Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Tue Jul 19 2022 Valid 12Z Fri Jul 22 2022 - 12Z Tue Jul 26 2022 ...Dangerous heat to persist over the Central U.S. through early next week... ...Overview... Guidance shows the axis of a strong upper ridge stretching across much of the south-central U.S. during the period, albeit with some uncertainty over exactly where the highest heights will be on a day-to-day basis. This ridge will keep hot and humid weather over the central/southern Plains for a majority of the period. Some southern locations could see readings approach or break daily records for highs and very warm nighttime lows. With somewhat less extreme anomalies, areas from the Tennessee/Ohio Valleys through the Mid-Atlantic and New England will experience multiple hot days as well. The West should see moderate temperatures relative to normal late week through the weekend with the approach/ejection of eastern Pacific upper trough energy, followed by higher readings over the Northwest early next week. The initial Pacific energy and other features across southern Canada and the northern tier U.S. will flow around the ridge and feed into a broad northeastern U.S./eastern Canada mean trough, supporting one or more waves/frontal systems and episodes of showers and thunderstorms from the northern tier into the East. Monsoonal moisture over the Southwest/southern Rockies will promote daily chances of showers and storms, some of which could lead to flash flooding. This activity may increase in coverage and intensity during the weekend and early next week. ...Guidance Evaluation/Predictability Assessment... Models and ensembles continue to agree with the large scale pattern of south-central U.S. ridging and progressive flow across the northern tier U.S. and southern Canada. However the guidance has been variable for details within the northern stream flow, the day-to-day specifics of exactly where strongest ridging will be (affecting specifics of the Southwest monsoon), and late period flow details over the Northwest. Guidance still appears to be trying to converge upon an intermediate solution for the shortwave tracking out of the Northwest as of Friday. Otherwise confidence remains low for nearby southern Canada energy, with differences leading to inconsistency for frontal/wave details between the northern Plains and northeastern U.S. Models/means are starting to show a shortwave crossing the Gulf of Alaska around Friday-Saturday and then progressing through western/central Canada. This feature would bring another front into the northern tier early next week. An average of the 12Z GFS/ECMWF/CMC and 18Z GEFS/12Z ECMWF means looked good for depicting this evolution, with the ECMWF/CMC running a little ahead of the other solutions. The 18Z GFS seemed too amplified with its upper trough. New 00Z GFS/CMC runs appear to fit well with the preference by early day 7 Tuesday. Meanwhile guidance increasingly diverges for Northwest U.S. flow by late in the period, demonstrated by the new 00Z GFS bringing a compact upper low into the northern Great Basin versus latest ECMWF/CMC runs building a stronger ridge. At the very least, even the GEFS mean is not very supportive of 00Z GFS specifics by next Tuesday, with the 18Z GFS ridge more representative. Teleconnections relative to the ridge that builds over the northeastern Pacific keep the door open for a little residual troughing over the Northwest while majority clustering leans more toward a ridge--but not as strong as the 12Z ECMWF/CMC. The 00Z CMC has trended somewhat weaker with its western ridge. The updated forecast started with a 12Z model composite early in the period and then transitioned to 50-60 percent total ensemble mean weight by days 6-7 Monday-Tuesday. This approach provided reasonable continuity for the shortwave ejecting from the Northwest early in the period and then increasingly accounted for detail uncertainties within the more agreeable mean pattern mid-late period--leaning somewhat more to upper ridging over the West by next Tuesday and reflecting the preferred average for the system moving through western/central Canada. ...Weather/Hazards Highlights... Continue to expect most of the greatest temperature anomalies to be over and near the central Plains through the period, with multiple days of highs 10-15F above normal. Some of the heat may also extend into parts of the Tennessee Valley. By Sunday-Monday a cold front may suppress the heat over the north-central Plains. Typically hotter southern Plains locations will see less extreme anomalies but overall there will be a broad area with highs reaching or exceeding 100F for highs, while very warm lows in the upper 70s to low 80s will provide little nighttime relief. This heat wave should bring scattered records, most likely over the southern Plains to lower/mid Mississippi Valley. Over the West, monsoonal moisture and associated diurnally favored showers/storms with locally heavy rainfall may keep parts of the Four Corners/Great Basin region within a few degrees on either side of normal during through the period. There is a general signal in the guidance that rainfall should increase in coverage and intensity during the weekend and early next week but with considerable uncertainty over the specifics. The initial shortwave ejecting from the Northwest and then lingering weak trough energy should keep that region near or a tad below normal through the weekend. The majority scenario of some degree of upper ridging building into the Northwest by next Tuesday should lead to a warming trend, with some highs possibly reaching up to 10-15F above normal. The combination of shortwaves aloft and surface waves/fronts will likely produce one or more episodes of showers and storms from the northern tier states into the East during the period, with some heavy rainfall possible. Currently the best signal for enhanced rainfall extends from the Midwest through the Lower Great Lakes into the Mid-Atlantic, but recent guidance inconsistency with important details at the surface and aloft temper confidence in the specifics for now. The Mid-Atlantic and Northeast will be on the very warm to hot side from late week through the weekend, with some locations possibly seeing more consecutive days of plus 5-10F or so anomalies for highs than previously experienced so far this summer. Temperatures should trend closer to normal from north to south by early next week as a couple fronts arrive. Persistent moisture will allow for multiple episodes of showers/thunderstorms over the Southeast/Florida and central Gulf Coast region. Best organization may be late this week. Highs should stay near normal over the Southeast. Rausch/Kebede 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