Extended Forecast Discussion NWS Weather Prediction Center College Park MD 252 PM 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 may persist over southern Texas into Friday as low pressure drifts over the region... ...Overview... The western CONUS ridge/eastern mean trough pattern will persist through the work week and become 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/New England Friday will push along a wavy cold front over the northeastern CONUS through this time. A trailing Pacific shortwave trough ejecting from the Washington/Oregon coast around midweek should round the western ridge and then amplify into the Midwest and vicinity 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... Latest guidance continues to agree well in principle for the western ridge and most aspects of northern stream flow, but with spread for details. This favors a starting point that consists of an operational model blend early followed by a transition to a model/mean blend. By the latter half of the period the operational component made some adjustments due to comparisons with other guidance. After early day 6 Saturday the forecast phased out the 00Z ECMWF in favor of the prior 12Z run due to Northeast Pacific upper low progression that has little support from other guidance. GFS input trended toward a split of 00Z/06Z runs due to a mix of more/less appealing details depending on the area. Models are still showing a lot of spread and variability for Elsa. GFS runs have maintained their weaker depiction at the surface but still recurve the shortwave energy as in recent days. UKMET/CMC runs maintain stronger systems at the surface and aloft but have displayed some timing differences from consensus track forecasts. After a brief trend toward the majority, the 00Z ECMWF ended up dissipating the mid level reflection over the Gulf mid-late week. The new 12Z ECMWF reverted back to a stronger system and consensus track. This now leaves the GFS in the weak minority. Meanwhile the blend/ensemble mean approach later in the period provides only gradual nudges in the forecast while individual solutions vary in the precise character of the upper trough amplifying into the Midwest and vicinity. 00Z/06Z models generally trended a bit weaker than continuity for the core of the trough. Models have been suggesting there will be an embedded low but with some variance for location. New 12Z runs seem to be gravitating toward the Upper Mississippi Valley--near the consensus latitude of recent cycles--and are a bit slower. ...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, though the threat for extreme totals has diminished somewhat compared to forecasts from recent days. However a persistent low level flow of Gulf moisture will feed into this slow moving disturbance, maintaining 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--but still with uncertainty for specifics. 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 interact with the front as it reaches the Mid-Atlantic/Northeast and produce heavy rainfall. The system forecast to reach the Midwest/Great Lakes this upcoming weekend could have access to some Gulf-sourced moisture and result in significant rainfall as well. Most guidance has been consistent over the past couple days in signaling the potential for some areas of heavy rain but it will take more time to resolve the magnitude/location/timing. 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 most days with locally higher readings possible. Several daily high temperature records are under threat across primarily the Great Basin each day. The only slight break over northern areas could be Wednesday-Thursday when a weak frontal passage may nudge highs down to near or slightly below 10F above normal. Meanwhile the strengthening and westward expansion of the upper ridge should produce a hotter trend with time over interior locations of California. 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 tend to see below normal highs due to rainfall with the Wednesday-Thursday wavy front and trailing late week/weekend system. The latter system's cold front may also bring a cooling trend into the central Plains by next weekend. Rausch/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