Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 233 PM EDT Thu May 10 2018 Valid May 10/1200 UTC thru May 14/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave crossing the Mid-Atlantic through this evening... ...Cold front crossing the Northeast/Mid-Atlantic tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models bring a progressive and rather weak shortwave out of the OH/TN Valley region today and across the Mid-Atlantic region late this afternoon and evening. Meanwhile, a cold front will be gradually sweeping across the Northeast later today and down over the central Mid-Atlantic region tonight. Model mass field spread is minimal with these features and so a general model blend will be preferred. ...Low-amplitude/progressive shortwave crossing the OH Valley and northern Mid-Atlantic on Saturday... ...Weak surface wave traversing quasi-stationary frontal zone... ...Frontal placement over Mid-Atlantic on Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 12Z GFS and 12Z ECMWF Confidence: Average The guidance bring a progressive and low-amplitude shortwave east across the OH Valley and northern Mid-Atlantic during the day on Saturday which will foster a weak wave of low pressure along the same aforementioned front settling down into the Mid-Atlantic region tonight. This boundary will lift back up north on Friday and by Saturday will be oriented quasi-stationary from central OH east across south-central PA and through southern NJ ahead of this next wave. The 12Z NAM is just a tad stronger and slower with the impulse and with a slightly stronger surface wave versus the 12Z GFS and 12Z ECMWF. The 12Z UKMET is seen as being perhaps a tad north of these solutions, but the 12Z CMC came in rather close to the GFS/ECMWF camp. In the wake of this system, the models do allow the front to settle a bit farther south down across the Mid-Atlantic on Sunday, with the 12Z NAM dropping the front down across NC and the 12Z GFS, 12Z UKMET and 12Z ECMWF all focusing it over central to southeast VA. The 12Z CMC drops the front rather close to the VA/NC border. Based on the model clustering and ensemble output, a blend of the GFS and ECMWF will be preferred across the region with this front and the wave activity traversing it. ...Broad upper trough crossing the Northeast on Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in very good agreement with the details of these height falls, so a general model blend will be preferred. ...Broad upper low evolution over the West through the weekend... ...Surface lows over the Great Basin and lee of the Rockies... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend...with the closed low General model blend...with front/wave activity Confidence: Slightly above average An upper trough digging in across the Pacific Northwest today will drop southeast across the Great Basin by Friday and rather quickly amplify into a relatively broad upper low. The system should become near stationary over the Intermountain West through Sunday. Meanwhile, the models focus multiple areas of low pressure across the Great Basin in vicinity of a front dropping down through the interior of the West and also downstream in the lee of the Rockies out across the central Plains. Overall, the model spread is rather minimal with the larger scale details and with the wave activity. The 12Z NAM though did appear to be perhaps a little strong with its closed low later in the weekend over ID. Will prefer a non-NAM blend with the closed low evolution, but a general model blend will the details of the fronts over the Great Basin and central Plains, along with the surface wave. ...Broad upper trough over the Gulf of Mexico/FL Peninsula... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average A broad upper trough of low pressure will gradually move east across the Gulf of Mexico and toward the FL Peninsula over the next couple of days. Most of the models are in good agreement with the broader mass fields, but the 12Z CMC is a bit sharper with its mid level reflection over the FL Peninsula through the weekend. Will prefer a non-CMC blend at this point. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison