Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 149 PM EST Wed Jan 22 2020 Valid Jan 22/1200 UTC thru Jan 26/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ ...Closed low off the Southeast coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ Preference: General Model Blend Confidence: Above average Closed vertically stacked low east of Florida will move eastward away from the coast through tonight. Subtle vorticity lobes rotating around the main closed feature will allow surface troughiness to persist towards the FL coast much of today, but any significant sensible weather impacts will remain offshore. While the NAM was most aggressive with lagging mid-level energy, it appears the latest 12Z NAM mass field is better clustered with the rest of the guidance resulting in similar surface trough axis placement. Therefore, opted for a general model blend for this system. ...Shortwave moving from New Mexico towards the Gulf Coast tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~ Preference: Gemeral Model Blend Confidence: Average Shortwave and accompanying weak surface low will dive southeast from New Mexico this morning to the Louisiana Gulf Coast tonight, before becoming absorbed in the large mid-level vortex developing on Thursday. The overall amplitude of both the mid-level features and at the surface is weak, and there is good agreement in the evolution among the various global models. The NAM has slowed its overall progression of this shortwave as compared to previous model runs. The ECMWF has good support from its ensembles, and the GFS has its own ensemble support, with some minor latitudinal differences separating the two camps. The CMC and UKMET is also in the middle of the EC/GFS/NAM clustering resulting in a general model blend. ...Trough moving onshore the Pacific Northwest Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~ Preference: Non-NAM/UKMET Confidence: Average A piece of energy shedding from a closed low near the Gulf of Alaska will eject eastward into the Pacific Northwest on Friday, accompanied by an intensifying, although still modest, Pacific Jet streak bringing heavy rainfall to the Northwest. The NAM continues to be exceptionally flat with its amplitude of this feature compared to the global consensus, likely due to a weaker anticyclonic jet streak and lagging more residual energy back into the main trough. The UKMET seems a bit too agressive with the magnitude of the shortwave, even after moving onshore. So while the timing looks reasonable compared to the clustering, the amplitude and strength of the shortwave will result in too high of QPF across northern California. Therefore, opted for a non-NAM/UKMET blend for this system. ...Binary interaction of closed lows Thursday-Saturday from the Plains into the OH Valley... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ Preference: 12Z NAM/UKMET/ECMWF, 12Z ECENS Confidence: Slightly below average Many details still need to be ironed out with two mid-level impulses moving through the Plains today into Thursday, and how they will interact through the rest of the week. Multiple features interacting create lower than usual confidence, but the leading shortwave moving through the northern Rockies should eventually become dominant and intense, especially late on riday night from the Missouri Valley and into the Ohio Valley. This should lead to strong cyclogenesis along a triple point across the Mid-Atlantic by Saturday, with this triple point extending from a primary surface low beneath the trailing upper trough over the Upper Midwest. Moisture drawn northward ahead of this system could be significant. When looking at the guidance, it appears as if the GFS struggles to handle a shortwave diving south through the Dakotas late Thursday through Friday. This will ultimately impact the evolution of this sytem and how far north the moisture gets pulled northward and eventually the progression of the surface low into the Mid-Atlantic region. In addition, the GFS has lacked run to run consistency which certianly has contributed to less confidence in the model. Therefore, the NAM/ECMWF/ECENS/UKMET are in good agreement through 60 hours, with the CMC too quick with the mid-level shortwave/trough axis. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Pagano