


Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
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407 FXUS02 KWBC 090756 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 356 AM EDT Thu Oct 9 2025 Valid 12Z Sun Oct 12 2025 - 12Z Thu Oct 16 2025 ...A strong coastal low could bring significant coastal flooding, beach impacts, wind gusts, and heavy rain to the East Coast... ...Heavy rain and flash flooding is a continued concern across the Southwest early next week... ...Overview... As the medium range period begins early next week, a strengthening low pressure system is forecast to move slowly north in the western Atlantic near the East Coast. This coastal low is forecast to bring strong onshore winds causing coastal flooding, rip currents, beach erosion, and heavy rain in the Mid-Atlantic and Northeast. Meanwhile, upper troughing in the West will draw tropical moisture and remnant tropical energy northward and bring potentially widespread heavy rain and some flash flooding into the Southwest early next week. This trough and another round of troughing in the West will maintain cooler than average temperatures as well as precipitation chances, including higher elevation snow. Upper ridging should prevail farther east in the central U.S., allowing for unseasonably warm temperatures, and rounds of rain in the north-central U.S. directed around the ridge. ...Guidance/Predictability Assessment... Model guidance shows okay agreement on the overall pattern but with important differences in the details. In the East, the coastal surface low shows some differences in position even as the period begins on Sunday. The 12Z CMC and the newer 00Z CMC are both farther east with the low compared to consensus, but then they linger the low closer to the coast into later Monday-Tuesday than consensus. GFS runs through the 12Z tended to be faster than preferred, but the 18Z GFS showed better alignment with the ECMWF runs. Overall leaned heavily toward the consistent ECMWF with some 18Z GFS inclusion. Models are trending toward having consolidated upper energies (from the Great Lakes and from the Atlantic merging in the Mid-Atlantic) by 12Z Monday, a little earlier than runs from a day ago. The newer 00Z guidance still shows spread though, including a slower 00Z GFS and faster 00Z ECMWF with the surface low track, so continue to watch for forecast changes to the low position and resulting QPF. The low should be gradually pulling east/away by Tuesday and beyond. In the West, upper troughing atop the Rockies Sunday is forecast to quickly lift northeast by Monday, with good agreement. Meanwhile another round of energy developing an upper low will be diving along the West Coast Monday-Tuesday. There is more model spread with this upper low position going forward. The 12Z CMC and UKMET were west of consensus by Tuesday, while the 12/18Z GFS runs and many GEFS ensemble members were east of the 12Z EC/EC ensemble preferred middle ground. The 00Z GFS trended west and the 00Z CMC trended east, fortunately for better model convergence. However, by Wednesday-Thursday the new 00Z ECMWF splits energy and pulls some west into the eastern Pacific into later week, whereas the GFS/CMC have a consolidated trough remaining in the West. Will monitor if other guidance like the 00Z AI/ML models follow suit, but for now the 00Z ECMWF seems like an outlier. Upper ridging in between the West and East troughs is at least agreeable, though its extent is less certain from day to day. The WPC forecast used a 12Z ECMWF/18Z GFS/12Z EC ensemble mean (in decreasing order) model blend for the early part of the medium range period, given the favorable ECMWF positions in the East and West. As the period progressed, used more ensemble mean guidance to a little over half the blend by days 6-7 given the increasing spread. ...Weather/Hazards Highlights... At the start of the period Sunday, a low pressure system in the western Atlantic is forecast to affect the East Coast. Heavy rain is possible for the Mid-Atlantic and Northeast, especially coastal areas like the Delmarva Peninsula into Long Island. A Slight Risk was maintained for Day 4/Sunday for coastal areas with a broader Marginal Risk in the Excessive Rainfall Outlook. By Day 5/Monday there is more uncertainty with rain amounts onshore. There could be potential heavier bands of rain; models generally indicate that around Boston could see heavier rain amounts, which combined with the urban area could cause flooding issues, but will show just a Marginal Risk for the coastal Mid-Atlantic to Northeast on Day 5 at this point and see how models trend. In addition to heavy rain threats, the combination of persistent and strong onshore winds, high surf, and above normal tides may lead to significant coastal flooding impacts along with strong rip currents and potential beach erosion. See Key Messages being issued by WPC for the latest on this system. Early next week, another round of tropical moisture and energy is forecast to enter the Southwest with a tropical system that is likely to develop behind Priscilla per the National Hurricane Center. Precipitable water values are likely to be near max values for this time of year, and PWs of 1.5 inches would even be in the 75th-90th percentile during the typical peak of monsoon season in early-mid August. The Southwest should also be in the right entrance region of the upper jet for good dynamical support for heavy rain. However, a limiting factor in terms of flash flooding could be somewhat limited instability under widespread clouds and rain, which could limit rain rates. Also, the current forecast shows the greatest rainfall totals to the southeast of where the heaviest rain could fall in the short range. Thus continue to hold off on any Moderate Risks at this time, but Slight Risks are in place across portions of Arizona and New Mexico for the Days 4-5 (Sunday and Monday) Excessive Rainfall Outlooks, and WPC will continue to monitor for potential upgrades. Elsewhere, the rounds of upper troughing in the West will promote precipitation, including higher elevation snow. Moderate to heavy snow is likely for the Cascades/northern Rockies Sunday, with some snow moving into the Sierra Nevada Monday-Tuesday, and lighter snow is possible for the Intermountain West/northern Rockies with the second trough as well. Additionally, a moisture plume/atmospheric river is forecast to move across California Monday ahead of a cold front. While it could be relatively fast-moving, some instability could be present and rainfall rates could reach an inch per hour, so have a Marginal Risk of excessive rainfall drawn up for parts of northern California on Day 5/Monday. Farther east, rounds of precipitation are possible in the Plains to Upper Midwest and Great Lakes region. Cooler than average temperatures are forecast particularly for highs in the West through next week underneath renewing troughing. Meanwhile, upper ridging in the central U.S. will lead to warmer than average temperatures. Highs in the 70s reaching as far north as the Dakotas Sunday will be 15-20 degrees above average. Temperatures there should cool behind a cold front into the workweek, but temperatures of 10 to 15 degrees above normal will last several days farther south, as unseasonably warm highs in the 90s continue for Texas and Louisiana. Warmer than average temperatures are forecast to stretch into the Midwest. Some cool highs along the East Coast early week should moderate close to normal as the week progresses. Tate 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 $$