Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Fri Feb 03 2023 Valid 12Z Mon Feb 06 2023 - 12Z Fri Feb 10 2023 ...Guidance/Predictability Assessment... Guidance solutions only seem reasonably well clustered aloft into Monday as an trough moves through the East and a stengthening trough digs into the West, with ridging in between. Differences grow quickly with the subsequent evolution of the western trough. Two general forecast scenarios seem to exist in guidance with recent GFS/Canadian runs showing run to run stream separation leading to an upper low closing off in the Southwest/northern Mexico Tuesday-Wednesday that is stronger then slower to eject downstream through the east-central U.S. next week compared to the ECMWF/UKMET. Ensemble members by and large showed similar progression trends as their parent models with the GEFS/Canadian/NAEFS ensemble means less progressive than the ECMWF ensemble mean. This remains a difficult emerging split flow forecast with low predictability, but still suspect that a solution on the less progressive side of the full envelope of guidance makes more sense given much guidance does develop a separated southern stream system of which often are on the slow side to eject. The WPC medium range product suite was accordingly derived from a composite blend of the 18 UTC GEFS mean and 12 UTC NAEFS/ECMWF ensemble means, given uncertainty of model details, to accomodate this along with WPC continuity and the 01 UTC National Blend of Models. The latest 00 UTC model runs do now show a significant slowing trend from the ECMWF/UKMET, bolstering forecast confidence to a degree. ...Weather/Hazard Highlights... A couple of rounds of light precipitation are expected to pass over the Midwest/Great Lakes into the Northeast early next week with northern stream dominated shortwave passages and approaching modest/lead frontal low/system. Areas downwind of the Lakes may have higher amounts than surrounding locations due to lake enhancement. Showers are possible along the Eastern Seaboard with some moisture return by Sunday from Florida into the eastern Carolinas and eastern parts of New England, but any heavier amounts look to remain offshore. For the western states, moderate precipitation is expected to overspread the West Coast to portions of the Intermountain West/Rockies by early next week. In general lower elevations coastal areas will have rain while areas farther inland/higher elevation will receive snow; with typical terrain enhancement across the coastal ranges and the Sierra Nevada. Then precipitation could overspread the central U.S. by Monday-Tuesday along and ahead of a low pressure/frontal system. The details of this precipitation including placement and precipitation type remain uncertain given the model differences. The current forecast shows enhanced rainfall amounts centered across the Southern Plains and Lower Mississippi Valley and surrounding areas by Tuesday-Wednesday with enhanced low/frontal system induced return Gulf of Mexico moisture inflow. The WPC experimental excessive rainfall outlook (ERO) will be highlighted by an emerging "marginal" risk area Tuesday into Wednesday. There is also some potential for snow/ice again on the northern periphery of the expanding precipitation shield across portions of the southern Plains to Midwest and interior Northeast next week, but this is subject to change with future forecasts. Subsequent eastern Pacific system approach Tuesday/Wednesday should offer modest system amplitude and associated moisture/rainfall potential across the Pacific Northwest along with terrain/mountain snows inland from the Northwest through the northern Great Basin/Rockies. Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml