Extended Forecast Discussion NWS Weather Prediction Center College Park MD 301 PM EDT Sun Oct 09 2022 Valid 12Z Wed Oct 12 2022 - 12Z Sun Oct 16 2022 ...Heavy rain and flooding are possible Thursday-Friday in the Northeast ahead of a strong cold front... ...Pattern Overview... A highly amplified and somewhat stagnant upper level pattern will be in place late week into next weekend, as an upper high and ridge hover from the eastern Pacific into the Northwest with a weak upper low farther south, and a deep trough from the Plains to the East Coast. Two or three well defined cold fronts are expected to pass from the Northern Plains to the eastern U.S., thus reinforcing the cool and autumnal airmass with generally below normal temperatures continuing. Ahead of the first cold front, Gulf moisture streaming in will lead to widespread rain trekking across the eastern half of the U.S. Wednesday-Friday. Rain is forecast to be particularly heavy in the Northeast around Thursday-Friday as the mid-upper level trough becomes negatively tilted, with gusty winds also a potential concern. Behind the initial front, lake effect/enhanced precipitation is possible downwind of the Great Lakes. The West is forecast to remain warmer than normal and mainly dry under the influence of the upper ridge, but moisture could return to the Southwest and Southern Plains next weekend. ...Model and Predictability Assessment... By day 3/Wednesday, model guidance continues to show good agreement that a potent trough will be in place across central North America, and its axis should shift slowly eastward Thursday-Friday as additional energy spills into the trough, rounding its shape and producing a closed low. There remains some north-south uncertainty in the exact centroid of the upper low, but regardless anomalously deep troughing will be well established over the east-central CONUS as shown by the full array of models. By the weekend, the trough is likely to remain in place, but its evolution appears more questionable as some energy may lift while additional energy digs into the western side. The 00Z/06Z GFS continues the closed low through Saturday while the 00Z ECMWF temporarily opens up the low before the extra energy spills in from the north. The exact axis of the troughing will affect frontal timing at the surface and there could be some additional shifts to the frontal position over the next few days. Regardless of these differences, a multi-model and ensemble blend sufficed for this strong trough pattern. Perhaps a bit more uncertain is the position of the weaker upper low feature near southern California. For the 00/06Z model cycle, the GFS and CMC were on the eastern side of the guidance, while the UKMET and ECMWF were west. GFS runs trended west with time since the previous model cycle, and GEFS members showed some west-east spread but even the GEFS mean was farther west than the deterministic guidance. However, continuity with the upper low position was farther east, so with this variability opted to go with a middle ground but leaning west solution favoring the ECMWF (which was a bit east of the UKMET) and the EC ensemble mean for this feature. The newer 12Z ECMWF came in east a bit of its previous run. The differences with the upper low are somewhat small but do become somewhat impactful for the timing of its gradual shift eastward that eventually could bring a source of lift for rain across the Southwest into the Southern Plains. ...Sensible Weather and Potential Hazards... The first strong cold front and the associated upper trough will bring a return to widespread showers and storms from the central Gulf Coast to the Ohio Valley and Great Lakes on Wednesday as deeper moisture is advected northward. The combination of increasing instability and favorable kinematic parameters in the warm sector may lead to some strong to severe thunderstorms in terms of high winds across southern parts of the Great Lakes region into the Ohio/Tennessee Valleys on Wednesday, and then perhaps across portions of the Northeast on Thursday, although confidence is still limited on exactly where these storms could develop. Rainfall amounts are likely to be highest in the interior Northeast Thursday and continuing into Friday as deeper Atlantic moisture is advected towards the northern Appalachians with an increasing low level jet. A Slight Risk area remains in place in WPC's experimental Day 5 Excessive Rainfall Outlook for this region. Terrain could enhance rain totals in areas like the Adirondacks and White and Green Mountains, but lower elevations could see heavy rainfall as well and generally have lower Flash Flood Guidance, leading to a broad risk for flash flooding. Elsewhere, lake enhanced showers (mainly rain but could be in the form of snow in Upper Michigan/far northern Wisconsin) are likely for the Thursday through Saturday time period, and showers could become more widespread with another frontal system by Sunday. Most of the West should remain dry through the latter part of the workweek with perhaps a few isolated showers/storms over Arizona and New Mexico into Texas, with coverage possibly increasing next weekend. Much of the northwestern U.S. and California should have above normal temperatures each day with the upper ridge remaining nearly anchored in place near the coast, and a brief warm-up is likely from the ArkLaTex region to the Ohio Valley ahead of the front on Wednesday. This will likely be followed by highs about 5-15 degrees below average to close out the workweek and going into next weekend from the Upper Midwest to the Ohio Valley and Great Lakes, with highs only in the 40s and 50s for most of these areas. Tate/Hamrick 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, experimental excessive rainfall outlook, 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/#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