Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1239 AM EDT Sat Apr 25 2020 Valid Apr 25/0000 UTC thru Apr 28/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Preliminary Evaluation with NAM/GFS Model Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Shortwave and associated developing low pressure moving from the Midwest through the Northeast ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: ECMWF/ECENS/UKMET/NAM through D2, ECMWF/ECENS D3. Confidence: Slightly below average A shortwave moving through the broad cyclonic flow across the east will dig across the TN Valley Saturday before interacting with several other impulses to amplify across the Mid-Atlantic/Northeast. The lead shortwave is likely to weaken as a secondary energy digs into the mean trough and becomes dominant. This will cause the surface low across the OH Valley to transfer towards the Tidewater of VA as new cyclogenesis, which will then lift E/NE through Monday into the Gulf of Maine. Through 48 hours, the mass fields, with the exception of the CMC, are in generally good agreement. However, in the 48-72 hours time frame, the NAM becomes much deeper with the closed low and degree of negative tilt from Ontario into Maine. The GFS/ECMWF and its ensembles are in generally good agreement in the upper trough Monday/Monday night as it closes off east of Massachusetts, but timing and intensity differences of the coupled jet structure lead to significant placement discrepancy with the surface low. The GFS is a bit slower and west of the ECMWF, which is slower than the CMC. The GFS is also warmer with its thermal structure, which seems unlikely in the presence of cold Canadian high pressure to the north. The ECMWF being in the middle, along with its good ensemble support, lends credence to this solution, and a heavy weight of ECMWF/ECENS is preferred in the blend. The UKMET and NAM are also usable, especially through 60 hours, but should have less weight on D3. Trough axis affecting the Northwest into the Upper Midwest through Monday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Average A long wave trough axis anchored along the Gulf of Alaska will help to pivot mid-level energy east into the west coast of Canada. This fairly weak trough axis will traverse the Canadian Rockies through Sunday, moving into Manitoba and Ontario by Monday. The impact of this trough axis will be minimal across the northern Rockies and Plains until it interacts with a bit more moisture, eventually becoming negativity tilted (strong forcing for ascent) across the Upper Midwest and Great Lakes region. The models are in fairly decent agreement, though there are some timing and amplitude differences. These variabilities are still within the model guidance clustering with only modest impacts to QPF/thermal difference overall. Shortwave energy affecting the Pacific Northwest on Monday into the Plains by Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z GEFS/12Z EC/ECENS Confidence: Average A second Pacific shortwave will translate along the base of the consolidating closed low over the Gulf of AK. This wave is drawn more northward with only the base rapidly swinging more negative through Vancouver Island late Sunday into early Monday. The trailing cold front and moisture plume press across the Coastal Range and into the Northern US Rockies. The timing and amplitude represented by the models do vary with the GFS a bit too fast and the UKMET entirely too slow based on the spaghetti plots. The 00Z NAM also remains a fairly dry outlier at this point as well. As the system continues to track east, the mass field difference remain consistent and do not diverge greatly. However, it is apparent by the end of Day 3 (late Monday) that the 00Z NAM is more progressive with the energy interacting with the trough off the East Coast. In addition, the 12Z UKMET was too slow and the CMC too inconsistent with its amplitude. Based on QPF alone, there are some wild differences that are not as tied to the typical mass field structure but rather the impulses that ride within the mid-levels. Regardless, based on the mass fields alone, felt better consensus among the 00Z GFS, 12Z EC and their respective ensemble means. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Pagano/Weiss