Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM 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 and Guidance/Predictability Evaluation... Guidance agrees well in depicting an amplified upper pattern from late week through the weekend, with a central U.S. ridge separating one trough/embedded low beginning to move into the West and another trough digging over the East Coast/western Atlantic (with a possible low over Maine and/or the Canadian Maritimes). By the first part of next week the core of the western trough energy should eject northeastward to yield a weaker/broader mean trough over the West, while the upper ridge reaching the east-central U.S. and downstream trough should remain rather amplified. This pattern should bring multiple days of precipitation to the Northwest/northern Rockies as well as potential for enhanced rainfall over parts of the Four Corners states, along with a period of cool temperatures as the upper trough/leading front push eastward. Meanwhile some locations in the northern Plains could see highs up to 20-25F above normal late week through the weekend with a few record highs possible, followed by a gradual cooling trend. The upper trough/embedded low near the East Coast will support a cool weekend and perhaps some showers over the Northeast. With GFS runs having settled into the primary cluster for the East Coast/western Atlantic upper trough over the past 24 hours, solutions are now similar in principle. One item of interest detail-wise is that by Sunday the 12Z ECMWF adjusted somewhat weaker with the core of the upper trough and less defined with the possible upper low versus a number of previous runs while other solutions are deeper than the 12Z ECMWF. A general blend would provide a stable forecast. Deeper trend in the new 00Z ECMWF supports this idea. For the deep trough reaching the West Coast by around early Saturday, the models have tended to be fairly similar up to about four days out in time before straying with details of where the embedded upper low may track and how quickly it will eject from the West. GFS/ECMWF runs have been erratic over recent days while the CMC has generally been on the slow side but trends faster in the new 00Z run. The multi-day consistency of the ensemble means for the overall trough would support continued inclusion of their solutions as part of the overall blend by the latter half of the period, with individual model differences canceling out. Thus guidance comparisons led to starting the updated forecast with the 12Z/18Z operational models Friday into Sunday and then trending toward half models and half 18Z GEFS/12Z ECMWF means by day 7 Tuesday. ...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. 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 with a fairly brief heat wave across the northern half of the Plains, with most areas seeing a couple days with highs reaching 20-25F above normal. 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. 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. 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