804
FXUS10 KWNH 311708
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1207 PM EST FRI JAN 31 2020
VALID JAN 31/1200 UTC THRU FEB 04/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES AND CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...EVOLUTION OF TROUGH OVER EASTERN HALF OF THE U.S. THROUGH
SUNDAY...
...COASTAL LOW TRACKING NORTH OFFSHORE OF NEW ENGLAND LATE
SATURDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~
PREFERENCE: BLEND OF 12Z NAM, 12Z GFS AND 00Z ECMWF
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
AN ELONGATED MID-LEVEL TROUGH AXIS WITH NORTHERN AND SOUTHERN
STREAM COMPONENTS WILL TRACK TO THE EASTERN U.S. THROUGH SATURDAY
EVENING. DOWNSTREAM OF THE TROUGH AXIS, SURFACE CYCLOGENESIS IS
EXPECTED TO OCCUR OFF OF THE MID-ATLANTIC COAST ON SATURDAY,
TRACKING NORTH OFFSHORE OF NEW ENGLAND THROUGH SUNDAY MORNING. THE
AGREEABLE ENSEMBLE MEANS WERE USED AS A BASELINE FOR WHERE THE
DETERMINISTIC MODELS SHOULD LIE. THE BASE OF THE NORTHERN
COMPONENT OF THE TROUGH AXIS SHOWS SOME DIFFERENCES SATURDAY NIGHT
NEAR THE NORTHERN MID-ATLANTIC REGION. THE 00Z UKMET IS WEAKER AND
NORTH WITH THE BASE OF THE TROUGH WHILE THE 00Z CMC IS DEEPER AND
FARTHER SOUTH. THE REMAINING 12Z NAM, 00Z ECMWF AND 12Z GFS ARE
SIMILAR BUT THE 12Z GFS IS THE MOST AGGRESSIVE WITH THE STRENGTH
OF THE BASE OF THE TROUGH AXIS. A BLEND OF THE 12Z GFS WITH THE
12Z NAM AND 00Z ECMWF ARE RECOMMENDED SINCE THEY FALL WITHIN THE
MIDDLE OF THE LATEST SPREAD AND MATCH SIMILARLY TO THE LATEST
ENSEMBLE MEANS.
REGARDING THE OFFSHORE SURFACE LOW, THERE IS GOOD AGREEMENT WITH
TRACK UNTIL THE LOW IS OFFSHORE OF NOVA SCOTIA, WITH A 12Z GFS AND
00Z ECMWF BLEND LIKELY CLOSEST TO THE MIDDLE OF THE MINOR SPREAD
UNTIL THAT POINT. REGARDING STRENGTH, A BLEND OF THE 12Z NAM, 12Z
GFS AND 00Z ECMWF IS REASONABLE, NOT INCLUDING THE WEAKER/OUTLIER
00Z CMC.
...PACIFIC NORTHWEST ATMOSPHERIC RIVER LEADING A LONGWAVE TROUGH
PUSHING INTO THE WEST ON SUNDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF NON 12Z GFS GUIDANCE
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
THERE IS REASONABLE AGREEMENT WITH THE EVOLUTION OF A LONGWAVE
TROUGH ACROSS THE WEST COAST INTO THE GREAT BASIN INTO EARLY NEXT
WEEK. HOWEVER, THE 12Z GFS WAS NOTED TO BE A BIT QUICKER THAN THE
CONSENSUS WITH THE LEADING EDGE OF THE TROUGH BY EARLY SUNDAY. THE
FASTER GFS ALSO STANDS OUT WHEN VIEWING ENSEMBLE SPAGHETTI HEIGHTS
(540 DAM AT 500 MB), WITH A TIGHTENING OF ENSEMBLE MEMBERS TOWARD
THE 00Z ECMWF MEAN OVER THE PAST FEW CYCLES VALID MONDAY EVENING
BUT WITH THE 12Z GFS AHEAD OF 95% OF THE AVAILABLE ENSEMBLE
MEMBERS. A NON 12Z GFS BLEND OF GUIDANCE LOOKS REASONABLE FOR THE
WESTERN U.S. TROUGH SINCE DIFFERENCES AMONG THE NON-GFS
DETERMINISTIC GUIDANCE ARE MINOR.
...LEADING SHORTWAVE TRACKING THROUGH SOUTHERN CANADA ON SUNDAY
WITH ACCOMPANYING SURFACE LOW...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: GENERAL MODEL BLEND
CONFIDENCE: AVERAGE
A LOW AMPLITUDE SHORTWAVE AT THE LEADING EDGE OF HEIGHT FALLS
ACROSS THE WESTERN U.S. WILL TRACK THROUGH SOUTHERN CANADA
SUNDAY/SUNDAY NIGHT WITH A CORRESPONDING LOW AT THE SURFACE. A
WARM FRONT WILL EXTEND SOUTHEASTWARD FROM THE LOW AND IMPACT THE
GREAT LAKES AND NEW ENGLAND WITH WARM ADVECTION DRIVEN
PRECIPITATION. WHILE THE 12Z GFS IS SLIGHTLY FASTER AND 00Z ECMWF
A BIT SLOWER, THE DIFFERENCES ARE SMALL ENOUGH THAT A GENERAL
MODEL BLEND LOOKS APPROPRIATE FOR THIS SYSTEM.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
OTTO
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