Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 213 PM EST Tue Jan 21 2020 Valid Jan 21/1200 UTC thru Jan 25/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with latest Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ ...Closed low off the Southeast Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ Preference: Non-NAM blend...for height fall timing/low placement 12Z NAM/NAM-conest...for surface low strength Confidence: Slightly above average The upper low dropping across the Southeast will continue east-southeast and offshore tonight before crossing just north of the Bahamas on Wednesday. Relatively strong cyclogenesis will occur over the next 12 to 24 hours, with low pressure then pulling east and well away from the U.S. by later Wednesday and Thursday. The 12Z NAM appears to be tucking its low center development a bit too far to the west and southwest (closer to the northern Bahamas) through 36 hours as the global models have come into a strong and consolidated agreement on a solution that is farther east by comparison. However, the global models may be collectively a tad too weak with the low center given the degree of sharp height falls/PV anomaly strength (suggested in Airmass RGB imagery) and potential for added latent heat/convective processes fostering lower surface pressures. The hires models (HREF) support the global model timing/positioning through 36 hours, and tend to be a little stronger than the global models but still may not even be strong enough. The relatively stronger NAM/NAM-conest strength appears more plausible, but with a global model blend for placement. ...Subtropical shortwave over the Southwest... ...Energy riding northeast toward the Upper Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ Preference: Non-NAM blend Confidence: Above average The models take a well-defined subtropical stream shortwave trough and vort center over AZ quickly off to the east-northeast tonight which will bring it over the central High Plains by early Wednesday. The energy will then lift up toward the Upper Midwest by late Wednesday while gradually weakening, and the remnants of this system should ultimately become absorbed by the stronger northern stream height falls amplifying out across the High Plains by Wednesday night. The 12Z NAM tends to hang onto a stronger vort center/700 mb reflection compared to the hires model suite (HREF) and the global models as the system rides up toward the Upper Midwest. A non-NAM blend is preferred for the mass fields with this system. ...Current upper low/trough crossing into the Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ Preference: General model blend Confidence: Above average The deep layer closed low just offshore the Pacific Northwest will weaken into a progressive trough as it crosses British Columbia through tonight, but is forecast to then reorganize and deepen over southern Alberta on Wednesday before dropping southeast across the northern High Plains. At least through Wednesday, the models are in good agreement with this system. ...Binary interaction of closed lows over the Plains on Thursday... ...Consolidated deep layer closed low over the OH Valley Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ Preference: Non-NAM blend... on Thursday GFS/CMC/ECMWF blend...on Friday Confidence: Slightly below average Guidance continues to suggest binary interaction of closed lows across the Plains on Thursday, with one closed low dropping southeast across the northern Plains, and another developing farther south over the central Plains/lower MO Valley by late Thursday. At least through Thursday, the 12Z NAM appears to be a deep outlier with the collective mass field evolution. By early Friday, the two closed low begin to consolidate and move through the OH Valley as one area of surface low pressure deepens over the Midwest, and a second one develops over the lower MS Valley and moves east across the Gulf Coast states. The 12Z GFS and 12Z NAM are farther north with the merged system relative to the 12Z non-NCEP solutions, with the NAM notably slower/deeper. Of the non-NCEP models, the UKMET is still the farthest south solution. The 12Z GEFS mean is actually a tad north of the GFS, with the 12Z CMCE and 00Z ECENS a little farther south, but not to the extent of the UKMET. The deterministic CMC/ECMWF solutions are well supported by their respective ensemble means. Based on the latest model spread/clustering, the stronger/slower NAM and the farther south UKMET appear to be the bigger outliers. The CMCE/ECENS suites tend to give better support to a consensus of the GFS/CMC and ECMWF solutions, as the GEFS suite may be overall too far north. So, a blend of the GFS/CMC and ECMWF will be preferred at this point for the Friday time frame, with a non-NAM blend for Thursday as the energy initially evolves over the Plains. ...Weak shortwave impulse skirting Vancouver Island early Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ Preference: Non-UKMET blend Confidence: Above average The models bring a highly progressive and low-amplitude shortwave embedded in deep layer southwest flow toward Vancouver Island early Thursday. The energy should clip at least northwest WA before weakening as it moves across mainland British Columbia. The 12Z UKMET appears to be a deeper outlier with the system, with the remaining guidance well clustered. Thus, a non-UKMET blend will be preferred at this point. ...Shortwave crossing the Pacific Northwest on Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ Preference: Blend of the 12Z GFS/CMC/ECMWF Confidence: Above average The models bring a progressive, low-amplitude shortwave in across the Pacific Northwest on Friday. The 12Z UKMET appears to be too progressive, with the 12Z NAM likely being too slow. The 12Z GFS/CMC/ECMWF solutions are clustered in between and more closely represent the model consensus, so a blend of these will be preferred. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison