Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1257 AM EDT Wed Jul 24 2019 Valid Jul 24/0000 UTC thru Jul 27/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Preliminary Model Evaluation, Including Preference and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Pacific Northwest into the Northern Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Slightly Above average Two distinct shortwaves will drive cold fronts through the NW into the Northern Plains this forecast period. The first, Wednesday, will move onto the Washington coast before lifting into Southern Canada to continue its eastward trajectory. While the primary forcing and shortwave will remain north of the border, the cold front crossing the northern tier of the CONUS will bring some QPF to the region. The second impulse, Friday, will follow a similar trajectory. While the guidance is in good agreement in the large scale evolution of these impulses shedding from a closed low to the north, the CMC is a bit fast compared to the global consensus, which is in otherwise very good agreement. ...Southwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Slightly above average A mid-level ridge expanding across the Four Corners will be the primary synoptic scale feature of concern. While the global suite is in good agreement with placement and timing of the ridge, there are some difference in the intensity, most notably with the UKMET being the strongest/most expansive. Additionally, the guidance shunts a shortwave around the southern periphery of the ridge and off the California coast, before bringing it back onshore Northern California Friday. There are, again, intensity differences with this feature which may have impact on QPF due to the monsoonal moisture in place. However, a general model blend still should suffice for now as these small scale features are tough to resolve on synoptic time scales, and since all the guidance has some semblance of this occurring a blend with the means should somewhat limit the differences noted for now. ...Remainder of the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The global suite is in good agreement with a longwave trough persisting along the coast, being reinforced by a secondary shortwave moving through the OH VLY/Mid-Atlantic Thursday. The biggest question mark across the east involves potential low pressure development on the tail end of the weakening cold front across the Gulf of Mexico by day 3. All guidance shows some vorticity spinning up across the Gulf, but thereafter the intensity and position waver considerably. There appears to be enough model agreement to support at least a mid-level wave in the Gulf Friday, but for now will compromise with a general model blend/means to wash out the deterministic differences. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Weiss