Extended Forecast Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Fri Sep 23 2022 Valid 12Z Mon Sep 26 2022 - 12Z Fri Sep 30 2022 ...Tropical Depression Nine over the Caribbean likely to intensify and may affect at least Florida by next week... ...Overview... The large scale pattern begins with an amplified ridge over the West and a trough over the East that will flatten with time as a shortwave trough approaches from the eastern Pacific and moves inland. The 15Z National Hurricane Center advisory forecasts a Tropical Depression Nine currently in the Carribean to undergo rapid intensification as it tracks north-northwestward toward the Gulf of Mexico with a landfall in South Florida Wednesday morning. Some specifics of this system will be sensitive to its speed and longitude as it reaches near Florida and timing of the expected weakening of the eastern U.S. upper trough. Expect the Great Lakes region to see some rainfall with the chilly cyclonic flow in place during the first half of the week, while the Northwest may see mostly light rainfall around midweek with the Four Corners states also seeing some potential for scattered rainfall. ...Guidance Evaluation/Predictability Assessment... The latest run of the GFS continues to favor a more western, slower track of Tropical Depression Nine that would result in double digit rainfall that's roughly 10+ inches heaver than the rest of the guidance with more impacts to the western part of the Florida Peninsula. The UKMET and CMC are more of a middle ground approach but lean closer to the ECWMF solution that is faster, clips Florida and then races out over the Atlantic quickly near the advancing front. It also suggests that the northern stream/trough over the East will help move the tropical feature along instead of cutting off/spinning to its death. The NHC's track is favoring an evolution closer to that of the ECWMF. Therefore the WPC's blend initially was a multi-model blend with lesser weighting of the GFS and then transitioned toward an ECWMF/GFS/GEFS and EC ensemble means compromise. There is still moderate spread with the details of the eastern trough beyond those noted from the 12Z ECMWF. Run-to-run variability persists with the timing of the trough pushing inland the Pacific Northwest, but is fairly common for that time frame but diverge in the later periods where troughing remains or if ridging tries to rebuild. ...Weather/Hazards Highlights... The dominant rainfall threat during the period will be with Tropical Cyclone Nine that may affect Florida and potentially other parts of the Southeast/East Coast. A front expected to stall over Florida before arrival of the system could provide an added focus for rainfall. Note that there is still considerable uncertainty regarding the ultimate track of this system by the latter half of the week. However into early Wednesday there is sufficient potential for heavy rainfall to introduce a Slight Risk area on the experimental Day 5 Excessive Rainfall Outlook over parts of the Florida Peninsula. Continue to monitor National Hurricane Center products for the latest information regarding this system. Expect the Great Lakes and vicinity to see periods of rain through the first half of the week with chilly and brisk cyclonic flow in place at low levels and the upper trough overhead. A few focused bands to the lee of the Great Lakes could produce some enhanced totals. The Pacific Northwest should see a period of light to perhaps isolated moderate rainfall around midweek with the frontal system forecast to push into the region. Scattered rain over portions of the Four Corners states may gradually increase in coverage over the course of the week. The evolution of the upper pattern will favor chilly temperatures over a majority of the eastern U.S. with best potential for highs up to 10-15F below normal over and near the Great Lakes/Ohio Valley, especially Tuesday-Thursday. Meanwhile the West will be on the warm side Monday-Wednesday with some areas from the Northwest into northern Rockies likely seeing highs up to 10-15F above normal, followed by a cooler trend closer to normal later in the week as the warm air reaches the High Plains. Campbell/Rausch Hazards: - Heavy rain across portions of the Southeast, Mon-Thu, Sep 26-Sep 29. - Heavy rain across portions of the Southeast, Tue-Thu, Sep 27-Sep 29. - Flooding occurring or imminent across portions of the Southeast. - High winds across portions of the Southeast, Mon-Wed, Sep 26-Sep 28. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Sep 26-Sep 27and Thu-Fri, Sep 29-Sep 30. - Heavy precipitation across portions of mainland Alaska, Wed-Thu, Sep 28-Sep 29. 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