Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Mon Feb 24 2025 Valid 12Z Thu Feb 27 2025 - 12Z Mon Mar 03 2025 ...Overview... Regular passages of shortwaves heading eastward near/along the Canadian-U.S. border to the East Coast of North America will tend to periodically reinforce the broad troughing that tends to maintain itself along the East Coast of the U.S. Meanwhile, a trend toward more of a split flow pattern is indicated by the ensemble means by next weekend as an upper low followed by a digging trough will attempt to undercut a ridge axis that tends to maintain itself over the western U.S. ...Guidance/Predictability Assessment... Ensemble means today continue to show fairly good agreement on the large-scale pattern evolution across the U.S. through the medium- range period. The deterministic guidance from the GFS however, differs quite a bit from the ECMWF and CMC in terms of the track of a clipper low pressure system that is forecast to reach the Great Lakes by Day 4-5 (Friday-Saturday), with the GFS showing a track much farther south than both the ECMWF and CMC which are similar to one another. The GEFS, on the other hand, shows a track that is farther north than the deterministic GFS, which places more confidence on the more northern track according to the ECMWF and CMC. Toward the latter half of the forecast period, the main concern will be the timing differences of the upper trough/low features moving into the western U.S. Ensemble means show relatively good agreement on the timing of the first upper low going across the Southwest this weekend and reaching into the southern Plains by next Monday. For the next trough digging into the West Coast by Sunday into Monday, agreement of ensemble means among models appear quite good for a Day 6-7 forecast. The EC mean remains the fastest while the GEFS is lowest; the CMC mean is in between. It is reassuring to see that the ECMWF deterministic solutions have progressively slowed down from the previous faster forecasts while the slow GFS solutions have progressively sped up, which leads to confidence that the model solutions are converging somewhere in between the fast and slow solutions. ...Weather/Hazards Highlights... A cold front into the East will spread generally light to moderate precipitation into Thursday. Some precipitation could be snow in the northern part of the precipitation shield across the Interior Northeast. A clipper system should bring an additional round of precipitation to the Great Lakes and Northeast Friday into Saturday, with moderate snowfall possibly enhanced by the lake waters across the upper Great Lakes Friday into Saturday, with mixed precipitation just to the south. A period of strong and gusty winds can also be expected on Friday across the northern Plains and perhaps into Saturday near the Great Lakes on the back-side of the system as cold air rushes in behind it. A building ridge should keep conditions quiet and dry across the West Thursday and Friday, other than a little light precipitation possible in the Pacific Northwest. The southern stream upper low moving across southern California Friday and inland next weekend may lead to light showers over California, the Southwest, and into the south-central U.S., with increasing rain chances in the southern Plains by next Sunday as moisture increases. There appears to be a better signal for the precipitation to spread farther east/northeast across the southern Plains Sunday into Monday. The northern stream trough moving through the eastern Pacific and into the West next weekend will also bring precipitation back into the forecast for the West Coast and Great Basin. Much above normal temperatures will be well established by Thursday across the West and into the northern/central Plains. The greatest anomalies will be across the Plains with daytime highs 20 to locally 30 degrees above normal, with 60s for highs as far north as Nebraska or perhaps even South Dakota at times. The above normal temperatures will spread south and east, with the West Coast trending cooler by early next week. Across the East, temperatures may initially be warm on Thursday, but should trend back towards normal (or below normal) by the weekend. Kong/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