467
FXUS10 KWNH 210453
PMDHMD
MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1152 PM EST MON JAN 20 2020
VALID JAN 21/0000 UTC THRU JAN 24/1200 UTC
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...
00Z MODEL EVALUATION WITH PRELIMINARY PREFERENCES AND FORECAST
CONFIDENCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~
..CLOSED LOW OFF THE SOUTHEAST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~
PREFERENCE: NON NAM/UKMET CONSENSUS
CONFIDENCE: SLIGHTLY ABOVE AVERAGE
UPPER LOW DROPPING ACROSS THE SOUTHEAST WILL CLOSE OFF AS IT EXITS
INTO THE ATLANTIC. THE GUIDANCE IS IN DECENT AGREEMENT WITH THIS
FEATURE CLOSING OFF VERY CLOSE TO THE COAST BUT REMAINING
PROGRESSIVE AS IT HAS SOME INTERACTION WITH A SHORTWAVE LEAVING
NEW ENGLAND. THE UKMET IS A CLEAR OUTLIER IN TERMS OF SPEED AND
INTENSITY OF THIS FEATURE, WHILE THE NAM MAINTAINS A SURFACE
FEATURE MUCH CLOSER TO THE COAST. WHILE AN INVERTED TROUGH
LINGERING NEAR THE COAST IS LIKELY BEFORE THE LOW PULLS AWAY,
WHICH MAY SPREAD SOME MOISTURE THROUGH LOW-LEVEL CONFLUENT FLOW
INTO FLORIDA, IMPACTS ARE EXPECTED TO BE PRIMARILY OFF THE COAST.
...IMPULSES MOVING ONTO THE PACIFIC NORTHWEST COAST THROUGH
THURSDAY...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~
PREFERENCE: NON GFS/UKMET TUESDAY, GEFS/ECMWF MEANS D2-D3
CONFIDENCE: SLIGHTLY BELOW AVERAGE
CLOSED UPPER LOW MOVING ONTO THE BRITISH COLUMBIA COAST WILL
WEAKEN TODAY AS IT LIFTS NORTHEAST. THE GFS IS DEEPER AND LINGERS
THE CLOSED LOW FURTHER EAST THAN THE GLOBAL CONSENSUS, WHILE THE
UKMET CONTINUES ITS CONUS-WIDE BEHAVIOR OF BEING GENERALLY TOO
PROGRESSIVE. AFTER A SHORT PERIOD OF SHORTWAVE RIDGING DURING
WEDNESDAY, A COMPLEX TROUGH FEATURE TWO DISTINCT SHORTWAVES WILL
APPROACH THE PACNW COAST THURSDAY. THE STRONGER FEATURE WILL
REMAIN IN THE GULF OF ALASKA, BUT A SECONDARY SHORTWAVE SPINNING
CYCLONICALLY THROUGH THE BASE OF THE TROUGH WILL ADVECT TOWARDS
OR/WA BY THE END OF THE FORECAST PERIOD. THE NAM/CMC ARE MUCH
FLATTER/FASTER WITH THIS FEATURE, LIKELY DUE TO STRONGER
DOWNSTREAM RIDGING ACROSS THE INTER-MOUNTAIN WEST, WHILE THE UKMET
IS FAST WITH BOTH ITS JET ENERGY AND SHORTWAVES MOVING INTO THE
COAST. THE GFS IS A BIT FASTER THAN ITS MEAN, WHILE THE ECMWF MAY
BE A BIT DEEPER THAN THE BLEND OF THE MEANS. FORTUNATELY, THE GEFS
AND ECMWF MEANS ARE VERY SIMILAR IN TIMING AND INTENSITY OF THE
ENERGY APPROACHING THE COAST, AND A BLEND OF THESE TWO IS
PREFERRED, WITH SOME WEIGHT ON THE OPERATIONAL ECMWF AS WELL TO
MAINTAIN SOME OF THE FINER QPF DETAILS IN THE TERRAIN.
..INTERACTION OF CLOSED SHORTWAVES IN THE PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~
PREFERENCE: 12Z ECMWF, 12Z ECMWF MEAN, 00Z NAM
CONFIDENCE: BELOW AVERAGE
GUIDANCE CONTINUES TO SUGGEST BINARY INTERACTION OF CLOSED LOWS
ACROSS THE PLAINS D2-D3, BUT THE LEVEL TO WHICH THIS OCCURS AND AT
WHAT TEMPORAL EVOLUTION REMAINS IN QUESTION. TWO SHORTWAVES WILL
LIKELY DIG FROM WESTERN CANADA INTO THE PLAINS, WITH A SHEARED
VORT LOBE RACING SOUTHEAST TO CLOSE OFF IN THE MISSOURI VALLEY
AHEAD OF A SECONDARY FEATURE WHICH IS PROGGED TO CLOSE OFF NEAR
THE DAKOTAS ON D3. THE UKMET IS AGAIN TOO WEAK AND MERGES THESE
FEATURES TOGETHER INTO A BROAD CLOSED LOW ACROSS THE MIDDLE OF THE
COUNTRY. THIS IS THE NOT THE GLOBAL CONSENSUS, AND IN FACT THE
TREND IN THE GUIDANCE HAS BEEN FOR SLOWER INTERACTION DUE TO A
FASTER PRIMARY SHORTWAVE AND A SLOWER SECONDARY LAGGING FEATURE.
THE ECMWF HAS BEEN QUITE CONSISTENT WITH ITS EVOLUTION THE PAST
THREE RUNS, AND AT THIS TIME IS CLOSE TO THE NAM EVOLUTION,
ALTHOUGH THE NAM IS LIKELY TOO FAR SOUTHEAST WITH THE LEADING
CLOSED LOW BASED OFF THE ENSEMBLE MEANS POSITION. THE GFS HAS
SHOWN VERY LITTLE RUN TO RUN CONSISTENCY WITH ITS PLACEMENT OF
THESE FEATURES, LEAVING THE PREFERRED BLEND.
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML
WEISS
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