Extended Forecast Discussion NWS Weather Prediction Center College Park MD 201 AM EST Mon Jan 31 2022 Valid 12Z Thu Feb 03 2022 - 12Z Mon Feb 07 2022 ...Heavy rainfall likely across the central Gulf Coast and Tennessee Valley on Thursday, with a significant winter storm from the Midwest to Great Lakes and interior Northeast... ...Overview... Mean troughing should dominate much of the CONUS through the medium range as strong upper ridging builds over both the western Atlantic and East Pacific. A shortwave initially over the Rockies on Thursday will drive a potent cold front eastward through Friday bringing widespread heavy rain to the South and a potentially significant winter storm from the Ohio 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, while northern stream shortwaves send a series of low pressure systems across the northern tier states. ...Guidance Evaluation/Predictability Assessment... Guidance continues to exhibit overall good agreement regarding an amplified shortwave initially over the Rockies on Thursday and into the Mid-South/East Friday-Saturday. There remain some differences in the shortwave timing especially into the East, though the CMC is notably more amplified with this system as a whole. 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. A general non-CMC model compromise seemed a good starting point for now through day 5 for this system which also maintained good continuity with the previous WPC forecast. After this, the guidance shows another couple of shortwaves rounding the top of the ridge and diving into the Southwest, the first on Friday and the next on Sunday. There continues to be some pretty significant variability in strength and timing of these systems, especially the second one. With that one, the GFS has consistently been much stronger in showing a deep closed low settling into the Southwest/northern Baja California Sunday-Monday. The ECMWF is back and forth between a similar closed low solution and a weaker/more progressive shortwave into the Plains. The 31/12z CMC has a nice middle ground. At this point, given the uncertainty and run to run inconsistencies, it seemed prudent to lean more on the ensemble means during the latter half of the forecast period, although ensemble plots show enough support amongst various members for either solution. Northern stream shortwaves will drive a train of low pressure systems across the northern Plains/Great Lakes region through the period. The models show better agreement overall on these than in the more volatile southern stream, but given timing and interaction with that southern stream, there remains plenty of uncertainty in the details. Some incorporation of the deterministic solutions late period helped to bring some added definition to these systems where the ensemble means may tend to wash out. ...Weather Highlights/Threats... Amplified trough out of the Southwest on Thursday will continue to threat for heavy rainfall and a significant winter storm to the north into the Thursday-Friday time period. Ample Gulf moisture will be drawn northward ahead of the trough and associated surface cold front resulting in widespread moderate to heavy precipitation from the lower Mississippi Valley into the Northeast. Best chance for heavy rainfall extends from the central Gulf Coast on Thursday into the southern/central Appalachians and interior East. The overall pattern continues to support a threat for excessive rainfall/flash flooding. Although plenty of uncertainties in the details linger, models seem to be better latching onto the greatest threat from the central Gulf Coast into the Tennessee Valley where anomalous precipitable water values, lift, and moderate instability should support several inches of rainfall across this region. On there north side, the threat for a significant winter storm into parts of the Ohio Valley/Great Lakes/interior Northeast will continue from the short range period. 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 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 Thursday-Friday. 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 Central U.S. to the Midwest and eventually the East by the weekend. Widespread daytime highs (and slightly less extreme overnight lows) as much as 10-25 degrees below average are likely with values as much as 30-35 below normal as far south as 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. The West Coast states should be near normal into weekend, trending slightly warmer the rest of the period 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