Extended Forecast Discussion NWS Weather Prediction Center College Park MD 201 PM EST Wed Feb 16 2022 Valid 12Z Sat Feb 19 2022 - 12Z Wed Feb 23 2022 ...Developing heavy rainfall threat across portions of the South early next week... ...Overview... The medium range period will begin Saturday with generally quiet weather, besides a clipper system bringing snow to the Great Lakes region. Then as next week begins, troughing is forecast to develop in the West and slowly track eastward along with a strong frontal system. Precipitation chances should increase in the West with this pattern and spread into the central U.S. once again by next Monday through Wednesday, with the possibility of northern tier snow and southern U.S. rain. ...Guidance Evaluation/Predictability Assessment... Recent model guidance shows good agreement overall with the large scale pattern through the middle of next week, though plenty of lingering uncertainty in the smaller scale details. To start the period, the surface low/clipper over the Great Lakes and upper-level energy supporting it continue to have good consensus among recent 00z/06z models. A compact closed upper low tracking south along the California coast ahead of the main larger scale trough, and weakening as it moves across northern Mexico, also has shown much better agreement in recent cycles, including the GFS which had been a bit of an outlier the past few cycles. Then, there remains good large scale agreement for energy to spill into the West east of an amplified eastern Pacific ridge by next Sunday-Monday. This should amplify early next week and shift slowly eastward as flow across the central and eastern U.S. shifts more zonal and then ridging. The 00z CMC (and to some extent the 06z GFS) are stronger than the ECMWF showing a closed low over the West next Tuesday. By Tuesday-Wednesday though, the CMC is very notably faster/farther south with the energy and thus was not included in the blend past day 5. The ECMWF has consistently been a little slower/less amplified with the trough, though the ensemble spread is large regarding the exact details/timing of embedded energies within the main trough. The WPC blend used a multi deterministic model blend of the 00z/06z guidance for days 3 and 4. After that, increased the ensemble mean contribution (in favor of the CMC) to help mitigate the late period detail differences. The resulted in some minor adjustments to the leading cold front into the Midwest/eastern U.S. at the end of the period compared to our continuity, but on an overall scale, todays WPC forecast does maintain good continuity in terms of the messaging from the overnight package. ...Weather Highlights/Threats... Lingering snow is forecast on Saturday across the Great Lakes region with the clipper system, with generally light to perhaps locally moderate amounts. Mainly dry conditions are expected elsewhere on Saturday other than a few showers possible in Florida, except that precipitation will be increasing in the Pacific Northwest and Northern Rockies with the upper trough coming in. Coastal and valley rain and mountain snow are likely over the Pacific Northwest spreading into California, the Great Basin, and the Rockies through the early part of next week. Snow could also spread farther east into the northern High Plains Sunday and into the rest of the northern tier states as the first half of the week progresses. The confidence in the axis of heaviest snow and snowfall amounts remains somewhat low. Farther south, moist inflow is forecast to return to the south-central and southeastern U.S., with increasing chances for heavy to possibly excessive rainfall. Models seem to be converging on portions of the Gulf Coast states/Tennessee Valley as the greatest threat for heavy rainfall next Monday-Tuesday, with some guidance suggesting the threat may continue into Wednesday over roughly the same area. There remain plenty of uncertainty in the details which likely are going to take another few days to resolve, but regardless, the pattern itself would support some sort of heavy rainfall/possible severe weather threat (as noted by SPC) early next week. Temperatures this weekend are expected to be above normal for parts of the West into the Plains, with the largest anomalies of highs 20+ degrees above average over South Dakota and Nebraska. Meanwhile, cooler to near average temperatures over the eastern third of the country Saturday will warm Sunday. As the pattern amplifies, the south-central U.S. to the East Coast will further warm through the first half of next week, with widespread highs 10-20F and lows 20-30F above normal. Meanwhile, a cold Arctic high is forecast to expand across the north-central U.S., leading to well below average temperatures initially across the northern High Plains and spreading southward (as far south and the OK/TX panhandles) through midweek. Temperatures in some places could be 30 or more degrees below normal, and highs in the single digits are expected for Montana and the Dakotas Monday and Tuesday. Santorelli/Tate 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, 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