Extended Forecast Discussion NWS Weather Prediction Center College Park MD 136 PM EST Sat Feb 08 2020 Valid 12Z Tue Feb 11 2020 - 12Z Sat Feb 15 2020 ...Heavy rain threat between the Southern Plains and Tennessee Valley/southern Appalachians next week... ...Overview and Guidance/Predictability Assessment... The forecast of the large scale pattern aloft has changed little over the past day, with eastern Canada into western U.S. mean troughing sandwiched between one ridge over the eastern Pacific and another ridge that should settle over Cuba and the Bahamas by late week/next weekend. This pattern will maintain the threat for episodes of heavy rainfall over portions of the southeastern quadrant of the country while occasionally bringing precipitation of more moderate intensity to parts of the West. For temperatures, the Rockies/Plains should see the most persistent below normal readings during the Tue-Sat period. The East/South will see above normal temperatures into Thu before a cooling trend Fri-Sat. While there is good agreement/consistency for the mean pattern, individual embedded features and periodic splitting of flow/stream interaction continue to provide some challenges in the forecast. The most significant issue during the period involves the interaction of the upper low that should start the period near the western U.S.-Mexico border and northern stream flow rounding the Pacific ridge and eventually helping to eject the upper low. Through the 00Z/06Z cycles there were two distinct clusters: the quicker group around the ECMWF-ECMWF mean and the slower majority including the GFS/CMC/UKMET and GEFS mean. Trend in recent runs has been a bit quicker for the slower members and a bit slower for the quicker members. Preference for the forecast remained between the slower and quicker groups, still tilting toward a slower solution. Latest 12Z/08 models seem to be converging upon a near-midpoint solution near the earlier preference, but given the low confidence in upstream shortwave details, may need to see another cycle before things start to settle down. This northern stream flow affects the evolution/speed of the exiting Southwest upper low, and continue to favor the slower non-GFS solutions there. After that, northern vs southern stream dominance remains quite uncertain as evidence by the run-to-run changes seen in the ensemble means. For next Fri/Sat, continue to see a large north-south spread in digging troughing into the West. With lower confidence with the leading shortwave from the same location (Gulf of Alaska) and inconsistencies heretofore, opted to split the ensemble means with WPC continuity which still favors a nearly closed low again in the Southwest. ...Weather/Hazard Highlights... Rainfall over the Southeast should briefly trend lighter early in the period as a wavy front settles near the Gulf Coast. Then expect the potential for another significant event around Wed-Thu as the upper low ejecting from northwestern Mexico/southwestern U.S. and interacting northern stream flow support northeastward-tracking low pressure that would enhance focus activity north of the leading Gulf Coast front and along a trailing cold front. The best clustering of guidance continues to highlight an area from the southern Plains into the southern Appalachians but there is still enough spread in system details/timing to temper confidence in specifics. Any rain that does fall may lead to flooding/flash flooding concerns given significant totals observed over recent days. Uncertainty in specifics of this system also causes difficulty in resolving the coverage and intensity of winter weather threats on the northern side of the moisture shield. Continue to highlight a 10-30% chance in the Winter Weather Outlook probabilities. The initial upper low over/near the Southwest will produce some rain and higher elevation snow in its vicinity, mainly over Arizona and New Mexico. Shortwaves dropping southeastward around the Pacific ridge aloft should bring one or more areas of rain/mountain snow across parts of the West, progressing from northwest to southeast. Most activity should be of light-moderate intensity. Within the area of below normal temperatures over the Rockies/central U.S., some locations in the southern High Plains may see highs 10-20F below normal Tue-Wed and parts of the Northern Plains/Upper Mississippi Valley could see one or more days with readings 10-20F or so below normal. Some of this cold air should reach the East by Fri-Sat with northern areas possibly declining to at least 10F below normal--displacing well above normal temperatures from Tue into Fri morning. Before the cooling trend some areas may see one or more days with lows 20-25F above normal and highs 5-15F above normal. This may support some isolated record highs around Florida near the upper high. 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 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