Extended Forecast Discussion NWS Weather Prediction Center College Park MD 157 AM EST Tue Mar 5 2019 Valid 12Z Fri Mar 8 2019 - 12Z Tue Mar 12 2019 ...Weather Pattern Overview... An active weather pattern is expected during much of the medium range period as a large scale trough originating from the Pacific amplifies over the Rockies and High Plains. This will induce surface cyclogenesis east of the Rockies and become a strong surface low as it tracks northeastward. A second disturbance is forecast to affect the West Coast region by early next week, and this should also lead to the development of the surface low over the southern plains by the end of the forecast period. ...Model Guidance Evaluation and Preferences... The models and ensemble means indicate reasonable agreement on the synoptic scale for the end of the week, and slightly better agreement compared to yesterday. One of the main differences on Friday is that the GFS based guidance indicate a more developed lead surface low crossing the Ohio Valley region, whereas the CMC/ECMWF/UKMET support more of an elongated surface trough. The strong surface low that is forecast to develop across the Plains and then track northeastward is indicating reasonably good agreement on Saturday morning across eastern Colorado as lee cyclogenesis gets underway. Model differences are more apparent by Sunday regarding the track of the surface low across the Midwest states and then the Great Lakes region. In terms of trends, both the EC mean and GEFS mean continue to trend stronger and slightly faster with this storm system, and the Canadian mean has trended closer to the GEFS and EC means compared to yesterday's runs. Similar to yesterday, the FV3 is faster than the model consensus and loses ensemble support. The GFS and its ensemble members are generally on the stronger side of the forecast guidance. Taking all of these factors into account, the forecast was primarily derived from the 12Z ECMWF/18Z FV3 and GFS/12Z CMC for the first two days, and then some of the ECMWF and EC/NAEFS mean for the second half of the forecast period. The WPC forecast is similar to the previous one regarding the track of the storm, except now it is forecast to be slightly more intense. ...Sensible Weather and Potential Hazards... Widespread rain and thunderstorms are expected to develop from the Gulf Coast to the Ohio Valley and southern Appalachians as a rich supply of Gulf moisture surges northward ahead of a strong cold front from the surface low. The heaviest rainfall is likely from eastern Texas to Tennessee, where a general 1 to 3 inches of rain is likely that may lead to some flooding issues based on the current forecast. Depending on where the surface low tracks, a corridor of blizzard conditions will be possible across parts of the northern plains, Upper Midwest, and western Great Lakes region. It is still too early to mention precise locations given current model differences. Another facet to this low pressure system will be the potential for strong to severe thunderstorms to develop in the warm sector, and this is something that the Storm Prediction Center is currently monitoring. More rain is likely across the central and southern plains by next Tuesday associated with the next storm system. Heavy snow will likely continue for another day on Friday across the higher elevations of the Intermountain West and Rockies as the strong Pacific disturbance crosses the region. Total snowfall amounts on the order of 1 to 2 feet are possible across parts of the central and northern Rockies, before gradually ending early Saturday. The northern-central Plains will likely continue to see below normal temperatures most days with highs tending to be 10-20F below normal with locally more extreme anomalies one or more days. The West will tend to see below normal highs for much of the period but morning lows should be above normal late this week. The southern and eastern U.S. should have a brief surge of warmth ahead of the front associated with the Plains/Great Lakes storm during the weekend, followed by a return to cooler weather. D. Hamrick Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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