Extended Forecast Discussion NWS Weather Prediction Center College Park MD 123 PM EDT Tue Jun 01 2021 Valid 12Z Fri Jun 04 2021 - 12Z Tue Jun 08 2021 ...Record Heat Likely Over Portions of the West to Northern Plains... ...Multiple Day Heavy Rainfall Event Likely For Parts of Southern Plains and Lower Mississippi Valley... ...Overview and Guidance Evaluation/Preferences... The upper level pattern is expected to undergo a pattern change through the period with ridging becoming more persistent and anchored off the Southeast U.S. while larger scale troughing settles over the Western CONUS. In between, lagging/residual troughing in place and southerly flow will lead to a plume of deeper Gulf of Mexico moisture and unsettled weather over the Southern Plains and Lower Mississippi Valley. From a synoptic view, the latest model guidance is in reasonable agreement and offers average to above average predictability for this cycle. The deterministic and ensemble guidance all advertise the western U.S. trough and eastern ridge developing over the course of the period. The largest mass field differences were noted to be across the Pacific NW with the timing and strength of the shortwave energy as well as off the Southern California coast with the potential development of a closed low. While days 3-5 were clustered fairly well, the ensemble means were used more heavily on days 6-7 to mitigate some of this uncertainty. Further east, weakness in the upper levels on day 3 over Texas could transition into a more developed trough by this weekend. At the surface, troughing or a frontal boundary may setup along the Texas coast and with the increasing southerly flow, a plume of deeper moisture is likely to override this. There are some differences in the QPF placement, with the 00Z ECMWF further west (slower) compared to the GFS and even the CMC (which is furthest east). So despite the relatively good agreement in the large scale mass fields, more mesoscale driven processes are likely driving the larger QPF differences which are difficult to pinpoint this far out. Overall the WPC blend consisted of a near equal blend of the 00Z ECMWF/CMC/UKMET and 06Z GFS for days 3-5 followed by mostly ECENS/GEFS means with some inclusion of the deterministic runs for day 6-7 given some of the uncertainty, though the ECMWF remained a larger proportion of the blend, especially for the QPF blend across the Southern Plains and Lower MS Valley. ...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 upper level trough. Over the course of the period, several inches of rain is expected and this region is already highly susceptible to any kind of heavy rainfall given much above normal precipitation over recent weeks. Elsewhere, conditions should dry out across the East into the weekend, with showers lingering over parts of the Southeast. Out West, a gradual increase of moisture over the Pacific Northwest is expected, with some activity also possible into the northern Rockies and eventually the northern tier. The greatest temperature departures will be found across the Interior West, Northern Rockies, and Northern Plains Friday and Saturday. Daytime highs are likely to reach 20F to near 30F above normal with large areas possibly breaking records for the date. The unseasonable heat will spread eastward toward the Great Lakes and Northeast later in the weekend and early next week with highs reaching 10-20F above normal. Further south across Texas, below normal highs are likely with all the clouds, unsettled weather, and widespread precipitation expected. For low temperatures, much of the CONUS will see normal to much above normal readings, with the greatest departures from normal confined to the Interior West, Northern Plains, and Northeast. Taylor 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