Extended Forecast Discussion NWS Weather Prediction Center College Park MD 201 PM EST Sat Jan 21 2023 Valid 12Z Tue Jan 24 2023 - 12Z Sat Jan 28 2023 ...Heavy rain/severe weather threat for the South Tuesday to the Eastern Seaboard midweek along with a heavy snow threat overtop from the south-central Plains to the Midwest and interior Northeast lingering into Thursday... ...Synoptic Overview... The weather pattern will remain quite stormy and progressive across much of the nation going next week on the heels of a lead Monday storm system exiting the Northeast by Tuesday. The next impactful low pressure storm 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 from the West to 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... Recent guidance has improved its overall synoptic scale depiction across the continental U.S. into mid-later next week. A composite blend of GFS/ECMWF/UKMET/Canadian guidance along with WPC continuity seems to offer good predictability and a reasonable forecast basis. System organization decreases and forecast uncertainty increases into Friday and Saturday as the eastern Pacific upper ridge interacts with shortwave energy from the Gulf of Alaska. This leads to quite varied digging of energies downstream into the West and subsequently the central and eastern states. Prefer an ensemble mean solution on the more amplified side of the full envelope of guidance considering the lead-in amplitude of the eastern Pacific upper ridge that may prove slow to be dislodged. This scenario seemed best shown by ECMWF ensembles at time of product creation. Since then, the 12 UTC models have strongly trended toward digging energies more sharply down over the West Coast to the lee of set ridge. ...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 southern High Plains and extending northeast across northern Oklahoma and southern Kansas on Tuesday, and then out across the Mid-MS and Ohio Valleys/eastern Great Lakes where a swath of enhanced wrapback snows will be possible. Heavy snow is then likely across the Appalachians through interior areas of the Northeast as the secondary low develops, with heavy rain/wind up 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/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