Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 AM 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 emphasize the past two ECMWF runs and 12Z CMC/18Z GFS during the first half of the period, followed by a transition toward 50-70 percent 12Z ECMWF mean/18Z GEFS mean (slightly more toward the ECMWF mean) with the remainder mostly lingering weight of the ECMWF runs. Recent trends are toward slower motion of the upper low near the southwestern U.S., allowing for somewhat lower heights over the central/eastern states and farther southward extent of the wavy front reaching the East and South during the first half of the week. Latest UKMET runs are on the fast extreme with the upper low due to being more aggressive with northern stream flow. By the latter half of the period the GFS shows less western troughing than most other guidance due to the Pacific ridge extending farther eastward. GEFS means hint at the GFS scenario for a time but ultimately end up closer to the majority cluster. Teleconnections relative to the positive height anomaly center associated with the eastern Pacific ridge favor the western troughing seen in the non-GFS cluster. A transitory ridge between defined shortwaves would still be possible though. 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. ...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. 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. 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. 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, with lowest readings most likely Thu-Fri when there should be decent coverage of highs 10-20F 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. 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 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