Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Sat Jun 11 2022 Valid 12Z Tue Jun 14 2022 - 12Z Sat Jun 18 2022 ...Dangerous/Record Heat from the Midwest into east-central/southeastern U.S. especially during Tuesday-Wednesday... ...Overview and Guidance/Predictability Evaluation... The latest guidance continues to show a fairly rapid transition from one amplified pattern to another, leading to significant weather changes over some areas during the period. Into midweek an upper trough will support below normal temperatures over the West (aided by flow around deep low pressure over southern Canada) while a strong eastern ridge will promote sufficiently hot conditions to challenge daily record highs from the Midwest into parts of the Southeast, with a central U.S. cold front and accompanying showers/thunderstorms separating the two extremes. Then during the latter half of the week expect the eastern ridge to give way to the trough continuing to progress across the northern half of the East, with rainfall of varying intensity continuing along the leading cold front, while a sharpening trough reaching the West Coast by Saturday encourages upper ridge amplification over the Plains. This new pattern should lead to well above normal temperatures over the northern half or so of the Rockies/Plains toward the end of the week. A consensus approach among the models early in the period and models/ensemble means later on continued to provide a fairly stable forecast with typical run-to-run refinements and adjustments. Among guidance available from the 12Z/18Z runs, the UKMET strayed to the southern fringe of the spread for the upper low tracking along and northeast from the northern Montana border so it had the least weight in the updated blend. The new 00Z run compares better to the majority. Meanwhile the latest CMC runs trend a lot flatter with northern tier flow that consensus says should amplify toward the East Coast late in the week. Thus the CMC was phased out of the blend after Thursday. Guidance is still refining details of individual impulses within the overall trough, affecting frontal specifics. Latest clustering suggests the leading front reaching the Great Lakes by Thursday may weaken in favor of an upstream front that becomes more prominent by Friday. Additional changes are certainly possible in upcoming model runs. For the upper trough nearing the West Coast, the 00Z GFS seems to complete a correction (begun in the 18Z run) from the earlier 12Z run that had pulled off a closed low offshore California. The 12Z GFS evolution had very little support from GEFS/ECMWF/CMC ensembles so it was not used in the forecast. Other models show some variability with this trough as well, supporting a blended/ensemble mean depiction. ...Sensible Weather/Threat Highlights... Strong low pressure evolving just north of the Canadian border and the supporting upper dynamics may produce some enhanced rain and even high elevation snow over the far northern Rockies and vicinity into Tuesday. The trailing front pushing through the Plains and into the Great Lakes may focus areas of locally moderate to heavy rainfall, but with continuing uncertainty regarding magnitude and location of highest totals. The combination of impulses in northwesterly flow aloft and a front aligned from the Great Lakes/Ohio Valley into the Mid-Atlantic/Carolinas Tuesday-Thursday may generate one or more episodes of convection. Again the guidance signals are very ambiguous with respect to the details of this activity. Meanwhile locations across the Southeast and Gulf Coast may see diurnally favored showers and thunderstorms on one or more days. The upper trough nearing the West Coast toward the end of the week should bring mainly light rainfall to parts of the Northwest. The large scale pattern at that time could bring enough moisture northward to support some rainfall over Arizona and the Four Corners region. Expect highs to be 10-20F above normal from the Midwest and parts of the Great Lakes into the Carolinas during Tuesday-Wednesday, with numerous locations challenging record highs. A broad area of record warm lows will be possible as well. Some plus 10-12F anomalies for highs could persist over the Ohio Valley/Great Lakes into Thursday but with less potential for daily records. Northern/central parts of the East should see a noticeable cooling trend by Friday-Saturday. Areas from the southern Plains into the Southeast will be on the hot side through the period with highs tending to be 5-10F above normal. The chilly upper trough crossing the West will hold highs to 10-20F below normal over the northern Rockies/Great Basin on Tuesday with less extreme cool readings on Wednesday. As the upper pattern transitions, California and the Great Basin will see a couple days of warm readings mid-late week followed by highs of 10-20F above normal becoming established over the northern-central Plains by Friday-Saturday. Areas along the West Coast should see modestly below normal highs when the upper trough reaches the area by Saturday. 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