Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 PM EDT Mon Mar 23 2020 Valid 12Z Thu Mar 26 2020 - 12Z Mon Mar 30 2020 ...Guidance/Predictability Assessment... The dominant focus of the forecast from late this week into the weekend will be an upper trough ejecting from the West and associated low pressure expected to track northeastward from the Central Plains. The combination of this system and a leading wavy front may produce an area of enhanced rainfall over or near the Ohio Valley region along with lighter amounts over a broader area. Behind this system the means show a tendency for zonal or broadly cyclonic flow by the start of next week but individual model runs and ensemble solutions show a wide variety of possibilities for amplitude and position of individual features. During days 3-4 Thu-Fri the guidance is similar for the fairly sharp upper trough moving through the West. Then solutions diverge for the timing of the feature as well as whether it remains an open wave or forms an embedded upper low for a period of time. This leads to considerable uncertainty for the track/strength/progression of the system. Thus far ECMWF/ECMWF mean runs have tended to be on the faster side of the envelope while the past 24-36 hours of GFS runs have been noticeably slower. However the 06Z GFS trended faster than the 00Z run and the new 12Z run has continued that trend. Latest UKMET runs are on the strong/northwest side of the spread. Meanwhile the 00Z CMC was weak/southeast and the new 12Z version adjusted more to the middle. The combat ion of latest trends, the relatively small scale of the evolution within the ejecting upper trough suggesting low predictability, and the moderately progressive nature of the overall pattern favor keeping the forecast close to continuity, leaning more toward the ECMWF/ECMWF mean in principle. Behind this system there are combined uncertainties from specifics of eastern Pacific shortwave energy as of early Sat as well as upstream flow across the North Pacific. ECMWF runs have had some degree of consistency with a shortwave crossing the southern half of the West by Sun-Mon (though still with vary different shape and timing depending on the run) while both the GFS and ECMWF have been erratic within the full range of upper ridging or troughing over the northeastern Pacific and northwestern U.S./western Canada by day 7 Mon. Ensemble members reflect this uncertainty as well. Overall flow is sufficiently progressive to allow a variety of solutions to be plausible from the multi-day mean perspective. An emphasis on the ensemble means appears most reasonable for now in light of teleconnection support for low amplitude mean flow based on strong positive height anomalies over the northeastern Atlantic and west-central Pacific in the D+8 charts. ...Weather/Hazard Highlights... The upper trough crossing the West during the latter half of the week will produce areas of mostly light to moderate rain and high elevation snow from central/southern California through the Southwest/Great Basin into the Rockies. Precipitation amounts over the central Rockies/High Plains will be sensitive to the exact details and timing of the upper system along with the surface low evolution. Current trends at least seem to be lowering the probability of highest totals that would result from the slowest/most closed side of the spread. Low pressure tracking from the Central Plains northeastward from Fri onward should produce a broad area of rain/showers and possibly strong warm sector convection over parts of the central/eastern U.S.. Current guidance is signaling that highest rainfall potential/runoff risks will be over the Ohio Valley region as moist flow ahead of the system interacts with a leading wavy front that settles into the region Thu-Fri. There may be some snow in the northern periphery of the moisture shield, from the northern and/or central Plains into the Upper Midwest/Great Lakes and Northeast. Uncertainties regarding precise system evolution and thermal profiles lead to low confidence in coverage/intensity of any wintry precipitation types. Expect the Northwest to see periods of rain and mountain snow of varying intensity as progressive flow from the northeastern Pacific into western North America carries along multiple features. Especially by the latter half of the period there is rapidly decreasing confidence in the southern extent of precipitation. Highest totals for the five-day period should be along favored terrain in the Olympics/Washington Cascades. The West will see below normal temperatures late this week with moderation over the weekend. Expect decent coverage of minus 10-20F anomalies for highs over central/southern parts of the West Thu-Fri. On the other hand a broad area of above to much above normal temperatures will spread from the Southern Plains and vicinity across much of the East late this week into the weekend. Highest anomalies will likely be for morning lows, up to 15-25F above normal versus 10-20F anomalies being more common for daytime highs. Multiple locations may see daily records for highs and/or warm lows from the Southern Plains eastward. Frontal passage will bring temperatures down to near normal over the eastern half of the country by Sun-Mon. The upstream pattern may bring another area of warmth into the Northern Plains region by next Mon. Rausch Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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