Extended Forecast Discussion NWS Weather Prediction Center College Park MD 210 PM EST Fri Mar 7 2025 Valid 12Z Mon Mar 10 2025 - 12Z Fri Mar 14 2025 ...Wetter/snowier pattern emerging for the West next week... ...Overview... As the medium range period begins Monday, a couple of southern stream upper/surface lows will surround a central U.S. upper ridge. One over the Southeast will likely produce some rain through the day on Monday before pulling away, while another in the eastern Pacific spreads light to moderate precipitation from Southern California into the Southwest as it moves inland. The latter will end up with a consolidating surface low in the south-central Plains by midweek and some generally light to moderate precipitation in the eastern half of the U.S. Wednesday-Thursday. Then there is good model agreement for a deep and phased upper trough to pivot through the eastern Pacific midweek into the West later week along with an atmospheric river, which will bring widespread rain and higher elevation snow across the West. By the end of the period, model agreement remains remarkably good for a strong surface low to develop across the central Plains in the lee of the Colorado Rockies. Farther east, bouts of upper ridging will allow for above normal temperatures across the central and eastern U.S. for much of next week. ...Guidance/Predictability Assessment... Overall, the latest model guidance continues to have a good handle of the large scale pattern over the next 3 to 7 days. However, varying degrees of spread still remain within some smaller scale features. Starting with the shortwave/small upper low and surface low moving through the Southeast, GFS trends from last night and the days prior continued today, showing a slower, stronger, and more compact surface low just off the coast of the Southeast U.S. (though still on the faster side of the otherwise fairly well clustered guidance) by 12Z Monday. Models have also come into better agreement with the QPF footprint in the deformation axis of the surface low, depicting steady moderate to borderline heavy precipitation from Georgia to the Carolinas through Monday, ending by early Tuesday. In the West early next week, the 12Z runs from the CMC and UKMET continued their trends from 00Z. These models depicted a slower upper low evolution which more favorably matched the EC/GFS consensus. Elsewhere, shallow shortwaves in the northern stream also showed some model spread that necessitated typical changes to the associated frontal and surface low timing. Into Wednesday and Thursday, models show reasonable agreement in the trough to move from the Southwest into the southern/central Plains and the Tennessee Valley and vicinity. A surface low should consolidate in the south-central Plains by Wednesday but there is spread in its track after that. Also complicating things are differences among models with respect to the strength and track of a northern stream shortwave scooting across northern Minnesota by 12Z Wednesday. The ECMWF remains the most bullish with this feature, which ultimately develops a stronger surface low near the Great Lakes by Thursday. Meanwhile model agreement remains good for troughing to make its way from the eastern Pacific Wednesday into the West Coast Thursday. The 00Z ECMWF and UKMET were quite aggressive in showing a closed low within the upper trough by Wednesday offshore of the Pacific Northwest and deep with the associated surface low. The 12Z runs of the those models continued to be bullish, and the 12Z GFS jumped on board as well. Will have to see if the 12Z runs of the AI/ML models agree with this, but the 00Z runs largely did not. By Friday, there is remarkable agreement amongst nearly all guidance for a deep surface low to emerge in the central High Plains ahead of the highly amplified trough axis. For the first half of the medium range period, the WPC forecast favored a general model blend of deterministic guidance, favoring the 00Z ECMWF and the 06Z GFS. Beyond Day 5, the blend gradually lessened the proportion of the deterministic models in favor of the EC and GEFS ensemble means as the period progressed. ...Weather/Hazards Highlights... On Monday, rain is looking increasingly likely across the Southeast/Carolinas near the surface low track. Model spread in the placement and amounts of the QPF has been reduced with this cycle, as most guidance now depicts a period of steadier moderate to even borderline heavy rain through the day and possibly the night. However, instability within the deformation axis on the cold side of the low looks to be minimal, which should limit any problematic rain rates. Thus, opted to leave the current null excessive rainfall risk as is. Meanwhile, some lower elevation rain and higher elevation snow is forecast to come into central and southern California Monday and spreading into the Southwest Tuesday, but this also appears to be below ERO thresholds. Then the main atmospheric river will come into the West ahead of the deep eastern Pacific/West trough by late Tuesday or Wednesday. There is some model variability on when exactly the initial push of the AR comes ashore, with some potential for that to occur on Tuesday night before 12Z Wednesday, so within the Day 5 ERO period. Decided to hold off from delineating a Marginal Risk on the Day 5 ERO because some models held off until Wednesday, but will have to keep a close eye on the timing of the AR and when the moderate to high rain rates begin. Areas of rain and higher elevation snow should spread across much of the West Wednesday-Thursday. High winds will also be a concern across much of the West. By next Friday, will also monitor the possibility of snow in the northern/central Plains on the backside of the surface low emerging in the central High Plains. Farther east, rain is forecast to spread across the Tennessee Valley and Southeast midweek ahead of a couple of frontal systems. Light snow is possible on the northern side around the Great Lakes region. This precipitation should spread across the Appalachians to Eastern Seaboard on Thursday, with some northern New England snow possible. Above average temperatures are likely early next week in the north- central U.S. underneath the upper ridge. Temperatures of 15-30 degrees above average could push highs well into the 60s from the Dakotas into Iowa. The upper ridge and thus the warmth will expand eastward across the Great Lakes/Ohio Valley and Mid- Atlantic/Northeast with temperatures generally 15-20 degrees above normal for Tuesday and Wednesday. Highs in the 70s are likely from the Lower Ohio Valley to Mid-Atlantic. Warmer than normal temperatures are forecast to spread across the southern tier as the week progresses, for warmer than normal temperatures most everywhere east of the Rockies. Temperatures could near 100F in south Texas by next Friday. Meanwhile the troughing across the West along with increasing clouds and precipitation will promote below normal temperatures especially for highs, growing in magnitude and area as the week progresses. Miller/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