Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Fri Mar 06 2020 Valid 12Z Mon Mar 09 2020 - 12Z Fri Mar 13 2020 ...Heavy Precipitation threat early-mid next week for Southern California/Southwest... ...Guidance/Predictability Assessment... A relatively progressive northern stream and somewhat less progressive southern stream are forecast across the CONUS during the medium range. At least through the first half of next week, models/ensembles showed relatively good consensus, but that degrades a bit toward the end of the forecast period. A couple northern stream shortwaves will accompany a front/low pressure system from the Mississippi Valley to the Great Lakes and Northeast Mon-Wed. The ECMWF/GFS showed decent consensus on this system. Farther west, across the east Pacific, a deep cutoff upper-level low is forecast by all guidance to approach Southern California by Tue-Wed, eventually starting to elongate and open up by Thu as it crosses the Four Corners region and interacts with additional shortwave energy farther north. Over the past several runs, models have shown a fairly large spread with respect to the timing/eastward motion of this feature, but that spread has started to reduce, with a convergence toward the center of the spread evident among ensemble members over the past couple runs. This strongly favors going toward the middle of the spread, which is represented by the ECMWF/GFS at least into early Thu (day 6). After that time, as the feature opens up and approaches the central U.S., timing differences among the guidance continue to be quite large. Both the ECMWF and the GFS solutions are a good bit faster than their respective ensemble means with the eventual central U.S. low pressure system by that time, so a rapid trend toward the ECENS/GEFS ensemble means was preferred during the day 6-7 time frame. ...Weather/Hazard Highlights... Showers and a few thunderstorms could produce locally heavy rain across portions of the Mississippi and Ohio Valleys ahead of the cold front on Mon. The system is also expected to produce a round of snowfall across portions of northern New England, especially Maine, Tue/Tue night as a surface low crosses the region. Portions of southern California and the Southwest will see a period of heavy precipitation potential Mon-Wed as the upper-level low moves across the region. Rain is likely for most areas, but snows are possible at the highest elevations of Southern California, and more likely farther north across portions of the Sierra. The heaviest rains are forecast across the Transverse and Peninsular Ranges in Southern California, where 1-3 inches of rain are possible (with locally higher amounts). Farther east, heavy rains are also forecast cross the Mogollon Rim. Farther east, moist southerly flow should focus showers and thunderstorms along stationary front from the Mid-Mississippi Valley to the central Appalachians Wed/Wed night. As the Pacific shortwave energy (former upper low) reaches the central U.S. by next Fri, showers and thunderstorms are expected to become more widespread from the Southern Plains to the Ohio Valley ahead of a cold front. Temperatures during the medium range are forecast to be near to above average across most of the CONUS, as the progressive northern stream keeps any cold air bottled up at the higher latitudes. High temperatures are forecast to be 5 to 15 deg F above average across most of the central/eastern U.S. through most of next week. Slightly below average high temperatures are forecast across portions of the Southwest as the upper low moves inland. Ryan 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