Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 145 AM EST Thu Feb 06 2020 Valid Feb 06/0000 UTC thru Feb 09/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Latest Model Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Full latitude trough impacting the Central/Eastern U.S... ...Embedded vigorous shortwave trough lifting northeast... ...Consolidating lows from the TN Valley to the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Above average A strong full latitude trough will continue to advance east through the central and eastern U.S. going through the end of the week. This will be facilitated by a vigorous shortwave lifting out of the base of the trough which the latest model guidance agrees will lift across the lower MS Valley on Thursday, cross the TN Valley and southern Appalachians Thursday night, and then eject northeast across the Mid-Atlantic and Northeast on Friday. This will drive multiple waves of surface low pressure along a strong cold front initially draped from the TN Valley down to the central Gulf Coast. The guidance strongly agrees in low pressure consolidating and deepening over the central Mid-Atlantic region by early Friday and then lifting northeast through southern and eastern New England by Friday evening as a trailing cold front then sweeps off the East Coast. The 00Z GFS is seen as being a tad faster and farther north with this consolidating surface low pressure and related track. The non-GFS deterministic suite of guidance and most of the 00Z HREF suite of guidance (NAM conest, ARW2, and NMMB) all favor a modestly slower and farther south track by comparison with rather good clustering. The 00Z ARW though does tend to favor the GFS track a bit more, but not to quite the same extent. Based on the majority consensus, and ensemble clustering, a non-GFS blend will be preferred for the smaller and larger scale details of this system. ...Shortwave crossing the Plains and OH Valley by Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average Strong flow will continue to over-top a broad but dominant eastern Pacific/West Coast ridge axis through the remainder of the week. This will allow subtle shortwave energy cresting the ridge to dive southeast across the central/northern Plains on Friday and then toward the OH Valley on Saturday. A weak area of surface low pressure and a front will be associated with this energy. The 00Z NAM appears to be somewhat of a slower and deeper outlier with this system, so will prefer a non-NAM blend with this system. ...Deep trough/cyclone crossing the Pacific Northwest Saturday... ...Separating energy over the Great Basin by Sunday... ...Downstream troughing over the northern Plains by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/CMC/ECMWF Confidence: Slightly above average A strong closed low will advance through the Aleutian islands and AK peninsula by Friday, with strong shortwave energy digging into the western Gulf of AK. This energy will then dive southeast toward British Columbia and then across the Pacific Northwest on Saturday. By early Sunday, a portion of this original energy will quickly eject downstream across the northern Rockies and over the northern Plains. Meanwhile, a split in the upper flow will allow for a substantial amount of energy to then dig southward over the Great Basin around the eastern side of a reorganizing and strengthening ridge offshore the West Coast. The models are in rather good agreement as the system crosses through the Gulf of AK through Friday, but the 00Z NAM tends to be perhaps just a tad slower than the global model consensus as the system sweeps through the Pacific Northwest. The 00Z NAM also becomes a deeper outlier with the energy by early Sunday that crosses through the northern Plains, and by being deeper, it ends up with a corresponding surface low track north of all of the global models. Meanwhile, with the energy lagging back over the Great Basin, the 00Z UKMET is a bit of a progressive outlier with the remaining models rather well clustered. Therefore, will favor a blend of the 00Z GFS, 00Z CMC and 00Z ECMWF to comprehensively account for both streams late in the period which is well supported by the latest ensemble means. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison