Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Wed Jun 15 2022 Valid 12Z Sat Jun 18 2022 - 12Z Wed Jun 22 2022 ...Heat over the northern/central Plains through the weekend likely to shift into the Midwest through Southeast next week... ...Overview... A very amplified upper pattern will be in place during the weekend, featuring a strong central U.S. ridge between troughs near the western and eastern coasts. Then flow should steadily trend toward a more typical summertime regime by next Wednesday when the main axis of westerlies will likely align across the northern tier while broad ridging (anchored by a high near the Lower Mississippi Valley) would cover a large part of the southern half of the lower 48. Widespread hot temperatures will prevail underneath the ridge, with highs reaching 100F as far north as the Dakotas during the weekend followed by the most anomalous high temperatures shifting more into the Midwest through Southeast during the early/middle part of next week. The amplified flow regime in place through the weekend should promote an early monsoon type pattern over the Four Corners states along with moisture and rain chances in the Northwest. Farther east, there will be potential for rain ahead of a warm front advancing into the Great Lakes/Northeast and scattered diurnal showers and storms across Florida. ...Guidance/Predictability Evaluation... The latest models and ensemble means maintain good agreement for the large scale pattern evolution through the period. Solutions develop typical spread for the upper high center (around or stronger than 594dm) expected to settle over or near the Lower Mississippi Valley by the middle of next week, and continue to vary with some of the details and timing of western U.S. upper trough/low energy ejecting into southern Canada. The 12Z ECMWF strayed to the fast side of the spread for the latter feature late in the period while the new 00Z run has adjusted slower. A weaker mean trough should persist along the West Coast once the initial feature departs, supported by modest incoming energy and an upper low that may reach near Haida Gwaii by next Wednesday. Within the trough near the East Coast, there is still some indecision as to the location of an embedded upper low which is most likely to be over or north/northeast of Maine during the first half of the period. Latest trends suggest that the upper trough could depart from the Northeast a little more quickly in response to the flatter flow upstream. The array of guidance generally favored an intermediate/consensus approach for the updated forecast, by way of a 12Z/18Z operational model blend transitioning to a model/mean mix by the latter half of the period. The resulting forecast provided reasonable continuity. ...Sensible Weather/Threat Highlights... The upper trough pushing inland over the West after early Saturday should bring light to locally moderate rainfall to parts of the Northwest. Precipitation extending into the northern Rockies during the weekend and perhaps into Monday (snow likely limited to highest elevations) could be locally heavy given the strong dynamics and available moisture crossing the region. It will take some additional time to resolve important details of the upper level system which will help to refine the forecast. The unusually early monsoon type pattern farther south will bring much above normal moisture for the time of year northward through the Four Corners states and vicinity 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, though with activity tending to decrease in the northwestern part of the Four Corners region. Currently there are mixed signals over how much rainfall the interaction of this moisture with the western front advancing into the Plains will produce. Farther east, the East Coast/western Atlantic upper trough and possible embedded low may bring a few showers to New England over the weekend. Then an area of showers and thunderstorms may push across the Great Lakes and possibly into the Northeast under northwesterly flow aloft and ahead of an advancing warm front. The Gulf Coast should see a diminishing of diurnally favored showers and thunderstorms into the weekend while the Florida Peninsula should see multiple days of diurnal showers/storms from the weekend into next week as the front pushing into the Southeast stalls. 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 persist into early next week. 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. As the heat extends into the Midwest through Southeast during Monday-Wednesday, plus 10-15F or so anomalies for highs should become common and may challenge daily record highs/warm lows. Before next week's warmer trend over the East, the northern half of the region will see highs 5-10F or so below normal this weekend. Also during the weekend, the upper trough crossing the West will bring the region a couple days of highs up to 10-15F below normal. More moderate cool temperatures will prevail over the West on Monday followed by areas of somewhat above or below readings. Rausch/Tate 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