Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1236 PM EDT Sun Mar 22 2020 Valid Mar 22/1200 UTC thru Mar 26/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Phasing streams today across Central US, building toward Northeast Cyclone late Mon/Tues ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z CMC/ECENS mean/UKMET/ECMWF blend with some NAM through 24.00z Confidence: Average to slightly below average GOES-WV suite depict a short-wave across the southern MO valley continuing an ENE trajectory, while the northern stream shows a mature compact low in Boreal Canada, with the nose of shortwave energy starting to descend along the NW periphery. These systems (dominated by the southern stream) will continue to advance toward the east coast, supporting a coastal low developing off the NJ coast sliding near the Benchmark and southeast of Nova Scotia from late Monday through late Tuesday. The trends continue to shift toward a more phased and mature cyclone, first hinted by the NAM a few days ago, with only the GFS and GEFS solutions continuing to be well south with much less northern stream influence, though the 12z GFS is starting to show some hints toward a stronger Commahead/western TROWAL (though also remain very warm, in line with this winter's negative bias). The 12z NAM however, depicts the strongest northern stream influence, tightening the overall gradient and without significant downstream blocking, is very rapid to accelerate and not support a stronger system (quite atypical). It is supported by the 00z CMCE suite but lesser so the 00z operational model which seems to be middle ground between the faster NAM and the slower/deeper wound up UKMET and ECMWF. The 00z ECENS mean, suggests a split in ECENS solutions but favoring a faster, more progressive than the operational, close to the CMC. Though both the 00z UKMET/ECMWF show good continuity. Given lower predictability of phasing stream systems, especially with mesoscale introduced latent heat release (spring-time magnitudes) this makes the uncertainty still quite high to solidly choose one camp over another, so will hedge toward a 00z CMC/ECENS mean focused blend with some UKMET/ECMWF operational blended in at this time. Some NAM may be introduced, especially early on Monday/Tuesday but trending away as the wave continues to accelerate away from the tighter clustering. Closed Low entering SoCal today, opening and rapidly crossing the CONUS: Southwest/Mon, Plains/Mid-MS Tues, Ohio Valley/Mid-Atlantic Wed ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z NAM/NAM-Conest and 00z ECENS/UKMET/ECMWF blend Confidence: Average GOES-W WV shows mature closed low just northeast of 30N130W, already showing signs of elongating/shearing into progressively increasing zonal flow that will dominate from Baja California to the East Coast though the first part of the week. By late Monday, the smaller but compact shortwave has flattened in the flow, but the CMC is already starting to lag the consensus, and is quickly removed from the preference. The 12z GFS, may have some latitudinal differences due to issues downstream from the prior system, and while it is better tempered than the 06z run and looks more in phase mass wise with the remaining guidance through the central US into he Ohio Valley; it shows a northward bias in the QPF, focusing on the deformation zone/elevated frontal boundary which is not heavily preferred given the overall pattern and transition to lower rooted convection in the early spring. The 12z NAM shows some similar northward bias, but slightly southward focus for the boundary/mass fields, though the NAM-Conest appears a better result for QPF than the operational. The 00z ECMWF is quite uncharacteristically fast and oddly south in the cluster to have tremendous confidence in its QPF axis too, but the mass fields are stronger agreed upon with the remaining UKMET, which has solid continuity and central position in the overall suite. As the system transitions to across the Appalachians supporting another East Coast cyclone, the overall cluster tightens as the faster UKMET/ECMWF/NAM solutions slow, and the CMC/GFS/GEFS pick up pace. Overall, will continue to keep with the preference from the MS to OH valleys into the east coast by the end of day 3 focused on a 00z UKMET/ECMWF and 12z NAM blend (though QPF blend is going to have other hi-res CAM influences initially trending toward ECENS position/timing over operational. Fast moving, mesoscale influence leads to lower than normal predictability, though the mass field clustering is good/solid to support average overall confidence in this blend. Closed low into PacNW Monday; elongating with northern stream cyclone crossing S Canada Tues/Wed, base of positive tilt trof slowly sliding down west coast by Wed ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 24.12z, non-GFS thereafter Exception: Greater influence of the 12z NAM and 00z ECMWF/ECENS, across US/Canada border Confidence: Above average through 24.12z, becoming slightly above thereafter Models continue to show solid continuity and track to the closed low hugging the AK panhandle and BC Coast through before affecting the Pacific NW Monday. The 12z NAM continues to be a bit broader with the inner core of the closed low (not as point focused, more of a ring) and so by Tuesday is a tad broader/leaning forward across BC/S Alberta with the northern portion of the trof. Still a general model blend is supported through 24.12z at above average confidence.... Thereafter the closed low begins to elongate shedding the northern stream wave eastward across the Southern Canadian Rockies, while the base stretches SW along the West Coast with broad diffluent flow in the larger zonal pattern across the US Rockies. By this time the 12z GFS, starts to move out of the overall good agreement, leaning faster, but only southward and then eastward...leaving the northern stream system much further south overall so generally less favorable overall, and will not be included in preference thereafter. The 12z NAM/ECMWF are a tad faster and therefore a bit further north with the forcing/surface low crossing southern Canada by Wed, relative to the slower CMC and UKMET. This is similar in the southwest portion of the trof with the UKMET a bit broader/stronger throughout its length. So overall a 12z NAM and 00z ECMWF is supported across the northern portion of the wave/along the northern tier, but more inclusion of the UKMET/CMC is supported across the CA Coast into the Intermountain west and lee of the central Rockies by 00z Thursday. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina