN PLAINS. SAME MODEL
PREFERENCES APPLY WITH 12Z GUIDANCE.
BROAD TROF DEVELOPING OVER THE GULF OF AK WILL CONTINUE TO PRESS
SOUTHEASTWARD WITH UPSTREAM SHORTWAVE ENERGY SWINGING THROUGH TO
PRESS HEIGHT-FALLS/TRIPLE POINT AND COLD FRONT THROUGH VANCOUVER
ISLAND AND THE PAC NW BY EARLY MONDAY. THIS UNDERCUTTING
SHORTWAVE WILL SWING ACROSS THE NORTHERN ROCKIES AND THE SOUTHERN
CANADIAN ROCKIES BY EARLY TUESDAY, SUPPORTING A WESTERN HIGH
PLAINS SURFACE CYCLONE. HERE THE 12Z NAM IS VERY STRONG/QUICK AS
IT ROTATES EASTWARD. THIS WILL OVERALL SHIFT THE CORE OF THE
UPPER LOW FARTHER EAST THAN HAS BEEN/CURRENTLY IS SUGGESTED BY THE
ENSEMBLE SUITE AND TRENDS. THE 12Z GFS AND 00Z UKMET ARE AS FAST
AS THE NAM BUT MUCH WEAKER OVERALL, SO THESE WOULD BE GENERALLY BE
FAVORED OVER THE NAM. THE SLOWER SOLUTIONS OF THE ECMWF/CMC, BY
LATE TUESDAY/WED, BOTH SUGGEST A GREATER INFLUENCE/TUG ON THE
SHORTWAVE LIFTING ACROSS THE CANADIAN ROCKIES FROM THE ARCTIC
STREAM, DRAWING BOTH NORTH AND WEST, AND STRENGTHENING THEM. THE
ECMWF IS MORE SO, INCLUDING AGAINST ITS ENSEMBLE SUITE MEMBERS.
THIS DOES NOT SEEM TO PLAY MUCH OF A ROLE IN THE REMAINING
UPSTREAM ENERGY/JET STREAK THAT PRESSES THROUGH THE PACIFIC NW
LATE TUESDAY INTO WED; SO FROM A CONUS PERSPECTIVE, THE ECMWF IS
VIABLE IN PREFERRED BLENDS. THE CMC IS A TAD WEAKER BUT MAY BE
VIABLE AS WELL IF DESIRED. SO ALL IN ALL, A NON-NAM SOLUTION IS
PREFERRED ACROSS THE NORTHWEST/NORTHERN ROCKIES AND THE NORTHERN
PLAINS, THOUGH WITH GREATER WEIGHTING TO THE GFS/UKMET.
CONFIDENCE IN THE OVERALL PATTERN IS HIGH, BUT WITH SOLID
DIFFERENCES IN TIMING/STRENGTH OF THE KEY INTERNAL SHORTWAVES AND
THEIR INFLUENCE ON SURFACE CYCLONE DEPTH/ORIENTATION, CONFIDENCE
REMAINS AVERAGE IN THIS BLEND.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
GALLINA/HAMRICK
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