Extended Forecast Discussion NWS Weather Prediction Center College Park MD 417 PM EDT Wed Jun 05 2019 Valid 12Z Sat Jun 08 2019 - 12Z Wed Jun 12 2019 ...Excessive Rain and Flash Flood/Flooding Threat to slowly spread across the Gulf coast and Southeast into the southern Appalachians and southern mid Atlantic this weekend into early next week... ...Guidance Evaluation and Preferences... The Days 3-7 500 mb heights and adjusted sea level pressures/fronts were derived from a blend of the 06z GFS/00z ECMWF/00z Canadian models this weekend, transitioning to a blend of the 06z GEFS/ and 00z ECMWF ensemble means next week amid growing forecast spread. ...Mid-South/Southeast/Appalachians... The system producing heavy rain over coastal Texas this morning is forecast to move east slowly across the lower MS Valley and southeast, eventually reaching the east coast early next week. The models/ensembles have shifted south this morning with the mid level circulation/sfc reflection 100-150 nm days 4-6. High moisture values persist with the 06z GEFS Mean indicating 2.25 inches of precipitable water forecast along the Gulf Coast from MS/Al/FL panhandle. The combination of convergence along the low and trailing front along with high moisture leads to a prolonged threat of heavy rain and flash flooding/flooding along the Gulf coast from southeast LA to the FL panhandle/northwest FL, and inland into the southern Appalachians and possibly the Piedmont of the Carolinas. WPC medium range QPF advertises 3-6" areal average amounts, with locally higher amounts possible in areas of cell training/back building/cell mergers near the Gulf coast and also favored upslope portions of southern Appalachians. ...Northern Rockies east across the northern Plains/upper Ms Valley/Great Lakes/Northeast... A significant/anomalous cooling upper troughing in northern stream flow starts in the northern Plains Sat and moves east into the upper MS Valley/upper Lakes Sunday and then northeast Monday 10 Jun to Tuesday 11 Jun. The ensemble mean guidance has overall recently converged on a more clustered forecast, with differences in the 06z GFS and 00z ECMWF lowering confidence in their respective forecast. The 00z ECMWF was an outlier in intensifying the closed low crossing Maine early next week, in contrast with the open wave shown in the ECMWF ensemble members. Likewise, in the trailing trough over the northern Plains early next week, the 06z GFS developed its own stronger closed low 700-500 mb. Given better continuity and agreement with the 00-06z GEFS and 00z ECMWF ensemble means, the means were preferred Mon 10 Jun to Tue 11 Jun. The result of the upper trough was includes weekend snows for northern Rockies higher elevations, and a period of rain and showers spreading eastward along/ahead of the main upper trough/surface frontal system. As the system approaches the east coast early next week, it may entrain deeper moisture from the southeast, so significant rain totals are possible for the mid Atlantic to New England. Petersen 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/Middle Mississippi Valley, the Tennessee Valley, the Ohio Valley, the Southeast, the Southern/Central Appalachians, the Mid-Atlantic, the Great Lakes, and the Northeast, Sat-Wed, Jun 8-Jun 12. - Flooding possible across portions of the Central/Southern Plains, the Middle/Lower Mississippi Valley, the Great Lakes, and the Ohio Valley. - Flooding occurring or imminent across portions of the Plains, the Mississippi Valley, the Great Lakes, the Ohio Valley, and the Northern Great Basin. - Flooding likely across portions of the Central Plains and the Middle Mississippi Valley. - Excessive heat across portions of the Southern Plains, Sat-Sun, Jun 8-Jun 9. - Much above normal temperatures across portions of California, the Pacific Northwest, the Central/Northern Great Basin, and the Northern Rockies, Mon-Wed, Jun 10-Jun 12. - Much below normal temperatures across portions of the Central/Northern Great Basin, the Central/Northern Rockies, and the Central/Northern Plains, Sat, Jun 8. 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