Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Thu Apr 04 2019 Valid 12Z Sun Apr 07 2019 - 12Z Thu Apr 11 2019 ...Overview... An ongoing progression of Pacific systems into and across the Lower 48 will bring active weather to a decent percentage of the country. The southwestern U.S./southern Rockies appear to be the one area that should have fairly dry weather. A leading upper trough over the central U.S. Sun and its associated surface system will spread a broad area of precipitation across the eastern half of the country Sun-Tue with some areas of heavy rainfall possible. During that same time frame expect a strong jet aimed at the northwestern states to bring areas of enhanced precipitation to the northern half of the West Coast inland to the northern Rockies. A dynamic upper trough forecast to crest the West Coast by Tue will continue inland to push a main precipitation focus eastward to the north-central Rockies then north-central Plains/Mississippi Valley and eventually the Ohio Valley and Great Lakes. There is an increasing guidance signal that this potent trough may support strong central U.S. storm genesis Wed-Thu. This presents a risk of wrapping enhanced snows from the Rockies to the north-central Plains/Upper Midwest, albeit with marginally cold air. Over the south-central U.S., guidance may be underestimating an additional threat of strong to severe thunderstorms along a trailing cold front. Meanwhile upstream, upper level trough energy reaching the northeastern Pacific may also approach the West Coast with some unsettled weather around next Thu. ...Guidance Assessment/Preferences... The WPC medium range product suite was primarily derived from a composite blend of the 00 UTC GFS/ECMWF and GEFS/ECMWF ensemble means. These guidance options seem fairly well clustered with the forecast evolution of mid-larger scale systems. A composite blend mitigates recent issues with guidance to maintain acceptable continuity with the embedded smaller scale systems and stream interactions. ...Weather Highlights/Hazards... Strong flow aloft across the Northwest will promote areas of terrain-enhanced rain and higher elevation snow from northern California and the Pacific Northwest into northern Rockies from Sun into early next week. Current guidance suggests best potential for heaviest activity will be centered along the West Coast near the California/Oregon border and the Oregon Cascades. By Tue the upper troughing moving into the West will begin to shift the best moisture focus eastward into the Great Basin and northern-central Rockies. Continued progression of this system should spread precipitation across the north-central Plains, Mid-Upper Mississippi Valley, and eventually Ohio Valley and Great Lakes by Wed-Thu. Some activity may be heavy and areas with ongoing flooding concerns will need to monitor this system. A period of low level upslope flow may add to totals over the eastward/northward facing slopes of the Rockies. In addition stronger trends for Wed-Thu low pressure in latest guidance raise the potential for strong winds to be an issue over some areas. There is also a threat of snow in the northern periphery of the wrapback precip shield from the n-central Plains to the Upper Midwest. The eastern half of the country will see a broad area of precipitation with the system progressing eastward from the Plains Sun onward. Ample flow of moisture from the Gulf will promote areas of heavy rainfall. Best potential for highest totals will be over/near the Lower Mississippi Valley and central Gulf Coast region and southern Appalachians. Convection may be strong to severe over southern areas. Check SPC outlooks as specifics become better resolved over the coming days. Significant rainfall is also possible from the Ohio Valley into northern Mid-Atlantic/Northeast. There are still significant detail uncertainties with this system so confidence in location/magnitude of heaviest rainfall remains somewhat lower than desired. Snow should be confined mostly to northern New England Mon-Wed in this pattern as moisture advects northward into a cooled/receding surface ridge. The warm sector of the central-eastern U.S. system Sun/Mon will offer some much above normal temperatures. Morning lows will be particularly anomalous with many locations 15-25F above normal Sun into Tue and some daily record warm low values may be challenged. The main upstream system will then spread a period of anomalous warmth across the Southwest then southern Plains and South-Southeast U.S. next week. 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