MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1242 AM EDT THU MAR 26 2015 VALID MAR 26/0000 UTC THRU MAR 29/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...FULL-LATITUDE TROF CROSSING THE EASTERN U.S. BY EARLY IN THE WEEKEND... ...STRONG COLD FRONT/ASSOCIATED SURFACE WAVES... PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF...WEIGHTED 2/3 TOWARD THE 12Z ECMWF FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE THE CURRENT WATER VAPOR IMAGERY SHOWED A PAIR OF STRONG SHORTWAVES AFFECTING THE OZARKS AND SOUTHERN ONTARIO...RESPECTIVELY. THE FORMER HAS HELPED IGNITE A LARGE CLUSTER OF SHOWERS AND THUNDERSTORMS ACROSS OK/AR WHICH HAS BEEN RESPONSIBLE FOR SEVERE WEATHER REPORTS AND FLASH FLOODING. ALL FEATURES MOVING FORWARD SHOULD BECOME MORE PROGRESSIVE IN NATURE AS HEIGHT FALLS PROJECT EASTWARD IN TIME. A COMPLEX ARRAY OF IMPULSES MOVING IN FROM CENTRAL CANADA WILL HELP DRAG THE UPPER TROF EASTWARD WITH THE SYSTEM EVENTUALLY REACHING THE WESTERN ATLANTIC BY LATE IN THE WEEKEND. THE ACCOMPANYING COLD FRONT WILL FEATURE A MULTITUDE OF SURFACE WAVES WITH THE GUIDANCE GENERALLY DIFFERING WITH REGARD TO THE POSITION AND INTENSITY OF EACH OF THESE LOWS. OVERALL...THE 00Z GFS/18Z GEFS MEAN HAVE TENDED TO BE A BIT QUICKER WITH THE SOUTHERN EXTENT OF THE UPPER TROF ON FRIDAY EVENING ACROSS THE SOUTHEASTERN U.S. THIS ULTIMATELY LEADS TO THE GFS SUITE OF SOLUTIONS BEING MORE PROGRESSIVE WITH THE EJECTING SURFACE LOW OVER THE WESTERN ATLANTIC. LATER IN THE PERIOD...THE 12Z CMC/UKMET STAND OUT AS BEING RATHER SLOW WITH THE BACK EDGE OF THE UPPER TROF. IN FACT...THE 12Z CMC CLOSES OFF A 534-DM UPPER LOW ACROSS THE MID-ATLANTIC BY 29/0000Z. THIS LEADS TO A MORE WRAPPED UP COASTAL SOLUTION WHICH KEEPS PRECIPITATION ACROSS THE MID-ATLANTIC INTO DAY 3. ENSEMBLE LOW PLOTS SUGGEST SUCH A SOLUTION IS A MINORITY AT THIS POINT. AS A WHOLE LIKE THE COMBO OF THE 00Z GFS/12Z ECMWF BUT WILL WEIGHT THE SOLUTION TWO-THIRDS TOWARD THE LATTER GIVEN THE THOUGHT THAT THE GFS IS TOO FAST INTO DAY 3. ...PROGRESSIVE SHORTWAVE REACHING THE PACIFIC NORTHWEST BY LATE FRIDAY... ...WELL-DEVELOPED SURFACE CYCLONE MOVING THROUGH THE NORTHERN TIER THIS WEEKEND... PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/21Z SREF MEAN FORECAST CONFIDENCE: BELOW AVERAGE A STOUT UPPER RIDGE ANCHORING THE WESTERN U.S. WILL QUICKLY GIVE WAY TO A PROGRESSIVE SHORTWAVE CROSSING THE PACIFIC NORTHWEST BY FRIDAY NIGHT. THE MODELS ALREADY SHOW SOME DISAGREEMENT WITH THE PATTERN...PARTICULARLY THE 12Z UKMET WHICH IS SLOWER AND SPREADS SOME OF THE VORTICITY DOWN TOWARD NORTHERN CA. THIS SOLUTION GIVES WAY TOO MUCH EMPHASIS ON A SOUTHERN SPLIT WHICH IS NOT VERY SUPPORTED BY THE GUIDANCE. MANY OF THE 00Z MODELS PLACE MORE EMPHASIS ON KEEPING THE SHORTWAVE INTACT ACROSS THE NORTHERN TIER STATES. LOOKING TOWARD DAY 3....THE 12Z ECMWF STARTS TO BECOME SLOWER THAN THE ENSEMBLE MEANS INCLUDING ITS OWN 12Z ECMWF ENSEMBLE MEAN. PREFER TO STAY ON THE MORE PROGRESSIVE SIDE AS SUPPORTED BY THE ENSEMBLE MEANS. WILL FAVOR A COMBINATION OF THE 00Z GFS WITH THE 21Z SREF MEAN. THE 00Z GFS IS ON THE SOUTHERN END OF THE ENSEMBLE SPREAD REGARDING THE LOW TRACK. SO WILL SPLIT THE DIFFERENCE BETWEEN THE TWO. ...SHORTWAVES CROSSING THE DESERT SOUTHWEST ON SATURDAY... PRELIMINARY PREFERENCE: BLEND OF THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: BELOW AVERAGE THIS AREA OF THE COUNTRY IS PLAGUED BY QUITE A BIT OF SPREAD AS THE REGION WILL BE AFFECTED BY A PAIR OF DISTURBANCES. AS MENTIONED EARLIER...THE 12Z UKMET IS DISPLACED SOUTHWARD WITH THE PACIFIC NORTHWEST SYSTEM WHICH BRINGS STRONGER HEIGHT FALLS INTO THE SOUTHWESTERN STATES. LURKING TO THE WEST ACROSS THE EASTERN PACIFIC IS ANOTHER SHORTWAVE EXPECTED TO APPROACH THE AREA LATE IN THE PERIOD. THE 00Z NAM/GFS AND 12Z UKMET ARE MORE EMPHATIC ABOUT CARRYING THIS ENERGY INTO THE MAP DOMAIN WHILE THE 12Z ECWMF/CMC SHOW A MORE SHEARED OUT SYSTEM. GIVEN THE SPREAD IN PLACE...WILL BLEND THE ENSEMBLE MEANS PENDING ADDITIONAL MODEL GUIDANCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER