Extended Forecast Discussion NWS Weather Prediction Center College Park MD 331 PM EDT Thu Jun 16 2022 Valid 12Z Sun Jun 19 2022 - 12Z Thu Jun 23 2022 ...Heat over the northern/central Plains through the weekend likely to shift into the Midwest through Southeast next week... ...Overview... The latest guidance is consistent in showing a transition from an amplified trough-ridge-trough configuration on Sunday toward a more typical summertime pattern by next Wednesday-Thursday, featuring a broad upper ridge across much of the southern half of the country and progressive band of westerlies across the northern tier states. Widespread hot temperatures will prevail underneath the evolving ridge, with highs reaching 100F as far north as the Dakotas into Sunday followed by the most anomalous high temperatures shifting more into the Midwest through Southeast from Monday onward. The amplified flow regime in place through the weekend should promote an early monsoon type pattern over the Four Corners states, while the strong dynamics ejecting through the northwestern states Sunday into Monday may help to produce locally heavy precipitation over/near the far northern Rockies. Canadian low pressure associated with this ejecting energy will push a front into the Plains, producing some areas of showers/thunderstorms. Farther east, there will be potential for rain ahead of a warm front advancing into the Great Lakes/Northeast and scattered diurnal showers/storms across Florida. ...Guidance/Predictability Evaluation... Trends in the latest guidance suggest a slightly more progressive pattern with the GFS trending particularly faster with the progression of the mean trough in the West. On day 3, a general model blend was utilized to mitigate te progressive output of the 06z GFS with respect to the western trough but also to find a middle ground between the closed upper low that is shared by the 00z EC/CMC and the open wave carried by the 00z UKMET and the 06z GFS. There's reasonable agreement between the selected models on the general contours of the upper ridge centered over the Deep South/Mississippi Valley. The 00z GFS was included in the general model blend on day 4 to help emphasize the piece of shortwave energy rotating through the mean trough in Montana. By day 5 the 00z GFS is swapped out for the 06z GEFS to moderate the attempt by the deterministics to split flow over the Northwest. Weighting is highest for the 00z EC and 06z GFS through day 5. The 00z ECE/CMCE were introduced through the rest of the period while the 06z GFS and 00z CMC removed by day 7. The 06z GFS was faster than the 00z EC with the upper low propagating along the British Columbia coast on day 6 while the ensemble means had more of a reasonable averaged solution. ...Sensible Weather/Threat Highlights... The strong upper trough ejecting through the northwestern U.S. during Sunday-Monday may focus some areas of locally moderate to heavy precipitation over/near the far northern Rockies. The vigorous dynamics, sufficient moisture, and recent significant precipitation supported the introduction of a Slight Risk area in the experimental day 4 excessive rainfall outlook (early Sunday into early Monday) over parts of western Montana. Highest elevations may see some snow with this system. The unusually early monsoon type pattern farther south will bring much above normal moisture for this 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 a front slowly advancing through the West, though with activity tending to decrease in the northwestern part of the Four Corners region. There are still mixed signals over how much rainfall the interaction of this moisture with the western front advancing into the Plains will produce. However the potential for some training/repeat activity may have to be monitored as consensus shows this Plains front becoming aligned west-east along the southern edge of the westerlies by Wednesday-Thursday. Farther east, the East Coast/western Atlantic upper trough and possible embedded low may bring some showers to New England through Sunday. 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, with some activity possibly on the heavy side. This front may slow down once it reaches the eastern Great Lakes and Mid-Atlantic/Northeast. The Florida Peninsula should see multiple days of diurnal showers/storms from the weekend into next week as the front pushing into area decelerates and eventually dissipates. The most anomalous temperatures during the period will be with a heat wave across the northern half of the Plains through Sunday and pushing into the Upper Midwest as well by Monday, with highs reaching up to 20-25F above normal. 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 at least in the upper 70s are forecast in portions of the north-central U.S. A front moving into the Plains should start a cooling trend/eastward shift of the heat, especially over the northern Plains. As the heat extends into the Midwest through Southeast from Monday onward, plus 10-15F or so anomalies for highs should become common and may challenge daily record highs/warm lows. Southern parts of the Plains will stay hot through the period but with anomalies tending to be in the plus 5-10F range. Before next week's warmer trend over the East, the northern half of the region will see highs 5-10F (locally more) below normal on Sunday, perhaps lingering into Monday over northern New England. Also from Sunday into Monday the upper trough crossing the West will bring the region a couple cool days with highs up to 10-15F below normal. After Monday the West will see various areas of somewhat above or below readings. Kebede/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 Hazards: - Heavy rain across portions of the Central Rockies, the Central Great Basin, the Northern Plains, the Northern Rockies, the Southern Rockies, the Northern Great Basin, the Southern Plains, and the Southwest, Sun-Mon, Jun 19-Jun 20. - Flooding possible across portions of the Upper Mississippi Valley and the Northern Plains. - Flooding occurring or imminent across portions of the Upper Mississippi Valley, the Pacific Northwest, the Northern Rockies, the Northern Great Basin, and the Northern Plains. - Flooding likely across portions of the Northern Plains. - Excessive heat across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Sun-Thu, Jun 19-Jun 23. - Excessive heat across portions of the Central Plains, the Lower Mississippi Valley, the Tennessee Valley, the Great Lakes, the Middle Mississippi Valley, the Southern Appalachians, the Upper Mississippi Valley, the Southeast, the Southern Plains, and the Ohio Valley, Mon-Thu, Jun 20-Jun 23. - Excessive heat across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Sun-Mon, Jun 19-Jun 20. - Excessive heat across portions of the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Great Lakes, and the Ohio Valley, Tue-Thu, Jun 21-Jun 23. 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