Extended Forecast Discussion NWS Weather Prediction Center College Park MD 235 AM EDT Mon May 24 2021 Valid 12Z Thu May 27 2021 - 12Z Mon May 31 2021 ...Overview... Upper ridging over Mexico will slowly build northward into Texas over the weekend, favoring troughing over California and in the East, but with near to above normal height CONUS-wide. Rainfall will be focused around a wavy frontal boundary from the central Plains to the East Coast. ...Guidance Evaluation and Preferences... Through the 12Z/18Z guidance cycle, the latest deterministic models showed reasonable clustering for the Thu-Sat period as low pressure along the front moves from the Plains to the Ohio Valley to the Mid-Atlantic. By then, uncertainty increases with a southern stream shortwave through Texas/lower MS Valley as well as the unfolding western trough and possible low pressure development just off the East Coast. With lackluster continuity in the models, trended toward a majority ensemble blend of the three systems (GEFS/Canadian/European) with a small weighting of the GFS/ECMWF/Canadian deterministic runs to offer just a bit of detail where appropriate. 00Z/01Z National Blend of Models informed most of the sensible weather grids with additional weighting to the ECMWF ensemble mean for temperatures/PoPs but a multi-model/ensemble blend for the QPFs. ...Weather Highlights/Hazards... Highest chances of rainfall during the period will likely be over the central Plains to the Corn Belt eastward to the central Appalachians along a wavy frontal boundary. As low pressure moves through the Central Plains on Thursday, an area of organized and moderate to heavy rain could shift through the Mississippi Valley into the Ohio Valley. Some rainfall amounts have the potential to be locally heavy in some convectively-enhanced areas. Areas in the East may see some light/modest showers as the front ebbs and flows in the Mid-Atlantic. For Thu-Fri, temperatures will be cool in the northern Plains to Upper Midwest, warm in the Southeast, and within several degrees of normal in between. For the Memorial Day weekend forecast, expect near to slightly below normal temperatures for many northern areas but near to slightly above normal temperatures for many southern areas. The Pacific Northwest may see temperatures more than 10 degrees above normal by next Monday. Rainfall may be scattered in many areas east of the Rockies and focused on one or two days over the central Plains to the Mid-Atlantic (where little rain has fallen this month). Fracasso 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