Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 111 PM EDT Tue Apr 09 2019 Valid Apr 09/1200 UTC thru Apr 13/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Preliminary Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Amplifying through Intermountain West by Wed spurring deep Plains cyclone, Wed into Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend but minimal weight on NAM Confidence: Slightly above average The NAM continues its trend of being on the north side of the generally small model envelope as the mid-level low center closes off across the Western High Plains. The GFS remains in remarkably good agreement with its run-to-run consistency, and by Wednesday night there is very good agreement in a closed mid-level low across Western KS, while the NAM remains north into NE. This is echoed in the surface low positions as well. The NAM has the strongest vorticity maxima rotating beneath the closed low, suggesting it may not even be in agreement with itself as this energy could pull the low center southward towards the general blend consensus. Despite this, a subtle NW and warm shift has been noted in thermal fields which suggests at least a small percentage of the NAM could be used thermally as the other guidance is trending towards that warmer solution across the Midwest. On day 1 the 00z/9 CMC/UKMET are a bit slow and broad with the upper feature, and should be used cautiously, but later on Tuesday the above preference is suggested. ...Great Lakes/New England (northern stream shortwaves)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average A series of shortwaves will interact across the Northeast. Although a general model blend can be used, the GFS/NAM/CMC appear to handle the shearing of the first two vorticity centers better as the flow becomes pinched ahead of a third closed impulse dropped around the upper low near 50N/50W. The 00z/9 ECMWF does not respond well to this increasing geostrophic flow and is likely too slow pushing the energy across Maine, while the 00z/9 UKMET is on the fast side of the model suite. ...Southeast (southern stream closed low)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Closed low clearly evident on WV imagery this morning across MS will drift eastward to be off the Southeast coast Wednesday morning. The UKMET is a bit weaker and then fast ejecting this feature, but otherwise the remaining guidance is in generally good agreement. ...Wed/Thurs shortwave entering Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 12Z/NAM or 00Z/CMC blend Confidence: Average A shortwave diving from the Gulf of Alaska will approach the Pacific Northwest Thursday. As this occurs it will likely shear out to the south in response to ridging developing across S Central Canada north of the significant cyclone in the middle United States. The guidance is in reasonable agreement diving this feature inland from the Pacific Coast beyond this forecast period, but the general trend has been for a slower evolution of this occurrence. The NAM seems to drive the trough too strongly into the ridge while the 00Z/9 CMC is an outlier with the amplification of the ridge across the Pacific producing a shortwave wavelength and leaving the main vorticity energy too far to the west. For these reasons a 12Z GFS/00Z ECMWF/00Z UKMET is preferred with average confidence. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Weiss