Extended Forecast Discussion NWS Weather Prediction Center College Park MD 302 AM EDT Mon Mar 10 2025 Valid 12Z Thu Mar 13 2025 - 12Z Mon Mar 17 2025 ...Potent system brings precipitation to the West into Thursday, the central U.S. Friday, and toward the east-central/eastern U.S. next weekend... ...Overview... The primary weather feature of concern later this week will be a deep and phased upper trough near the West Coast by early Thursday that closes off an embedded upper low over the Plains on Friday while spinning up a strong surface low. The upper trough will bring widespread rain and higher elevation snow across the West on Thursday. Then hazards associated with the surface low pressure system will include heavy rain and severe thunderstorms in the Mississippi Valley beginning Friday and into the Southeast and Tennessee/Lower Ohio Valleys Saturday. Convection should reach the Eastern Seaboard Sunday. Snow is possible on the backside of the low in the northern half of the Plains into the Upper Midwest Friday-Saturday. Meanwhile areas of strong winds are likely, which could cause fire danger especially in the southern Plains. Behind that system, another upper trough is forecast to approach the West this weekend and spread additional precipitation there. The leading Pacific trough crossing the West will bring below normal highs to that region while the leading ridge (and possibly a weaker one farther east) should promote above normal temperatures over the central/eastern U.S., gradually lessening in scope with time. ...Guidance/Predictability Assessment... Model guidance remains in good/better than average agreement with the synoptic pattern through the weekend, as the upper trough moves through the West Thursday and consolidates energy to develop a low aloft that supports a quickly strengthening surface low that tracks across the central Plains to Upper Midwest. The exact depth of the low is still in question, with operational guidance generally deeper than AI/ML models in the 970s. The WPC forecast blend was based on deterministic models favoring the 12Z EC and 18Z GFS during the first half of the medium range period. Into early next week, most guidance shows a low amplitude ridge behind the main upper trough, with additional troughing forming upstream in the eastern Pacific toward the West Coast. The trough will support a surface low that continues to vary quite a bit with its depth considering differences in supporting shortwave energy within the more predictable medium to larger scale upper trough. The 12Z CMC was among the strongest with the surface low in the 970s 12Z Sunday but the 00Z GFS came in almost as strong. The manual forecast stays on the conservative side depth-wise given the wide spread among dynamical and ML guidance at this time. The orientation and timing of the trough also have some model spread. In particular, the 12Z control run of the ECMWF was slower/farther southwest with the trough axis compared to the bulk of other guidance, including the EC-based AI/ML models, so leaned away from that. The 00Z EC has adjusted favorably somewhat eastward. Into the later period, the forecast blend included and gradually increased the proportion of GEFS and EC ensemble means to about half Day 6 and more Day 7 with the increasing spread. ...Weather/Hazards Highlights... On Thursday, the tail end of a weak atmospheric river and possible convective showers behind it could bring moderate to heavy precipitation to southern California, and a Marginal Risk remains in place in the Day 4 ERO. More broadly, areas of rain and higher elevation snow are forecast across much of the West into Thursday. Higher elevation snow could be heavy across the Sierra Nevada and into the terrain of the central Great Basin and Mogollon Rim. Widespread high winds will also be a concern in the West on Thursday. Ahead of this system, an initial shortwave will produce some light to moderate rain across the Southeast on Thursday. Precipitation remains more questionable farther north, but with a general focus for light precipitation from the Great Lakes/Ohio Valley region to the Northeast. As the primary upper trough moves into the central U.S., there is high confidence in surface low development/consolidation in the central Plains by Friday with strong fronts. On the backside of the low, snow could spread across the central High Plains and into the Dakotas on Friday and into the Upper Midwest on Saturday. Some of these areas may initially see rain in the warm sector, and a transition zone of ice is also possible. Rain and thunderstorm chances emerge ahead of the cold front across the Mississippi Valley Friday. The Storm Prediction Center is highlighting the best severe potential from parts of the Midwest southward almost to the west-central Gulf Coast on Friday. Most guidance shows heavy rain rates beginning late Friday into Friday night that could cause flooding concerns. The first take at the Day 5 ERO for Friday indicates a Marginal Risk for the Lower/Middle Mississippi Valley and Mid-South. Rain totals are forecast to become even heavier by Saturday centered in the Tennessee Valley, and SPC indicates severe potential for the Tennessee Valley and Southeast. As the upper trough and surface fronts move east, rain and thunderstorms will overspread the East on Sunday. Winds are another possible concern near the deep low track, as well as in the Plains behind the cold front. Currently the guidance shows the potential for highest wind speeds over the southern Rockies/High Plains around Friday, likely producing fire weather concerns. In addition southerly winds in the warm sector could get fairly strong over/near the Appalachians and East Coast next weekend. Additional rounds of precipitation are likely in the West late this week into the weekend as another frontal system or two approach. Rain amounts in the Pacific Northwest to northern California look to stay below thresholds for any excessive rainfall risk through Friday, but chances for heavy precipitation (lower elevation rain and higher elevation snow) could increase by the weekend for the Pacific Northwest into California. Above average temperatures are likely over most areas east of the Rockies to start the period. Temperature anomalies of 20 to as much as 35 degrees above normal are forecast Thursday for the northern Plains to Midwest as highs reach the 60s and 70s. Farther south, temperatures in Texas and Louisiana could reach the 80s while localized areas like far South Texas can expect 90s, even approaching 100F. Warmer than normal temperatures will gradually shrink in area late week into the weekend as possibly multiple cold fronts track east. The Midwest and Great Lakes can expect plus 20-30F anomalies on Friday but more limited to the Great Lakes on Saturday, and warmer than normal temperatures by 10-20F are likely in the Northeast over the weekend. Daily record highs look fairly isolated across the central to eastern U.S., but there could be more widespread record warm lows from the Midwest through the East Friday-Sunday if the morning mins hold for the calendar day. In the West, the upper troughing along with clouds and precipitation will promote below normal temperatures spreading across the region mid- late week. Highs are forecast to be generally below average by 15-20 degrees for the central Great Basin and Southwest, while lows of 5-15 degrees below normal are likely. Temperatures should moderate somewhat over the weekend as the trough pulls away, but another trough approaching could lead to another bout of cool temperatures there early next week. 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