Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1250 PM EDT Thu May 02 2019 Valid May 02/1200 UTC thru May 06/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Southern stream trough/wave(s) crossing the South lifting northeast across the OH/TN Valleys... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS and 00z ECMWF/CMC blend Confidence: Average A series of southern stream shortwave impulses will continue to lift northeast from the southern Plains up across the OH/TN Valleys and into the Mid-Atlantic region going into the weekend. This will allow multiple waves of low pressure to lift up along a frontal zone draped across the region. While the initial wave (currently in AR) weakens and shears through New England, the 12z NAM continues to be over amplified, slowing a bit. The 00z UKMET also appears to be a bit more amplified and delays the frontal boundary through the Mid-Atlantic and New England by early Sat. The second wave, that is currently tracking out of Northern Old Mexico finds a favorable environment to enhance slightly across TX into the Mississippi River Valley by Sat, but the 12z NAM once again is a clear outlier supporting a very strong upscale response that it maintains through the Appalachians with associated deep surface inflection. The 12z GFS is a shade fast, typical of day 3 bias relative to the CMC/ECMWF, but in this setup, it is typical the EC/CMC may be a bit slow too. While the UKMET is more inline (middle-ground) with this wave in timing relative to other guidance making it more preferable, but the location (south) of the front due to a stronger but slower wave across the Mid-Atlantic makes it a bit more uncertain for a high inclusion. All in all, a 12z GFS and 00z ECMWF/CMC blend is preferred with potentially some UKMET if the boundary/QPF axis is shifted a bit further north through day 3. Given weak waves and the importance/placement of convection and its affects on the boundaries/waves confidence is only average in this blend. ...Low to mid-level trough impacting the FL Peninsula... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Average Tropical wave rounding the western side of Subtropical High continues fairly good continuity and overall guidance agreement. However, as the wave lifts into the northern stream, the over-amplified NAM deepens it and draws it further north. Thinking this may be a bit too much and would support a non-NAM blend at slightly above average confidence. ...Southern stream closed low approaching CA... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Closed low off the southwest US coast continues to advance under strong model agreement. There is a bit of model difference into late Sunday with the magnitude of stretching toward the deepening trof in the northern stream...affecting some locations across the Sierra Nevada. However, given the agreement it is difficult to discern a particular positive/negative trend that a general model blend will be a solid choice. Given the overall agreement, confidence remains above average ...Height falls traversing the northern Plains/Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS and 00z ECWMF/CMC blend Confidence: Slightly above average Broad vortex over NW Canada will shed some energy southwest into south central Canada by late Fri, under influence of strong anticyclonic jet streak out of S AK. The cyclone rapidly deepens and is fairly well agreed upon through Sat, but by Sunday, the 12z NAM has begun to open the circulation indicating greater elongation/stretching, opposed by the GFS/ECMWF and slightly slower CMC. The UKMET is a bit faster and while more compact than the NAM, it draws upstream energy to lead to larger spread in the lower levels. As such will favor a 12z GFS and 00z CMC/ECMWF blend. Confidence is slightly above average ...Digging trough across Northwest/Northern Rockies Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS and 00z ECMWF/CMC blend Confidence: Average to slightly below average Another AK jet streak and associated shortwave from the Pacific stream will undercut the larger scale weakening vortex over SW Canada by the end of the weekend. The 12z NAM was faster and very amplified in a fairly sizable shift in timing across the Southern Rockies by the end of the forecast period. The 12z GFS also showed some increased amplification, and given the orientation of the remaining polar vortex retrograding into the N Yukon, this does make some meteorological sense. Will incorporate some the 12z GFS to hint at this timing with the slower 00z ECMWF/CMC. All in all there is average confidence to slightly below average confidence in a 12z GFS and 00z ECMWF/CMC blend for this region on day 3. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina