175
FXUS10 KWNH 301849
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
148 PM EST THU JAN 30 2020
VALID JAN 30/1200 UTC THRU FEB 03/0000 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
12Z MODEL EVALUATION
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...EVOLUTION OF TROUGH OVER EASTERN HALF OF THE U.S. THROUGH SUNDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~
PREFERENCE: BLEND OF 12Z ECMWF/UKMET...SUPPORTED BY 12Z GEFS MEAN
AND 00Z ECMWF ENSEMBLE MEAN
CONFIDENCE: AVERAGE
DOWNWIND OF A SHARP WESTERN U.S. RIDGE, NORTHWESTERLY FLOW WITH
SOUTHERN AND NORTHERN STREAM COMPONENTS WILL ABSORB A LOW SHEARING
OUT OF MEXICO, FORMING A FULL-LATITUDE TROUGH OVER THE EASTERN
U.S. THROUGH SATURDAY. THE TROUGH DOES NOT CONSOLIDATE AND SWING
INTO A NEUTRAL OR NEGATIVE TILT, WITH ASSOCIATED CYCLOGENESIS,
UNTIL MOVING OFFSHORE OVER THE WEEKEND. AT THE SURFACE, LOW
DEVELOPMENT OCCURS FRIDAY NIGHT ALONG THE NORTH CAROLINA COAST IN
THE LEFT EXIT OF A STRONG SOUTHWESTERLY JET STREAM. EMBEDDED
UPPER-LEVEL IMPULSES IN THE TROUGH VARY AMONG THE GUIDANCE, BUT
THERE IS DECENT AGREEMENT ON POSITION AND MOVEMENT OF THE LARGE
SCALE FEATURES.
THE TILT OF THE SOUTHERN PORTION IS MORE POSITIVE THAN IN PREVIOUS
RUNS, AND THE UPPER-LEVEL ENERGY SKIRTS ACROSS THE SOUTHEAST
STATES A TAD MORE QUICKLY IN THE GFS/ECMWF COMPARED TO PRIOR RUNS.
THE UKMET HANGS BACK A BIT MORE, LOOKING MORE LIKE CONTINUITY AND
THE OLDER ENSEMBLE MEANS, BUT STILL CLUSTERED FAIRLY WELL WITH THE
ECMWF, GFS. THE NOW QUICKER AND MORE OPEN SOUTHERN STREAM WAVE
SLOWS THE COLD FRONTAL PROGRESSION OVER THE FL PENINSULA FRIDAY
NIGHT AND RESULTS IN A WEST TO EAST SWATH OF RAINFALL OVER THE FL
PENINSULA ON DAY 2.
THE 12Z CMC IS AN OUTLIER IN PRODUCING SUCH STAUNCH RIDGING IN THE
IMMEDIATE WAKE OF THE SYSTEM AS IT GETS PAST THE LOWER MISSISSIPPI
VALLEY. THE 12Z GFS MAY BE USED, BUT WITH A LITTLE BIT OF CAUTION
AS IT LOOKS OVERLY DEVELOPED WITH THE VERY SHORT WAVELENGTH SYSTEM
IN THE NORTHERN STREAM OVER THE GREAT LAKES / NORTHEAST SATURDAY.
THE NAM HAS SOMEWHAT OPPOSITE THE ISSUE SEEN IN THE CMC,
MAINTAINING COLDER HEIGHTS OVER THE SOUTHERN PLAINS / LOWER
MISSISSIPPI VALLEY, WITH LITTLE ENSEMBLE SUPPORT.
...PACIFIC NORTHWEST ATMOSPHERIC RIVER LEADING A LONGWAVE TROUGH
PUSHING INTO THE WEST ON SUNDAY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PREFERENCE: BLEND OF 12Z ECMWF / UKMET...SUPPORTED BY 12Z GEFS
MEAN AND 00Z ECMWF ENSEMBLE MEAN
CONFIDENCE: AVERAGE
AN ATMOSPHERIC RIVER REACHES THE WASHINGTON COAST LATER TODAY AND
WAIVERS NORTH/SOUTH THROUGH FRIDAY NIGHT BEFORE SHIFTING DOWN THE
OREGON COAST SATURDAY. THIS OCCURS IN ADVANCE OF A LONGWAVE TROUGH
THAT REACHES TO CENTRAL CALIFORNIA AS IT PUSHES INLAND SUNDAY. THE
DILEMMA COMES WITH THE EXACT AXIS OF HEAVY PRECIPITATION ON DAY 2
AND THE TIMING OF THE TROUGH THAT MOVES ASHORE ON DAY 3. THE ECMWF
REMAINS A STEADY 6 TO 12 HOURS BEHIND THE REST OF THE GUIDANCE
WITH THE TROUGH AXIS, SO IT HAS QPF INLAND ON DAY 3, ESPECIALLY
OVER THE NORTHERN ROCKIES. LOOKING AT HOW ENSEMBLE SPAGHETTI PLOTS
HAVE EVOLVED OVER MULTIPLE MODEL CYCLES, THE MODEL CAMPS HAVE BEEN
STEADY IN THEIR PREDICTIONS, SUGGESTING THIS IS JUST A CASE OF
NORMAL BIASES. THE ECMWF IS PROBABLY A BIT TOO SLOW, BUT THE GFS
ERRS ON THE FAST SIDE. IN PARTICULAR, IT LOOKS LIKE THE GFS IS TOO
QUICK IN PHASING CUTOFF ENERGY OVER THE SOUTHWEST U.S. BACK INTO
THE ZONAL FLOW. THE UKMET OFFERS A NICE MIDDLE GROUND, SO WE
RECOMMEND AN ECMWF/UKMET BLEND, ALTHOUGH THE GFS IS REALLY ONLY
MINIMALLY FASTER.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
JACKSON/BURKE
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