Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Thu Aug 29 2019 Valid 12Z Sun Sep 1 2019 - 12Z Thu Sep 5 2019 ...Hurricane Dorian forecast to affect Florida and parts of the Southeast U.S. by this weekend/early next week... ...Expected Weather Pattern... An upper level ridge centered over the Four Corners region on Sunday and a broad trough over the north-central U.S. is expected to prevail going into the early part of the week. An upper low off the Pacific Northwest coast will likely move inland and spur the development of a surface low and cold front across southern Canada and the northern Plains by the end of the forecast period. Hurricane Dorian will be steered by a building upper level ridge over the western Atlantic and likely result in a turn towards the west-northwest towards Florida by early next week. ...Model Evaluation... Beyond Sunday night, model spread increases substantially in the eventual evolution of the closed low/trough near the Pacific Northwest, with the GFS faster to bring an embedded shortwave impulse inland compared to the ECMWF and CMC, and the UKMET remains stronger with the upper level ridge over the Intermountain West. Confidence is below average by Tuesday and beyond owing to big timing and amplitude differences noted across southern Canada, and a mainly ensemble blend was incorporated into the forecast by that time. In regards to Dorian, the GFS remains to the north of the model consensus, and the latest 00Z CMC, ECMWF, and UKMET appear to be close to each other on Monday as the storm approaches Florida. ...Sensible Weather... The main weather story will be Hurricane Dorian and its eventual track towards the Southeast U.S. late Sunday and into Monday, with the Florida Peninsula likely to be directly affected. Heavy rain is expected across much of central Florida and eventually towards the Florida Panhandle by Tuesday as the storm is expected to track in that general direction, although less certain by that time. Forecast rainfall amounts have increased some since the previous forecast and more concentrated near the expected track, and damaging winds can also be expected along with storm surge near the coast. The National Hurricane Center has additional information pertaining to the hurricane and its forecast over the next several days. Elsewhere across the continental U.S., a relatively dry weather pattern is likely across much of the central and western U.S. next week owing to the large upper ridge in place and the lack of any major storm systems. There will likely be some episodes of showers and storms from the Dakotas to New England with shortwave impulses tracking eastward around the ridge, but no significant heavy rainfall events appear likely away from the southeastern U.S. Temperatures are forecast to be about 5 to 15 degrees above average across the western U.S. early in the forecast period before returning closer to normal values by the end of next week. Slightly below normal temperatures return to the northern Plains by midweek after the passage of the cold front. Hamrick Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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