Preliminary Forecasts
Issued by NWS
Issued by NWS
321 FXUS02 KWNH 080653 PREEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 252 AM EDT Fri Aug 8 2025 Valid 12Z Mon Aug 11 2025 - 12Z Fri Aug 15 2025 ...Heat returns to the Midwest/Great Lakes/Northeast next week... ...Overview... Central CONUS troughing will yield to strong downstream ridging over southeastern Canada that will help usher in much warmer temperatures to the Northeast 1/4 of the Lower 48. Strong upper ridging over the northeastern Pacific is forecast to retrograde, allowing digging troughing to settle into the Pacific Northwest. Cooler than normal temperatures will replace the warmer than normal temperatures by later in the week. ...Guidance/Predictability Assessment... The latest 12Z/18Z guidance showed reasonable agreement on the upper level pattern through the period, except for the northeastern Pacific into the Northwest. There, the models (dynamical and AI/ML) have been inconsistent and split on how to handle shortwaves ridging up and over the ridge. However, the 12Z deterministic models were deeper/slower than the ensembles generally showed (except the GFS where the 18Z was better clustered with the other 12Z guidance). In addition, the ECMWF AIFS ensemble was slower than its dynamical counterpart, lending credence to the slower determinstic-led solution. Thus, utilized a super majority blend of the deterministic guidance through next Thursday but with limited confidence (as even the AI models have wavered in their forecasts). Along/east of the Divide, the broader consensus was a sufficient starting point. ...Weather/Hazards Highlights... A cold front over the Great Lakes (on Monday) back to the Plains will be a focus for some locally heavy rain Monday into Tuesday as it slowly pushes to the east and southeast into the Midwest. To the south, a lingering stationary boundary draped along the I-10 corridor amid higher than normal moisture levels will also act as an impetus for some heavier rain. Both of these areas, for Monday and Tuesday, are denoted with a Marginal risk of flash flooding (excessive rainfall). In addition, much of New Mexico and into southeastern Arizona may see some localized modest rainfall amid sensitive terrain. A Marginal risk exists there for Monday. For the rest of the week, rainfall chances will increase over the eastern 1/3 of the country as the northern frontal boundary wavers over the region. Temperatures will warm into the Northeast to near record levels Mon-Wed with highs into the 90s. This will push HeatRisk levels into the Moderate (level 2) to Major (level 3 out of 4) category after a relatively cool/comfortable start to August. Lingering heat over the Southwest will slowly subside through the period though temperatures will remain slightly above normal. On the flip side, increased troughing into the Pacific Northwest will cool temperatures rather smartly from 5-15 degrees above normal Monday to 5-10 degrees below normal by Thursday (WA/OR). To the south through coastal CA, temperatures will hover near to below normal as the cooler than normal summer carries on. Fracasso 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 $$