Extended Forecast Discussion NWS Weather Prediction Center College Park MD 306 AM EDT Sun Mar 16 2025 Valid 12Z Wed Mar 19 2025 - 12Z Sun Mar 23 2025 ...Central Rockies/Plains to Upper Midwest and northern Great Lakes/Northeast Snowstorm Threat into mid-late week... ...Northwest wet pattern via a series of systems this week... ...Guidance/Predictability Assessment... The WPC medium range product suite was mainly derived from a composite of reasonably clustered guidance of the 12 UTC ECMWF/Canadian/UKMET valid for Wednesday into Friday in a stormy pattern with overall above average forecast confidence. This solution has good ensemble and National Blend of Models support while maintaining good WPC continuity. Lingering system specific timing/focus variances have recently been well mitigated by a composite as consistent with predictability. Latest 00 UTC models are well in line with this solution, including the GFS that favorably trended back toward concensus. Preference shifts to the still compatible GEFS/Canadian/ECMWF ensemble means that offer a more consistent forecast basis at longer time frames through next weekend amid steadily growing uncertainty. ...Weather/Hazards Highlights... The main weather story to highlight for later this week remains being the growing guidance signal for a late winter snowstorm that may produce windy to blizzard conditions. Cyclogenesis over the Plains Tuesday will follow with a deepening low track to the Midwest/Great Lakes midweek and to eastern Canada by Thursday. This will combine with secondary cold frontal cooling to enhance upslope in an emerging wrap-around heavy snow threat from the north-central Rockies/Plains to the Upper Midwest and northern Great Lakes into Wednesday/Thursday. There may also be a band of moderate rains over the Upper Midwest adjacent/south of the rain/snow transition line, but no WPC Excessive Rainfall Outlook (ERO) threat area has been introduced. A wavy trailing cold front will have less moisture than an earlier week system, but will align and sweep an axis of showers and thunderstorms over the central to eastern U.S. Thursday/Friday, with wintry weather possible for interior/northern Northeast. Most activity exits the East Coast by next weekend. Well upstream, a protracted series of steadily progressive and moderately amplified Pacific systems will pool lead moisture feed/IVT to spread repeat periods of organized precipitation inland from the West/Northwest through the Rockies in a wet pattern. Moderately heavy rains and terrain focusing snows are most likely via channeled moisture into the Pacific Northwest in this periodic pattern. While no WPC ERO threat area has yet been introduced, the cumulative effect of multiple systems may lead to local runoff issues to monitor. Subsequent modest downstream rain chances may emerge next weekend over the central to eastern U.S., albeit with uncertain system details and return flow developments. Well-above average temperatures by as much as 15-20 degrees will proceed the the initial mid-week system over the Midwest and central/southern Plains, with temperatures into the 90s possible in the southern Plains Tuesday. The focus will shift eastward with the system to the Northeast Wednesday, possibly lingering into Thursday depending on progression of the following cold front. Temperatures from the central to eastern U.S. will be briefly below average following cold front passage then trend back towards just above average conditions (5-10 degrees) into next weekend. In contrast, conditions will begin below to well below average across much of the West mid-next week before trending closer towards average by next weekend. Schichtel 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