Extended Forecast Discussion NWS Weather Prediction Center College Park MD 210 AM EST Sun Feb 13 2022 Valid 12Z Wed Feb 16 2022 - 12Z Sun Feb 20 2022 ...Mid-late week system to bring potential for heavy rain and severe weather from the south-central to eastern 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 an upper trough/low likely centered near the Four Corners early Wednesday, which will track eastward and phase with 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 and Thursday. 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, before additional troughing enters the Pacific Northwest by Sunday. ...Guidance Evaluation/Predictability Assessment... Model guidance continues to show fairly good agreement with the overall pattern described above, but with detail differences that could be impactful to the sensible weather. The bulk of guidance still shows evidence to maintain the closed low within the western U.S. trough to start the period early Wednesday, then quickly join with northern stream troughing in the central U.S. by Thursday. Over the past day or so, guidance has trended toward 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. The 12Z CMC continued its position southwest of other solutions with the western upper system and then shear it out more dramatically farther east, resulting in a weaker surface pattern. The newer 00Z CMC is in somewhat better alignment with its upper level pattern but its surface low may be displaced south of a preferred position. An average of GFS/ECMWF/UKMET runs from the 12Z/18Z cycles once again served to reflect these model trends toward a slightly faster front and initially weaker low but also maintain a measure of continuity from the previous forecast. 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 by late in the week, with GFS runs strongest and ECMWF runs weakest with this feature, and confidence remains minimal with the specifics. However there is decent agreement on an upstream shortwave/cold front approaching the Pacific Northwest over the weekend. Preferences for the system over the West and continuing eastward favored starting the forecast with the 12Z/18Z GFS and 12Z ECMWF and UKMET for about the first half of the period. Then the blend incorporated some of the 18Z GEFS/12Z ECMWF means by the weekend given decreasing confidence in some details. ...Weather Highlights/Threats... Showers and thunderstorms will become widespread over the central U.S. on 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 spreading toward much of the Eastern Seaboard on Thursday and Thursday night. Current forecasts show the Southern Appalachians could see particularly high rainfall totals given terrain enhancement there. 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 given that wintry weather could be within a fairly narrow band, and a faster forecast low/front track may temper snowfall amounts. Gusty winds are possible with the system as well, and at this point appear most likely near the Northeast coast on Thursday night in strong southerly flow ahead of the quickly strengthening surface low. 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 light precipitation may reach the northern Pacific Northwest/Rockies by Friday, which could increase in amounts by Saturday. 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 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 southern half of the Plains into the Mississippi and Ohio/Tennessee Valleys Wednesday into the Eastern Seaboard on Thursday. Daily records could be set for some locations, especially for warm lows in the East on Thursday, while a few record high maxima could be challenged as well. On the backside of the front, temperatures should flip to near or below average, shown in the Great Basin/Rockies and north-central U.S. on 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, while central parts of the Plains could even reach 20F above average with temperatures in the 60s by Sunday. Tate/Rausch 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