Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 PM EDT Tue Jun 14 2022 Valid 12Z Fri Jun 17 2022 - 12Z Tue Jun 21 2022 ...Heat wave expected across the northern/central Plains Friday through the weekend, slowly moderating and shifting slightly eastward early next week... ...Overview... A strong mid-upper high is forecast to take hold of the central U.S. late week into the weekend, with some gradual suppression into next week. Expect widespread hot temperatures underneath the ridge, with highs reaching 100F as far north as the Dakotas. The central U.S. ridge will separate an unseasonably deep trough/low moving from the West Coast late week into the Northwest while weakening early next week and troughing across the Northeast. This pattern should allow for an early monsoon type pattern to set up in the Four Corners states along with moisture and rain chances in the Northwest, as well as possibilities for rain in northwest flow across the Great Lakes region, and scattered diurnal showers and storms across Florida. ...Guidance/Predictability Evaluation... Guidance remains in good agreement with the overall upper level/surface pattern through early next week. The upper high/ridge will flirt with or exceed 594dm at the 500mb level at times as it meanders around the lower half of the Mississippi Valley, with only small variations in model guidance. Troughing across the Northeast is also fairly agreeable initially, though the biggest differences lie in the potential and timing for an upper low to close off around Sun-Mon over the Northeast/southeastern Canada, which could affect surface low placement. The 00Z UKMET was particularly deep with this upper low while some ECMWF runs including yesterday's and today's 12Z runs were weaker. The 00Z ECMWF seemed like a good middle ground, however. Meanwhile with the western troughing, there are some detail differences for energy within the trough, including late this week when some models like the UKMET indicate splitting energy with two small closed lows within it. There remain some slight timing differences in its ejection eastward as well--the 00Z GFS was on the faster end. Overall, model agreement was sufficient to use a multi-model deterministic blend favoring the 00Z ECMWF and 00/06Z GFS for the beginning of the period, with perhaps more of a deterministic models component compared to a typical distribution of models/means even through the end of the period given the fairly good model agreement. ...Sensible Weather/Threat Highlights... The cold front reaching the East Coast late this week will produce some showers and thunderstorms with some rainfall also possible farther back to the west. The deep upper trough setting up near the East Coast and possible upper low over Maine and/or the Canadian Maritimes may bring multiple days of cool and at times showery weather to the Northeast. Recent models have increased rain amounts across the Great Lakes states this weekend into early next week with an impulse moving through the northwest flow pattern. The Southeast and Gulf Coast regions will see diurnally favored showers and thunderstorms late this week and then over the Florida Peninsula from the weekend into next week as the front pushing into the Southeast stalls. The upper trough reaching the Northwest coast by Friday night or early Saturday should initially bring light to locally moderate rainfall to parts of the Northwest. Precipitation extending into the northern Rockies by the weekend and early next week (snow likely limited to highest elevations) may become heavier depending on exactly how energy ejects from the mean trough and the degree of interaction with leading moisture flow from the south. The unusually early monsoon type pattern will bring much above normal moisture for the time of year northward through the Four Corners states and vicinity from late this week through the weekend, supporting an increase in coverage and intensity of rainfall across the region. Rain/thunderstorms should continue into early next week as the moisture interacts with the front slowly advancing through the West. The most anomalous temperatures during the period will be with a heat wave across the northern half of the Plains, with most areas seeing a couple days with highs reaching 20-25F above normal this weekend. This heat may pivot around the central portions of the Plains where plus 10-20F anomalies may be more persistent. Some daily records for highs and warm lows will be possible, with even some potential for a few monthly records for warm lows, given that lows in the upper 70s are forecast in portions of the north-central U.S. A front moving into the Plains should start a modest cooling trend/eastward shift of the heat early next week. The East will see a pronounced cooling trend heading into the weekend, with highs up to 5-10F below normal over the Northeast. By early next week the Plains/Mississippi Valley upper ridge may reach far enough east to bring a return of hot weather to the Tennessee Valley and Southeast, with decent coverage of plus 10-15F high temperature anomalies next Tuesday. Cool air pushing into the West late week through the weekend will support highs up to 10-15F below normal before readings trend closer to normal early next week. Tate/Rausch 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