Extended Forecast Discussion NWS Weather Prediction Center College Park MD 451 PM EDT Fri Apr 30 2021 Valid 12Z Mon May 03 2021 - 12Z Fri May 07 2021 ...Heavy Rainfall Threat across the South into Tuesday/Wednesday... ...Guidance/Predictability Assessment and Preferences... Guidance agrees that an active weather pattern will continue next week as two significant troughs cross the southern tier states and result in heavy rain and some severe thunderstorms. An warming upper level ridge becomes established over the Intermountain West mid-later next week ahead of the next Pacific storm system to reach the West Coast by next Friday. An additional series of impulses into the northern tier of the central and eastern U.S. may amplify by later next week downstream of the western ridge. Models and ensembles offer below normal forecast spread through medium range time scales in an early May pattern with good run to run continuity. The WPC medium range product suite was derived from a composite blend of 00/06 UTC models and ensembles days 3-5 (Mon-Wed) along with the 01 UTC National Blend of Models. The 06 UTC GFS/GEFS and 00 UTC ECMWF/ECMWF ensemble mean solutions are best clustered into days 6/7 in a pattern with continued above normal predictability. Latest 12 UTC guidance remains in line. ...Weather/Hazards Highlights... Multiple rounds of moderate to heavy rainfall are likely to focus next week across the South as multiple disturbances cross the region. The region that appears most favored for excessive rainfall from Texas and the lower MS/TN Valleys through the Mid-South/Central Gulf Coast states into the southern Appalachians. Most of this should fall during the Tuesday-Wednesday time period with deepening moisture/instability and favorable upper support. This may be enough to cause some flooding, particularly where convective training develops or across areas that will have already received noteworthy prior rains. Periods of frontal focusing convection will meanwhile also focus from the central Plains through the Midwest, OH Valley and Northeast with impulse passages. Terrain enhanced snows are also possible back over the central Rockies early next week. In terms of temperatures, highs are expected to be about 5-15 degrees above average for much of the eastern U.S. ahead of the front for early next week, with some 90 degree readings likely across portions of the Virginia and North Carolina Piedmont on Tuesday. This will be followed by a return to more seasonal to below normal temperatures to close out the week behind the cold front. Across the western U.S., heat is expected to build in response to the upper level ridge, with highs 10-20 degrees above normal possible for the middle to end of the week for portions of the Intermountain West and the Desert Southwest. This will equate to some 100+ degree high temperatures for the lower elevations of eastern California and southern Arizona. Hamrick/Schichtel 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 Hazards: - Flooding possible across portions of the the Middle Mississippi Valley and the Southern Plains. - Flooding occurring or imminent across portions of the Middle/Lower Mississippi Valley and the Southern Plains. - Flooding likely across portions of the Lower Mississippi Valley. - Heavy rain across portions of the Middle/Lower Mississippi Valley, the Central/Southern Appalachians, the Tennessee Valley, the Southeast, the Southern Plains, and the Ohio Valley, Mon-Wed, May 3-May 5. - Heavy snow across portions of the Central Rockies, Mon, May 3. - Severe weather across portions of the Central/Southern Plains and the Middle/Lower Mississippi Valley, Mon, May 3. - Much above normal temperatures across portions of California, the Northern/Central Great Basin, and the Pacific Northwest, Tue-Thu, May 4-May 6. 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