Extended Forecast Discussion NWS Weather Prediction Center College Park MD 302 AM EDT Wed Jun 22 2022 Valid 12Z Sat Jun 25 2022 - 12Z Wed Jun 29 2022 ...Excessive heat will continue across parts of the South on Saturday, finally beginning to moderate by Sunday... ...Overview... Broad upper level ridging over the Southern U.S. will finally begin to weaken and break down this weekend as a shortwave through the northern tier to the north begins to amplify as it reaches the Great Lakes and especially the Northeast early next week. Meanwhile, monsoonal moisture will continue to persist into the Four Corners region through much of the period with potential for heavier to excessive rains along the southern half of the Rockies this weekend with the arrival of a surface front and trailing low level upslope flow. The pattern looks to become more amplified by early next week across the CONUS with troughing in the East and the arrival of a closed upper low towards the West Coast, and ridging building in between over the interior West. ...Guidance/Predictability Evaluation... The latest guidance was in fairly good agreement the first couple of days both with a weak/lingering cutoff low off the Northeast Coast (which should get pushed eastward by the westerlies) and also with the compact low/shortwave along the U.S./Canadian border this weekend. The GFS gets a little fast with leading energy as it moves into the Great Lakes, but bigger uncertainties arise late period with reinforcing energy dropping into the trough from central Canada with the CMC being much stronger with this energy and actually advertising a closed low north of Lake Superior on Day 7. Detail/timing differences also are in question with the leading energy as it moves into the Northeast day 6-7 as well. Elsewhere, the GFS has consistently been faster bringing a closed low towards the West Coast by early next week. The remainder of the deterministic guidance is slower, which is also more consistent with the ensemble means. This also has implications downstream for arrival of the ridge and consequently temperatures across the northern High Plains late period. The early period agreement allowed for a general blend of the deterministic guidance for days 3-4, weighted more towards the ECMWF which seemed most consistent with the ensemble means. Removed the GFS from the blend after day 4 due to its issues with the West Coast upper low, and the CMC with it's issues with reloading energy into the Great Lakes trough. Late period, relied heavily on the ensemble means to help mitigate late period differences in the West, but did continue incorporation of the ECMWF for some added system definition. ...Sensible Weather/Threat Highlights... Anomalously high monsoonal moisture for this time of year, likely tied at least in part to an eastern Pacific tropical system, will continue streaming into the Four Corners states into early next week. Locally heavy to excessive rainfall is possible, particularly over sensitive burn scar areas and considering the multiple day repeating nature of this activity. Rainfall may trend heavier over parts of Colorado/New Mexico by the weekend as a front dropping south through the region and trailing low level upslope flow could interact with the moisture already in place. Models showed enough agreement for the inclusion of a slight risk in northeast New Mexico on the experimental day 5 ERO. Moisture will continue rounding the top of the ridge through the Plains, while interacting with a cold front through the Upper Midwest, where some increased threat for organized showers is possible. The cold front should be fairly progressive through the Midwest and into the East this weekend, but with enough moisture and instability along the boundary present, some locally higher totals seem likely, specific amounts and locations tho remain highly dependent on still uncertain timing of the front. A front settling across the southeast into Saturday should also bring a period of enhanced rainfall to parts of the Florida peninsula. Excessive heat across the Southern U.S. should finally begin to wane some, especially in parts of the Southeast, by this weekend. Anomalies averaging 10 to 15 degrees above normal will continue across the lower Mississippi Valley and Southern Plains with another few days of records both for daytime highs and warm overnight mins. By early next week, temperatures all across the South should finally trend back towards normal. Relatively cooler temperatures with well below normal highs are likely to be most persistent over parts of New Mexico and Colorado given the monsoonal clouds and rain coverage. The northern High Plains may also see cool highs from Saturday into Sunday. The West Coast states should see highs 5-15F above average through about Tuesday as upper ridging moves through the region. Santorelli 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