Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 334 AM EDT Mon Sep 16 2019 Valid Sep 16/0000 UTC thru Sep 19/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep Latitude Western Trof Entering the West; Reinforced by Closed Low Late Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Slightly above average 07Z Update: Earlier issues with the 12Z CMC seem to have been resolved with the 00Z run, such that a general model blend is preferred. ---previous discussion--- Fairly good agreement in the latest model guidance that a pair of shortwaves will work through the Pacific Northwest and into the northern Rockies and northern Plains during the forecast period. First shortwave that is currently moving onshore the west coast will rotate quickly into Montana and North Dakota by Day 2. Here, earlier discrepancies between the UKMET and the rest of the guidance with respect to the speed have mostly been resolved. The UKMET might remain a bit faster than the others, but a general model blend should provide a reasonable solution. The secondary shortwave that then drops into the Pacific Northwest by Day 2/3 is fairly agreed on. The one exception would be the 12Z CMC, which is too far south and amplified with the closed low, as it takes it into northern California. Meanwhile, the rest of the guidance is north across Oregon and more positively titled. ...Southwest Shortwave, Moving through Central High Plains into Northern Plains/MN by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 48 hours; non-GFS through 84 hours Confidence: Slightly above average 07Z Update: With the initial shortwave rounding the base of the trough on Day 2, agreement is pretty good with the latest model guidance. As the shortwave approaches the northern Plains, the GFS comes out too fast and while the UKMET and NAM are a bit too deep, its position agrees well with the 00Z ECMWF/CMC. As such, less weight is given to the GFS for Day 3. ---previous discussion--- Weak shortwave over the Four Corners region currently seen in water vapor imagery will continue to drift north/northeast over the forecast period and gradually become absorbed into the large scale troughing over the western US. The shortwave is expected to reach the central Plains late Monday and then into the northern Plains and Upper Midwest by Tuesday. The various deterministic models offer fairly similar solutions with just slightly varying degrees of strength and timing (CMC a bit fast; ECMWF slower/west). Overall, a general model blend is preferred. ...Gulf of Mexico Tropical Wave... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 2/3rd UKMET, 1/3rd GFS blend Confidence: Average to Slightly Below Average Guidance has come into better agreement that a weak surface wave moving westward over the central/western Gulf of Mexico will gradually take on better organization in the next few days as it approaches the Texas Gulf Coast. The system is expected to produce locally heavy rainfall somewhere along the coast by Day 3. Guidance has some latitudinal differences but for now, a consensus of the GFS and UKMET (with more inclusion of the UKMET by Day 3) is preferred. Forecast confidence is average at first, then drops to slightly below average by Day 3. ...Hurricane Humberto... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Official NHC Forecast Best Proxy: GFS/ECMWF Confidence: Below Average 07Z Update: The latest ECMWF, along with the GFS, are the best proxies for the latest official NHC track. The UKMET and NAM continue to be too fast and the CMC, while not bad in the first 24-36 hours, is considerably slower and to the right of the track beyond that period. ---previous discussion--- Hurricane Humberto continues to strengthen given warm waters and favorable environmental conditions. Its slow motion has taken a gradual north/northeast direction and this is expected over the next several days. The latest guidance is in reasonable agreement with the official NHC advisory track through about 24-36 hours, but beyond that, there is sizable spread in the latest model guidance. The NAM and UKMET are the faster solutions, as Humberto gets picked up in the approaching mid-latitude trough earlier. Meanwhile, the CMC/ECMWF stall the system much longer and therefore are the slowest and further south solutions by Day 3. For this cycle, the GFS is the best proxy for the track through the entire forecast period, although there remains some deviations from the latest official NHC track. In general, forecast confidence drops off considerably beyond 36-48 hours. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Taylor