Extended Forecast Discussion NWS Weather Prediction Center College Park MD 321 PM EDT Fri Oct 25 2019 Valid 12Z Mon Oct 28 2019 - 12Z Fri Nov 01 2019 ...Well below average temperatures expected for much of the West/Plains next week... ...Overview and Guidance/Uncertainty Assessment... Guidance still shows a strong northeastern Pacific mean ridge aloft (extending into northwestern North America at times) supporting an amplified mean trough over the lower 48, while another ridge persists off the southeastern U.S. coast across the Florida Peninsula and into the Gulf of Mexico. While there is consensus on the general pattern, models and ensembles remain conflicted over the character of the CONUS trough. The latest cycle yields little change in overall clustering with the GFS/GEFS generally on their own in showing a more progressive trough digging into the central U.S. by Tue-Wed versus remaining guidance that has the strong western Canada flow dropping into the West. Teleconnections relative to the strong positive height anomaly center just off the Alaska Panhandle in the multi-day means support a more positively tilted mean trough such as what the ECMWF cluster depicts. In addition the pattern already established plus recent verification and historical model biases all appear to add up to a higher probability that the general ECMWF/ECMWF mean/CMC/UKMET scenario should be more correct. Recent trends/biases suggest that the 00Z Canadian could be a little slow with its closed low, favoring a blend with the well-clustered 00Z ECMWF/UKMET and ECMWF mean. Within the ECMWF cluster there is a signal for the ejecting western trough/upper low to generate what could be a fairly potent area of low pressure somewhere within the Midwest/Ohio Valley/Great Lakes region into Canada by the latter half of the week. Among solutions depicting this feature there has been considerable spread and run-to-run variability so confidence in specifics is fairly low. By late in the period into next weekend, ensemble agreement actually increases (even adjusting for longer lead times) with northeast Pacific ridging and broad central CONUS troughing. ...Weather Highlights/Threats... Areas from the Interior West through the Plains will see the coldest temperature anomalies in the coming week. A strong front dropping south from Canada early in the week will likely bring highs down to 20-40F below normal, especially over parts of Montana/Wyoming/Colorado, for Tue-Wed. Some areas will already be 20-30F below normal on Mon. Readings over the central two-thirds of the lower 48 should moderate somewhat by next Fri but remain well below normal. The cold temperatures Mon-Wed in particular may challenge daily records for lows and/or cold highs. Some of this chilly air may reach southern California and the southern Rockies as the front dips into Mexico. Strong high pressure building over the northern and then central Rockies will support a period of strong winds to its south. Within this pattern expect the best potential for some meaningful snow to extend over parts the northern two-thirds of the Rockies and then across the central Plains and into the Upper Midwest/western Great Lakes. Ejection of a fast-moving lead shortwave may bring one area of snow from the central Rockies northeastward during the early part of the week. Canadian energy dropping into the West should bring another area of snow south-southeast across the Rockies, with any areas of snow to the east/northeast during Wed-Fri sensitive to precise track and strength of possible low pressure. Consult the latest WPC day 4-7 winter weather probabilities for highlighted areas. Assuming a solution closer to the 00Z ECMWF cluster verifies, the front over the Plains will likely hang up for a time before progressing eastward later in the week. This would allow for an increasing flow of moisture into the eastern half of the country and the potential for areas of heavy rainfall. Fracasso/Rausch Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Southern Plains, Tue-Wed, Oct 29-Oct 30. - Heavy rain across portions of the Northeast, the Central Appalachians, the Mid-Atlantic, the Southern Appalachians, the Great Lakes, and the Ohio Valley, Thu-Fri, Oct 31-Nov 1. - Heavy snow across portions of the Central Rockies, the Central Plains, and the Southern Plains, Tue, Oct 29. - Heavy snow across portions of the Middle Mississippi Valley, the Great Lakes, and the Upper Mississippi Valley, Mon, Oct 28. - Flooding possible across portions of the Northern Plains. - Flooding occurring or imminent across portions of the Middle Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains. - Flooding likely across portions of the Northern Plains. - Much below normal temperatures across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Northern Plains, the Northern Rockies, the Southern Rockies, the Middle Mississippi Valley, the Northern Great Basin, the Upper Mississippi Valley, the Southern Plains, and the Southwest, Mon-Wed, Oct 28-Oct 30. - Much below normal temperatures across portions of the Central Plains, the Central Rockies, the Lower Mississippi Valley, the Central Great Basin, the Northern Plains, the Tennessee Valley, the Great Lakes, the Northern Rockies, the Southern Rockies, the Middle Mississippi Valley, the Northern Great Basin, the Upper Mississippi Valley, the Southeast, the Southern Plains, the Ohio Valley, and the Southwest, Thu-Fri, Oct 31-Nov 1. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml