Extended Forecast Discussion NWS Weather Prediction Center College Park MD 310 PM EDT Wed Sep 21 2022 Valid 12Z Sat Sep 24 2022 - 12Z Wed Sep 28 2022 ...Dangerous Fiona forecast to slam toward the Canadian maritimes Saturday with transition from Hurricane to a deep extratropical storm... ...Pattern Overview... Guidance agrees to build an amplified/warming western North American upper ridge this weekend into next week with the decay of a hot ridge over the southern tier U.S.. This transition would allow energetic mid-latitude and northern stream shortwave troughs to more robustly dig downstream to carve out an amplified east-central North American upper trough to focus cooler/unsettled weather and possibly offer some connection to tropical lattudes to monitor by mid-later next week. ...Guidance Evaluation/Predictability Assessment... Model guidance remains agreeable with the track of Hurricane Fiona toward the Canadian Maritimes even as it transitions to a very deep extratropical low during the medium range period. WPC and the National Hurricane Center will also continue to monitor the tropics regarding Invest 98L, which is likely to form into a tropical cyclone in the Caribbean per the NHC Tropical Weather Outlook. The 00z EC was a bit more progressive than the 00z GFS with the cold front moving toward the Gulf Coast next Sunday into Monday. The latest 00z ECMWF/GFS runs were awfully bullish with the depth and track of the tropical system moving through the Caribbean and Gulf next week. The GFS has trended closer toward the basin of the Gulf of Mexico while the EC track has trended closer to western Cuba by next Wednesday with several inches of qpf forecast by both models. Ensembles are much more reserved with qpf maxima associated with this system. Enough uncertainty surrounds this system and the interaction of it's associated moisture with an approaching cold front to tamp down NBM qpf maxima over southern Florida and effectively preserve WPC continuity through the middle of next week. ...Weather/Hazards Highlights... A shortwave trough tracking across the north-central U.S. will combine with energy from northern Canada to deepen a trough with its axis in the east-central U.S. for the early part of next week. This trough and a couple of frontal systems at the surface should help produce some increasing rainfall chances from the Great Lakes to the Ohio Valley into the weekend, shifting into the Eastern Seaboard by later Sunday into Monday near the frontal system, with some lake enhanced rainfall behind it. The western U.S. should see generally dry conditions during the medium range period. Showers and storms are possible across the Florida Peninsula and may increase in coverage by around Tuesday and beyond as there is potential for tropical moisture streaming in. However, opted to target a decent decrease in Florida rainfall amounts compared to the NBM in this time window for now given the uncertainty with fueling tropical influences. A lingering upper ridge will favor continued warmth for the Southern Plains and Lower Mississippi Valley through the weekend prior to moderating frontal passages down across much of the central and eastern U.S., with highs in the 90s and perhaps isolated 100s, which are 10-15F above average. As upper ridging develops in the West, warmer than average temperatures by around 5-10F are forecast for the first part of next week, bringing the Desert Southwest temperatures well into the 100s. Schichtel/Kebede 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, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml