Extended Forecast Discussion NWS Weather Prediction Center College Park MD 405 PM EDT Thu Aug 04 2022 Valid 12Z Sun Aug 07 2022 - 12Z Thu Aug 11 2022 ...Monsoonal pattern remains active across the Southwest with additional heavy rainfall likely... ...Overview... Guidance agrees on an eventual amplifying trend to the upper pattern next week. General upper ridging over much of the central/southern lower 48 Sunday-Monday should build more strongly over parts of the Rockies/Plains by mid-late week. This evolution combined with ridging downstream from a mean trough over Alaska should support gradual trough amplification over eastern North America. An upper low off the West Coast will likely lift northward and may brush the Pacific Northwest around Wednesday-Thursday. The most prominent areas of potentially significant rainfall will be within the persistent monsoonal moisture shield over the West and along/ahead of a cold front pushing southeastward from the Upper Great Lakes/Central Plains to the East Coast/Mid-South. The pattern transition will lead to a cooler trend from initial heat over the eastern half of the country, along with a shift of very warm to hot weather from the Northwest into the northern half of the Plains. ...Guidance Evaluation/Predictability Assessment... As has been the case lately, there are some detail differences within the more agreeable large scale evolution. The most significant one appears to be with the shortwave crossing the northern tier early in the week, affecting the strength/track of an associated frontal wave as well as the corresponding rainfall pattern. Recent GFS runs have been deeper than other models and have even depicted an embedded closed low at some valid times. This results in a deeper/northward surface wave in the GFS. The new 12Z run is still on the deep side aloft but has partially trended toward the remaining guidance. After Tuesday there is fairly typical spread with energy that reaches the East, as well as for an upstream southern Canada system that ultimately feeds into the developing eastern North America mean trough. Farther west the GFS/GEFS end up a bit east of the ECMWF/CMC and their means with the Rockies-Plains upper ridge by next Thursday but all of these solutions are within typical guidance error ranges that far out in time. Finally, a compromise timing looks good for the eastern Pacific upper low that should eject northeastward by mid-late week. 12Z/06Z GFS runs trended faster toward the 00Z ECMWF but the new 12Z UKMET is slower through the end of its run early Wednesday. Based on the current guidance array, the updated forecast started with a 00Z/06Z operational model composite for the first half of the period. This included slightly less than typical GFS input due to question marks for its northern tier evolution. The blend transitioned to a model/ensemble mean mix later in the period to yield an intermediate solution, balancing the good pattern agreement but some decrease in confidence for specifics. ...Weather/Hazards Highlights... The Southwest and Four Corners region will be one area of focus for episodes of potentially heavy rainfall and flash flooding with persistence of monsoonal moisture. The best possibility of enhanced rainfall over Colorado/New Mexico may be around Sunday-Monday followed by a lighter rainfall trend/southward suppression of moisture. The Southwest should see periods of rain during most of the period while the large scale pattern evolution may promote a northward expansion of moisture/rainfall into the Great Basin by midweek with some locally heavy totals possible here as well. Some Slight Risk areas are depicted in the experimental Days 4-5 Excessive Rainfall Outlooks given guidance signals for heavy rainfall potential and already wet ground conditions. Meanwhile, expect a fairly broad area of rainfall to push steadily south and east from the Upper Great Lakes/Midwest with time as a supporting cold front pushes into the East. It is likely that some locations will see a period of heavy rainfall with this front. Instability and deep moisture supported maintenance of the Slight Risk area for excessive rainfall over parts of the Upper Great Lakes/Midwest, though some lingering uncertainty exists for specifics. Very warm to hot temperatures over the Northwest from Sunday into the early part of next work week will shift over into an increasing portion of the northern half of the Plains by Tuesday-Thursday. High temperatures may reach up to 10-15F or so above normal at some areas. These values should be below daily records except perhaps for a few isolated locations. Meanwhile very warm to hot weather initially from the Midwest through Northeast/Mid-Atlantic will trend cooler over the course of the week as cool temperatures over the northern Plains on Sunday (highs up to 10F or so below normal) spread southeastward with time. This trend should yield near to slightly below normal highs over much of the East by next Thursday. The monsoonal moisture/rainfall over the Southwest and vicinity will tend to keep highs several degrees below normal on most days. Rausch Hazards: - Heavy rain across portions of the Great Lakes, Midwest, and Ohio Valley, Sun-Mon, Aug 7-Aug 8. - Heavy rain across portions of the Central and Southern Appalachians, Ohio Valley, and Tennessee Valley, Tue-Wed, Aug 9-Aug 10. - Heavy rain across portions of the Central High Plains and Central and Southern Rockies, Sun-Mon, Aug 7-Aug 8. - Heavy rain across portions of the Southwest, Sun-Thu, Aug 7-Aug 11. - Heavy rain across portions of the Great Basin, Tue-Thu, Aug 9-Aug 11. - Flooding possible across portions of the Middle Mississippi Valley and the Ohio Valley. - Flooding occurring or imminent across portions of the Ohio Valley and the Northern Plains. - Excessive heat across portions of the Central Plains and the Middle Mississippi Valley, Sun, Aug 7. - Excessive heat across portions of the Southern Plains and the Lower Mississippi Valley, Sun-Tue, Aug 7-Aug 9. - Excessive heat across portions of the Northeast, Sun-Mon, Aug 7-Aug 8. - Excessive heat across portions of the Pacific Northwest and the Northern Great Basin, Mon-Tue, Aug 8-Aug 9. - Excessive heat across portions of the Northern High Plains, Tue-Thu, Aug 9-Aug 11. 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, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml