Extended Forecast Discussion NWS Weather Prediction Center College Park MD 237 PM EDT Mon Jul 05 2021 Valid 12Z Thu Jul 08 2021 - 12Z Mon Jul 12 2021 ...Elsa is forecast to cross the eastern Carolinas on Thursday and may result in heavy rainfall near the Carolina Coast and potentially southeastern New England Friday... ...Repeating heavy rain may persist over southern Texas into the weekend as low pressure lingers over northern Mexico... ...Overview... The western CONUS ridge/eastern mean trough pattern will amplify this weekend as a shortwave trough from the Pacific rounds the ridge before stalling over the Upper Mississippi Valley Saturday. The upper ridge over the Great Basin/Desert Southwest will strengthen in the wake of the ridge-riding trough and intensify the ongoing heat wave across The West. An initial shortwave trough pushing east from the Great Lakes to eastern Canada/New England by Friday will drag a weak cold front over the northeastern CONUS through Friday before it lifts back as a warm front ahead of the ridge-riding shortwave trough over the weekend. Tropical Storm (or Depression at that point) Elsa is forecast to push off the Carolinas on Thursday and lift northeastward toward the 40/70 benchmark while an upper trough/low stalls over northern Mexico. These areas may see locally heavy rainfall during the period. ...Guidance/Predictability Evaluation... The most recent guidance has come into much better agreement with the ridge-riding shortwave trough that stalls near the Upper Midwest and with the timing and strength of Elsa. The 06Z GFS and 00Z ECMWF formed a reasonably-clustered pairing with their ensemble means and each other to serve as a good starting point through the period. The 15Z NHC points were used for Elsa for the morning update. Multi-day ensemble trend has been slower with the trough/upper low settling into the Upper Midwest and Great Lakes which was captured by the GFS/ECMWF well. This blended solution was utilized for the sensible weather elements as well, mostly via the 12Z/13Z National Blend of Models. ...Weather Highlights/Hazards... An upper low/trough that stalls over northern Mexico through next week will support a repeating rain threat over that region continuing for Thursday and perhaps well into the weekend, though the threat for extreme totals continues to diminish. However a persistent low-level flow of Gulf moisture will feed into this slow-moving disturbance, maintaining a flooding threat. Heavy rain will accompany Elsa as it tracks through the eastern Carolinas Thursday. Please continue to monitor products from the National Hurricane Center for the latest Elsa forecast track information. With a track very near southeastern New England on Friday, coupled with an approaching cold front, heavier rain may also fall over Cape Cod and perhaps other areas of southeastern New England. That cold front may also bring an area of modest to perhaps heavier rain to upstate New York and the Adirondacks/North Country. The ridge-riding trough forecast to reach the Upper Midwest by Saturday will have access to Gulf-sourced moisture and should result in modest to perhaps significant rainfall for the northern Plains through the Corn Belt to the western Great Lakes as the system becomes blocked/stalls. The heat wave over a significant portion of the West will continue at least into next week as the Great Basin/Southwest upper ridge restrengthens in the wake of the ridge-riding trough. The Coast Ranges, Great Basin, and northern Rockies/Columbian Basin may all see highs 10-15F above normal each day with locally higher readings possible. Several daily high temperature records are under threat across primarily the Great Basin each day with a slight western shift to California this weekend as the ridge axis drifts west. The only slight break over the Pacific Northwest looks to be Thursday when a weak frontal passage nudges highs down to near or slightly below 10F above normal. Meanwhile the strengthening and westward expansion of the upper ridge should promote a hotter trend with time over interior locations of California where temperatures will climb into the 100s and 110s. The southern High Plains/Texas will likely see highs 5-12F below average for most of the week due to cloudiness and rain from the persistent upper level disturbance drifting over that region. The Midwest and Great Lakes will see below normal highs due to rainfall on Thursday and the over the weekend with the next system. The latter system's cold front may also bring a cooling trend into the central Plains by the weekend. Fracasso/Jackson 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, 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