Extended Forecast Discussion NWS Weather Prediction Center College Park MD 332 PM EST Fri Feb 07 2020 Valid 12Z Mon Feb 10 2020 - 12Z Fri Feb 14 2020 ...Heavy rain threat between the Southern Plains and Tennessee Valley/southern Appalachians next week... ...Overview and Guidance/Predictability Assessment... Most guidance shows mean troughing aloft from eastern Canada through the western half of the lower 48, between an eastern Pacific ridge and northwestern Caribbean ridge that passes over Cuba and the Bahamas. This pattern should favor highest rainfall totals over the southeastern quadrant of the country, along with above normal temperatures over the East and below normal readings over parts of the West and into the Plains. Within this general pattern there are multiple uncertainties that lead to lower confidence in various forecast details. Already in the first half of the period there are some differences and/or trends with the upper low forecast to track along or a little south of the southern California/Arizona border and approaching northern stream flow that influences its ejection, with corresponding effects on flow over the eastern half of the country. Then there are additional question marks regarding upstream flow that may feed into the western mean trough late in the week as well as for shortwave details to the east. The overall approach of the updated forecast was to introduce some changes where the latest ensemble guidance suggested it was prudent to do so, couched in a deterministic blend, followed by a transition toward a supermajority weighting of the 00Z ECMWF mean/06Z GEFS mean. The deterministic 00Z ECMWF was maintained to add some detail to the forecast though confidence in such details was low. A bit slower motion of the upper low near the southwestern U.S. and a less amplified northern stream shortwave into the Pac NW Tuesday would allow for more westerly vs southwesterly flow aloft east of the Rockies Wed-Thu, suggesting that any frontal wave would be weaker and farther east than thought 24 hrs ago. The GFS continued to favor the northern stream vs southern stream in the East, but would need more continuity in the ensembles to prefer that solution. Recent GEFS members hint at the GFS scenario for a time but overall end up somewhat in between the ECMWF ensembles and GFS. Teleconnections relative to the positive height anomaly center associated with the eastern Pacific ridge favor the western troughing seen in the non-GFS cluster. Specifics of the mid-late week forecast over the central/eastern U.S. will depend on how the combined shortwave uncertainties work out. The preferred guidance cluster would have a system tracking from the central U.S. through the Great Lakes and Northeast which may limit the northward extent of warming ahead of the front. ...Weather/Hazard Highlights... The southeastern quadrant of the lower 48 should see the highest potential for significant precipitation during the period, in particular from eastern Texas through the Lower Mississippi Valley and Tennessee Valley/southern Appalachians. A wavy front pushing through the South toward the Gulf Coast may produce one episode of rainfall early in the week followed by a short reprieve. The combination of the upper low ejecting out of extreme northwestern Mexico and interacting northern stream energy, along with flow overrunning the front that settles near the Gulf Coast by midweek, may produce another period of significant rainfall around Wed-Thu. Confidence is lower for specifics of this second event though but the potential for higher totals may be greater than the preceding event. In light of recent heavy rains in the Southeast, will need to monitor where the potential for heavier totals may occur. Farther north, mostly light snow is possible over New England with the leading eastern front and with a system brushing the northern tier. The mid-late week system could produce a broader area of wintry weather from parts of the northern-central Plains into the northern Mid-Atlantic/Northeast--but again with details that are uncertain at this time. Over the West, the upper low tracking close to the southern California/Arizona border should produce some areas of rain and higher elevation snow over parts of the Southwest/southern Rockies. Higher totals may be possible along the CO/NM border. Energy flowing around the eastern Pacific ridge aloft may generate one or more periods of mostly light-moderate rain/mountain snow between the Pacific Northwest and northern Rockies, with lower than average confidence in timing and coverage. Some of the precipitation could extend farther south if this energy is sufficiently amplified. Expect areas from the west-central U.S. into the Plains to see the coldest temperatures relative to normal during the period (about 5-15F below normal). On the other hand the eastern states will likely see above normal temperatures during the period, with plus 10-25F anomalies for morning lows and plus 5-15F anomalies for highs, centered over the Southeast but extending northward into the Mid-Atlantic. Fracasso/Rausch Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php - Heavy precipitation across portions of the Southern Rockies, the Southern Plains, and the Southwest, Tue-Wed, Feb 11-Feb 12. - Heavy precipitation across portions of the Southwest, Mon-Tue, Feb 10-Feb 11. - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, between Mon-Tue, Feb 10-Feb 11 and Wed-Thu, Feb 12-Feb 13. - Heavy snow across portions of the Southern Rockies, the Central Rockies, the Central Great Basin, and the Southwest, Mon-Tue, Feb 10-Feb 11. - Flooding possible across portions of the Central Appalachians, the Northern Plains, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Ohio Valley. - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Tennessee Valley, the Northern Great Basin, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Pacific Northwest, and the Ohio Valley. - Flooding likely across portions of the Southeast and the Mid-Atlantic. - Much below normal temperatures across portions of the Central Rockies, Mon-Tue, Feb 10-Feb 11. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon, Feb 10. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml