Extended Forecast Discussion NWS Weather Prediction Center College Park MD 206 AM EST Sun Feb 9 2025 Valid 12Z Wed Feb 12 2025 - 12Z Sun Feb 16 2025 ...Active weather pattern on tap for the medium range period with periods of heavy rain and winter weather across parts of the West and the Central-Eastern U.S.... ...Overview... Guidance still shows multiple systems producing significant weather from the middle of the week through next weekend. First, a lingering wavy front initially over the southern tier and developing low pressure lifting northeastward late Wednesday into Thursday will produce an area of heavy rainfall and flooding concerns over parts of the southeastern quadrant of the lower 48 with snow from the central Plains/Midwest into the Northeast. Then a vigorous eastern Pacific system will bring heavy rain and mountain snow to California during the latter half of the week with some heavy snow extending into the Rockies. Continued progression of the system's upper trough will likely support another area of low pressure reaching the East by Sunday, with additional heavy rain possible over south-central areas and snow from the Upper Midwest into Northeast. Both eastern systems may have a wintry mix transition zone between rain/snow areas. The approach of a farther north Pacific system should bring some moisture into the Pacific Northwest next weekend. The northern-central Plains should see the most pronounced cold anomalies, while gradually increasing Pacific influence should help the West to moderate from its cold temperatures as of midweek. The Gulf Coast and far Southeast will should see the most days of above normal temperatures. ...Guidance/Predictability Assessment... An operational model composite of the 12Z ECMWF/18Z GFS/12Z CMC/12Z UKMET, in order from more to less weight, provided a reasonable starting point for the early-middle part of the forecast. Guidance clustering has steadily improved for the system affecting the East, with recent GFS trends bringing it more in line with the majority ECMWF cluster--though the ECMWF has elongated the upper trough a bit compared to some earlier runs in a nod to a compromise. Machine learning (ML) models still show some spread for upper trough details so consensus may still make some modest adjustments for the surface low and/or trailing cold front in future runs. The favored blend's depth is consistent with the ML model average. The system approaching the West Coast has been getting gradually stronger in recent days, while some north-south track spread persists. ML models generally favor a track into the Pacific Northwest, which the multi-model blend accommodates. There has been a modest slower trend noted over the past day or so. Greater differences exist with QPF specifics. Days 6-7 next weekend shifted rapidly toward more 18Z GEFS/12Z ECens mean input, by Sunday reaching 70 percent, while transitioning toward only the old 00Z/08 ECMWF for operational model detail at that time. Latest CMC runs stray to the slow side with the emerging western trough by Sunday, while the 18Z GFS strayed to the fast side with eastern U.S. low pressure at that time. The 12Z ECMWF also leaned a bit fast with the upper trough by Sunday, with the ensemble means and 00Z/08 ECMWF matching best for timing. ML models show a fair amount of spread for the eastern U.S. surface details by Sunday, with the flatter CMC depiction still potentially in play based on one ML model solution. However most other ML models side closer to the favored ensemble means and old 00Z ECMWF. The new 00Z ECMWF run seems to have nudged a bit in this direction. Farther west, guidance shows better than average agreement on another Pacific system whose farther north track should ultimately bring the eastern periphery of its circulation toward the Pacific Northwest. ...Weather/Hazards Highlights... An initial wavy front over the southern tier, nearly parallel to upper flow, along with anomalous moisture will promote an ongoing focus for heavy rainfall along and north of the boundary as of early Wednesday. An upper trough emerging from the West should develop an embedded low that tracks northeastward into Thursday. Guidance is maintaining the signal for excessive rainfall with flash flood potential from the Lower Mississippi Valley into the southern half or so of the Appalachians during the Day 4 Excessive Rainfall Outlook time frame. The latest issuance will reflect fairly minor adjustments to the Slight Risk and surrounding Marginal Risk areas based on latest guidance. Rainfall from the previous day would make this region increasingly sensitive to additional rainfall. By Day 5/Thursday, the cold front trailing from departing low pressure should reach the Southeast with the possibility of locally heavy rainfall (most likely over northern Florida into Georgia). At this time there is a fair amount of spread for specifics and this region has dry antecedent conditions with high flash flood guidance values. Thus did not depict a risk area at this time but will continue to monitor for any trends toward better clustering and/or rain rates on the higher end of the envelope. Guidance still differs on some of the details of moisture arriving into California around Wednesday-Wednesday night ahead of a vigorous eastern Pacific system. Various model solutions fall within the established Marginal Risk area on the Day 4 ERO so that area remains unchanged. There is somewhat better agreement for heaviest activity on Day 5/Thursday with favorable moisture anomalies/enhanced IVT values, favoring introduction of a Slight Risk area over a majority of coastal California and extending into favored terrain of the Sierra Nevada. This area reflects the best overlap of heaviest forecast rainfall and current sensitivities from either wet antecedent conditions or burn scars. Continued progression of this system will spread areas of heavy snow farther inland to the Rockies, and then by next weekend support another eastern U.S. system that may generate additional heavy rainfall over or near some areas expected to see significant totals from the previous event. Both systems affecting the East may produce areas of potentially disruptive wintry precipitation. Probabilities of 0.25 inch in the form of snow suggest the best potential for significant accumulations will extend from the central Plains through the Midwest and then parts of the Great Lakes and Northeast/northern Mid-Atlantic. At this time the axis of next weekend's potential event looks to be a little northward of the one this Wednesday into Thursday. A transition zone of freezing rain and/or sleet may exist between the snow area and rain to the south. Continue to monitor forecasts as guidance refines important details. Another Pacific system coming into the picture by the weekend may spread some precipitation into the Pacific Northwest. Expect moderate amounts overall but some localized enhancement will be possible. The northern and central Plains will see the most persistent below normal temperatures from Wednesday through the weekend, with most days 15-30F below normal aside from the central Plains moderating briefly on Friday. Cold air will extend into the West, and in particular the Northwest, though with a gradual trend toward less extreme anomalies heading into the weekend as Pacific flow gains influence. A few locations in the Northwest could see daily records for lows/cold highs on Wednesday. Anomalous warmth should be confined mostly to the Gulf Coast and far Southeast. Parts of Florida could see record highs on one or more days, while readings could get close to records on Wednesday farther west. Systems tracking through the East will briefly bring some of this warmth northward on Thursday and again during the weekend. Rausch 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