Extended Forecast Discussion NWS Weather Prediction Center College Park MD 240 AM EDT Sat Oct 5 2024 Valid 12Z Tue Oct 08 2024 - 12Z Sat Oct 12 2024 ...Heavy rainfall becoming more likely across the Florida Peninsula into next week... ...Overview... An upper trough (anchored by an upper low that may track over or near New England) will settle over the East for a few days next week as an upper ridge upstream tracks from the West to Central U.S. bringing a period of climatologically warm weather. By later next week, the leading edge of a Pacific trough will produce gradual height falls over the Northwest with some generally light precipitation to accompany. The main rainfall focus over the CONUS will be over parts of Florida, due to the combination of abundant tropical moisture in addition to a Gulf of Mexico disturbance and a front draped across the peninsula. ...Guidance/Predictability Assessment... Guidance continues to show some typical differences in the details for the evolution of the upper trough settling over the East and the anchoring low. There is some question on timing and placement of the upper low and the associated surface low mid- to late week, but a general model compromise seemed to provide a good middle ground solution. Timing of the next trough into the West next Thursday and beyond becomes very uncertain with the CMC much quicker than the better consensus. The GFS is also faster than the ECMWF but still within the overall spread. Prefer a blend of the ECMWF, GFS, and ensemble means for this feature as details become very unclear late period. The main feature of interest during the period though is still evolution of a possible tropical system in the Gulf of Mexico. Lows may spin up along the frontal boundaries in the eastern Gulf/northern Florida/western Atlantic while another feature that is more concerning for forming a possible tropical system (possibly partially consisting of remnant energy from what was Eleven-E in the East Pacific) may evolve over the western Gulf. Guidance has generally come into better agreement on the development of some sort of tropical or sub-tropical system tracking into Florida but remain very uncertain on the timing and north-south placement of that. There does seem to be an uncertain slightly faster and more northerly trend. The CMC is by far the slowest piece of guidance and was not preferred. WPC worked with a blend of the GFS and ECMWF which were solidly in the middle of the spread and consistent with latest NHC thoughts as well. Please consult the NHC outlooks for the latest information on features of interest over the Gulf. ...Weather/Hazards Highlights... The heaviest rainfall potential for next week will be over the Florida Peninsula, with low pressure (that could be tropical or subtropical) over the Gulf of Mexico shifting eastward with time but with considerable model variability on placement and timing. Regardless of tropical development, enhanced/above average tropical moisture will be in place and funneled into a wavy front draped over the state. This should produce multiple days of moderate to heavy rainfall, and Marginal Risks are in place in the EROs for much of the Florida Peninsula for Days 4-5/Tuesday-Wednesday. If the trends continue, it is likely at least a slight risk will be needed, but confidence is still too low on where to place that at these lead times. Heavy rain potential may continue beyond Wednesday, depending on timing of any potential tropical system. Elsewhere, the upper low over/near New England should allow for some lake- enhanced rain within in westerly flow across the Great Lakes. A mean frontal zone with one or more embedded waves should reach near the northern Pacific Northwest by early-mid week, producing some periods of light to locally moderate rain and non- zero chances of snow in the highest elevations. Widely scattered showers are possible at times across the Four Corners states into parts of the south-central U.S., but anything beyond light rain is unlikely. The strong and persistent western-central U.S. upper ridge will promote an extended period of well above normal temperatures over that part of the country. Gradual eastward drift of the ridge axis will shift the highest anomalies from the West into the Plains by Tuesday with some northern locations could reach 20-25F above normal. Height falls slowly pushing in over the West Coast will support a trend toward near normal temperatures by Wednesday or Thursday. Temperatures over most of the East should cool starting as upper troughing sets up near the East Coast. This may lead to frost/freeze concerns across portions of the Upper Great Lakes region and interior Northeast, with the timing around the median to a bit late for the first frost/freeze of the season. Santorelli 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 forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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 https://www.wpc.ncep.noaa.gov/#page=ovw