Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1203 PM EDT Sun Mar 31 2019 Valid 12Z Wed Apr 03 2019 - 12Z Sun Apr 07 2019 ...Overview... Today's guidance remains fairly agreeable and consistent in showing a progression of shortwaves from the Pacific into and across portions of the Lower 48, with a corresponding series of surface systems. The northwest periphery of strong low pressure off the East Coast on Wed may have some influence on New England's coastal areas as the system tracks northeastward. Then shortwave energy over the West on Wed will make steady progress and push a wave/frontal system across the central/eastern states during the latter half of the week. The northern part of incoming Pacific energy Thu-Fri should weaken as it heads into a developing western Canada ridge but the southern part will likely continue across the southern U.S. and northern Mexico. Then a fairly strong shortwave should reach the West Coast around Sat with continued progression thereafter, perhaps followed by yet more energy brushing the Pacific Northwest late next weekend. The combination of these systems will likely bring precipitation to most of the CONUS at some point during the Wed-Sun period, with the southern third or quarter of the West the most likely area to stay dry. ...Guidance Assessment/Preferences... Model/ensemble clustering has improved dramatically for the storm off the East Coast as of early Wed with a location just southeast of the 40/70 benchmark. However note there are some smaller but locally significant differences that persist even in the short-range time frame. Otherwise guidance continues to agree fairly well with the existence of each feature in the Pacific/CONUS stream but still displays spread/uncertainty for specifics. Favored keeping a consensus approach that was obtained through a blend of the deterministic models (00Z GFS/ECMWF/Canadian and 06Z GFS/FV3-GFS) along with continuity during the period. This matched quite well with the ensemble consensus but with a bit more detail. The shortwave and associated low pressure reaching the Plains around Thu agrees fairly well in the guidance up to that time. Solutions then differ on exactly how energy will be distributed within the overall trough aloft--along with strength and track of best-defined surface low pressure. Fast moving northern tier energy may also feed into the upper trough as it reaches the eastern U.S., providing added complexity to the forecast. This type of evolution tends not to be easily resolved in the extended time frame. Middle ground solution was employed. By early Fri ensemble members are still varied north-south but have trended toward a consensus position near southern Indiana between the more southerly ECMWF ensembles and more northerly GEFS ensembles. That system should exit off the coast near the NY bight per the best multi-ensemble overlap. Farther upstream composite blend represents established consensus with little continuity change for the southern stream Pacific shortwave that eventually heads into the southern Plains, as well as for the vigorous shortwave reaching the West Coast around early Sat. Establishment of Pacific troughing south of Alaska will temper height falls a bit into the Pacific Northwest. ...Weather Highlights/Hazards... The series of systems affecting the West will bring at least two or three periods of enhanced rain and high elevation snow. Expect highest totals for the five-day period to be along favored terrain from northern California/Sierra Nevada through the Pacific Northwest. Moisture will extend through the Intermountain West and northern-central Rockies, with some significant precipitation over these areas as well but with less extreme totals relative to areas near the coast. The system emerging into the Plains on Wed and reaching the East Coast toward the end of the week will spread a broad shield of precipitation across the eastern half of the country with embedded convection. SPC has noted a 15% chance of severe thunderstorms on Wed/Thu over OK/lower MS Valley, respectively. There is still less than desired agreement on areas of heaviest rainfall but at least localized pockets of moderate to heavy rainfall may be possible over parts of the sensitive eastern Plains/Mississippi Valley region and then into the Northeast. The northern periphery of the moisture shield may contain snow with best potential from the north-central Plains into New England. Today's guidance is showing a stronger signal for heavy rainfall potential over parts of the southern Plains and possibly into the Lower Mississippi Valley from about Fri night through the weekend. This activity should be encouraged by the combination of an approaching southern stream shortwave aloft and low level Gulf inflow interacting with a front expected to stall near the Gulf Coast. During the day Wed most precipitation with the western Atlantic storm should be mostly confined to areas near the New England coast. Steady progression of systems across the Lower 48 will provide some day-to-day variability of temperatures. Within this pattern the general evolution of mean flow will likely be toward more above average heights aloft with time, corresponding to increasing coverage of above average temperatures from midweek through the weekend. The areas of clouds and precipitation accompanying each system will tend to favor greater warm extremes for morning lows with some areas of plus 10-20F anomalies. In terms of five-day averages the Interior West into the Plains should see warmest temperatures relative to climatology. Plus 10F or greater anomalies for highs are most likely over the parts of the Plains Fri-Sun. Fracasso/Rausch 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