Extended Forecast Discussion NWS Weather Prediction Center College Park MD 305 PM EDT Thu Jun 23 2022 Valid 12Z Sun Jun 26 2022 - 12Z Thu Jun 30 2022 ...Heavy to excessive rainfall threat across parts of the Southern Rockies this weekend with excessive heat across the South and Northwest moderating by early next week... ...Overview... A broad upper level ridge over the southern half of the CONUS will be in place through much of the medium range period, forcing storm tracks through the northern tier. A vigorous shortwave through the Upper Midwest/Great Lakes will amplify some as it moves into the Mid-Atlantic and the Northeast early next week. Behind this, amplified ridging will build over the Northwest U.S., and slide into the northern Plains as a closed low/upper trough settles over the Pacific Northwest by around next Wednesday. Meanwhile, monsoonal moisture will continue to persist into the Four Corners region through much of the period, though the best potential for heavier to excessive rains will be across the southern half of the Rockies this weekend. ...Guidance/Predictability Evaluation... Rolling waves of low pressure along the northern tier states and a staunch southern ridge are captured well by a general model blend (GMB) through day 4. A blend of both deterministics and probabilistic models are utilized on day 5 before a predominantly ensemble mean blend is utilized to depict the synoptic flow through the rest of the period. On days 3 and 4 a GMB of the 00z EC/CMC/UK and 06z GFS were used to depict the upper trough as it glides across the Upper Midwest/Great Lakes. Differences between the GMB with respect to the timing/intensity of an approaching upper-level low prompted the introduction of the 00z GFS/ECE and 06z GEFS. The 00z GFS/UKMET were replaced by the 00z CMCE on day 6 to align more with the 00z ECE and 06z GFS/GEFS. The day 7 pattern and uncertainty with respect to an upper level shortwave making its way into the Pacific Northwest is captured best by the ensemble means. ...Sensible Weather/Threat Highlights... Anomalously high monsoonal moisture for this time of year, likely tied at least in part to Tropical Storm Celia in the East Pacific, will continue streaming into the Four Corners states into early next week. Locally heavy to excessive rainfall will be possible each day, particularly over sensitive burn scar areas and considering the multiple day repeating nature of this activity. The best chance for impactful rainfall looks to be over parts of Colorado/New Mexico mainly through Sunday with favorable upslope flow interacting with the moisture already in place. A slight risk was maintained across northern New Mexico on the experimental day 4 excessive rainfall outlook where good model agreement overlapped with areas that have seen anomalous rainfall already. A slight risk was introduced over parts of the same area on day 5 due to the continued stream of heavy rainfall. 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 though remain highly dependent on still uncertain timing of the front. A weak boundary settling across the Gulf Coast as well as the next cold front dropping into the region, should allow for enhanced rainfall into the middle of next week from Florida and along the Gulf Coast. Excessive heat across the Southern U.S. should finally begin to wane this weekend though anomalies around 5 to 10 degrees above normal will continue across the lower Mississippi Valley and Southern Plains on Sunday, with a handful 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. In the West, ridging through the region should present an excessive heat threat across parts of the Northwest through Monday with the above normal temperatures then tracking through the Rockies, Plains, and Midwest Tuesday-Thursday. Kebede/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 Hazards: - Heavy rain across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Southern Rockies, the Southern Plains, and the Southwest, Sun-Mon, Jun 26-Jun 27. - Flooding occurring or imminent across portions of the Upper Mississippi Valley, the Northern Plains, and the Northern Rockies. - Excessive heat across portions of the Lower Mississippi Valley, the Central Great Basin, the Southern Plains, the Northern Great Basin, California, the Southeast, and the Pacific Northwest, Sun-Mon, Jun 26-Jun 27. - Excessive heat across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Southeast, the Southern Plains, and the Ohio Valley, Sun, Jun 26. 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