Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Sat Jan 21 2023 Valid 12Z Tue Jan 24 2023 - 12Z Sat Jan 28 2023 ...Midweek storm to spread a heavy rain/severe weather threat to the South early next week, working up the Eastern Seaboard midweek along with a heavy snow threat from the central Rockies/Plains through the interior Northeast... ...Synoptic Overview... The weather pattern is expected to be active but progressive across much of the nation going into next week with the Monday storm system over the Northeast exiting the region by early Tuesday. The next and potentially more impactful low pressure system will be gathering strength across the Gulf Coast early in the week and then track in a general northeasterly direction across the Ohio Valley and then the Northeast U.S. by Thursday. A building West Coast/western Canada upper ridge as a +PNA pattern tries to develop will herald a return to colder conditions across much of the central and eastern U.S. as a broad upper trough develops downstream of this ridge through the end of the week. ...Guidance/Predictability Assessment... The 00Z guidance has improved its overall synoptic scale depiction across the continental U.S. through the middle of the week, although the 00Z CMC was not available at the time of this writing. The UKMET/GFS/ECMWF are in relatively close agreement with the low track through Thursday, and the 12Z CMC is generally northwest of the 00Z model consensus. Forecast uncertainty increases going into Friday and Saturday as the upper ridge eventually breaks down by shortwave energy from the Gulf of Alaska impinging upon it. At the time of the fronts/pressures creation, the 18Z GFS differed considerably from the model consensus for days 6 and 7, so it was not used beyond Thursday. A general deterministic model blend sufficed as a starting point through Wednesday, and an increase of the ensemble means up to about 60% by Saturday was incorporated to account for increasing mesoscale uncertainties. ...Weather/Hazard Highlights... After the departure of the East Coast storm system Monday, attention turns to the next major storm system that is forecast to develop over Texas on Tuesday and then track northeast across the Ohio Valley and then the Great Lakes through Wednesday night, and then reaching the Northeast U.S. by Thursday as a new surface low likely develops near the coast. The best heavy rainfall potential exists across eastern Texas, Louisiana, and into Mississippi on Tuesday, where a Slight Risk of excessive rainfall is now in effect for the Day 4 period with the potential for some 2 inch rainfall totals, some of which may fall within a relatively short period of time. Areas from southern Louisiana to the Florida Panhandle will also be in a favorable kinematic and thermodynamic environment for potential severe weather per recent SPC outlooks. There will likely be a noteworthy swath of wintry weather from the Texas Panhandle and extending northeast across northern Oklahoma and southern Kansas on Tuesday, and then across the Ozarks and portions of the Ohio Valley where several inches of snow accumulation will be possible. Heavy snow is looking more likely across interior portions of the Northeast U.S. as the secondary low develops, and heavy rain and wind near the coast as the low continues to intensify. Temperatures are expected to generally be on the order of 10 to 20 degrees below average from the Intermountain West to the Central Plains for early in the week, and slightly above average across most of the eastern U.S. By the end of the week, most areas across the nation should be near average to 10 degrees below average as broad upper trough and cyclonic flow aloft keep any anomalous warmth at bay. Although a colder pattern is coming, there is no imminent sign of any major arctic airmasses surging south from Canada. Hamrick 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