Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM 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 12Z ECMWF could be a little slow with its closed low, favoring a blend with the ECMWF mean and prior ECMWF run as well as the 12Z CMC. However the new 00Z CMC has come in with an even slower upper low. 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. For the purposes of the manual forecast the 12Z CMC and ECMWF mean along with the 00Z/24 ECMWF offered the most similar cluster to reflect the general potential for wave development. By late in the period the GFS and especially GEFS mean are also questionable in their depiction of a weaker upper ridge rebuilding over the northeastern Pacific versus the ECMWF/ECMWF mean/CMC. ...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. 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 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. 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 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