Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1110 AM EST Sun Feb 11 2018 Valid Feb 11/1200 UTC thru Feb 15/0000 UTC ...See NOUS42 KWNO (ADMNFD) for status of the upper air ingest... ...12Z Model Evaluation with Preliminary Preferences/Confidence... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Departing Low Pressure System Moving Quickly Northeast to near Labrador by Monday Afternoon... ...Trailing Cold Front Largely Exiting the Eastern Seaboard by Monday Night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM Blend Confidence: Above Average Over the next 24 hours, model mass fields are in excellent agreement overall, and a general model blend is preferred with high confidence. However, as the surface high builds into the Great Lakes in the wake of the departing low, the 12Z NAM is far more expansive with the high than any other models across much of the eastern CONUS and Gulf of Mexico, with MSLP as much as 2-3mb higher than the consensus of other models. The preference, therefore, is to exclude the NAM from the blend for this system, despite fairly good agreement in the first 12-24 hours. ...Sharply Digging Shortwave Trough Along the West Coast Amplifying Into a Large, Positive-Tilt Trough over the Western US by Tuesday... ...Surface Low in the Great Basin Monday-Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 12Z GFS, 00Z ECMWF, UKMET Confidence: Average As the shortwave sharply digs along the Pacific Northwest coast today, setting up further trough amplification tomorrow and the development of a closed low on Tuesday, model agreement is fairly good overall. Differences in the model mass fields mostly emerge on Wednesday, and relate to how fast the trough begins to deamplify and eject east into the Western US. Increasing height falls in the Northwest as the next digging wave arrives will contribute, but given the size of the trough and associated closed low near the California coast, the preference is to trend to the slower model solutions. In this case that means a preference toward the GFS, ECMWF and UKMET. The 12Z NAM and 00Z CMC deamplify the trough and eject it east faster, but the tendency for large, closed lows aloft is for them to devolve slowly. The GEFS and ECMWF Ensemble means are also reasonably close to the GFS and ECMWF to lend more robust support to the slower solution. Additional differences exist between the GFS, ECMWF, and UKMET in the placement and details with the upper level low, but confidence is not high enough in any one scenario for it to be clearly preferred. ...Southward Shift in Northern Stream Jet over Canada Tuesday-Wednesday with Next Shot of Arctic Air... ...Shortwave Digging into the Pacific Northwest Tuesday Night... ...Additional Shortwaves Ejecting Across the Northern Tier of States as Jets Begin to Phase... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 00Z ECMWF, EC ENS mean Confidence: Slightly Below Average Models generally show a similar amplitude and wavelength of this digging wave, and thus the primary differences appear to be related to timing. The 00Z CMC appears to be the fastest, while the 12Z GFS appears to be the slowest. The ensemble means (GEFS, ECMWF, and CMC) lie in the middle, and are closest to the the 00Z ECMWF (and secondarily the 00Z UKMET and 12Z NAM). This also translates to similar timing differences with the Arctic cold front that will be pushing south through the Canadian Prairies on Wednesday. The 12Z GFS is also slowest there, with a surface low position generally to the northeast of other available models. The 00Z ECMWF has the best support from other global models, and is very consistent with the positioning of synoptic features with its ensemble mean. Therefore, the preference is for a blend of the 00Z ECMWF and 00Z ECMWF Ensemble Mean. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Lamers