Extended Forecast Discussion NWS Weather Prediction Center College Park MD 217 AM 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 could produce some rain into 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. 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... There is some model spread even early in the medium range period next week with the details of some features that could cause sensible weather impacts. The first of note was the shortwave/small upper low and surface low moving through the Southeast. Fortunately the 18Z and now the newer 00Z GFS have slowed down and are in better alignment with the non-NCEP guidance compared to older GFS runs that were quite fast. However there are still some differences in the orientation of the upper low opening up, e.g. a positively tilted shortwave would keep QPF suppressed southeastward into GA/SC and offshore. But many of the GFS- and EC-based AI/ML models indicated QPF farther north in the Carolinas. Second, in the West early next week, the EC and GFS suites showed good agreement in the timing of the upper low moving in--but the 12Z CMC and especially the UKMET were faster. The 00Z CMC and UKMET both slowed and more favorably matched the EC/GFS consensus. Shallow shortwaves in the northern stream also showed some model spread that necessitated typical changes to the associated frontal and surface low timing; the surface low north of the Great Lakes Tuesday trended deeper compared to the previous forecast. 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. Meanwhile model agreement is good for troughing to make its way from the eastern Pacific Wednesday into the West Coast Thursday. The new 00Z ECMWF is rather aggressive in showing a closed low within the upper trough by Wednesday offshore of the Pacific Northwest and deep with the associated surface low. Will have to see if the 00Z runs of the AI/ML models agree with this. A little more spread arises by Friday as the 12Z CMC brings a shortwave in the eastern Pacific upstream and disrupts the trough a bit, while the 18Z GFS may be a bit west with the trough axis. A deep surface low looks to emerge in the central High Plains by next Friday ahead of the trough axis. For the early part of the medium range period, the WPC forecast favored the 12Z ECMWF with lesser proportions of the 18Z GFS, 12Z CMC, and the 12Z EC ensemble mean. Gradually lessened the proportion of the deterministic models and eliminated the CMC in favor of the ensemble means as the period progressed. The means reached half the blend by Day 7 though with a healthy proportion of the 12Z ECMWF. ...Weather/Hazards Highlights... On Monday, rain is possible across the Southeast/Carolinas near the surface low track. There is some model spread in the placement and amounts of the QPF, plus instability looks to be on the low side limiting rain rates, to preclude any excessive rainfall risk at this point. 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. However, on Tuesday night, the main atmospheric river may push ashore in southern Oregon and northern California ahead of the deep eastern Pacific/West trough. While Wednesday should be the wetter day overall, the initial push of the AR inland with associated moderate to high rain rates looks like it may occur before 12Z Wednesday, thus during the Day 5 ERO period. Have a Marginal Risk drawn up in the Day 5 ERO to cover Tuesday night, but will have to keep a close eye on the timing of the AR. 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. 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