Extended Forecast Discussion NWS Weather Prediction Center College Park MD 424 PM EDT Tue Oct 11 2022 Valid 12Z Fri Oct 14 2022 - 12Z Tue Oct 18 2022 ...Pattern Overview... Guidance generally agrees upon an amplified upper pattern during the period, with one ridge moving into the Northwest U.S./western Canada from the eastern Pacific and another over the North Atlantic holding a mean trough over the eastern half of North America. An upper low initially offshore southern California should eventually drift into the Southwest while an upstream trough likely splits just off the West Coast during the first half of next week. The most active weather will be associated with wavy frontal systems on the southern/eastern side of the mean trough, as well as ahead of the upper low that moves into the Southwest. Multiple periods of lake effect precipitation are also likely given the combined mean trough aloft and chilly cyclonic flow behind individual surface waves/frontal systems. The forecast pattern will support unseasonably warm temperatures over the Northwest, while a broader area of well below normal temperatures should reach the eastern half of the country into southern Rockies/High Plains early next week versus the less extreme anomalies forecast over the Upper Midwest into Great Lakes/Ohio Valley at the end of this week. ...Model and Predictability Assessment... The large scale pattern has good agreement as well as internal consistency relative to teleconnections on the strongest height anomaly centers, suggesting good predictability of the mean flow. However there are notable differences for one or more important but lower-predictability shortwaves within the eastern upper trough as well as for the upper low moving into the Southwest and shortwave energy approaching the West Coast. The 12Z GFS has strayed a bit on the fast side with the leading front crossing New England during Friday-Saturday and also has a stronger embedded wave. Larger scale differences develop with the trailing shortwaves/surface fronts, with GFS runs generally on the fast side and ECMWF tending to be the slowest (but the new 12Z ECMWF has adjusted somewhat faster). Interestingly, the 12Z UKMET/CMC and 00Z ECMWF become a little faster than the GFS and 12Z GEFS/00Z ECens for the Southwest upper low. The new 12Z ECMWF has adjusted a little slower here as well. Meanwhile recent trends are mixed for where the southern stream component of splitting eastern Pacific shortwave energy will end up by early next week. Given the lower predictability elements within the more confident mean pattern, preference sided with an intermediate solution where differences existed. Thus the updated forecast started with an operational model composite for about the first half of the period and transitioned to a model/mean blend thereafter. In terms of QPF, amounts were raised from the NBM across the Great Lakes to better account for lake effect precip and increased light amounts in other parts of the east-central U.S. to account for the typically low NBM bias for such amounts and intermediate frontal timing. ...Sensible Weather and Potential Hazards... The first strong cold front associated with the long-term upper trough will bring moderate to locally heavy rain across central and eastern New England on Friday, with the potential for some 2+ inch totals. Guidance is gradually improving its signal for heavy rainfall potential by way of at least plus 2-2.5 standard deviations for precipitable water values and a general pattern favorable for bands of rain that could exhibit some training. This scenario may be sufficient to counter recently dry conditions so the experimental Day 4 Excessive Rainfall Outlook has introduced a coordinated Slight Risk area that incorporates about the southern/eastern three-fourths of Maine. Negative tilt of the upper trough and the tight surface pressure gradient may support strong and gusty winds as well. To the west, lake enhanced rain and snow showers are likely across the Great Lakes for the Friday through Saturday time period. Showers could become more widespread late weekend into next week with another frontal system and trailing cold cyclonic low level flow. Timing differences in the guidance for this latter front keep confidence fairly low for rainfall amounts/coverage over the eastern U.S. early next week, ranging between fairly modest to significant. Meanwhile showers and thunderstorms will likely increase in coverage over the Southwest and then into Texas from Sunday into early next work week, as the upper low tracking into the region from the Pacific spreads moisture out to its east. Some of this moisture may interact with a couple fronts forecast to drop southward over the Plains. Much of the northwestern U.S. as well as northern California into parts of the Great Basin should have above normal temperatures each day with the upper ridge anchored over or near the region, with some highs reaching 10-15F above normal. On the other hand, a series of fronts pushed along within/around the eastern upper trough will bring progressively colder temperatures to areas east of the Rockies. Late this week the coolest anomalies (up to 10-15F below normal) should extend from the Upper Midwest into Great Lakes/Ohio Valley. Then expect increasing coverage of highs 10-20F below normal (lows 5-15F below normal) over the Midwest/East next Monday-Tuesday. The southern Plains and vicinity will be quite warm Friday-Saturday but then the region (into the southern Rockies) will trend colder as rainfall spreads across the region. Rausch/Hamrick Hazards: - Heavy rain across portions of the Northeast, Fri, Oct 14. - Heavy rain across portions of the Southwest, the Southern Rockies, and the Southern Plains, Sun-Mon, Oct 16-Oct 17. - Flooding occurring or imminent across portions of the Southeast. - Much below normal temperatures across portions of the Central Plains, the Middle Mississippi Valley, the Tennessee Valley, the Ohio Valley, and the Lower Great Lakes, Mon-Tue, Oct 17-Oct 18. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sat-Mon, Oct 15-Oct 17. 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