Extended Forecast Discussion NWS Weather Prediction Center College Park MD 339 PM EDT Mon Apr 29 2019 Valid 12Z Thu May 02 2019 - 12Z Mon May 06 2019 ...Flooding/Flash Flooding Threat in the Short Range Continues into Thursday for the Southern Plains/Lower Mississippi Valley... ...16Z Update... The overnight model guidance maintained a similar pattern as described previously with the closed upper low in Canada and troughing across the central U.S. Regarding the southern stream upper low tracking through the eastern Pacific and into California by early next week...the EC runs have been consistently slower than the GFS runs for at least a couple of days. However, the last couple of EC runs have been trending just a bit faster, and the 00Z GFS and mean trended slower, which made for much better model agreement. Thus, was able to incorporate the 00Z GFS suite in this forecast, along with the 00Z EC/EC mean, and the 00Z UKMET (through day 5) and 00Z CMC, which all lined up well. The 06Z GFS went against the trend, however, moving the low farther eastward and beginning to phase it with the northern stream trough in the West by day 7/Mon, so excluded that run from the forecast. For additional information on sensible weather, please see the previous discussion. Tate ...Previous Discussion... ...Overview and Assessment of Model/Ensemble Guidance and Predictability... It remains the case that a large closed upper circulation settles over western Canada this week as a series of northern stream troughs with height falls and swaths of precipitation dig into the Northwest and eastward over the wintry Rockies then U.S. northern tier. There remains potential for some degree of phasing with a southern stream flow of impulses/height falls working underneath during this period from the Pacific inland over the U.S. southern tier. The GFS/GEFS/FV3 have tended to be on the progressive side of the full envelope of solutions while recent ECMWF runs and to a lesser extent ECMWF ensembles and UKMET have been on the slower side of the forecast envelope. The WPC medium range product suite was mainly derived from a composite of the ECMWF/ECMWF ensemble mean. This considers blocky upstream flow and inherent slow nature of initially closed lows. ...Weather Highlights/Threats... Dynamic troughing crossing the n-central U.S. and cooled temperatures favors some early May Upper Midwest/Great Lakes snows. A lead and wavy frontal system will progress late week across the central then eastern U.S. Deepening inflow/moisture from the Gulf of Mexico will feed into convectively active warm sector meso-boundaries as well as a stark baroclinic zone overtop. Strong to severe thunderstorms with some heavy rain and flash flooding/flooding potential will threaten the Southern Plains and Lower Mississippi/Ohio Valleys Thursday. Flooding remains possible as particularly the Mississippi Valley has had flooding concerns for weeks, and with the convective nature of the precipitation flash flooding is possible as well. Less defined activity presses over the East and South into Friday/Saturday. The front shifts and stalls mainly offshore from the weekend into early next week in a drier post-frontal pattern as new upstream trough energies with more limited precipitation work back into the West in a continued split flow regime. 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 Hazards: - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Thu-Sat, May 2-May 4. - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Mon, May 6. - Flooding possible across portions of the Plains, the Mississippi Valley,and the Great Lakes. - Flooding occurring or imminent across portions of the Mississippi Valley, the Northern Plains, the Great Lakes, the Northern Great Basin, the Southern Plains, and the Ohio Valley. 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