Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Sat May 18 2019 Valid 12Z Tue May 21 2019 - 12Z Sat May 25 2019 ...Overall Weather Pattern... The upper level pattern across the continental U.S. will remain quite amplified and slow to change next week. A hot upper level ridge over the southeast U.S. becomes anchored over the region and gradually becomes stronger for the second half of the upcoming work week. Across the western U.S., a large scale upper trough will be dominant as multiple shortwave perturbations keep conditions cool and unsettled. This will also be slow to move given the expected development of an omega block type pattern upstream over the eastern Pacific. Lead main weather features include a strong low pressure system for the Plains and Upper Midwest Tue/Wed, followed by weaker lows and frontal boundary meanderings from the Southwest to the Northeast U.S. later week overtop the Southeast ridge. The pattern offers a periodic local threat for strong to severe convection and potential for cell training/excessive rainfall. ...Guidance/Predictability Assessment... The 06 UTC GFS and 00 UTC ECMWF seem well clustered with GEFS/ECMWF ensemble solutions Tue into Thu and a composite seems reasonable, but run to run continuity issues limit forecast confidence. Opted to quickly tranistion to a blend of the ensembles later Thu into next weekend amid growing forecast spread and uncertainty. ...Weather Highlights and Hazards... Numerous showers and thunderstorms continue to be in the forecast through the middle of next week from the Plains to the Upper Midwest then eastward. Multiple rounds of MCS activity are likely with both of the low pressure systems that are progged to track across the Plains. This will have the potential to produce very heavy rainfall capable of producing flash flooding, and severe weather is also likely across much of the Midwest states based on recent SPC forecasts. Additional heavy rain is also possible from the next storm system tracking eastward from the Intermountain West later in the week, although details on timing and placement continue to remain less clear at this time. There will also be a dichotomy of temperature anomalies given the amplified flow pattern in place. Temperatures are expected to be well above normal to near record warmth across much of the southeastern U.S. owing to the strength of the upper ridge, and this will also serve to keep rainfall chances minimal. Afternoon high temperatures may exceed 100 degrees for parts of Georgia and South Carolina by later in the week. The opposite will be the case across much of the western U.S. and also the northern Plains with readings on the order of 10 to 20 degrees below climatology, which will be under the influence of the upper level trough and to the north of the low tracks. Heavier late season snows are also likely for the Sierra Nevada to the northern Rockies for the middle of the week. D. Hamrick/Schichtel 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