Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 202 PM EST Sun Feb 25 2018 Valid Feb 25/1200 UTC thru Mar 01/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation...with latest model preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep surface low lifting northeast across Ontario today... ...Trailing cold front sweeping through the Eastern U.S... ...Surface wave developing just offshore southern New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models take a deep surface low away from the upper Great Lakes region today and up across Ontario. This low will advance up across Quebec tonight through early Monday. A trailing cold front meanwhile will be sweeping across the Eastern U.S., although the guidance agrees in hanging up the front a bit along the central and western Gulf Coast region. Additionally, there will a wave of low pressure developing just offshore southern New England later today that will lift northeast up toward the Canadian maritimes on Monday. All of the models show good agreement generally with the mass field evolution of these features and so a general model blend will be preferred. ...Shortwave ejecting across the Four Corners/High Plains... ...Ejecting east across the Mississippi/Ohio Valleys on Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A shortwave will cross the Four Corners region today and then rapidly eject east toward the Mississippi Valley and Ohio Valley on Monday. The energy will then cross parts of the Mid-Atlantic and Northeast by Monday night. The models are in good agreement with their mass field details of this system and as a result a general model blend will be preferred. ...Shortwave arriving over the Pacific Northwest today... ...Closed low evolution over the Southwest by Monday... ...Advancing east toward the southern High Plains by Wednesday... ...Surface low development over the central Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 12Z ECMWF Confidence: Average The next in a series of western North American shortwaves will dig into the Pacific Northwest today along with a progressive cold front. The guidance is in good agreement with this energy digging sharply south down across California on Monday which will lead to the development of a compact and rather robust mid level low center that drops down along the coast of central and southern California before then pivoting east over areas of the Desert Southwest by Tuesday. The guidance is in good agreement on the mass field evolution of this system through Monday, but then begins to show spread thereafter over broader areas of the Southwest and toward the southern High Plains. The 12Z NAM becomes a slower and deeper outlier as the height falls cross especially southern California and areas farther east through Tuesday and Wednesday reaching toward the southern High Plains. The 12Z GFS is the most progressive solution, but also now has strong support from the 12Z ECMWF which trended faster with this cycle. The 12Z UKMET and 12Z CMC are just a little slower than the GFS and ECMWF, but it was noted that the CMC also becomes rather weak and flat as the energy reaches the southern Plains which results in a more progressive surface wave evolution. As the energy approaches the southern High Plains, all of the guidance agrees on developing low pressure over the central Plains along a front. Based on the latest model trends and clustering, a blend of the GFS and ECMWF will be preferred surface and aloft which has good support from the latest GEFS mean. ...Shortwaves over the northern Rockies/Plains through Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models bring another northern stream shortwave down from western Canada and across the northern Rockies Monday and Tuesday, followed by another one through Wednesday with all of the energy ultimately ejecting east out across the northern Plains. Spread with the initial shortwave is quite minimal, but there is some modest spread mainly with the depth of the second shortwave by Wednesday as it traverses the northern Plains. Will prefer a general model blend at this time with both shortwaves. ...Strong upper trough offshore the Pacific Northwest Wednesday... ...Strengthening surface low approaching Vancouver Island... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS, 12Z UKMET and 12Z ECMWF Confidence: Average The guidance agrees in dropping another shortwave trough south from the Gulf of Alaska on Tuesday which amplifies sharply into a strong and larger scale trough near British Columbia and approaching the Pacific Northwest by Wednesday. A deepening surface low will be approaching Vancouver Island with a trailing cold focused offshore the Washington and Oregon coastal ranges by the end of the period. The stronger model clustering at this point resides with the 12Z GFS, 12Z UKMET and 12Z ECMWF which have better ensemble support as well. The 12Z NAM tends to be less robust with the height falls/surface low deepening, and the 12Z CMC now appears to be the model that is a bit too slow. Will prefer a GFS/UKMET/ECMWF blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison