Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Wed Mar 22 2023 Valid 12Z Sat Mar 25 2023 - 12Z Wed Mar 29 2023 ...Overview and Guidance/Predictability Assessment... A wonky upper-level pattern, featuring a series of shortwaves across the northern tier states this weekend will evolve into a much more zonal flow by early next week. A deep upper low is forecast to arrive over the West Coast early next week and slowly make its way inland through mid-week. As far as guidance is concerned, a general model blend consisting of the 00z EC/CMC/UKMET and 06z GFS were used almost exclusively through day 4, when the 06z GEFS was introduced to help mitigate uncertainties around the complicated northern tier pattern. The 00z UKMET was dropped by day 5 because it tries to overamplify an upper ridge over the Great Basin and an upper low downstream over the Midwest. The 00z ECE is introduced on day 6 when the ensemble means make up a majority of the blend. This is continued through day 7, with the inclusion of the 00z CMCE, since they resolve the western trough reasonably well compared to the deterministic guidance. the most notable uncertainty during the medium range resides in the early part. ...Weather/Hazards Highlights... The system tracking northeast from the Ohio Valley/Great Lakes on Saturday will bring rain and snow to the Great Lakes and Northeast with some light to locally moderate rain farther south along the trailing cold front. The best potential for meaningful snow will be from the central-upper Great Lakes through interior and northern portions of New England, with a developing triple point low off the New England coast by Sunday helping to keep cold air in place. This system's trailing front should lift back north across the Gulf Coast as a warm front Sunday into Monday, providing a focus for potentially heavy rainfall. Therefore the day 5 (12Z Sunday-12Z Monday) Excessive Rainfall Outlook introduces a Marginal Risk area over portions of the South. Current guidance signals suggest that an embedded Slight Risk area may be warranted at some point once a better defined axis for highest rainfall totals becomes evident. Elsewhere, a weak shearing system may produce some precipitation across the central Plains and vicinity during the weekend and a wave crossing the East early next week should spread some rain (perhaps some snow north) across the region. The shortwave energy and possible upper low moving through the West during the weekend will support periods of rain and mountain snow from the northern/central West Coast into the Rockies. Most amounts should be in the light to moderate range. Then the upper trough with embedded low forecast to amplify just off the West Coast should start to increase precipitation totals across northern/central California based on the most likely trough/low position. Model spread and variability is still enough to temper confidence in specifics though. Expect much of the West and portions of the northern Plains to see well below normal temperatures during the period. In general, the coldest readings should be from Saturday into Monday with the Great Basin, central Rockies, and eventually far northern Plains possibly seeing highs at least 20-25F below normal. Some of the cold air may spill into the central Plains on Sunday-Monday. Some locations may approach or set daily records for cold highs during the weekend. Temperatures over the Northwest should be less extreme but still be mostly below normal. Meanwhile from Saturday into early Tuesday the East will tend to see near to above normal temperatures and some variability with system progression. Warmest readings versus normal will tend to be over the Southeast, with some record warm lows possible if the early morning temperatures hold for the calendar day. After a system passes through around Tuesday, the East may begin to see some moderately below normal readings while winds could strengthen over the Northeast by Wednesday. Kebede/Rausch 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