Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1108 AM EST Sun Feb 16 2020 Valid Feb 16/1200 UTC thru Feb 20/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model evaluation with preferences & confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Great Lakes/Gulf through East Coast system(s)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 06z GFS and 00z ECMWF/CMC blend Confidence: Slightly above average Broad global cyclonic flow currently exist across the CONUS with a highly sheared shortwave moving through Old Mexico into the Gulf Region sparking some disturbed weather across the Gulf Coast that will shift into the Southeast by Monday. Guidance is fairly solid in the remaining evolution of this pattern in advance of still broad but sharpening of a trof across the North Central Plains into the Snake River Plain by Monday morning. The leading edge of the height-falls in combination with a digging Arctic shortwave will amplify through the Great Lakes Monday into Tuesday. There remains modest model spread mainly in the spacing and timing of these waves between each other. The 00z UKMET trended much weaker with the lead Pacific energy, while the NAM appears to go to the opposite extreme though the resultant surface wave is congruent with the remaining guidance/ensemble suite it is a bit too strong with the surface wave and moisture flux into the system to be acceptable in a blend at this time (this also reduces convergence/QPF across the south as a result). The 12z GFS trended a bit faster with the shortwave emerging out of the Northern Rockies, which tracks the surface wave a bit too fast through the Great Lakes into the north-east. The 06z run is more in line with the flatter CMC and slightly slower ECMWF which appear to be the normal biases, once blended fit nicely toward verification...so will support a 06z GFS/ECMWF/CMC blend with this system crossing the Great Lakes through the South and East Coast from late Monday through the end of the forecast period. ...Developing positive tilt Western trof with winter precip in Southern High Plains Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS and 00z CMC/UKMET blend Confidence: Average Further west, as the tail end of the initial shortwave swings out of the Rockies into the Great Lakes on Tuesday; reinforcing shortwave energy over-tops the amplifying Pacific Ridge dropping into the developing larger scale trof over the West by Wed. This wave, in combination with emerging shortwave energy out of the east-central Pacific (under the Pacific ridge, as well as lingering frontal zone across TX into the Southern High Plains will set up the next system with the potential for wintry problems by late Wed into Thursday. Here, there is much more substantial spread, keying on the timing of the the central Pacific shortwave/moisture transport through the Desert Southwest into the area of concern. Here the ECMWF shows the greatest timing differences being quite slow with the wave, mainly as it lost some energy to the northern stream along the western side of the developing Pacific ridge, which delays the energy advancing as well as dropping the focus further south. So as the shortwave from the northern stream drops, it does not phase/amplify delaying its ejection into the Plains. The 12z GFS and 00z CMC are much faster with this shortwave capture and start to break out increased QPF across the southern High Plains/TX by 00z Thursday. Even though it is typical of the GFS to have a fast bias, the similarity in timing presented by the 00z CMC and UKMET suggest less or no influence of the ECMWF in a preferred blend at this time. While not favored due to typical deeper/over-amplified solution through the West; the 12z NAM is also faster like the GFS/CMC with this energy, providing some confidence, as a stronger more amplified system should be slower. Confidence in average in a 12z GFS and 00z CMC/UKMET blend for this feature. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina