Extended Forecast Discussion NWS Weather Prediction Center College Park MD 347 PM EDT Tue Nov 02 2021 Valid 12Z Fri Nov 05 2021 - 12Z Tue Nov 09 2021 ...Overview... The medium range period will be characterized by an upper ridge with its axis gradually shifting from the Four Corners late this week into the Plains early next week, separating mean troughing in the East and the eastern Pacific into the West. A series of fronts coming into the Northwest will keep precipitation chances high there, while a front and developing low pressure system off the East Coast will spread some rain across Florida and up the Southeast coast. ...Guidance/Predictability Assessment... Models continue to show good agreement in a quick moving shortwave across the Lower Great Lakes and Northeast and also a southern stream shortwave through the Southeast on Friday. Uncertainty in the southeast system increases by the weekend though as models suggest amplification of the shortwave spinning up a surface low off the Southeast Coast. The 00z CMC/UKMET are both stronger/slower with the system as it lifts through the Western Atlantic early next week. The 06z GFS is ok early on, but by early next week it may be too quick/weak to eject the system eastward. WPC favored a blend towards the 00z ECMWF and ensemble means for this system which also maintains good continuity with the previous shift. A persistent train of shortwaves coming into the Pacific Northwest shows considerable variability as they track across the northern U.S. and southern Canada this weekend into early next week. Again, the 06z GFS becomes probablematic as its quicker to break down the ridge and much faster with one shortwave Sun-Tues. The next system drops in from Alaska early next week and the GFS is considerably stronger and farther south with this system next Mon-Tues, but does have some support from the 00z CMC as well. Run to run varibility with the deterministic solutions and spread in the enesmbles suggest enough uncertainty that sticking closer to the ensemble means is best at this time. ...Weather/Hazards Highlights... A front over the western Atlantic, Florida peninsula, and the Gulf of Mexico and a developing surface low along it will cause rainfall over much of Florida on Friday as ample moisture streams in. As the low tracks northeastward into the western Atlantic, some rain is expected on the backside for the coastal Carolinas and possibly into parts of the Mid-Atlantic and Northeast Friday into Saturday, but how far west precipitation reaches will depend on the surface low track in the western Atlantic. Current forecasts do not show rainfall reaching very far inland, given a more offshore track of the low. Abundant moisture ahead of frontal systems and upper-level shortwaves edging in from the Pacific will result in periods of enhanced precipitation during the latter half of the week into early next week near the West Coast. Through the period, the Pacific Northwest/far northern California can expect the heaviest precipitation, with normal terrain enhancements and higher elevation snow. Precipitation is likely to spread into the Intermountain West and Rockies as well, with amounts there increasing by next Monday into Tuesday. Behind the aforementioned front in the Gulf, a cold surface high pressure system will maintain below normal temperatures across the southeastern CONUS through the weekend, with highs 10-15F below average and highs/lows 5-10F below normal farther west and north into southern portions of the Mississippi Valley and the Ohio Valley. Some of these regions could see overnight temperatures dip into the mid to low 30s which could result in the first frost of the season for some places. Meanwhile, a more persistent upper-level ridge indicated with this forecast cycle over the west-central U.S. should lead to temperatures that are above average by 10-20 degrees over the Plains and stretching into the Midwest. Periods of unsettled weather will keep highs somewhat below normal over the West Coast on most days. Santorelli/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 Hazards: - Heavy precipitation across portions of California, the Pacific Northwest, and the Northern Great Basin, Mon-Tue, Nov 8-Nov 9. - Heavy rain across portions of the Southeast, Fri, Nov 5. - Flooding occurring or imminent across portions of the Northeast. - Flooding likely across portions of the Middle Mississippi Valley. - High winds across portions of the Mid-Atlantic, Sat-Sun, Nov 6-Nov 7. - Much below normal temperatures across portions of the Lower Mississippi Valley, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Fri-Sun, Nov 5-Nov 7. 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