Extended Forecast Discussion NWS Weather Prediction Center College Park MD 136 AM EDT Wed Jun 29 2022 Valid 12Z Sat Jul 02 2022 - 12Z Wed Jul 06 2022 ...Overview... Guidance agrees fairly well on the large scale pattern, featuring a Rex block configuration with ridging over northwest Canada and an upper low anchoring a mean trough off the West Coast. Meanwhile, a broad mean trough over eastern Canada will extend into the northeastern U.S., while southern tier U.S. ridging holds strong and also builds into the Rockies and northern Plains. The eastern North America mean trough will support one or more rainfall-focusing frontal systems to the east of the Rockies while the trough near the West Coast will keep nearby temperatures on the cool side and occasionally bring unsettled weather to the Northwest. The National Hurricane Center is monitoring a broad area of low pressure over the northwestern Gulf of Mexico, with flow around the southern tier upper ridge possibly bringing this feature and its moisture into the western Gulf Coast region. Expect hot temperatures to expand over the central U.S. during the first half of next week as the Plains ridge aloft becomes more pronounced. ...Guidance Evaluation/Predictability Assessment... The latest models and ensembles continue to show very good consensus on the large scale pattern, though with some lingering uncertainties in the details, which may take until the short range period to resolve. This includes individual shortwaves within the Canadian trough whose influence affects frontal positions east of the Rockies, as well as the details of the upper trough near the West Coast. In the West, models suggest some interaction/merging of an initial low off the Pacific Northwest with a compact low dropping south out of the Gulf of Alaska. This should act to reinforce the upper trough through the period, with a slight west-northwest drift of its main axis. By early next week, shortwave energy rounding the base of the trough should eject into the Northwest, but there are some timing differences with this which has implications for QPF across the northern Rockies/high Plains late period. For the northwestern Gulf feature, latest model runs have backed off slightly and mostly don't show much of a surface or upper level reflection by the start of the medium range period. The ECMWF is the most pronounced with this feature, although hesitate to call it an outlier because given the tropical nature of this feature, its not out of the realm of possibilities. Regardless, uncertainty is low at best for both persistence of this feature and exactly where it will track. The WPC forecast for the overnight package used a blend of the operational deterministic models for days 3-5 with more inclusion of the ensemble means days 6-7 (up to 50 percent) to try to mitigate the differences seen with the Western U.S. trough. This maintains good continuity with the previous WPC forecast as well. ...Sensible Weather and Potential Hazards... Moisture associated with a tropical feature into the West Gulf region may enhance rainfall across parts of the lower Mississippi Valley and into the Deep South, though very uncertain on both QPF amounts and impacts. See the latest from the National Hurricane Center on this. Showers and storms may also linger farther east into the Southeast into this weekend with the presence of a weakening boundary and impulses moving through the flow aloft. Farther north, a front initially oriented from the Great Lakes into the Midwest will push gradually southeastward and support organized areas of showers and storms along and ahead of it. Some rainfall may be heavy from the central Plains into the Mid-Atlantic and southern New England, with deceleration of the front later in the weekend helping to maintain the potential for some locally significant totals. Possible interaction with southern tier moisture is yet another factor that will require monitoring. Monsoonal moisture over the Four Corners region may promote scattered areas of heavier rainfall with impulses and moisture lifting northward between upper ridging to the east and the trough near the West Coast. This West Coast trough may produce periods of rainfall over parts of the Northwest and there is a signal for increasing rainfall near the Canadian border around early next week as some energy ejects from the trough. Moisture/convection could also extend across the northern Plains/Upper Midwest by next Monday-Tuesday ahead of a High Plains wave and leading warm front with eventually may stall across the region by Tuesday into Wednesday. Rainfall may return to parts of the Northeast by next Tuesday as well associated with a weak area of low pressure near the coast. The greatest concern for temperatures during the medium range period will be with heat likely to build again across the central and northern Plains by early next week in response to an upper level ridge. Highs around 10 to 15 degrees above normal is possible for parts of the north-central Plains, equating to temperatures in the mid to upper 90s. Southern Plains locations will see slightly hotter conditions as well but with less extreme anomalies. Out West, below normal highs will spread gradually inland from the West Coast due to nearby upper troughing with a few locations with highs 10-15F below normal around Sunday-Monday. In the East, a lingering frontal boundary should keep both daytime highs and overnight lows near normal through most of the period. Santorelli/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