Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sun Jun 19 2022 Valid 12Z Wed Jun 22 2022 - 12Z Sun Jun 26 2022 ...Expansive area of excessive heat likely to persist across the South into next weekend... ...Overview... A broad upper level ridge centered over the Lower Mississippi Valley (and drifing slowly westward into next weekend) will be the most prominent feature during the medium range period with widespread excessive heat expected across much of the South. To the north, expect weak and progressive systems to ride the top of the ridge through the Central U.S. and Midwest with troughing along both the East and West coasts. Monsoonal moisture will likely continue into at least the middle of the week too across the Four Corners region. ...Guidance/Predictability Evaluation... Model guidance remains in good agreement on the overall pattern, especially with respect to the strong and broad ridge across the Southern U.S.. Systems through the northern tier show typical detail and timing differences, mostly able to be resolved for now with a general model blend (more deterministic models the first half of the period, with more ensembles by the end). One notable place of uncertainty is off the East Coast regarding a cut off low drifing southward, and then possibly retrograding back towards the coast by Thursday or Friday. The GFS has been pretty consistent in showing this low lingering off the Northeast Coast and then quickly getting picked up by the main westerly flow and pushed eastward. Meanwhile, the ECMWF, UKMET, and CMC all support something lingering more off the Carolina coasts and then eventually retrograding slowly westward, although the CMC seems much to far south and actually takes this feature back towards Florida next weekend. Ensemble means generally support their deterministic counterparts, though significantly weaker owing to increased variability in individual member solutions. However, given the uncertainty, leaning on the ensemble means late period seemed prudent at this point for this feature. ...Sensible Weather/Threat Highlights... Anomalously high monsoonal moisture for this time of year, likely tied at least in part to eastern Pacific tropical systems, will continue streaming into the Four Corners states at least through midweek and possibly later into the week as well. Locally heavy to excessive rainfall is possible, particularly over sensitive burn scar areas and considering the multiple day repeating nature of this activity. A showery/stormy pattern could also set up through Friday in central parts of the Plains and Mississippi Valley as a front becomes aligned west-east, with some potential for rain and storms to train in some areas. Farther east, a round of rain is forecast near a warm front in the Northeast with rain forecast to spread into the Mid-Atlantic by Wednesday and beyond. How much rain then lingers across the East Coast will be dependent on the aforementioned upper low/trough feature's existence and track. A surface low/cold front through the Upper Midwest next weekend may also be accompanied by showers and storms. Big westher story though continues to be the broad ridge over the Southern U.S. with anomalously warm temperatures across the Plains and eastward next week. The greatest anomalies (generally 10-15+ above normal) will shift into the South Wednesday-Friday, with high temperatures in the mid-upper 90s and low 100s and lows well into the 70s meaning little relief overnight in many areas. Daily record high max and min temperatures are likely to be widespread. Relatively cooler temperatures with well below normal highs are forecast particularly for New Mexico given the monsoonal clouds and rain coverage, while near normal temperatures stretch through the Rockies and West Coast states. Santorelli 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