Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Tue Mar 28 2023 Valid 12Z Fri Mar 31 2023 - 12Z Tue Apr 4 2023 ***Strong low pressure to produce some severe thunderstorms, episodes of heavy rainfall, and windy conditions across portions of the Plains and Midwest late week into the weekend*** ...Synoptic Overview... The main weather story will be the strong low pressure system developing across the Central Plains and the Midwest to close out the work week. As the trough from the western U.S. ejects over the western High Plains, lee cyclogenesis is expected to commence over eastern Colorado Thursday night and a well organized low pressure system will evolve over the Central Plains along a rather strong frontal boundary. Severe storms, heavy rainfall, and gusty winds will be making weather headlines going into Friday and persisting into early Saturday. This system then moves in a general northeastward direction towards the Great Lakes by Saturday and then to southeastern Canada by Sunday. Meanwhile, the next upper level trough/closed low from the Gulf of Alaska reaches the Pacific Northwest by Sunday and brings another cold front across much of the western U.S. to reinforce the cool weather pattern. This front/upper trough may also result in a surface low developing over the central/southern Plains by next Monday, albeit probably a little weaker than the previous event. ...Model Guidance/Predictability Assessment... The 00Z model guidance suite has come into better focus on the storm evolution for Friday and into the weekend, with most of the guidance trending towards a stronger solution, which the GFS was portraying over the past few runs with a closed low developing over the Upper Midwest. The ECMWF is slightly faster than the other guidance, but still close enough to merit a general model compromise through Saturday. Looking ahead to early next week, the GFS is stronger with a northern stream system near North Dakota and Minnesota, but more in line with the CMC/ECMWF across the Pacific Northwest as the main trough builds in. By Tuesday, the GFS is a little slower with the trough progression across the Rockies, but the greatest model differences are noted off the West Coast as a potential reinforcing shortwave follows behind the main trough. A gradual increase to about 50% ensemble means was incorporated by next Tuesday. ...Weather/Hazards Highlights... The most impactful weather during this forecast period is expected on Friday in association with the strengthening low pressure system across the Plains and Midwest, and March will not be going out like a lamb here. Perhaps the greatest concern will be the elevated threat of severe thunderstorms in the big warm sector extending from the greater Chicago metro area to the ArkLaTex region based on the latest Storm Prediction Center outlook. A combination of both strong kinematics and instability parameters will create a favorable environment of severe storms with increasing wind shear and thunderstorm updraft potential, and this is something that will need to be closely monitored in the days ahead as the event enters the short range. In addition to the intense convection, widespread windy conditions are likely to develop across a broad expanse of the Plains and Midwest as the surface pressure gradient tightens, with gusts in excess of 40 mph expected behind the cold front. There has also been a trend for a band of moderate to locally heavy snow from southern South Dakota to southern Minnesota to the northern Great Lakes, which is where the deformation band northwest of the main surface low is expected to track. The potential exists for some 6-12 inch totals across parts of this region. Swaths of heavy rainfall are also likely farther south from the Ohio Valley to the Deep south, but the relatively progressive nature of this storm system should keep rainfall totals from becoming extreme. Therefore, only a Marginal Risk of excessive rainfall is currently warranted in the Day 4 outlook, and a lingering Marginal Risk area near the Gulf Coast on Day 5. Elsewhere across the nation, reloading of upper level troughing over the northwestern U.S. by the weekend and continuing into early next week will support multiple days of rain/mountain snow with terrain enhancement from the Pacific Northwest and northern California into the central and southern Rockies, with the moisture shield pushing gradually farther southeast with time. Heavy snow is likely for the Cascades and the Olympic Mountains where a few feet of snow accumulation is expected for the higher elevations. Significant snow may reach the Sierra by Tuesday. Showers and thunderstorms are expected to return to locations from the Deep South to the Ohio Valley again on Tuesday as the next storm system gets better organized across the central Plains. Much of the western U.S. will continue to have cooler than normal temperatures for most of this forecast period as the upper level trough becomes anchored over the region. The best potential for highs 15 to 25 degrees below normal will be Friday across the Dakotas as the first upper trough passes through, and then over a broader expanse from the West Coast to the Dakotas early next week as the next trough settles in. Upper level ridging extending from a Gulf of Mexico upper high should result in warm and humid conditions to rebuild across the south-central U.S. Thursday and spread into the Mississippi Valley Friday and the East by Saturday, with highs generally 5-15F above average and lows around 15-25F warmer than normal. The warm weather is likely to continue in early next week as well. A few record warm low temperatures could be tied or set. Hamrick 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, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml