Extended Forecast Discussion NWS Weather Prediction Center College Park MD 157 AM EST Sun Feb 26 2023 Valid 12Z Wed Mar 1 2023 - 12Z Sun Mar 5 2023 ...A series of active storms for the West through the period and emerging late week storm development across the southern then eastern states with heavy rain and thunderstorms... ...Synoptic Overview... The month of March is expected to begin like a lion across much of the south-central U.S. as a potent southern stream disturbance generates a well defined surface low over the Southern Plains on Thursday, and then is forecast to track across the Mid-South and then exit the East Coast Friday night. A weaker lead disturbance is expected across the Northeast U.S. prior to this event on Thursday. Surface high pressure then builds across the Eastern U.S. in time for the weekend. Meanwhile, the West Coast region remains active with another low pressure system dropping south from the Gulf of Alaska by Saturday, and surface cyclogenesis is once again possible over the western High Plains going into next Sunday. ...Guidance/Predictability Assessment... The model guidance has improved since this time yesterday in regards to the expected timing and evolution of the low pressure system across the southern U.S. for the second half of the work week. The 00Z ECMWF and GFS are now similar in timing with the shortwave passage, and the CMC/UKMET are slightly slower going into Friday. The GFS is still on the stronger side and a little farther north with the low track compared to the model consensus, but not to the same degree as yesterday. So the trend overall has been for a stronger system. For the next major trough building in across the West Coast region next weekend, the CMC/GFS/ECMWF agree well for a day 7 forecast, although the CMC is a little stronger and more offshore with the surface low. The WPC fronts/pressures were primarily based on a multi-deterministic model blend through Thursday, and then increasing the use of the ensemble means to about 50% by the weekend. ...Weather/Hazard Highlights... The Western U.S. will continue to remain unsettled going into the middle of next week as the trough rebuilds, with heavy snow likely for the northern Arizona mountains, while snowfall intensity begins to wane across the Sierra as the surface low tracks inland. High winds are also a good possibility Thursday north of the evolving frontal boundary over the Central Plains where a strong surface high will be building in from the north. Meanwhile, heavy rain and thunderstorms are likely to develop across portions of the Mid-South and southern Appalachians late Wednesday into Thursday, and there is a Marginal Risk area for Day 4 in the excessive rainfall outlook for portions of that area. Additional rainfall is becoming more likely going into the end of the week, and some of this may be heavy at times across the southeastern U.S., mainly from northern Mississippi to North Carolina where the best forcing for ascent is likely to reside. The potential exists for a couple inches of rainfall going into Friday, and a new Marginal Risk area for excessive rainfall is now warranted for the Day 5 period to account for this, with a possible Slight Risk area needing to eventually be added once models come into better agreement. In terms of temperatures, much of the central/eastern U.S. should have readings of 10-20F above normal through Thursday, and potentially up to 25 degrees above normal on Wednesday across the Ohio Valley. Readings should return to with 5 degrees of climatological averages by next weekend for most areas east of the Rocky Mountains. The West will see a persistent cool pattern through the entire week with the Intermountain West and Rocky Mountains most consistently having highs on the order of 10-20F below normal, but nothing all that extreme in terms of arctic blasts is currently expected, with the exception of some 10s for highs across North Dakota and Minnesota Wednesday and Thursday. 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