Extended Forecast Discussion NWS Weather Prediction Center College Park MD 111 PM EST Sun Feb 27 2022 Valid 12Z Wed Mar 2 2022 - 12Z Sun Mar 6 2022 18Z Update: The 12Z deterministic guidance is generally in above average agreement on the large scale pattern through the end of the week, with the highest level of confidence in the southern stream and the building upper trough over the Intermountain West by the weekend. Initially the GFS/GEFS is a bit stronger with a shortwave crossing the south-central U.S. for the middle of the week, but differences at the surface are less noticeable and thus still comparable to the other guidance. The 12Z GFS is also more progressive with an ejecting shortwave and surface low across the central Plains and Midwest by Saturday, and ahead of its ensemble mean. There is more spread in the guidance across southern Canada for the weekend, and the GFS is more out of phase with the CMC/ECMWF across eastern Canada. This will tend to introduce more uncertainties in the forecast for days 6 and 7. The WPC forecast was primarily based on a multi-deterministic blend, including the 6Z GFS, through early Friday, and then gradually increasing percentages of the GEFS/ECENS whilst still maintaining some of the 00Z ECMWF and CMC. /Hamrick ...Overview... Expect a significant change in the upper level pattern over the course of the period, with a western U.S. ridge/broad eastern trough as of Wednesday transitioning toward an amplified northern Plains through western U.S. trough/eastern ridge configuration by next weekend. As this evolution occurs, precipitation over the Pacific Northwest and northern Rockies will spread across more of the West, to be followed by a broad area of various precipitation types developing over the central U.S. as low pressure tracks through the Plains and Upper Great Lakes. Early in the period a northern tier wave may spread some snow across areas from the Upper Midwest into the Northeast. Western/central states will see a pronounced cooler trend in temperatures, from well above normal to below normal, while above normal temperatures over the southern half or so of the East should expand northward next weekend. Far northern tier areas will tend to be colder than normal on most days. ...Guidance Evaluation/Predictability Assessment... The latest cycles of guidance maintain the recent theme of better than average agreement for the large-scale pattern evolution but continued differences for some details. Subtle differences in evolution of southern Canada energy flowing into/through the eastern North America mean trough continue to produce greater than average spread for the specifics of a surface wave that may track from the Midwest through the Northeast from Wednesday into early Thursday. CMC/UKMET runs have consistently been on the stronger and northern side of the model spread for this wave. The notable change in the past day has been with the 00Z GFS/GEFS mean trending to a slower/weaker version of the CMC/UKMET scenario, extending a modest trend from the 18Z cycle. This leaves the 12Z ECMWF still the new 00Z run on the weak and suppressed side of the spread. The preferred solution adjusted the wave's track somewhat northward from previous cycle given relative support from the means but maintained a fairly weak depiction due to the considerable spread. Meanwhile guidance is still in the process of refining the forecast of upper troughing that moves into the West. 00Z runs so far are adding support to the idea of a slightly slower/sharper lead shortwave reaching the West Coast, leaving the 12Z ECMWF/ECMWF mean a bit on the faster side. The new 00Z ECMWF has adjusted slower. This energy should ultimately cross the West and eject through the Plains, supporting a Plains through Upper Great Lakes surface system from late week through the weekend. Consistent with trends seen farther west, this system has adjusted a little slower over the past day. Low-predictability trailing energy dropping into the mean trough (as eastern Pacific ridging steadily builds) continues to complicate the forecast of the leading impulse to some degree. Still, there is better than average agreement regarding the fairly deep trough forecast to be over the West as of day 7 Sunday. The 12Z/18Z operational model blend used for the first half of the period provided the desired adjustment for the eastern U.S. wave while representing an intermediate solution for the shortwave entering the West. Then a trend toward more even weight of models and ensemble means later in the period accounted for the good pattern agreement but uncertainty in some of the details. ...Weather Highlights/Threats... Rain and high elevation snow from the Pacific Northwest/northern California into northern Rockies as of midweek will spread across more of the West later in the week, while trending lighter along the West Coast, as an upper trough moves into and through the region. Continued progression of this energy should support a central Plains into Upper Great Lakes surface low and frontal system late week into the weekend, with a corresponding broad area of precipitation over the central U.S. Best potential for wintry precipitation types will extend from the northern half of the High Plains into the Upper Great Lakes and eventually New England, with a band of significant snow possible to the northwest of the surface low track. Rainfall of varying intensity will be possible over the rest of the central/east-central U.S. Well ahead of this system, a northern tier wave may spread snow across an area from the Upper Midwest into New England from Wednesday into Thursday. Thus far guidance has not been agreeable with details of the surface wave so coverage and amounts of snow have lower than average confidence. A lower-probability scenario could lead to a somewhat farther southward axis. A majority of the lower 48 will see above normal temperatures on Wednesday, with areas along the central/eastern Canadian border as well as the western Gulf Coast being the main exceptions. Then the West and northern-central Plains will trend steadily cooler with time while above normal readings over the southern half of the East expand northward by next weekend. Expect the warmest anomalies of plus 20-25F or so for highs to be over the central Plains Wednesday through Thursday or Friday. Other warm areas may see plus 10-20F anomalies with some locally higher readings possible. Northern Plains into Rockies locations may see highs 10-15F below normal by next Sunday. Rausch/Hamrick Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml