Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 PM EDT Tue May 30 2023 Valid 12Z Fri Jun 02 2023 - 12Z Tue Jun 06 2023 ...Well above normal to near record temperatures from the Upper Midwest to the Northeast into late week... ...Broad multi-day thunderstorm and local heavy rain threat continues for parts of the Plains/Rockies... ...Overview... Latest guidance maintains the idea of a blocky large scale pattern dominated by a Great Lakes-Midwest upper ridge/high that gradually retrogrades through the weekend and settles over the northern Plains into central Canada early next week. Meanwhile diffuse troughing initially over the West may contain multiple shortwave impulses, with low predictability for the details but with consensus showing a gradual weakening trend for this energy while a southern stream Pacific trough/low approaches California. The forecast pattern should lead to continued episodes of locally heavy showers and thunderstorms from the northern Rockies/High Plains southward into the southern Plains. While this synoptic theme has held up well over recent days, latest guidance has really gone astray for details within eastern North America mean troughing that has been advertised to develop downstream from the upper ridge. Thus compared to past days, confidence has declined with respect to some temperature and precipitation specifics over the East after Friday. Well above normal temperatures will prevail from the northern Plains into Northeast on Friday, with eastern locations trending cooler thereafter, while the Northwest should also see multiple days of very warm to hot weather. ...Guidance Evaluation/Predictability Assessment... On day 3 a general model blend consisting of the 06z GFS and 00z EC/CMC/UKMET. Higher weighting was given to GFS and EC to highlight the southern stream shortwave energy spinning through the Southwest on Friday. The EC The 00z EC/ECE suite diverged from the rest of the guidance beyond day 4. ...Weather/Hazards Highlights... Slow evolution over the large scale pattern over the central and western U.S. should maintain the threat for showers and thunderstorms over parts of the Rockies and Plains during the period. A gradual weakening of initial shortwaves/upper low(s) over the West/Rockies with time should lead to a gradual decrease in heaviest rainfall totals though. Areas from the Sierra Nevada into Great Basin may see some increase of scattered activity by the weekend or early next week as the upper trough/low approaches California. The Day 4 experimental Excessive Rainfall Outlook (12Z Friday-12Z Saturday) reflects two primary areas of emphasis for flash flood potential. A Slight Risk area already depicted over parts of Montana into a small part Wyoming in the previous Day 5 issuance will be extended farther south in this new Day 4 issuance per guidance signals and favorable pattern/anomalous moisture. In addition a Slight Risk area will be introduced over a region centered on the south-central Plains, with guidance now offering sufficient clustering along with upper diffluence to recommend this area. Note that the western half of this area should be more sensitive due to recent rainfall. The Day 5 outlook (12Z Saturday-12Z Sunday) depicts a Marginal Risk area from the north-central Rockies south-southeast into the southern Plains, with a general signal for some locally intense rain rates but no pronounced areas of focus at this time. Rockies/Plains convection should continue to some degree for the rest of the period, though heavy rainfall should become more isolated. The trough/upper low nearing California may promote some increase in showers/thunderstorms over the Sierra Nevada/Great Basin by the weekend or early next week. Over the East, issues with the upper pattern significantly reduce confidence in rainfall specifics, though in general expect the potential for some showers/storms with a couple cold fronts dropping south during the period. There will also be potential for rainfall near the southeastern coast, depending on the evolution of a southern stream low/trough. Well above average temperatures will be common across the northern Plains, Upper/Middle Mississippi Valley, and the Great Lakes/Ohio Valley regions late this week into early next week under the ridge/high aloft. High temperatures in the 80s to low 90s could approach or exceed a few daily record highs late this week into the weekend, with slight moderation possible early next week. Anomalous warmth will also extend across the Northeast into Friday with temperatures of 15-20F above normal likely to set some record highs before a cooling trend for the weekend with some upper-level energy and a backdoor cold front. Expect the Northwest to see a warming trend that could bring highs 5-10F above normal on Friday and at least 10-20F above normal through next Tuesday. Ejection of a northeastern Pacific upper low could dent the heat briefly during the weekend. Meanwhile, much of the southern tier will tend to see near to moderately below normal temperatures, with the best focus for highs 5-15F below normal settling into the central-southern Rockies/High Plains by the weekend and early next week. 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