Extended Forecast Discussion NWS Weather Prediction Center College Park MD 225 PM EDT Sat Oct 26 2024 Valid 12Z Tue Oct 29 2024 - 12Z Sat Nov 02 2024 ...Heavy snow and wind threat for the north-central Rockies and nearby High Plains Tuesday-Wednesday... ...Heavy rain threat for the Plains/Midwest mid-later next week... ...General Overview... An amplified upper-level trough about to dig into the Pacific Northwest will spread highly unsettled weather through much of the western U.S. early next week to include potentially heavy high- elevation snow, gusty winds and colder temperatures. This trough will then push eastward against a warm and expanding upper ridge over the central to eastern U.S., resulting in a wavy sharp front across the mid-section of the country where a moderately heavy rain event is forecast from the Plains through the Mississippi Valley and Midwest for the latter half of next week. The trailing portion of the front is forecast to stall, followed by a resurgence of moderate/heavy rain over the southern Plains late next week and into the weekend. ...Guidance/Predictability Assessment... Forecast spread seems lower than normal Tue/Wed and a guidance blend seems to offer a solid forecast base. The model spread on the timing of a low pressure wave developing along the front over the central Plains on Day 4 remains a noticeable issue by Day 5 when the wave is forescast to head toward the Great Lakes. The GFS remains the fastest guidance while the deterministic ECMWF, CMC, and Ukmet all depict a slower and more amplified wave. On the other hand, both ECMWF and CMC have sped up the eastward progression of the wave from previous runs. Meanwhile, the ensemble means from the GEFS, EC, and CMC all show very good agreement on placing the wave near/over the central Great Lakes by Thursday morning, which is faster than the slow guidance from the EC, CMC and Ukmet. The WPC blend adopts a solution that is very close to the consensus of the ensemble means for this low pressure wave. In addition, there has been a gradual trend for the models to place the pre-frontal moderate to heavy rainfall farther south toward the southern Plains Days 4 to 5. The WPC blend for the medium-range forecast period is based on 40% from the 00Z EC/EC mean, 40% from the 06Z GFS/GEFS, and 20% from the 00Z CMC/CMC mean, but with the 06Z GFS minimized on Day 5. ...Weather/Hazards Highlights... Guidance continues to show excellent agreement that a cold front associated with a digging upper level trough from the Pacific will be steadily moving through the western U.S. early next week. Periods of rain, high-elevation snow, windy and colder conditions are expected to overspread much of the region with frontal passage. Locally high winds could impact portions of the southern Rockies and southern High Plains as the colder airmass digs into the region. This may also lead to the onset of frost/freeze for some of these areas for the first time this season. Modest cyclogenesis will advance a front across the northern Plains and upper Midwest through early next week. This front is forecast to sharpen with time as it continues to push against an expansive high pressure system across the eastern and southern U.S. Snow will linger over the northern to central Rockies and into the northern High Plains behind a low pressure wave. The snow could be heavy for the higher elevations of Wyoming Tuesday into Wednesday given upper divergence and lower level upslope flow. Accumulating snow could spill into the nearby High Plains and Black Hills as well. Ahead of the sharpening front, a long fetch of return flow from the Gulf of Mexico appears to initiate and support a threat of heavy rain from the central/southern Plains through the Mississippi Valley and into the Midwest with embedded thunderstorms midweek. The trailing portion of the front is forecast to stall over the southern Plains where moderate to heavy rainfall could linger and then expand northeastward by next weekend. The WPC Day5/Wed-Thu Excessive Rainfall Outlook introduced a Marginal Risk area given potential for training and favorable upper trough and right entrance region jet dynamics. In the meantime, precipitation associated with the next Pacific system and long- fetch moisture is forecast to re-focus moderate precipitation into the Pacific Northwest through latter next week, with high- elevation snow reaching into the northern Rockies. The digging trough in the West will usher in and sustain colder than normal temperatures for pretty much the entire western U.S. through late next week. In contrast, high temperatures reaching into the upper 80s to lower 90s will challenge some daily records across the southern Plains to the mid-South early next week. The expanding upper ridge together with a long fetch of strong and gusty southerly winds at the surface will send the warmth well to the north and east, reaching into the Great Lakes and eventually New England through the middle and late next week. High temperatures reaching well up into the 70s to near 80 degrees will be enough to set some new daily record high temperatures from the Great Lakes to New England Wednesday and Thursday. Temperatures across the country appear to moderate by next weekend as the upper troughing weakens in the West while a large high pressure system builds in the eastern U.S. with Gulf moisture returning across the southern Plains. Kong/Schichtel 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