Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Sun May 09 2021 Valid 12Z Wed May 12 2021 - 12Z Sun May 16 2021 ...Overview, Guidance Evaluation and Preferences... Latest model guidance continues with the theme of keeping a broad positively-tilted trough across the northern tier states in contrast with an anchoring ridge in the West as the next upper trough reaches the Pacific Northwest next weekend. The positively-tilted trough in the East will tend to push the most active weather near the Gulf Coast and the Southeast midweek further into the Gulf and into the western Atlantic by the end of the week. For the trough arriving across the Pacific Northwest next weekend, models show some expected uncertainty regarding its timing and degree of interaction with the cooler airmass over interior western Canada. The ensemble means are relatively agreeable with each other regarding this feature. The GFS and GEFS show a typically faster progression relative to the ECMWF and CMC, as the trough moves into the northern Rockies. The WPC medium-range forecast package was based on the consensus of the 00Z ECMWF/00Z EC mean, the 06Z GFS/GEFS mean, as well as some contribution from the 00Z CMC and CMC mean. This yielded a solution very close to WPC continuity. ...Weather Highlights/Hazards... Some moderate to perhaps locally heavy rainfall will likely extend near/along the Gulf Coast to begin the medium-range period on Wednesday while lighter rain should continue over parts of the Southeast into Thursday. Then a high pressure system will feed drier air from the north and push the surface front gradually southward into the Gulf and down the Florida Peninsula. Florida may initially see varying intensity of rainfall but a developing frontal wave east of Florida will tend to guide the most active weather offshore. Scattered areas of rainfall may extend from the northern Rockies through parts of the Plains/Mississippi Valley ahead of a wavy front behind the eastern U.S. upper trough. Some of this activity could drop further south into the central Plains during the weekend before sliding eastward under upper-level northwesterly flow but low confidence is relatively low at this time. Elsewhere, some precipitation should develop across the northern Rockies on Friday and then expand eastward into the northern Plains during the weekend. Some wet snow is possible in the higher elevation during the night. Areas from the central/southern Plains through the Southeast will see unseasonably cool highs on Wednesday with broad coverage of minus 10-20F anomalies. A few locations could challenge daily records for cool highs. The Southeast and to a lesser extent farther back into Texas may still see highs at least 10-15F below normal on Thursday. Other portions of the East will likely be below normal as well but with less extreme anomalies. A moderating trend over the South and East should yield temperatures within a few degrees on either side of normal by next Sunday. The upper ridge moving into the West and then the Plains will favor an area of temperatures 10-20F above normal from California and Oregon into the Great Basin with plus 5-10F or so anomalies extending into the central Rockies/Plains. An approaching upper trough should gradually erode this area of warmth but recent slower/weaker trends for the trough in general plus uncertainty over the character of the trough suggest a slower and less pronounced cooling trend. Kong/Rausch 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