Prognostic Meteorological Discussion
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000 FXUS10 KWNH 220504 PMDHMD MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 103 AM EDT SAT JUL 22 2017 VALID JUL 22/0000 UTC THRU JUL 25/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GFS/NAM INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. ...SYSTEM APPROACHING THE PACIFIC NORTHWEST MONDAY/TUESDAY... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM/GFS BLEND CONFIDENCE: BELOW AVERAGE THE MODELS ARE STRUGGLING WITH HOW MUCH...IF ANY...MID-LEVEL VORTICITY IS SHEARED EASTWARD INTO BRITISH COLUMBIA BY TUE MORNING. THE 00Z GFS AND ESPECIALLY THE 12Z ECMWF ARE SUGGESTIVE THAT A SIZABLE PORTION OF THE FEATURE IS PUSHED INTO SWRN CANADA WHICH ALLOWS THE ENTIRE SHORTWAVE TO BECOME MORE ELONGATED. ENSEMBLE SPAGHETTI HEIGHTS SUPPORT MORE IN THE WAY OF KEEPING THE ENERGY COMPACT/TOGETHER LIKE THE 00Z NAM/12Z UKMET/CMC. HOWEVER...THE 00Z NAM TIMING IS IN THE MIDDLE OF THE DETERMINISTIC GUIDANCE AND IF ANYTHING...ENSEMBLES SUPPORT A SLOWER PROGRESSION. THEREFORE A 00Z NAM/GFS BLEND IS RECOMMENDED AT THIS POINT IN TIME...GIVEN THE 00Z GFS IS A BIT SLOWER THAN THE NAM...BUT CONFIDENCE IS BELOW AVERAGE GIVEN THE ORIGIN OF THE SYSTEM SOUTH OF THE ALEUTIANS AND LONGER TIME FRAME BEFORE VERIFICATION. ...UPPER LOW NEAR CALIFORNIA SUNDAY/MONDAY... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE GUIDANCE SHOWS GOOD AGREEMENT WITH THIS FEATURE. ...SYSTEM MOVING THROUGH SOUTH-CENTRAL CANADA LATE MONDAY... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z ECMWF/UKMET BLEND CONFIDENCE: AVERAGE THE 00Z NAM IS A BIT FASTER WITH THIS SYSTEM BY MON MORNING...AND 00Z GFS A BIT SLOWER ALOFT...WITH IMPACTS TO THE FRONTAL PROGRESSION IN THE DAKOTAS MONDAY. A COMPROMISE OF THE 12Z UKMET/ECMWF IS PREFERRED HERE WITH ABOVE AVERAGE CONFIDENCE GIVEN THEIR MIDDLE OF THE ROAD PLACEMENT. ...SHORTWAVE MOVING EAST FROM S-CNTRL CANADA TODAY TO THE GREAT LAKES SUN AND INTO THE NORTHEAST U.S. ON MON... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z ECMWF CONFIDENCE: AVERAGE BY 00Z/24...THE 00Z NAM ENDS UP A BIT SLOWER WITH THE 850-700 MB LOW ASSOCIATED WITH THE MID-UPPER LEVEL SHORTWAVE AND DOES NOT HAVE AS MUCH OF AN EXTENSION TOWARD THE SOUTHEAST AS NOTED IN THE REMAINING DETERMINISTIC MODELS. THE 00Z GFS IS A BIT WEAKER WITH THE MID-LEVEL REFLECTION OF THE SHORTWAVE. THE 12Z CMC BECOMES A BIT SOUTH WITH THIS FEATURE COMPARED TO THE OTHER MODELS...AND THE 12Z UKMET WAS A BIT FASTER/ELONGATED WITH THIS FEATURE BY LATE MONDAY. THE 12Z ECMWF APPEARED TO BE A DECENT COMPROMISE. FOR RAINFALL FORECAST PREFERENCES, SEE OUR QPF DISCUSSION (QPFPFD). ...SHORTWAVE MOVING THROUGH THE NORTHERN MID-ATL LATE TODAY/SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE 00Z NAM AND 12Z CMC ARE A BIT STRONGER WITH THIS 850-700 MB REFLECTION OF THIS SYSTEM BUT THEY OTHERWISE AGREE WITH THE OTHER DETERMINISTIC MODELS FOR TIMING OF MASS FIELDS INCLUDING A WEAK SURFACE WAVE. FOR RAINFALL FORECAST PREFERENCES...SEE OUR QPF DISCUSSION (QPFPFD). www.wpc.ncep.noaa.gov/html/model2.shtml www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml OTTO $$

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