Extended Forecast Discussion NWS Weather Prediction Center College Park MD 338 PM EDT Tue Apr 02 2019 Valid 12Z Fri Apr 05 2019 - 12Z Tue Apr 09 2019 ...Overview... Noticeable model differences emerge quite early in the medium-range period. These differences continue to bring more uncertainties further into the forecast period. Despite these differences, a general eastward progression of a negatively-tilted mid to upper-level trough can be expected across the western U.S. through the weekend. The trough should move into the Plains on Monday as a low pressure center develops and then tracks toward the Ohio Valley and the lower Great Lakes by next Tuesday. Best chance of heavy precipitation will span multiple days across areas closer to the Pacific Northwest coast, while southeastern Texas should see the best chance of heavy rain on Saturday. The rain should continue to spread east and northeast and then move into the East Coast Monday and Tuesday. ...Guidance Assessment/Preferences... Model guidance this morning continues to show noticeable differences starting this Friday over the mid-section of the country as well as just off the East Coast. These differences prove to have significant impacts on the model solutions across the U.S. further into the medium-range period. The first difference is regarding the placement of a frontal wave in the vicinity of the Ohio Valley on Friday, where the GFS continues to indicate that the wave will develop much farther north toward the Great Lakes whereas the ECMWF maintains that it will develop over Tennessee. The ECMWF also maintains a secondary low development off the Carolina coast on Saturday, an idea that the Canadian model agrees but the GFS continues to reject. Uncertainties continue to grow as we head into early next week as models have not yet resolved into a stable solution for much of the eastern two-thirds of the country. This was indicated by a large difference between their ensemble means and their deterministic solutions. Nevertheless, the ensemble means from the ECMWF, GFS, and Canadian models show quite good agreement for a low pressure center to track from the central Plains toward the lower Great Lakes from Monday into Tuesday. A blend of these ensemble means yielded good continuity from the previous WPC medium-range package also. Therefore, the WPC morning medium-range grids were derived from a consensus of the 00Z ECMWF/00Z EC mean and the 06Z GFS/06Z GEFS with more emphasis toward the ECMWF solutions for days 6 and 7. Please refer to the previous discussions for further details on model preferences. ...Weather Highlights/Hazards... Continue to expect periods of enhanced rainfall/higher elevation snow from the central/northern West Coast into the northern Rockies. Some locations along the most favored terrain from northern California/Sierra Nevada into western Washington/Oregon may see at least several inches liquid over the Fri-Tue period. The northern Rockies should see lesser but still significant totals. Individual systems affecting the Pacific Northwest coast may also be accompanied by periods of strong winds. Confidence in precipitation coverage and intensity decreases during the first half of next week as guidance diverges for amplitude/timing of significant features. Leading area of precipitation over the East, possibly including some snow over New England, should depart after Fri night. Some pockets of locally heavier precipitation are possible but there is not a clear signal for where such activity may occur. From Fri night onward the shortwave aloft approaching/reaching the southern Plains along with strengthening flow of Gulf moisture interacting with a stalled front will likely lead to a heavy rainfall threat over the southern Plains/Lower Mississippi Valley and possibly extending to the east/northeast. Low pressure tracking northeastward from the southern Plains should eventually help to spread moisture over much of the eastern half of the country. Depending on how this system evolves there may be some bands of significant rainfall in middle/northern latitudes between the Plains and East Coast. Plains/Mississippi Valley areas sensitive to additional rainfall should monitor forecasts for this system. The overall pattern should favor modestly below normal highs over the West Coast states into the northern Rockies but with a warming trend over southern areas. Lows should be above normal through the period (some plus 10-15F anomalies). Most areas east of the Rockies should see above to much above normal temperatures, though with a cooling trend behind the front reaching the eastern states late in the period. Morning lows may be 15-25F above normal over parts of the northern Plains and Midwest around Sun-Mon with some daily record warm low values possible. Kong/Rausch Hazards: - Heavy precipitation across portions of California, the Central Great Basin, the Pacific Northwest, and the Northern Great Basin, Fri-Sun, Apr 5-Apr 7. - Heavy rain across portions of California and the Pacific Northwest, Fri-Sat, Apr 5-Apr 6. - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Sat, Apr 6. - Heavy rain across portions of the Southeast, the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Sun, Apr 7. - Heavy rain across portions of the Southeast, the Mid-Atlantic, and the Southern Appalachians, Mon-Tue, Apr 8-Apr 9. - Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Sat-Sun, Apr 6-Apr 7. - Heavy snow across portions of the Northeast, Fri-Sat, Apr 5-Apr 6. - Flooding possible across portions of the Northern Plains. - Flooding occurring or imminent across portions of the Central Plains, the Lower Mississippi Valley, the Northern Plains, the Tennessee Valley, the Middle Mississippi Valley, the Upper Mississippi Valley, the Great Lakes, and the Ohio Valley. - Flooding likely across portions of the Upper Mississippi Valley and the Northern Plains. - High significant wave heights for coastal portions of California and the Pacific Northwest, Sat-Sun, Apr 6-Apr 7. 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