Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 PM EDT Sun May 02 2021 Valid 12Z Wed May 05 2021 - 12Z Sun May 09 2021 ...Weather Pattern and Model Guidance... Models and ensembles remain in above average agreement days 3-7 and offer good run to run continuity. This bolsters forecast confidence in a pattern expected to significantly amplify over medium range time scales as upper troughs work into the West and the East to sandwich a warming west-central U.S. upper ridge. Variance remains with the timing and strength of smaller scale systems, but guidance composites tend to mitigate these differences consistent with predictability. Accordingly, the WPC medium range product suite was primarily derived from a blend of best clustered guidance of the 06 UTC GFS/GEFS mean, the 00 UTC ECMWF/ECMWF ensemble mean and the 13 UTC National Blend of Models. The latest 12 UTC models and ensembles remain very much in line with this forecast strategy. ...Weather/Hazards Highlights... Heavy showers and storms remain likely from the central Gulf Coast into the southeast Wednesday into Thursday, with additional enhanced activity up across the East near a wavy front. A developing coastal low Friday and Saturday along a trailing front with renewed upper trough support should produce unsettled coastal conditions to include some moderate rains for the Mid-Atlantic and Northeast. Upstream over the western U.S., heat is expected to build in response to the upper level ridge, with highs 10-20 degrees above normal possible Wednesday-Friday. This will equate to some 100+ degree high temperatures for the lower elevations of eastern California and southern Arizona. With the passage of the cold front on Saturday with emergence of an upper trough over the West, seasonal to below normal temperatures are expected for the weekend. Trough amplification offers potential for some moderate precipitation from the Pacific Northwest to the cooling Northern Rockies where terrain enhanced snows are possible. Meanwhile, an emerging downstream return flow pattern over the south-central U.S. may set the stage for an expanding rainfall/strong convection threat with deepening Gulf moisture and instability. 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 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