Extended Forecast Discussion NWS Weather Prediction Center College Park MD 132 PM EST Mon Feb 19 2024 Valid 12Z Thu Feb 22 2024 - 12Z Mon Feb 26 2024 ...Overview... An upper level trough/deep cyclone establishes itself briefly across southeast Canada/the Northeast Saturday morning, cooling the region off temporarily, before zonal flow in the northern stream scoots it out to sea. A phased trough moves into the West by next Monday, bringing more precipitation to the region. ...Guidance/Predictability Assessment... The guidance shows rather good agreement until late in the period, when the 00z ECMWF outpaces the remainder of the guidance suite. The pressures, winds, 500 hPa heights, and QPF were based on a blend of the 06z GFS, 00z ECMWF, 00z UKMET, and 00z Canadian. Ensemble means were used for most fields late in the period. The remainder of the grids were primarily based on the 13z NBM, which were then modified to fit the forecast QPF, PoP-wise. ...Weather/Hazards Highlights... Precipitation should increase in coverage and intensity (to some degree) over portions of the Ohio Valley Thursday within a moisture plume in a warm air advection regime. Rainfall amounts of an inch or two are likely in the Ohio Valley, with locally higher amounts. Some competing factors are in place regarding whether this rainfall will lead to a flash flooding threat. Some instability combined with good dynamical support (left exit region of the jet) may lead to high rainfall rates (in this case, 0.5-1" in an hour). Deep west-southwesterly flow could allow for some cell training, but at the moment, MU CAPE appears to max out in the 250 J/kg range. Flash flood guidance is fairly low in and near the eastern KY and WV coal fields, as you'd expect. The excessive rainfall outlook shrank the area of the Marginal Risk across the Ohio Valley to Central Appalachians, conforming to the area of lowest flash flood guidance. The precipitation should reach the East Thursday-Friday with snow possible in parts of the Northeast. Northern New England has a relatively higher probability of seeing notable snow along with the potential for a period of brisk winds. There is still uncertainty with the snow amounts and placement. Behind this system, parts of the Great Lakes may see mostly light snow from a combination of lake effect and lake enhanced activity caused by nearby fronts. The West will see a break from precipitation around Thursday-Friday with a bout of ridging aloft. An eastern Pacific upper low and its surface reflection will meander and gradually drift closer to the West Coast, spreading precipitation chances to California by late Friday-Saturday. By Sunday model guidance is more agreeable that precipitation should spread into the Pacific Northwest and California with some moisture spreading farther inland into the Intermountain West. Areas from the Plains/Midwest eastward will see above normal temperatures Thursday with the exception of a cooler Florida Peninsula. Temperatures look to moderate closer to average in the East late week after a cold frontal passage or two, likely reaching below average for highs in the Northeast Saturday. Meanwhile renewed upper ridging in the west-central U.S. will promote temperatures warming even further by the weekend into early next week for much of the Plains and Mississippi Valley. Temperatures 15-30F above normal for late February will be common in the Great Plains as forecast highs get into the 80s for much of Texas early next week with 60s making in roads into the Dakotas. Meanwhile the western U.S. should be near to slightly above normal. Roth 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 forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw