Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EDT Fri Oct 4 2024 Valid 12Z Mon Oct 07 2024 - 12Z Fri Oct 11 2024 ...Potentially hazardous heat will persist across the Southwest through Monday... ...Chances for heavy rainfall across the Florida Peninsula will increase into next week... ...Overview... The upper pattern over the CONUS next week should settle into a slower-evolving pattern dominated by mainly large scale features. An upper ridge slowing moving from the Western to Central U.S. will support much above normal temperatures while a trough settling over the East (anchored by an upper low that may track over or near New England) will bring a cooler trend. The leading edge of a Pacific trough will produce gradual height falls over the Pacific Northwest into late next week and bring some precipitation to the northern parts of the region. Farther south, expect the main rainfall focus over the Lower 48 to be over parts of Florida, due to the combination of abundant tropical moisture in addition to one or more Gulf of Mexico surface features 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. Some question on timing and placement of the upper 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 and weaker shortwaves ahead of it becomes uncertain late next week. The WPC forecast used general model compromise through the period, with more ensemble mean inclusion late period. The main feature of interest during the period though is still evolution of possible tropical features in the Gulf of Mexico. Early week, one wave may track into the central/east-central Gulf while another feature (possible remnant energy from Eleven-E in the East Pacific) may evolve over the western Gulf. Models and ensembles have shown some improvement in the signal for these features to phase early next week as they approach Florida and interact with a wavy front across Florida into the Gulf. Through the 12z/18z guidance, models were in agreement with this evolution but showed some significant differences in timing. The 00z GFS tonight came in quite suppressed to the south with little to no tropical development. Uncertainty in any sort of tropical development across the Gulf remains very high. 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 slow- moving low pressure over the Gulf of Mexico along with a wavy front draped over the state and a broad area of anomalous moisture extending over/east of the Gulf. There is still a fair amount of uncertainty for details though. Enhanced moisture and potentially heavy rainfall is expected through the week across at least the southern half of Florida, and this is supported for now with marginal risks on the Day 4/Monday and Day 5/Tuesday Excessive Rainfall Outlooks. Precipitation may be further enhanced by any possible tropical system approach, but regardless, models agree on a multi-day heavy rainfall signal across parts of Florida. Elsewhere, the frontal system into the Northeast on Monday may generate rainfall which should shift out of the region with the cold front by mid week. 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. 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 on Monday, with some highs at least 10-15F above normal, more into the Plains by Tuesday-Thursday when some northern locations could reach 20-25F above normal. Expect numerous daily records for warm minimum and maximum temperatures, especially over the Southwest through Monday. 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 moderate starting Monday to near or somewhat below normal 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