Extended Forecast Discussion NWS Weather Prediction Center College Park MD 245 AM EDT Wed Jun 02 2021 Valid 12Z Sat Jun 05 2021 - 12Z Wed Jun 09 2021 ...Record Heat possible from parts of the Northern Plains into the Northeast.... ...Multiple Day Heavy Rainfall Event Likely For Parts of Southern Plains and Lower Mississippi Valley... ...Overview and Guidance Evaluation/Preferences... A large scale trough entering the Northwest U.S. at the start of the period (Saturday) should finally suppress the strong Western U.S. ridge that will be anchored over the region during the now short range period. Settling and amplification of this trough across the West into early next week will result in rising heights for the East and a shift of much above normal temperatures/possible record heat across much of the northern tier. Meanwhile, in between, lagging/residual troughing in place over the Southern Plains and Lower Mississippi Valley will promote unsettled weather and potentially heavy rainfall over an already overly saturated region through the weekend. Overall, the guidance shows reasonable agreement to warrant a general model blend for days 3 and 4. After this, more significant and typical differences in the details of individual systems begins to increase. While all of the guidance suggests amplification of the Western U.S. troughing through the period (and resulting build of the East ridge), there are some timing and intensity differences regarding individual systems dropping into the mean trough which translates to greater structure uncertainties late period. As such, a quick increase towards the ensemble means for days 6-7 was imperative to help mitigate the differences. Farther east, the models show fairly good agreement with the presence of the Southern Plains low/trough, but placement and timing (the ECMWF is a bit west/south, and the CMC farther east) remain in question. These smaller scale details seem to be driving some fairly large QPF differences across parts of Texas into the Lower Mississippi Valley regarding placement and intensity of the heaviest rainfall axis, details of which are difficult to resolve this far out. Thus, prefer a blend towards the ensemble means at this point which represent a good middle ground solution. ...Weather Highlights/Hazards... A multi-day heavy rainfall event is looking more likely across portions of Texas, Louisiana, and into the ArkLaTex region with the persistent source of deeper Gulf moisture interacting with a Southern Plains upper level trough and frontal boundary reflected at the surface. Models continue to suggest the potential for several inches of rain, or more, within a region which has seen well above normal precipitation over recent weeks. Elsewhere, much of the East should remain dry although showers may linger over parts of the Southeast. Out West, a gradual increase in moisture over the Pacific Northwest is expected, with some activity reaching into the northern Rockies and eventually the northern Plains and Upper Mississippi Valley. For temperatures across the CONUS, much above normal temperatures will shift from the Great Basin/northern Plains this weekend, into the Upper Great Lakes and Northeast early next week. Daytime highs 15 to 20 degrees, locally higher, above the average may approach or exceed both daytime high and warm overnight low records for a number of locations across the northern tier. Farther south, below normal highs are likely the first half of the period, at least, across much of Texas and Louisiana due to continued unsettled weather and clouds. The West Coast should trend cooler through the period as amplified troughing becomes established over the region. Santorelli 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