Extended Forecast Discussion NWS Weather Prediction Center College Park MD 140 PM EST Sun Jan 30 2022 Valid 12Z Wed Feb 2 2022 - 12Z Sun Feb 6 2022 ...Heavy precipitation likely to impact the central and eastern U.S. later this week, including a winter storm from the Central Plains to Great Lakes and interior Northeast... 18Z Update: Overall the 12Z model guidance suite is in good overall agreement on the magnitude and timing of the central-eastern U.S. storm system for the middle of the week, and a multi-deterministic model blend sufficed as a starting point in the forecast process. The axis of highest snow/sleet probabilities is very slightly adjusted southeast with this forecast update from Missouri to Michigan, and significant icing remains a threat just south of this corridor across northern Arkansas, southeast Missouri, and western portions of Tennessee and Kentucky. Lesser amounts of ice are still possible across portions of northern Texas and eastern Oklahoma. After this front and its precipitation emerges off the East Coast, a cold but mainly dry weather pattern is expected across the majority of the nation for next weekend. By this time, the GFS remains more amplified with both a trough dropping southeastward across the northern Rockies and a cut-off low over the southwestern U.S., so less weighting was applied to the GFS and more to the ensemble means for days 6 and 7. The previous forecast discussion is appended below for reference. /Hamrick ...Overview... Mean troughing should dominate much of the CONUS east of the Rockies as strong upper ridging builds over both the western Atlantic and East Pacific. A shortwave initially over the Southwest on Wednesday will drive a potent cold front eastward through Friday bringing widespread heavy rain to the South and a potentially significant winter storm from the mid-Mississippi Valley to the interior Northeast. Additional waves of shortwave energy dropping down the east side of the ridge in the West, should help reinforce mean troughing across the central U.S. through next weekend. ...Guidance Evaluation/Predictability Assessment... Guidance has come into overall good agreement regarding an amplified shortwave initially across the Southwest on Wednesday and into the Southern Plains/Mid-South Thursday-Friday. There remain some minor differences in the shortwave timing (ECMWF has been consistently slightly faster than the GFS), which ultimately affects frontal timing, especially into the East. Albeit differences in timing and placement, guidance shows this energy may ultimately combine with a northern stream shortwave through the Great Lakes/Northeast late this week to help induce a deepening surface low well off the Northeast Coast. Given the overall agreement, a general model compromise between the latest runs of the deterministic models seemed a good starting point for now through day 5 for this system which also maintained good continuity with the previous WPC forecast. Next energy drops into the mean trough out of the West by Friday and the models continue to struggle both with strength and timing of the shortwave. Recent model runs have been back and forth between a weaker/faster shortwave and a stronger/slower possible closed low lingering over the Southwest for a day or two. At least through the latest 12z/18z (yesterday) guidance, the ECMWF and CMC are weaker and faster while the 18z GFS is notably more amplified/slower. The bulk of the ensemble guidance would support something more towards the quicker ECMWF/CMC so that's the way the WPC forecast leaned tonight. Yet another shortwave rounding the top of the ridge drops into the Northern Rockies by Saturday. Much of the guidance shows the shortwave progress rather harmlessly south and eastward into the northern/central Plains on Sunday, but the last few runs of the GFS have been quite aggressive with deepening this energy and a closed low forming over the Southwest. Ensemble plots suggest the GFS is likely much too deep with this, and the actual solution may be somewhere in the middle of a significantly weaker/faster ECMWF and the GFS (similar to the 12z CMC). The best course of action for the WPC forecast for next weekend was to stay close to the ensemble means, with lesser influence from the CMC and ECMWF just for some added system definition across the board. ...Weather Highlights/Threats... The deepening trough in the West will initially bring light to moderate precipitation across the central/southern Rockies and the Four Corners region on Wednesday. Ahead of this, ample Gulf moisture will be drawn northward ahead of the trough and associated surface cold front. This should result in widespread moderate to heavy precipitation from the southern Plains into the Northeast Wednesday and Thursday. The best chance for heavy rainfall extends from the Southern Plains and Lower Mississippi Valley into parts of the lower Ohio/Tennessee Valleys to the Appalachians and the East. The overall pattern would certainly support at least local spots excessive rainfall/flash flooding, but the exact locations remain quite uncertain and dependent on smaller scale detail differences, and impeded by an overall lack of instability. Possibly the bigger threat however is the increasing potential for a significant winter storm on the backside of this system from the central Plains into the Midwest/Lower Great Lakes and eventually the interior Northeast. Heavy accumulating snow is likely, while possible impactful sleet and freezing rain just to the south within the transition zone between the rain to the south and snow to the north. Exact amounts of any wintry precipitation remain in flux at this point and highly dependent on the lower-confidence details of ejecting shortwave energy, frontal waves, and timing of colder temperatures. Above average temperatures (generally +10-15F) will spread across the East Wednesday-Thursday. Meanwhile, as arctic high pressure dives into the central U.S. behind the cold front midweek, downright chilly and much below normal temperatures will spread from the northern Rockies/High Plains all the way as far south as Texas. Widespread daytime highs (and slightly less extreme overnight lows) as much as 10-25 degrees below average are likely with some locally higher spots especially Thursday across parts of Oklahoma and north/central Texas. These temperatures may moderate slightly as they shift east into the Ohio Valley/Gulf Coast states next Friday and the East on Saturday, though Texas remains below average through the end of the week. The West Coast states should be near normal through much of next week owing to amplified ridging across the East Pacific. Santorelli 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