Extended Forecast Discussion NWS Weather Prediction Center College Park MD 346 PM EDT Mon Sep 26 2022 Valid 12Z Thu Sep 29 2022 - 12Z Mon Oct 03 2022 ...Hurricane Ian is forecast to intensify over the eastern Gulf of Mexico then slow as it tracks off the Florida Gulf coast later this week, increasing the threat for excessive rain from Florida into the Southeast among other tropical cyclone impacts... ...Overview... Confidence is increasing in a slower Ian tracking over the northeast Gulf near or along the Florida Gulf coast Wednesday into Friday. The system is forecast to weaken prior to landfall, but the slower system will increase the risk for excessive rainfall for Florida into the Southeast. Please see the latest WPC and NHC products for more information on Ian forecast and impacts. Elsewhere, the progression of of an eastern Pacific trough/low over the northern Rockies Thursday and the northern Plains over the weekend. ...Guidance Evaluation/Predictability Assessment... A slower and a bit farther east track to Ian from Thursday and Friday then becomes more uncertain east-west with the 12Z ECM farther west and the 12Z GFS farther east (and the 12Z UKMET even farther east). However, all 12Z guidance has come in slower and gaining less latitude this weekend before sliding east early next week. Remarkable agreement between the 00Z ECMWF and 06Z GFS gave confidence in relying on those models through Day 6 for both the frontal progressions across the CONUS and QPF over the northern Rockies and the heavy Ian-related QPF in the Southeast. That agreement continues with the 12Z ECMWF/GFS, particularly for the ridge developing up the West Coast Friday and low/trough this weekend over the north-central Rockies. The 12Z CMC/UKMET continue to differ from the GFS/EC consensus like they did at 00Z, so those models were replaced with the GEFS and ECENS means for Days 6/7. ...Weather/Hazards Highlights... Hurricane Ian is forecast produce notable rainfall and wind threats during the period to Florida and the Southeast. A stalling front over FL will then lift north with the system. Strong high pressure tracking from the Great Lakes and stalling over the Northeast into Saturday and then reinforced with high pressure from Hudson Bay to New England Sunday/Monday will help to enhance the winds/onshore flow to the north of Ian. The heavy rain threat lifts from northern Florida Thursday night through Friday, with the QPF focus over the Carolina Coast Friday before lifting toward and into, but possibly not through the Mid-Atlantic over the weekend into Monday. The experimental Day 4 Excessive Rainfall Outlook maintains Slight/Moderate Risk for northern Florida into southeast Georgia. A Day 5 Moderate Risk has been raised from the greater Charleston to greater Savannah metro areas with the Slight Risk continuing for far northern Florida, much of Georgia, all of South Carolina, and southern North Carolina. The combination of anomalous moisture and the upper trough/low emerging from the Northwest should produce areas of locally heavy rainfall in portions of the Four Corners states and up the central to northern Rockies Thursday/Friday. This spreads onto the northern Plains Saturday into Sunday. Snow Levels drop to around 9000ft in the northern Rockies under this upper low. Cloud cover/rain from Ian and Canadian High pressure farther north will make most of the eastern CONUS with max temps as much as 10-15F below normal into this weekend. The northern High Plains will be quite warm on Thursday with max temps least 15F above normal. This moderates a bit as it shifts east over the rest of the Northern Plains Friday/Saturday. The upper trough/low drifting into the Rockies/High Plains will bring moderately below normal highs in its vicinity Friday/Saturday with above normal temperatures returning to the Pacific Northwest coast Saturday/Sunday under the building ridge. 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 Hazards: - Heavy rain across portions of the Southeast, the Mid-Atlantic, and the Southern Appalachians, Fri-Sat, Sep 30-Oct 1. - Heavy rain across portions of the Southeast and the Mid-Atlantic, Thu-Fri, Sep 29-Sep 30. - Flooding possible across portions of the Southeast. - Flooding occurring or imminent across portions of the Southeast. - High winds across portions of the Southeast and the Mid-Atlantic, Thu-Sat, Sep 29-Oct 1. - High winds across portions of the Mid-Atlantic, Sat-Mon, Oct 1-Oct 3. 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