556 FXUS02 KWBC 221958 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 358 PM EDT Mon Jun 22 2026 Valid 12Z Thu Jun 25 2026 - 12Z Mon Jun 29 2026 ***Additional heavy rain for the Central Plains and very hot conditions for the Desert Southwest through Friday*** ***Hazardous heat to develop this weekend across the South*** ...General Overview... A relatively zonal upper level flow pattern is expected to be in place for the beginning of the forecast period Thursday, and the upper ridge over the Southwest states weakens after Friday. This will be due to an amplifying trough over the northwestern quadrant of the country over the weekend, bringing a welcomed cool down after a hot week. This strong trough will support an organized low pressure system that will emerge from the Rockies to the central/northern Plains with a relatively potent cold front crossing the Pacific northwest and Intermountain West. This will likely result in a downstream upper ridge developing over the east- central U.S. towards early next week with a building heatwave over the South. ...Guidance/Predictability Assessment... Most of the latest 00/06Z UTC guidance remains well-clustered on the general pattern through the medium range period late this week, through the weekend, and into early next week. Guidance indicates the pattern will begin to shift from more zonal to amplified flow first as a broad upper-trough begins to dig over the western U.S. and then as an upper-high develops over the southeastern U.S. Variable upper-wave timing in the flow not surprisingly leads to a bit more uncertainty on temperatures and precipitation, particularly later in the period as the mean upper-flow begins to shift northward over from the Rockies eastward, though the NBM looked like a good starting point overall through at least the late week. The guidance begins to diverge a bit more into the weekend particularly as one upper-wave rounds the trough and then ejects eastward onto the northern Plains, leading to deep lee cyclogenesis and system development. The 00Z CMC is much faster/more southerly compared to the 00Z/06Z GFS and then 00Z ECMWF which is the slowest. Heavier precipitation over the northern Rockies/Plains and throughout the Midwest into the Ohio/Tennessee Valleys looks likelier compared to the drier NBM, though differences with the timing/progression of upper-waves/surface system reflection lead to greater uncertainty on coverage and general location. The updated WPC forecast was based on an initial composite blend of the 00Z ECMWF/ECMWF AIFS/CMC/UKMET and 06Z GFS given the good agreement on the main features. The CMC was removed mid- to late period (UKMET is also time-limited) and replaced by a contribution from the ECens/GEFS means given the noted divergence in the solutions and the more outlier nature of the CMC with this guidance cycle. ...Weather/Hazards Highlights... Multiple mesoscale convective systems are likely to affect much of the central Plains and extending eastward to include the Ohio Valley through the end of the week and into the weekend, with some areas getting an additional 2-4 inches of rain over already saturated grounds from recent heavy rainfall. A lingering frontal boundary with shortwave energy aloft and strong moisture convergence will provide enough instability and lift to sustain these thunderstorm complexes, and some of these storms could produce flash flooding. A day 4/Thursday Slight Risk ERO stretches from the central Plains to the Ozarks with a day 5/Friday Marginal ERO from the Ozarks vicinity east in to the Ohio/Tennessee Valleys to cover this threat. Some strong to severe thunderstorms are also a distinct possibility, particularly across the western High Plains on Thursday. At least scattered thunderstorm chances look to continue through the Midwest into the Ohio/Tennessee Valleys into the weekend as a frontal boundary lingers and then lifts northward through the region. Elsewhere across the nation, rainfall increases for Washington and Oregon to close out the work week with the storm system moving through the region, and a larger area of heavier rainfall develops across the Dakotas as the main surface low ejects eastward over the northern Plains by the weekend. Heavy precipitation is looking more likely along the northern Rockies on the back side of the system while heavy rain and a possible risk for flash flooding is also looking more likely across portions of the northern Plains Sunday. Scattered showers and thunderstorms are also expected for the East Coast through Saturday with increasing low level moisture in place. The widespread above average heat levels across the western third of the nation are likely to continue going into Thursday, with 110s likely for the lower elevations of the Desert Southwest, and 90s extending as far north as southern Idaho. A strong cold front brings relief from the heat starting Friday and becoming even more noticeable going into the weekend as highs return to below average by late June standards, whereas overnight lows should be less anomalous. The opposite holds true further east as the upper-high begins to dominate the weather pattern. Highs across the southern High Plains are likely to increase into the 100s while a combination of highs in the 90s and high humidity with bring heat indices into the 100-105 degree range (locally up to 110) across the South. This level of heat will be more likely to be a danger to anyone without adequate cooling or hydration, particularly outdoors. Unfortunately, this looks to be a prolonged heat wave lasting into next week and likely expanding further north in coverage. Putnam/Hamrick 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 forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw $$