Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 PM 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... An upper trough/low that is likely to be centered near the Four Corners early Wednesday and then phase with a Plains/east-central U.S. mean trough as it continues eastward will be produce the most active weather over the lower 48 during the forecast period. The ejecting upper system 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. There is still uncertainty in the precise axis of meaningful snow though. By Friday-Saturday expect a clipper system tracking near the Canadian border to bring a cold front into the northern tier and some snow into the Great Lakes while a steadily weakening (but initially quite strong) eastern Pacific upper ridge drifts toward the West Coast. Another Pacific upper trough with leading frontal system may reach the West Coast by Sunday. ...Guidance Evaluation/Predictability Assessment... The agreement in the overall pattern and the forecast philosophy in response to guidance behavior remains fairly consistent. The multi-day trend has been weaker/faster for the Plains through eastern Great Lakes evolution of the system affecting the central/eastern U.S. mid-late week, but with good continuity for intensification from the eastern Great Lakes onward in response to northern stream dynamics. CMC runs have been persistently different from the majority cluster--tending to be weaker and more sheared but lately showing improved definition for low pressure over the eastern half of the country albeit with a more southern track. The GFS has actually trended a bit stronger with its surface low over the past 12 hours of runs through the 12Z cycle and the consensus average has nudged a fraction west with its precip shield versus previous cycle. Thus it is hoped that guidance may be starting to stabilize better around a midpoint even with some shuffling of individual runs in response to lingering differences in details of northern stream flow and energy reaching the western U.S. A composite of the 06Z GFS and 00Z ECMWF/UKMET continued to provide the best template for the evolution of this system, with only modest nudges from continuity. As for the rest of the forecast, clustering still looks better than average for the system expected to track near the Canadian border around Friday-Saturday in response to strong western Canada flow settling into the east-central North America mean trough. Spread/variability with exact amplitude of the resulting upper trough lead to some differences with the timing and southward extent of the trailing front reaching into the central and eastern U.S. Noticeable differences exist for the Pacific trough approaching the West Coast. GFS runs have varied within the middle to slower part of the envelope, with the new 12Z run being one of the slower versions. ECMWF runs have been fairly stable in the middle so far, while the 00Z CMC was a bit fast but adjusted back some in the 12Z cycle. Latest GEFS means are slower than the 00Z ECMWF mean but not as slow as the 12Z GFS. Some of the spread for this trough may be due to uncertainty over how much if any energy may separate from the southern part of the feature farther upstream (as seen in 00Z and new 12Z ECMWF differences). A weak shortwave that may drop into the West ahead of this trough is rather small in scale and has below average predictability, with low confidence in a specific solution. This cycle's forecast considerations led to a starting blend consisting of the 18Z GFS/12Z ECMWF/12Z UKMET for the first half of the period, followed by some inclusion of the 06Z GEFS/00Z ECMWF means along with the 06Z GFS/00Z ECMWF. ...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. Probabilistic forecasts of 0.25 inch liquid in the form of snow reflect the uncertainty in this aspect of the forecast, with values generally below 50 percent for any particular location but with a decent signal that there should be a band of enhanced snow somewhere within the favored zone. 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, with light to locally moderate precipitation spreading southeastward farther into the West by Sunday. Some moisture may linger over the far Southeast/Florida. Confidence in coverage and intensity of rainfall is still on the lower side but helped by a lighter trend in recent GFS runs which had been a heavy extreme. 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, with some 10-20F below average readings possible over parts of the central/east-central U.S. mid-late week and then moderating closer to the East Coast. Coldest anomalies should be over/near Minnesota around Thursday with some places 20-30F below normal. An increasing portion of the West and eventually the northern/central Plains should warm up to above average once again by the end of the week into the weekend. 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. 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