MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 137 PM EST FRI JAN 30 2015 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...INCLUDING THE NAM/GFS/UKMET/GEM AND THE ECMWF ...UPPER TROUGH GOING NEGATIVE TILT OVER NEW ENGLAND LATER TODAY AND TONIGHT... ...STRENGTHENING COASTAL LOW... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE CURRENT WATER VAPOR IMAGERY SHOWS A DEEP UPPER TROUGH BEGINNING TO GO NEGATIVE TILT ACROSS THE NORTHERN MID-ATLANTIC AND SOUTHERN NEW ENGLAND. THE MODELS ADVERTISE SURFACE LOW PRESSURE REDEVELOPING NEAR THE BENCHMARK TODAY AND THEN DEEPENING TO SOUTHWEST OF NOVA SCOTIA BY EARLY SAT AS THE TROUGH CLOSES OFF ALOFT. THE TREND IN THE GUIDANCE OVER THE LAST DAY OR SO HAS BEEN TO SHIFT THE REDEVELOPING LOW CENTER A LITTLE FARTHER OFFSHORE. THE 12Z NAM AND 12Z GFS SUPPORT THE CURRENT GLOBAL MODEL CONSENSUS. SO...A GENERAL MODEL COMPROMISE WILL BE FAVORED AT THIS POINT. ...ELONGATED UPPER TROUGH AND CLOSED LOW IMPACTING THE SOUTHWEST AND NORTHWEST MEXICO... PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF...THROUGH 48 HOURS 12Z GFS...48 HOURS TO 84 HOURS CONFIDENCE: AVERAGE ALL OF THE MODELS SHOW AN ELONGATED N/S TROUGH AXIS FROM SOUTHERN CA SOUTH DOWN TO JUST WEST OF THE BAJA PENINSULA WITH MULTIPLE EMBEDDED VORT CENTERS. THE MOST SIGNIFICANT OF WHICH IS OVER SOUTHERN CA CURRENTLY. WV/IR SAT IMAGERY SHOWS A WELL-DEFINED SUBTROPICAL MOISTURE CONNECTION ASSOCIATED WITH THE TROUGH...AND THE GUIDANCE BRINGS A LARGE AMOUNT OF VORT ENERGY AND MOISTURE INTO THE SOUTHWEST OVER THE NEXT COUPLE OF DAYS. THIS ENERGY WILL ADVANCE EAST AND DEEPEN INTO A FAIRLY BROAD CLOSED UPPER LOW BY LATER TODAY OVER THE SOUTHWEST. ON SAT AND SUN...THE ENERGY THEN GETS SUPPRESSED SOUTHWARD INTO NORTHWEST MEXICO AND THE ADJACENT BAJA PENINSULA IN RESPONSE TO STRONG NORTHWESTERLY NORTHERN STREAM FLOW OVER THE CENTRAL AND NORTHERN ROCKIES. THE 12Z NAM IS A BIT STRONGER THAN THE MULTI-MODEL CONSENSUS BY LATER SUN AND MON. THE 12Z UKMET AND 12Z ECMWF HAVE THEIR RESPECTIVE LOW CENTERS SQUASHED A BIT FARTHER SOUTH AND EVEN A LITTLE SOUTHWEST OF THE GLOBAL MODEL CONSENSUS BY THE END OF THE PERIOD. THE STRONGER MODEL CLUSTERING TENDS TO FAVOR A BLEND OF THE 12Z GFS AND 12Z ECMWF THROUGH ABOUT 48 HOURS...AND THEN MORE TOWARD THE GFS THEREAFTER. THE 12Z GEM FAVORS CLUSTERS REASONABLY WELL WITH THE 12Z GFS. WILL SUGGEST A 12Z GFS/12Z ECMWF BLEND THROUGH 48 HOURS...AND THEN THE 12Z GFS THEREAFTER THROUGH THE REMAINDER OF THE SHORT RANGE PERIOD. ...SHORTWAVE ENERGY AMPLIFYING FROM THE MID MS VALLEY TO THE MID-ATLANTIC STATES... ...ASSOCIATED SURFACE LOW... PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF CONFIDENCE: BELOW AVERAGE A SHORTWAVE NOW ENTERING CENTRAL BRITISH COLUMBIA WILL BE DIGGING SOUTHEAST DOWN INTO THE NORTHERN/CENTRAL PLAINS LATER SAT AND INTO SUN. THIS ENERGY COUPLED WITH A MORE SUBTLE SHORTWAVE ON ITS HEELS DROPPING DOWN FROM THE NORTHWEST TERRITORIES WILL PLAY A KEY ROLE IN THE EVOLUTION OF SURFACE LOW PRESSURE THAT IS CURRENTLY FORECAST TO DEVELOP OVER THE LOWER MO AND MID MS VALLEY REGION BY EARLY SUN BEFORE THEN AIMING EAST TOWARD THE OH VALLEY AND MID-ATLANTIC STATES SUN NIGHT AND MON. AS WAS THE CASE YESTERDAY...THE QUICKER AND MORE AMPLIFIED 12Z UKMET SUPPORTS SURFACE LOW DEVELOPMENT THAT IS STRONGER AND NORTH OF THE MODEL ENVELOPE. THE 12Z NAM AFTER ABOUT 36 HRS SUGGESTS A STRONGER/SHARPER SHORTWAVE TROUGH AND A LOW TRACK NORTH OF THE MULTI-MODEL CONSENSUS AS WELL...BUT NOT TO THE EXTENT OF THE UKMET. THE 09Z SREF MEAN GENERALLY FAVORS THE NAM DETERMINISTIC SOLUTION. THE 00Z GEM WAS NOTABLY FLATTER AND SUPPORTED ITS SURFACE LOW DEVELOPMENT DOWN TOWARD THE LOWER MS VALLEY AND THE GULF COAST STATES THROUGH THE PERIOD. HOWEVER...THE 12Z GEM HAS TRENDED WELL NORTH AND ACTUALLY IS VERY CLOSE TO THE WELL CLUSTERED 12Z GFS AND 12Z ECMWF SOLUTIONS. THE GEM/GFS AND ECMWF CLUSTER IS SUPPORTED BY THE LATEST GEFS MEAN AND ECENS MEAN AS WELL. WILL FAVOR A BLEND OF THE GFS AND ECMWF AS A RESULT...BUT CONFIDENCE WILL STILL REMAIN LIMITED FOR AT LEAST THIS CYCLE GIVEN THAT THERE ARE STILL FAIRLY SIGNIFICANT LATITUDINAL DIFFERENCES SEEN IN THE GUIDANCE ACROSS ESPECIALLY THE OH VALLEY AND MID-ATLANTIC REGIONS...WITH THE UKMET AND TO A LESSER EXTENT THE NAM FARTHER NORTH...AND THERE STILL BEING A BIT OF SCATTER WITHIN THE GEFS AND ECENS LOW PLOTS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON