379 FXUS02 KWBC 290631 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 231 AM EDT Tue Sep 29 2026 Valid 12Z Fri Oct 02 2026 - 12Z Tue Oct 06 2026 ...Major Multi-day South-Central to East-Central U.S. Excessive Rainfall/Flooding threat this week with tropical connections... ...Guidance/Predictability Assessment... Guidance overall remains agreeable on the synoptic split pattern over the nation comprised of an energetic and progressive northern stream and an impactful southern-stream upper-low/surface systems set to slowly work over the south-central U.S. this week. Forecast spread and predictability seem improved with lastest guidance. Favor a broad model/ensemble/machine learning guidance composite that should tend to mitigate lingering smaller scale variances as consistent with individual predictability. The main upper-low will begin to weaken/transition into an open wave and become absorbed within the northern stream as a potent cold front catches lead wavy frontal boundaries over the south- central U.S.. Moderating frontal surges early and later period will impact the transition of an expected prolonged period of heavy rainfall from the south- central to eastern U.S. this week and then the suppressing and confinment of heavy rain focus to the southern/southeast U.S. into next week. The 01 UTC NBM seemed to provide a good compromise QPF. ...Pattern Overview and Weather/Hazards Highlights... A closed upper trough/low with wavy frontal systems will shift slowly eastward over the South-central U.S. later week in southern stream split flow. Widespread excessive rainfall/flooding threats over the South-central U.S. will slowly shift across the East- central/Southern U.S. as further focused by Gulf/Southeast Coast frontal genesis. This event will be fueled by a tropical moisture connection from current East Pacific Hurricane Polo set to weaken with landfall/track across Baja California and Northwest Mexico. There will also develop an increasingly deep and protracted lead Gulf inflow pattern with tropical influence. This expansive multi- day threat should prove slow to progress late week wedged between upper ridges over the Southwest and Southeast U.S.. Activity focus will then slowly work downstream into the East. Expansive WPC Excessive Rainfall Outlook Marginal Risk areas with embedded Slight Risk areas cover the Southern Plains through the Tennessee Valley and Central Gulf Coast states then into the Appalachians and vicinity for the Day4/Friday and Day5/Saturday periods. Meanwhile, systems within a more progressive/zonal mean northern stream flow will support passage of a series of wavy frontal systems across the U.S. northern tier of the nation from the Northwest through the Northeast this week. These will act to provide a northern rainfall shield focus and over-running for lifting moisture/clouds and deliver moderating post-frontal fall temperatures to spread/sink southward with high pressure settling. This scenario will also act to focus/confine a lead heavy rainfall main threat axis to The South and the Southeast early next week. Accordingly, the WPC Excessive Rainfall Outlook (ERO) offers anomalously large Marginal and Slight Risk areas from the South- Central to East-central U.S. on Day4/Thursday and Day 5/Friday. The Day 4 also includes a Southern Plains Moderate Risk. Activity will progress slowly from the East-central U.S. to the East later period with the greatest confidence in additional heavy rainfall shifting from the Southern Plains/Middle Miss Valley to the Tenn/Lower Miss Valleys, as well as possibly into the northern Mid- Atlantic. These EROs and supporting WPC Hazards Outlook areas are all linked below. Upper-ridging will lead to a period of above-average temperatures over the western U.S. including highs into the 90s and low 100s for central/southern California and the Desert Southwest. Some heat may reach hazardous levels for southern California this weekend. Schichtel 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, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw $$