Extended Forecast Discussion NWS Weather Prediction Center College Park MD 138 PM EDT Thu Jun 30 2022 Valid 12Z Sun Jul 03 2022 - 12Z Thu Jul 07 2022 ...Overview... Broad cyclonic flow aloft will be in place across the north-central to Northeast U.S. for the beginning of the period Sunday-Monday as an anomalous upper low lingers over far northern Quebec. Eventually this low should lift northward next week as a few weaker shortwaves move through across the far northern tier states. Out West, another synoptic scale upper low will weaken and lift through the Pacific Northwest as a second low drops down from the Gulf of Alaska, offering renewed troughing along the West Coast for much of the period. In between, and upper level ridge will build from the Rockies into the Plains with anomalously warm temperatures, especially the early part of next week. At the surface, a quasi-stationary frontal boundary draped from the north-central Plains to the Mid-Atlantic will focus showers and storms, with some locally heavy rainfall. ...Guidance Evaluation/Predictability Assessment... The 00z/06z suite of guidance remains in very good agreement on the synoptic pattern through much of the period. There remain, however, some mesoscale detail differences with the individual shortwaves that will govern the magnitude and extent of heavy rain across the Plains and Midwest. These differences could take until the short range to fully resolve. Regardless, a blend of the deterministic models worked well through day 5. After this, increased the blend of the ensemble means to help temper some addition differences, with less of the CMC by late period due to issues with a shortwave in west-central Canada. This approach maintained reasonable continuity with the previous WPC forecast as well. ...Sensible Weather and Potential Hazards... Scattered showers and storms are expected across the Southeast this weekend with the presence of a weakening frontal boundary and weak impulses moving through the flow aloft. Farther north, a front initially oriented from the Northeast into the Ohio Valley and central Plains will push gradually eastward during the weekend and support organized areas of showers and storms along and ahead of it. Some rainfall may be locally heavy from the central Plains into the Mid-Atlantic on Sunday as moisture converges along a quasi-stationary frontal zone. This front may continue to be a focus for rainfall into early next week as well. Monsoonal moisture over the southern Rockies is also expected to lead to mainly diurnally driven showers and storms, with weak shortwaves and moisture lifting northward between upper ridging to the east and the trough near the West Coast. The West Coast trough will likely produce periods of rainfall over parts of the Northwest, and there continues to be a signal for a period of heavier rainfall near the Canadian border early next week. Some mesoscale convective systems could also extend across the northern Plains/Upper Midwest, aided by northern tier surface features and shortwaves emerging from the West, with models showing potential for at least locally heavy to excessive rains. A slight risk was added today to the day 5 experimental excessive rainfall outlook for parts of the Upper Midwest where models show the best signal for heavy rains, within an area of significant moisture and instability presence. The greatest concern for temperatures will be with heat expected to build again across the central and northern Plains by early next week in response to a strengthening upper level ridge. Highs of 5-15 degrees above normal are possible over the central Plains, equating to temperatures in the mid 90s to low 100s. Southern Plains locations will see a slightly hotter trend as well, but with less extreme anomalies. Out West, below normal highs will spread gradually inland from the West Coast during the weekend into early next week due to nearby upper troughing. A few locations may see highs 10-15F below normal around Sunday-Monday. Expect a moderating trend closer to normal heading into midweek. Across the eastern U.S., a stable upper pattern of westerlies across the Northeast and ridging over the South should keep both daytime highs and overnight lows within a few degrees of climatological averages through most of the period. Santorelli/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, 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