Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 PM EDT Thu Oct 13 2022 Valid 12Z Sun Oct 16 2022 - 12Z Thu Oct 20 2022 ...Pattern Overview... Guidance continues to show a persistent amplified pattern, with eastern U.S. troughing held in place by strong ridges over the Northwest U.S./western Canada and the Atlantic. The Northwest ridge will be part of a long-term Rex Block configuration, with an initial upper low crossing the Southwest and then energy within the southern part of a splitting eastern Pacific trough forming a new upper low offshore California by midweek. This pattern will support well below normal temperatures over the eastern half of the country as well southern Rockies/High Plains, along with very warm temperatures over the Northwest. The Southwest upper low should produce heavy rainfall from parts of the Southwest to the Texas Gulf Coast into early next week. The Great Lakes will see multiple days of lake effect precipitation (including some snow) while a developing system early in the week may bring meaningful precipitation to the Northeast. ...Model and Predictability Assessment... Within the eastern U.S. mean trough, the main evolution of interest involves digging central Canada energy that should form an upper low over or near the Great Lakes by early next week. Then consensus tracks this upper low eastward and then northward, with developing/consolidating low pressure likewise lifting northward with time. Recent slower trends in the GFS through the 12Z run have led to improved clustering for low pressure/frontal progression over the Northeast. In fact the 12Z UKMET/CMC are even a little faster than the 12Z GFS with the Northeast front. Models/ensembles still depict the splitting of eastern Pacific trough energy early next week. There is generally typical scatter for whether the southern stream closed low ends up offshore California. However predictability appears lower for the northern energy that ultimately rounds the western ridge and drops into southern Canada and northern CONUS. Thus there has been a fair amount of variability for the associated frontal system and anchoring wave. Some of the spread/continuity differences correspond to recent stronger trends for the Northwest ridge. This latter trend also affects if/when an upstream front may reach western Canada (and possibly far Northwest U.S.) after midweek. Agreement is steadily improving for the timing and weakening process of the upper low crossing the Southwest early in the period. For associated QPF there is reasonable agreement/continuity across the southern Rockies-High Plains but there has been a noticeable trend for greater suppression of the eastern Texas/central Gulf Coast portion of the rainfall shield. The array of latest guidance recommended starting the updated forecast with a 00Z/06Z model composite for the first half of the period, followed by a transition to a model/mean mix as detail uncertainties increase. 13Z NBM QPF appeared reasonable over many areas, though it seemed somewhat on the light side along the front dropping through the South and Florida Peninsula, and by late in the period with lake effect activity. ...Sensible Weather and Potential Hazards... Heavy rainfall is likely to develop over the Southwest and southern High Plains Sunday and then focus over southern/coastal Texas on Monday, aided by a potent but gradually weakening closed low crossing the Southwest and a surface front pushing through the southern Rockies/Plains. The most confident area for significant rainfall extends from far eastern Arizona to near the Big Bend of Texas on Sunday with a Slight Risk area depicted in the experimental Day 4 Excessive Rainfall Outlook. Confidence is lower in the location of highest rainfall totals farther east on Monday and soil conditions become drier as one moves east as well, so additional time will be needed to assess any flash flood threats to the east of the southern High Plains. The clouds and rainfall will keep high temperatures 10-20F below normal. Within the long-term eastern upper trough, Canadian energy digging into a Great Lakes upper low will develop a potent surface wave and frontal system that could produce areas of moderate to heavy rainfall over the Great Lakes and Northeast on Monday and Tuesday. Important timing differences in the guidance are becoming less pronounced but are still enough to maintain some uncertainty in coverage/amounts of enhanced rain. Well below average temperatures (minus 10-20F anomalies, locally greater for Tuesday highs in the central Appalachians) will spread through the eastern half of the country behind this system, with areas of lake effect rain/snow gradually decreasing in coverage/intensity after midweek. High pressure building over the Midwest and into the Southeast in the wake of a cold front will support a broad area of dry weather. The persistent Northwest upper ridge will keep the region's temperatures well above normal through the period, with each day featuring some plus 10-20F anomalies. Scattered record highs will be possible. Rausch/Kebede 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