Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1201 AM EST Sun Feb 09 2020 Valid Feb 09/0000 UTC thru Feb 12/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Digging trough over the Great Basin/Southwest on Sunday... ...Energy ejecting east toward the southern Plains by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z ECMWF/ECENS and 18Z GEFS Confidence: Slightly above average A split in the upper flow developing across the Western U.S. will allow for a substantial amount of shortwave energy to dig southward over the Great Basin and into the Southwest U.S. on Sunday around the eastern side of a strong deep layer ridge developing offshore of the the West Coast. All of the guidance shows a well-defined and fairly robust upper low developing and dropping south through California by Sunday evening. On Monday, the energy is expected to begin moving east, and by Tuesday should be ejecting out across the southern Plains. The 00Z GFS has trended slower with its height fall evolution with this system compared to its last 12 to 24 hours worth of cycles, and is getting closer to the non-NCEP model consensus. However, it still ultimately ends up being the most progressive solution after about 48 hours as the height falls eject out across the southern Plains Tuesday through early Wednesday and is still an outlier as a result. The 00Z NAM has made a dramatic shift in timing and is much faster than 24 hours ago with its height fall timing, with the NAM now overall a little slower than the GFS, but faster than the non-NCEP model suite as the energy reaches the southern Plains. Of the non-NCEP models, the 12Z ECMWF is a little faster than the 12Z UKMET/CMC solutions. Ensemble clustering at this point from the 18Z GEFS and 12Z ECENS suites strongly favor the 12Z ECMWF upper trough evolution and thus a blend of these solutions will be preferred at this time. ...Northern stream troughing over the northern Plains by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A portion of the upper trough currently over the Northwest U.S. will quickly eject downstream across the northern Rockies, northern Plains and toward the Upper Midwest going through Sunday. On Monday, the energy should be shearing across the Great Lakes and Northeast. The model spread is minimal, so a general model blend will be preferred with this energy. ...Northern stream trough/front over the Midwest by Tuesday... ...Energy crossing the Great Lakes/Northeast on Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Above average The guidance indicates a northern stream trough and attendant cold front dropping southeast from Canada and crossing the northern Plains late Monday and arriving across the Midwest on Tuesday. On Wednesday, this energy will cross the Great Lakes, OH Valley and the Northeast. The models overall show good agreement with this system, with some exception to the 12Z UKMET which becomes a little deeper than the remaining model guidance as the energy advances toward the Northeast. So, while model spread is modest, will prefer a non-UKMET blend with this feature. ...Quasi-stationary front over the Gulf Coast states by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend...12Z ECMWF/ECENS and 18Z GEFS weighted Confidence: Average The models all agree in placing a quasi-stationary front across the Gulf Coast states by Tuesday, which is expected to play a key role in what is likely to be a multi-day excessive rainfall event (see latest QPFERD) for the region. The boundary should remain draped across the region through Wednesday with some southward drift as a weak surface wave exits through the Mid-Atlantic region. The model spread with the placement of the front is modest with the global models, but the 00Z NAM is seen as placing its boundary a bit farther north relative to the lower MS and TN Valley which results in a northward displacement of its heavier QPF swath compared to the global models. The slower trend of the 00Z GFS with its upstream height fall evolution across the Southwest and southern Plains favors its farther south frontal placement in concert with the non-NCEP suite of guidance. The ejecting height falls across the southern Plains Tuesday and Wednesday is expected to foster a highly divergent flow pattern aloft across the lower MS Valley and portions of the TN Valley in vicinity of the front and will be one of several key ingredients coming together for a significant multi-day rainfall event. Additionally, there is expected to be an area of low pressure that develops near the upper southeast TX coastal plain by early Wednesday in response to the stronger height falls approaching from the west. The 00Z GFS is seen as being a tad too strong with this development at least through early Wednesday. The model preference at this time for the lower MS Valley/TN Valley and entire Gulf Coast region is weighted toward a non-NAM consensus given concerns about the NAM frontal placement, but with strong weighting toward the ECMWF and the GEFS/ECENS means given the upstream preferences over the Southwest U.S. ...Shortwave crossing British Columbia Monday night... ...Energy dropping southeast across the northern Rockies Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS and 12Z ECMWF Confidence: Average Large uncertainty still exists with a shortwave that will advance east across the Gulf of AK on Monday and then very quickly southeast across British Columbia Monday night. The energy is expected to slide down across the northern Rockies on Tuesday within strong deep layer northwesterly flow. The 00Z NAM by far is a very slow outlier with this progression of this feature. The 12Z CMC is on the slow side as well, but the 00Z GFS/12Z UKMET and 12Z ECMWF solutions are all more progressive and have much better ensemble support from the 18Z GEFS/12Z ECENS suites. The UKMET though overall appears too flat, so at this point, a blend of the GFS and ECMWF will be preferred. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison