Extended Forecast Discussion NWS Weather Prediction Center College Park MD 157 PM EST Sat Feb 12 2022 Valid 12Z Tue Feb 15 2022 - 12Z Sat Feb 19 2022 ...Mid-late week system to bring potential for heavy rain and severe weather from the south-central to east-central U.S. and wintry weather from the Midwest through Great Lakes and interior Northeast... ...Overview... The dominant focus of the medium range forecast will be a sharp upper trough likely centered from the northern Rockies through California as of early Tuesday. This feature, possibly containing an upper low for a brief time, will track eastward through midweek and then become incorporated into a Plains/east-central U.S. mean trough. This evolution aloft will lead to surface cyclogenesis and strong frontal systems in the central U.S., drawing moisture northward from the Gulf of Mexico and producing notable precipitation from the Plains eastward next Wednesday into Friday. Expect rain and thunderstorms in southern areas, while snow and wintry weather are likely on the northern and western side of the precipitation shield across the central Rockies/Plains and through the Midwest, Great Lakes, and interior Northeast. By Friday-Saturday expect a weaker clipper system tracking near the Canadian border to bring a cold front into the northern tier while a steadily weakening (but initially quite strong) eastern Pacific upper ridge drifts toward the West Coast. ...Guidance Evaluation/Predictability Assessment... Latest models and ensembles have been showing some incremental adjustments for the upper system initially dropping into the West and associated surface evolution through the week. To start the period, guidance is keeping the western trough a little more open and by early day 4 Wednesday gives mixed signals for whether there will be a closed low--though still with majority support to favor showing one in a single deterministic forecast. Either way the recent trends have been for a more open feature as it ejects into the Plains, leading to a somewhat weaker and faster surface system from the Plains through Midwest and Great Lakes. Low pressure does eventually strengthen farther northeastward as northern stream dynamics increasingly influence the system. Latest CMC runs stray southwest of other solutions with the western upper system and then shear it out more dramatically farther east, resulting in a weaker surface pattern. An average of GFS/ECMWF/UKMET runs from the 00Z/06Z cycles provided a measured adjustment from continuity. It will be interesting to see if persistence of a weaker scenario in the CMC foreshadows additional weakening/progression in other solutions, such as seen in the new 12Z ECMWF. Beyond the early period detail differences, the combination of upstream energy diving into/through the West from Wednesday onward and northern stream troughing that reaches the Plains/Mississippi Valley still contribute to some of the uncertainty in forecasts of this system over the course of the period. Lingering southern tier shortwave energy, with fairly low predictability for specifics, may have an effect on frontal waviness and precipitation toward the end of the period. Elsewhere, continuity is fairly good in principle for the system forecast to track near the Canadian border/Upper Great Lakes around Friday-Saturday while typical differences exist for precise timing of the trailing front. Models vary for a weak and small-scale shortwave rounding the Pacific upper ridge and then dropping into the West late in the period. Confidence is currently minimal for specifics of this feature. However there is decent agreement on an upstream shortwave/cold front approaching the Pacific Northwest later next Saturday. Preferences for the system over the West and continuing eastward favored starting the forecast with the 06Z GFS/00Z ECMWF and 00Z UKMET for about the first half of the period. Then the blend incorporated some of the 06Z GEFS/00Z ECMWF means by days 6-7 Friday-Saturday given decreasing confidence in some details. ...Weather Highlights/Threats... Underneath the upper low/trough over the West Tuesday into Wednesday, expect light to moderate precipitation in the form of lower elevation rain and mountain snow to spread from California and Great Basin/Northern Rockies into the Central Rockies. Showers and thunderstorms will become more widespread over the central U.S. by Wednesday into Thursday as surface low pressure consolidates in the High Plains and advects substantial moisture from the Gulf of Mexico northward into the Plains, Mississippi/Tennessee/Ohio Valleys, and eventually the Appalachians and Eastern Seaboard. Strong storms are possible, with the Storm Prediction Center outlook showing some severe threat for parts of the southern Plains into the Lower Mississippi and Tennessee Valleys and vicinity on Wednesday and Thursday. There could also be flash flooding concerns where heavy rainfall occurs, possibly in similar regions and into the Southern Appalachians. Continue to monitor forecasts as uncertain details of these potential threats become better refined. At the same time, expect a band of snow in the colder air on the northwestern periphery of the system. The best potential for meaningful accumulations currently extends from central parts of the Plains and Midwest/Middle Mississippi Valley into the Great Lakes region and interior New England, while mixed precipitation/ice cannot be ruled out in the transition zone between the snow and rain. Totals/location of any snow will be very sensitive to precise strength and track of the system, and wintry weather could be within a fairly narrow band. Strong winds may be possible in the gradient between the surface low and high pressure to the northwest, and then possibly along parts of the East Coast within the southerly flow ahead of the system. Recent trends toward low pressure being weaker and faster, at least from the Plains through Ohio Valley/Great Lakes, could temper snowfall and wind speeds somewhat. Dry conditions should prevail over much of the lower 48 behind this system. By Friday or Saturday the system along the Canadian border may bring some snow into the Upper Great Lakes while a little light precipitation may reach the northern Pacific Northwest/Rockies. Some moisture may linger over the far Southeast/Florida but with low confidence in coverage and intensity of rainfall at this time. The change and progression of the overall pattern will be evident in temperatures over the course of next week, as warmer than average temperatures push eastward through the workweek ahead of the trough/frontal system and cooler temperatures spread behind the cold front. Highs of 10-20F above average and lows 15-30F above normal will be shunted from the Plains on Tuesday into the Mid-Mississippi and Ohio Valleys (while persisting in the Southern Plains) on Wednesday, then into the Eastern Seaboard on Thursday. Some lows in the East could challenge daily records for warmth if they hold for the calendar day. On the backside of the front, temperatures should flip to near or below average, first over the West and spreading to the Rockies, Plains, and Midwest Wednesday and Thursday before tracking into the eastern third of the country for the latter part of the week while moderating. Best potential for temperatures 10-20F below average will be over the southern half of the Rockies/High Plains and Upper Midwest into the Great Lakes. An increasing portion of the West and eventually the Plains should warm up to above average once again by the end of the week. Parts of the Great Basin and vicinity could see highs at least 10F above normal. Rausch/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