Extended Forecast Discussion NWS Weather Prediction Center College Park MD 217 AM EDT Mon Jun 21 2021 Valid 12Z Thu Jun 24 2021 - 12Z Mon Jun 28 2021 ...Heat intensifies late week over the interior Northwest/West toward record levels... ...Heavy rain threat for the mid-section of the country late this week... ...Guidance/Predictability Evaluation... The WPC medium range product suite was derived from a composite of best clustered solutions of the 18 UTC GFS/GEFS mean, 12 UTC ECMWF/UKMET and NAEFS/ECENS means along with the 01 UTC National Blend of Models days 3-4 (Thu-Fri) in a pattern with above average continuity and predictability. Prefer a solution more in line with the still compatible GEFS/NAEFS/ECENS means starting next weekend amid growing forecast spread. Developing differences include hot ridge transitions over the West, but especially with longitudinal focus of downstream trough amplification over the central U.S. as energies dig lee of Rex blocking. 00 UTC model guidance does not seem to clarify the differences. ...Weather Highlights/Hazards... An upper low just off northern California is forecast to meander offshore later this week as a hot ridge builds inland through the Northwest. This will allow temperatures to climb to 15-25+ degrees above normal from Washington/Oregon to the northern Rockies, and more generally 5-15 degrees above normal along and west of the Rockies. Record highs are likely from the Pacific Northwest to the northern Rockies, with afternoon temperatures peaking well over 100F are forecast for the interior sections of the West. Little to no rainfall is expected to ease the high heat throughout the broad region. Downstream, robust upper trough digging from south-central Canada will solidify a wavy and fortified cold front to move steadily over the central to eastern U.S., inviting moisture return by later week. Well organized showers and storms will significantly increase rainfall/runoff potential along and ahead of the front from the Midwest to the Mid-South, Southern Plains and across the Ohio Valley and Appalachians to the Northeast. Schichtel 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, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml