Extended Forecast Discussion NWS Weather Prediction Center College Park MD 202 AM EDT Tue Oct 24 2023 Valid 12Z Fri Oct 27 2023 - 12Z Tue Oct 31 2023 ...Overview... Mean troughing across the West will dominate the medium range period (Friday-Tuesday) as a couple of shortwaves drop in acting to reinforce and amplify the trough. Models suggest some separation of streams this weekend as southern stream energy dives into the Southwest (with a possible closed low) and northern stream energy slides across the northern tier. In response, upper ridging will build over the Southeast/East. This pattern should support a multi-day period of enhanced rainfall over parts of the central U.S., with pronounced contrast between unseasonably cold conditions over the West/Plains and very warm weather farther eastward. ...Guidance Evaluation/Predictability Assessment... The WPC forecast for tonight blended the latest operational runs early in the period and mixed in some of the GEFS/ECens means later on to account for decreasing confidence in exact details within an overall agreeable large scale pattern. The most notable differences in the guidance arise this weekend with the next shortwave as it drops through the West. There is still plenty of uncertainty and run to run variability in the timing and strength of this system (some models show a closed low), and the new 00z GFS run for tonight came in significantly stronger/more cut off with the low late in the period, lingering it over the Southwest for longer, rather than opening up and pushing east like some other guidance/the ensemble means show. There are also timing differences with northern stream energy skirting the Northern Plains this weekend. Synoptically speaking though, confidence in the forecast is higher than average with mainly just these smaller scale differences in the details to be worked out. ...Weather/Hazards Highlights... Instability and anomalous moisture will continue to fuel at least moderate rainfall along a wavy front near the Southern Plains and a small marginal risk was continued on the Day 4/Friday ERO across northeast Texas to Oklahoma where guidance suggests some locally enhanced totals, over a region that should also see heavy rainfall in the short range period. Activity should become heavier and more widespread this weekend into the Mid-Mississippi Valley/Midwest/Ohio Valley though as the front briefly stalls and allows for possible repeat/training of storms. There is still some uncertainty on exactly where the heaviest totals set up, but fairly dry antecedent conditions may limit the flash flood threat overall, allowing for just a marginal risk for now on the Day 5/Saturday ERO. Lighter rain should also extend into the Great Lakes/Northeast from the weekend into early next week. Out West, additional precipitation/higher elevation snows will move eastward across the Region this coming weekend followed by a drier trend as the moisture contributes to the enhanced rainfall area farther east. Potential exists for some snow in the northern fringe of the precipitation shield but specifics remain very uncertain and require monitoring. Renewed and amplified troughing across the West will continue a prolonged period of below normal temperatures, with daytime highs 15-30 degrees below normal (locally colder over Montana late this week) to spread across much of the interior West and the Northern/Central Plains. By next Monday-Tuesday, much below normal temperatures could sink well into the Southern Plains/Texas. A few daily records are possible within this cold air mass. Meanwhile, well above normal temperatures across the Central U.S. and the Midwest will shift east and settle this weekend across the East/Southeast as upper ridging builds over this region. Expect a broad area of highs 10-20 degrees above normal with some morning lows 20-25 degrees above normal. Daily records are possible, with record warm lows likely to be more numerous than record highs. As the upper ridging weakens and retreats back to the south early next week, temperatures should moderate back closer to normal across the Southeast and up the East Coast. 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 forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw