Extended Forecast Discussion NWS Weather Prediction Center College Park MD 142 PM 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... Overall, the latest models and ensembles continue to show good large scale agreement on the medium range period pattern, but continued uncertainty in the details of individual systems which could have notable impacts for sensible weather threats/precipitation type. For the leading Eastern system, models have trended slightly sharper with the shortwave compared to a day ago, and do have some timing uncertainties, but overall, a blend of the latest operational models served as a good starting point for the first half of the period. The shortwave into California later this week also shows good initial agreement, but the CMC is slightly flatter with this wave than the GFS/ECMWF. By next weekend, details of this system over the Southwest become more murky and some bigger timing uncertainties of the trough emerge as it ejects into the Plains on Sunday. At this point, favor sticking close to WPC continuity and the ensemble means (with some modest inclusion of the GFS/ECMWF for added system definition). ...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 continue not to advertise any ERO risk areas 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, so a Slight Risk area over a majority of coastal California and extending into favored terrain of the Sierra Nevada remains in place. This area reflects the best overlap of heaviest forecast rainfall and current sensitivities from either wet antecedent conditions or burn scars. If current forecasts hold, it is possible an eventual upgrade to a moderate risk may be needed across southern California for particularly the burn scar areas. 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. Santorelli/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