Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Sat Feb 04 2023 Valid 12Z Tue Feb 07 2023 - 12Z Sat Feb 11 2023 ...Guidance/Predictability Assessment... Model guidance this morning continues to exhibit higher-than-normal uncertainty from midweek next week onward across the eastern two-thirds of the country. The first system of concern will be on the timing and amplitude of a shortwave/upper low that is forecast to eject out from the Southwest into the central U.S. The subsequent evolution of this system over the eastern U.S./East Coast later next week will be further complicated by a simultaneous flow amplification across the U.S. with a potentially much amplified ridge over the western U.S. while a large closed low could develop near/off the West Coast. In addition, a shortwave rapidly entering the Pacific Northwest by around Wednesday would further complicate the pattern evolution in the eastern U.S. late next week as the wave could positively reinforce a surge of polar air down the Plains during the latter part of next week. The WPC medium range product suite through medium range time scales was primarily derived from a composite blend of 40% from the 06Z GEFS/00Z+06Z GFS, 40% from to 00Z ECMWF/EC mean, and 20% from the 00Z CMC and CMC mean. ...Weather/Hazard Highlights... Early next week rounds of light precipitation will pass over portions of the Great Lakes and the Northeast region with shortwave passages and the approach of a lead low/frontal system. There may be lake enhancement of the snowfall for the favored areas downwind of the Great Lakes which could result in higher amounts than surrounding locations. Moderate precipitation is expected to overspread the West Coast and inland to the Intermountain West and Rockies region early next week. For most of lower coastal areas the precipitation will likely fall as rain and then transition to snow for the mid-base to highest elevations; with typical terrain enhancement across the coastal ranges and the Sierra Nevada. As the low pressure system advances eastward the precipitation ahead of it could overspread the central U.S. 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 from northeastern Texas through the Ozarks from late Tuesday into Wednesday, where a slight risk of excessive rainfall has been introduced over the region given the best low-level moisture convergence and favorable right entrance region upper jet dynamics. This was surrounded by a marginal risk area extending from the eastern two-thirds of Texas late Tuesday to the mid-Mississippi Valley on Wednesday and into early Thursday. The northern edge of the precipitation shield set to spread/shear across the East later next week also maintains the potential for a swath of snow/ice across portions of the cooled Southern Plains to Midwest and interior Northeast. Upstream 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. There is though an aforementioned and growing guidance signal that this leads to the amplification of the overall flow significantly into later next week across the nation and adjoining oceans, but with limited precipitation re-emergence later next week to monitor. Kong/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