Extended Forecast Discussion NWS Weather Prediction Center College Park MD 304 AM EDT Wed Aug 03 2022 Valid 12Z Sat Aug 06 2022 - 12Z Wed Aug 10 2022 ...The Southwest Monsoon Resumes a Very Active Phase Late This Week... ...Heavy rain likely across parts of the Upper Midwest on Saturday... ...Overview... Guidance expects a fairly typical summertime pattern with the main band of westerlies across southern Canada and northern tier CONUS, though with upper ridging to the south tending to be somewhat stronger than the climatological mean. An upper low should lift very slowly northeastward offshore the West Coast. The models and ensembles agree on the large scale pattern but significant shortwave differences develop within the westerlies from fairly early in the forecast. As a result confidence decreases for surface front/wave details and in turn for associated areas of rainfall which could be heavy at times over portions of the northern half of the central/eastern U.S. Meanwhile the monsoonal pattern over the West should become more pronounced again late this week and likely remain fairly active through the weekend and perhaps into next week. ...Guidance Evaluation/Predictability Assessment... The upper ridge across the southern/eastern portion of the lower 48 was captured well by the deterministic guidance and ensemble means throughout the period. There's uncertainty with respect to the upper trough moving across southern Canada and the Northwest beginning on day 3. The 18z GFS has consistently attempted to split the upper flow across the aforementioned region while the 12z EC/UK have a more uniform solution. The 12z CMC agrees with the GFS with respect to the split flow solution. These discrepancies are manifested in the QPF as the EC and UK have a stronger signal for heavy precip across the Upper Midwest while the GFS has a weaker QPF footprint. Nonetheless, a general model blend was utilized to split the difference here. The day 3 blend was used once again for day 4 as a slightly more progressive yet weaker shortwave displayed in the 12z EC/UK was used to mitigate a more pronounced yet slower solution posed by the 18z GFS and 12z CMC. The 18z GEFS and 12z ECE were introduced into the blend by day 5 to help with spread presented by the latest deterministic guidance with respect to embedded shortwave impulses swinging through the Great Lakes. Ensembles were predominant in the blend by days 6 and 7 to account for general spread along the East Coast. ...Weather/Hazards Highlights... Expect hot temperatures over northern half of the Plains into the Midwest late this week into the weekend, eroding from the northwest as a cold front approaches. Some highs may reach 10-15F above normal and a few record highs may be possible over the High Plains. Very warm conditions should extend into the Great Lakes/Northeast through the weekend with some gradual cooling early next week. Over the West, maximum temperatures will tend to be somewhat below normal over the Great Basin/Southwest and vicinity due to persistent clouds and periods of rain. The Northwest should trend more above normal as some degree of upper ridging builds. Highs could locally reach 10-12F above normal. Parts of the Pacific Northwest may experience heat risks this weekend as a result. For precipitation, the main threats for flash flooding will be associated with monsoonal moisture over the Southwest/Great Basin/Rockies as well as with fronts/waves over northern and central parts of the U.S. east of the Rockies. The combined signals for rainfall and already wet conditions over the Desert Southwest into the central Rockies/Great Basin late this week into the weekend support some Slight Risk areas in the experimental days 4-5 Excessive Rainfall Outlooks. Farther east, one area of potential focus for significant rainfall will be over the Ohio Valley, Central Appalachians and Northeast along a front that stalls and then returns north as a warm front late this week into the weekend. A trailing wavy front progressing eastward from the Northern Plains may also generate some areas of heavy rainfall between the northern half of the Plains and eastern U.S. from the weekend into next week. 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 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