Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 PM EDT Thu Jul 01 2021 Valid 12Z Sun Jul 04 2021 - 12Z Thu Jul 08 2021 ...Threat of heavy rain lingers near the Gulf Coast into next week as Tropical Storm Elsa could impact Florida by midweek... ...Overview... The large scale pattern is expected to become less amplified and more typically summer-like during the medium range period as the upper trough over the northeastern U.S. lifts into the Canadian Maritimes early in the week. A seasonably strong upper ridge is forecast over the Four Corners states, while a weak upper trough/low may move across the south-central CONUS and help cause continued rain chances, while the main jet stream/westerlies meander over the northern U.S. and southern Canada. Additionally, what is now Tropical Storm Elsa has the potential to impact Florida around midweek. ...Guidance/Predictability Evaluation... In terms of the overall midlatitude pattern, guidance is pretty agreeable with the pattern described above. A mainly deterministic model blend was able to be used especially for the first part of the forecast period. The 00Z CMC was removed by around midweek as it had a stronger upper low in the Eastern Pacific offshore of the Pacific Northwest with a different evolution compared to other models. There were some fairly minor differences with shortwaves in the northern stream, which were handled by transitioning to a blend favoring more of the agreeable GEFS and EC ensemble means later in the period. However, with Tropical Storm Elsa, guidance is quite variable in terms of its track and strength. The 00Z ECMWF as well as most of its ensemble members take a weaker Elsa fairly far east of Florida into the western Atlantic. Meanwhile, the 00Z/06Z GFS take a stronger Elsa into the eastern Gulf of Mexico, impacting the western Florida peninsula, while GEFS members vary quite a bit on their low tracks. The 00Z CMC appeared in between, and the 00Z UKMET clustered fairly well with the GFS runs, but the 12Z UKMET opens Elsa into an open wave by around Monday. Thus, uncertainty is rather high with Elsa, and its track and strength uncertainties feed on each other, as a stronger system could influence its environment more and push westward compared to a weaker system drifting/turning northeastward. The WPC forecast followed the NHC track, which was closer to the GFS runs and the 00Z UKMET. ...Weather Highlights/Hazards... With an initial weakening front in the Southeast, and lowering heights over the south-central U.S., there will be support for persistent showers and thunderstorms in the Gulf Coast states next week. The heaviest rain may be across portions of Texas, with multi-inch totals likely to accumulate over a few days. Farther west, some late-day monsoonal type showers and thunderstorms are likely each day over the Central/Southern Rockies through the medium range period. Periods of rain are forecast along and ahead of a front from the north-central to northeastern U.S. And, heavy rainfall and flooding will be a threat where Elsa ends up tracking, along with high winds near its track. Current forecasts show heavy rain for portions of the Florida Peninsula and across the Georgia and Carolina coast around Wednesday into Thursday with Elsa. The historic heat wave will continue to lessen in magnitude by the medium range period as the ridging weakens, but temperatures nearing and exceeding 100 degrees (depending partially on elevation) remain expected for the Great Basin and Northern Rockies through much of next week. Some rain showers over the northern Rockies may offer slight relief to the heat but they will do little to ease the growing drought over much of the West. The north-central U.S. can also expect a hot day on the 4th of July before a cold front brings temperatures down toward normal on Monday into Tuesday. Temperatures will generally be a few degrees cooler than average in the south-central U.S. through the week with the cloudiness and showers. Meanwhile, a cooler than average July 4th is forecast for the Northeast, but temperatures warm into the 90s by Tuesday. Tate 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