Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 AM EST Thu Mar 6 2025 Valid 12Z Sun Mar 09 2025 - 12Z Thu Mar 13 2025 ...Overview... A moderately active pattern with three significant systems of note. An upper low ejecting from the Southern Rockies/High Plains early Saturday may produce a small area of High Plains snow and then open up and develop a surface wave along with Southeast U.S. enhanced rainfall. A trailing upper ridge building into the West should weaken as it reaches the eastern states. A couple lows developing over the East Pacific, one nearing the West Coast next Monday (reaching the central U.S. Wednesday) and the second around Wednesday. Both will likely bring some focused rain/mountain snow to the West with the latter storm expected to bring the potential for heavier totals. Meanwhile, Great Lakes/Northeast upper troughing should flatten after Monday while a wavy mean frontal boundary over southern Canada and the Northeast may dip into the northern tier as the first Pacific system moves inland. ...Guidance/Predictability Assessment... Overall guidance has had run-to-run agreement with the large scale pattern and evolution of multiple systems, but there continues to be some medium to smaller scale details that are up for debate. While the the latest ECMWF has trended a bit closer to the CMC solution for the low exiting the Southern Rockies out into the Plains, it remains on the slower side of the envelope. The amplifying eastern Pacific trough once again has good agreement with a low closing off as it approaches the West Coast. The UKMET has trended toward the notion of closing off a low however it does so more than a half a day behind and still moving faster than the other guidance. The upper system should reach the Rockies/Plains by next Wednesday, with typical spread for exact timing. A model/mean blend yields a Plains/Midwest surface low depth close to the average of ML models. There is still a decent amount of spread for the potential Wednesday system near the West Coast. Some dynamical models show a rather vigorous surface low, while CMC runs are a few hours later to develop their strongest low. Initial blend consisted of the 12Z ECMWF, 18Z GFS and 12Z UKMET. By mid-period the UKMET was dropped and replaced with the 12Z GFS along with increased weighting of the GEFS and EC ensemble means through the end of the extended period. ...Weather/Hazards Highlights... Guidance remains split whether training convection/heavy rain will continue over northern Florida/southern Georgia for Sunday so opted to maintain no risk areas for the Day 4 period. If the ECMWF/UKMET solutions come to fruition those areas could receive 2 to 4 inches with locally higher maximums. Waves along a front may bring one or more episodes of mostly light snow to the northern Great Lakes/Northeast from the weekend into next week. The West Coast will be ramping up for a multi-day wet period. Over the weekend an eastern Pacific trough will direct an atmospheric river into Vancouver Island with some precipitation extending into northwestern Washington state. With an upper low possibly closing off near California by early Monday (with associated surface development), it may take until early next week for an atmospheric river event to bring heavier rain to portions of central and southern California, along with heavy snow for the Sierra and eventually moving inland across the higher terrain of the Intermountain West. Additionally, this pattern will favor gusty winds. Another system is anticipated impact the West Coast by midweek with heavier and more widespread precipitation and locally strong winds; however the details remain uncertain. Above average temperatures will expand southward/eastward from the Northern Plains into next week. The Northern Plains should return closer to normal by next Wednesday as a front sags south from Canada. Locations from the northern-central Plains through the Midwest and eventually into the northern Mid-Atlantic should see one or more days with highs reaching 15-30F above early March averages. This warmth may push highs well into the 60s from the Dakotas into Iowa and into the 70s as far north as the Middle Mississippi Valley and parts of the Mid-Atlantic. Campbell/Rausch 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