Extended Forecast Discussion NWS Weather Prediction Center College Park MD 426 PM EDT Mon Jun 01 2020 Valid 12Z Thu Jun 04 2020 - 12Z Mon Jun 08 2020 ...Gulf of Mexico tropical threat and persistent heat over the central U.S... ...Western U.S. heat to give way to much cooler temperatures after Friday... ...Overview and Guidance/Predictability Assessment... After a very brief relaxation in flow amplitude into the start of the period Thu, the pattern looks to repeat some aspects that have just occurred. These include eastern Pacific/West Coast upper trough amplification and ejection of another leading low-latitude upper low (albeit on a path to the east of the one that brushed the Northwest this past weekend), a strong ridge building into the central/east-central U.S. with an amplifying East Coast/western Atlantic trough, and strong ridging over the central Atlantic. This time there will also be a possible Gulf of Mexico tropical system which NHC/WPC is monitoring. At this time the most sensitive part of the tropical forecast appears to be the relative timing of the system as it tracks northward and the upper ridge building across the central U.S. A relatively small change in one and/or the other from current consensus could lead to greater adjustments for track by early next week. Recent verification and the current array of guidance--agreeing better than average in principle, boosting confidence in the large scale pattern--provided decent support for using an even blend of the 06Z GFS/GEFS mean and 00Z ECMWF/ECMWF mean as the starting point for the updated forecast. In the West, the GFS continues to be a bit faster than other solutions for the ejecting upper low. Some of the slowest solutions verified too slow for the previous upper low, and upper flow surrounding the ejecting low will be accelerating, so the slow edge of the spread (represented by the 00Z CMC) could be too slow. Toward the end of the period the 00Z ECMWF separated flow within the West Coast trough more than other solutions. For the East Coast/western Atlantic trough, per its tendency the 00Z ECMWF was on the deeper/slower side. This morning's verification for the current trough reaching the western Atlantic also recommended an intermediate solution. ...Weather/Hazard Highlights... The best potential for highest rainfall totals over the lower 48 during the Thu-Mon period may be along/inland from parts of the central-eastern Gulf Coast depending on the track/timing of the possible Gulf tropical system. A front dropping into the Southeast by Sun-Mon could provide an added focus for moisture, whether from the tropical system itself or carried within the flow to its east. Farther north a leading front should dissipate once it reaches the Mid-Atlantic and points west, followed by the front that ultimately reaches the Southeast. Showers and thunderstorms of varying intensity may accompany both fronts. The amplifying upper trough nearing the West Coast and upper low ejecting ahead of it will promote one or more episodes of locally enhanced precipitation over portions of the Northwest and some other locations extending into the northern-central Rockies. By the start of next week the arriving upper trough may be deep enough to support a little snow at the highest elevations of the Northwest. Locally strong/heavy convection will be possible over parts of the Northern Plains/Upper Midwest with the combination of western impulses rounding the upper ridge and interaction with the trailing part of the reinforcing eastern U.S. cold front. The most persistent area of well above normal temperatures will be over the central U.S. In particular the central/south-central High Plains should highs 15-20F above normal from late this week into the weekend. A sizable area of plus 5-15F anomalies should continue over the Plains into next Mon. The heat will extend into the West through Fri, also with some plus 10-20F anomalies. Then the arriving upper trough will bring a pronounced cooling trend, leading to highs up to 10-15F below normal over the West Coast states and northern Rockies into western Great Basin by next Mon. Within the area of heat the best possibility for some scattered record highs should be Thu and perhaps into Fri. Over the East, northern areas will be somewhat above normal late this week and then trend slightly below normal as cool high pressure builds in behind the second front. Southern areas will tend to be near to slightly below normal for highs. Rausch Hazards: - Heavy rain across much of the Gulf Coast region from eastern Texas to all of Florida including portions of the Southeast, Fri-Mon, Jun 5-Jun 8. - Severe weather across portions of the northern Plains, Thu, Jun 4. - Flooding occurring or imminent across portions of the lower Mississippi Valley, the northern Plains, the northern Rockies, the Midwest, and the Carolinas. - Flooding likely across portions of the Southeast and the Midwest. - Much above normal temperatures across portions of the Intermountain West, central Great Basin, into the northern and central Rockies, and the northern and central High Plains, Thu-Fri, Jun 4-Jun 5. - Much above normal temperatures over the central High Plains, Sat-Mon, Jun 6-Jun 8. Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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