Extended Forecast Discussion NWS Weather Prediction Center College Park MD 410 PM EDT Mon Jun 29 2020 Valid 12Z Thu Jul 02 2020 - 12Z Mon Jul 06 2020 ...Pattern Overview... The expectation is for a Plains/southern Rockies/northern Mexico upper ridge and separate ridging over the Northeast Pacific/Alaska which will position a mean trough over the eastern Pacific/West Coast which leads to some retrogression during the medium range period. A departing short-range New England upper low/trough will be replaced by a somewhat broader eastern Canada/Northeast trough. Ridging initially over central/east-central Canada should gradually weaken and allow for increasing progression across southern Canada and the northern tier U.S. later in the period. This evolution should lead to flatter Northeast flow aloft by early next week. Farther south the guidance still suggests the development and persistence of a possible upper level low between the lower half of the Mississippi Valley and Southeast--a feature important due to its potential to support areas of significant rainfall. ...Guidance Overview & Assessment... The mean trough aloft near the West Coast is agreeable in principle but detail differences persist, due in part to short-range differences in how flow around an eastern Siberia upper low ejects across Alaska and beyond followed by how much ridging extends into Alaska. Ruled out the 00z Canadian here and chose a blend of the 06z GFS/00z ECMWF/00z UKMET. For the eastern Canada/Northeast trough, morning guidance showed good agreement until Saturday morning before diverging. Such dispersion was also hinted at in the 00z and 06z ensemble mean solutions. With some slight retrogression for troughing near/offshore the Northwest, one would expect similar retrogression downstream near the Northeast/Great Lakes. The only guidance suggesting such this morning was the 06z GFS, so late in the medium range period chose a compromise of the 00z ECMWF ensemble mean, 00z NAEFS mean, and 06z GFS eliminating the Canadian and ECMWF from contention (believing that their mid-continent ridge was too strong). The guidance shows good agreement in respect to the upper low/trough over the Southeast, but it's possible further adjustments occur as it gets closer in time to the present. ...Weather/Hazard Highlights... The expected weakness aloft over/near the Southeast will support potential for areas of enhanced rainfall near the central and eastern Gulf coast. However guidance is still in the process of trying to settle down on a stable solution for this feature so confidence is no better than average for locating the most favored areas for highest totals between the Lower Mississippi Valley/central Gulf Coast region and Southeast/southern Mid-Atlantic/eastern Gulf coast. Some showers/thunderstorms are possible with the front reaching New England late this week as well as with one or more fronts over the northern tier, with mixed signals regarding intensity and coverage of rainfall are seen, particularly across the Upper Midwest, Great Lakes, and Northeast. From late week onward expect scattered diurnally favored convection over the central/southern Rockies. The forecast pattern will promote a persistent area of warm temperatures around 10-15F above normal centered over the Upper Mississippi Valley and Great Lakes. At times, some of this warmth will extend back into the Northern Plains, while eastward extent into New England should be limited to early and late in the period--ahead of the front dropping south from Canada and then after its eventual return as a warm front. The rest of the Plains will start the period moderately above normal but then trend closer to normal. At the same time most of the West will trend toward near/slightly above normal readings after starting with single-digit negative anomalies for highs on Thu, with building of heat across the Desert Southwest -- high temperatures near 120F are possible in Death Valley. The Pacific Northwest coast may remain slightly below normal due to proximity of the upper trough. Portions of the Southeast and vicinity may also be a little below normal due to periods of clouds/rainfall but the Florida Peninsula could see one or more days of slightly above normal readings. Roth/Rausch 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 Hazards: - Flooding possible across portions of the Upper/Middle Mississippi Valley, the Great Lakes, and the Northern Plains. - Flooding occurring or imminent across portions of the Central Plains, the Upper/Middle Mississippi Valley, and the Northern Plains. - Flooding likely across portions of the Northern Rockies. - Excessive heat across portions of the Central Plains, the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Southeast, and the Southern Plains, Thu-Fri, Jul 2-Jul 3. - Much above normal temperatures across portions of the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Thu-Sun, Jul 2-Jul 5. - Much above normal temperatures across portions of the Southwest, Sun-Mon, Jul 5-Jul 6. 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