Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Sat May 6 2023 Valid 12Z Tue May 9 2023 - 12Z Sat May 13 2023 ...Overview... A quasi-zonal upper level flow pattern with a broad upper ridge over the central/northern Plains and an arriving upper trough centered over the West Coast is expected for Tuesday. This trough is forecast to amplify further going into the middle of the week across the Intermountain West and Rockies, and this will tend to build the ridge that will be downstream from the Gulf Coast to the Midwest, and a trough axis across the Northeast states that exits on Thursday. The western U.S. trough should then reach the western High Plains to close out the work week with an increase in shower and thunderstorm chances across the central U.S., and generally above normal temperatures east of the Rockies in response to the upper ridge aloft. ...Guidance/Predictability Assessment... Model guidance agrees well on the overall synoptic pattern described above through about Wednesday, and a general model blend suffices as a starting point in the forecast process through this time. Model uncertainty increases some going into the end of the week with the CMC/ECMWF in a similar location but the GFS centered a bit more to the northeast with the main upper low, but greater differences in regard to expected mesoscale features that develop. There is a general consensus that the ridge axis over the east-central U.S. will tend to limit the eastward progression of the front. By next Saturday, the CMC becomes stronger with an upper trough just off the East Coast. The ensemble means accounted for about half of the forecast blend by the second half of the week. ...Weather/Hazards Highlights... Showers and storms are expected to increase in coverage across much of the Plains states going into the Tuesday-Wednesday time period as moisture advection from the Gulf of Mexico increases ahead of the arriving cold front from the Rockies. A Marginal Risk for the Day 4 ERO is planned across portions of NE/KS, and also across much of central and southern Texas. The heaviest convection for Day 5 is currently favored across portions of eastern Texas and the ArkLaTex region and the northern Plains, and a Marginal Risk area is planned for both of those areas. The potential exists for eventual Slight Risks in future updates once the main QPF axis becomes more apparent. Looking ahead to Thursday/Friday, additional moderate to locally heavy rainfall is expected across mainly the southern Plains, with the potential for several inches of rain in some areas of Texas. There will likely be enough cold air aloft to support lowering snow levels across portions of the Northern Rockies, and late season snow is probable for the higher elevations of Wyoming and Montana during this time. In terms of temperatures, highs will likely be running 5 to 15 degrees above early May averages from the central/southern Plains to the Ohio Valley to start the week, and then reaching into the Midwest states and the Great Lakes region going into the middle of the week. Warmth builds across the Pacific Northwest by Friday into Saturday with highs potentially up to 20 degrees above mid-May averages. It will likely be slightly below average across portions of the West Coast states and the Intermountain West in association with the upper trough through Wednesday before a moderating trend commences, but overnight lows should be closer to average here and generally above average east of the Rockies. 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