Extended Forecast Discussion NWS Weather Prediction Center College Park MD 139 AM EDT Sun Jul 04 2021 Valid 12Z Wed Jul 07 2021 - 12Z Sun Jul 11 2021 ...Elsa is forecast to impact Florida and the Southeast through midweek with potential for heavy rainfall and high winds... ...Repeating heavy rain is may persist over southern Texas into Friday as low pressure drifts over the region... ...Overview... The western CONUS ridge/eastern trough persists through the work week and becomes more amplified next weekend as the upper ridge over the Great Basin/Desert Southwest strengthens. A leading shortwave trough pushing east from the northern Great Lakes Wednesday to eastern Canada Friday will push along a wavy cold front over the northeastern CONUS through this time. A trailing Pacific shortwave trough rounds the upper ridge, ejecting from the WA/OR coast Wednesday morning and is expected to amplify into a Midwest/Great Lakes by Saturday, supporting another area of low pressure and associated frontal system for the northern half of the country east of the Rockies. The primary features of interest at lower latitudes will be Tropical Storm Elsa which should impact Florida and parts of the Southeast through the middle of the week, and an upper trough/low drifting southwest from Texas into northern Mexico that may produce heavy rainfall over southern Texas (and northern Mexico). ...Guidance/Predictability Evaluation... Overall a deterministic 12Z/18Z global model blend (the 12Z CMC was unavailable for the forecast) transitioning to a GFS/ECMWF blend with some of their ensemble means produced a decent first guess forecast. For Elsa, the 18Z and now 00Z GFS continue a trend toward a weaker and less wet system crossing northeast over northern Florida Wednesday and the coastal Southeast through Thursday. The UKMET continues to be slower, but stronger with a western track like the GFS while the CMC is the strongest with an eastern Florida Peninsula track and the ECMWF is the slowest, though it does have more of a system than in prior days with an eastern track. Given this uncertainty of timing/strength/track the heavy rain threat is somewhat diminished from previous days, but there is still potential for this system to be impactful. Meanwhile there is good agreement in principle for the shortwave crossing the northeastern quadrant of the lower 48 and a second shortwave amplifying into the Midwest next weekend after rounding the western upper ridge. The 18Z and now the 00Z GFS jump ahead to a faster timing with the latter wave which is a typical bias of the FV3 GFS. ...Weather Highlights/Hazards... An upper low/trough drifting southwest over southern Texas into northern Mexico through next week will support a repeating rain threat over that region continuing for Wednesday into Friday, with a somewhat diminished threat for as much repeating heavy rain as indicated in recent days. However, ample Gulf moisture will be available to this slow moving disturbance, so there is a flooding threat. There is still some potential for heavy rain and high winds for parts of Florida and the coastal Southeast from Elsa Wednesday into Thursday. Please continue to monitor products from the National Hurricane Center for the latest Elsa forecast track information. The wavy front pushing east from the Midwest/Great Lakes will produce periods of rain that could be locally moderate/heavy. On Friday tropical moisture from Elsa may converge on the frontal pattern over the Mid-Atlantic/Northeast and produce heavy rainfall. The system forecast to reach the Midwest/Great Lakes this upcoming weekend looks to interact with Gulf-sourced moisture and result in meaningful rainfall as well. The heat wave over a significant portion of the West will continue at least through next weekend as the Great Basin/Southwest upper ridge restrengthens. The Northwest and northern Great Basin should 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. 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 with slightly below normal temperatures over the Midwest when rainfall is forecast. Jackson/Rausch 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