Extended Forecast Discussion NWS Weather Prediction Center College Park MD 211 PM EDT Sat Oct 12 2024 Valid 12Z Tue Oct 15 2024 - 12Z Sat Oct 19 2024 ...Overview... As the medium range period begins Tuesday, upper troughing will settle in across the eastern half of the U.S., leading to below normal temperatures along with frost/freeze concerns for the north- central U.S. to Northeast, along with lake-enhanced precipitation. Meanwhile upper ridging (aside from embedded energy) will set up atop the Interior West, and this ridge is forecast to shift eastward into the central U.S. through the week with warmer than average temperatures underneath it. The pattern in the West is forecast to flip to troughing by midweek to late week with a couple rounds of reinforcing energy. This will cool temperatures there and lead to increasing precipitation chances, including higher elevation snow. ...Guidance/Predictability Assessment... Model guidance are in reasonable agreement regarding the evolution of the synoptic pattern across the eastern half of the country next week. Ridging in the Central U.S. slowly shifting east and an equally slow moving East Coast trough moving into the Atlantic are captured well by the deterministic and ensemble guidance. There's uncertainty around a mid-to-late week trough that is forecast to propagate from the Gulf of Alaska into the western CONUS. A more progressive and more amplified wave pattern is depicted by the Euro suite while the GFS and Canadian suites suggest the development of a split flow pattern over the West with a cut-off low over the Southwest by late next week. The GFS and Canadian suites have shown some run-to-run consistency for this split flow solution. Despite this, the GEFS and CMCE have more spread in their solution than the ECE. For days 3 and 4, the blend consists of the 06z GFS and 00z ECMWF/CMC. The UKMET was a bit too aggressive with a ridge axis and shortwave energy in the West on days 3 and 4 respectively. A more ensemble-centric blend is favored beginning on day 5 and the 00z EC was removed from the blend by day 6 due to it's outlier solution regarding the mid-level pattern in the West/Central U.S.. ...Weather/Hazards Highlights... Behind a surface low pressure system pulling north of New England by Tuesday and underneath the upper trough causing cool westerly flow, lake-enhanced and terrain-enhanced precipitation is likely from the Great Lakes region into the Interior Northeast and into the central Appalachians. Colder temperatures should allow for snow especially in the higher elevations. Precipitation should taper off Wednesday, and the East is likely to be dry for later week as a cool surface high sets up behind a secondary cold front. The exception could be across South Florida, which is forecast to see return flow of moisture by late week for increasing rain and thunderstorm chances. The developing and reloading upper trough and multiple surface fronts moving into the West will gradually push precipitation into the northern/central West Coast by Tuesday and through the northern Rockies into Wednesday-Thursday. While there is good confidence in the overall event, unresolved specifics of the upper trough lead to greater uncertainty with respect to the southward/eastward extent of precipitation as well as magnitude. Expect relatively higher totals over favored coastal areas and the Cascades. Higher elevation snow is likely by midweek, which may be the first snow of the season in some locations given the warm Fall in the West thus far. While details vary, model guidance generally shows precipitation spreading east through the Interior West/Rockies into Thursday, and by Friday Gulf moisture may stream in just ahead of the upper trough for some increasing rain chances in the Plains to Upper Midwest. An upper ridge aligned over the Rockies into Tuesday and then shifting eastward by mid and later week will promote well above normal temperatures in its vicinity. The biggest anomalies are forecast across the northern Rockies and High Plains Tuesday- Wednesday, where highs into the 70s and 80s are 15-25 degrees above average for mid-October. These warm temperatures will shift into much of the Plains and Midwest by Thursday-Friday. For much of the eastern U.S., temperatures are forecast to be below average by 10-15 degrees Tuesday-Wednesday underneath cool high pressure. Morning lows may cause frost/freeze concerns from the north-central U.S. through the Midwest/Great Lakes and Northeast/Appalachians. Expect some moderation there by Thursday- Saturday. Meanwhile, the upper trough and frontal surges coming into the West will lead to below normal temperatures spreading gradually inland for the latter half of the week. These colder temperatures may also lead to additional frost/freeze concerns for still susceptible growing areas. Kebede/Tate 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 (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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