Extended Forecast Discussion NWS Weather Prediction Center College Park MD 157 AM EST Mon Feb 12 2024 Valid 12Z Thu Feb 15 2024 - 12Z Mon Feb 19 2024 ...General Overview... An overall progressive and quasi-zonal upper level flow pattern can be expected across the continental U.S. for the end of the week, and a low pressure system is forecast to track from the Great Lakes to the Northeast U.S. Coast by Friday along with a modified arctic airmass settling south across the Dakotas and Montana. A northern stream trough originating from central Canada is forecast to drop southward across the Upper Midwest and Great Lakes region by Saturday, and this will reinforce the cold weather pattern across much of the central and northern Plains for the weekend with a strong surface high settling southward from Canada. For the Gulf Coast region, a southern stream trough will induce surface cyclogenesis over the western Gulf and result in increasing showers and thunderstorms from Texas to the Central Gulf Coast. Unsettled conditions are also expected to make a return to portions of the West Coast region with multiple rounds of precipitation likely over the upcoming week. ...Guidance/Predictability Assessment... Most of the continental U.S. has average model agreement going into Thursday, but the main exception to this is across the West Coast region where models have recently struggled with timing and location of lead Pacific shortwave energy reaching the coast. The 00Z CMC is at odds with the model consensus across the northeast Pacific on Thursday, portraying a much stronger upper low, whereas the other guidance supports the idea of an elongated trough over British Columbia and a ridge axis just off the coast, so a non-CMC model blend works best for the West Coast early in the forecast period. Interestingly, this difference becomes much less noticeable going into Friday and the weekend across the same region as the feature on Thursday lifts north away from the region, and fits the consensus better. Going into the weekend elsewhere across the nation, the GFS is stronger with the trough dropping south from central Canada and has a greater surface high over the central/northern Plains region. By next Monday, the CMC is considerably slower with the Gulf trough and less amplified with the next Pacific storm system approaching California. Taking these factors into account, the WPC fronts/pressures forecast was primarily based on a GFS/ECMWF/UKMET blend with some previous continuity early on, and then gradually increasing contributions from the ensemble means heading into Sunday and Monday. Temperatures were also reduced a few degrees from the NBM across the north-central U.S. given the strength of the Canadian surface high behind the cold front, and this has been the trend over the past few days. ...Weather/Hazards Highlights... Looking ahead to Thursday and Friday, a low pressure system is expected to develop over the western Gulf in advance of approaching southern stream upper trough energy and advect increasing moisture northward and over a developing warm front, and this will likely result in widespread showers and thunderstorms across southern Texas and into the central Gulf Coast region. The guidance favors South Texas for some local downpours starting overnight Thursday, and a Marginal Risk is shown for the Day 4 ERO given initial growing ensemble probabilities. The heavy rainfall signature quickly increases across the South/Southeast Friday and next weekend as a main frontal low tracks eastward across the northern Gulf of Mexico and Florida underneath a northern stream arctic front digging down through the central then eastern states. Therefore, a Marginal Risk area is planned for much of the Texas Gulf Coast region on Day 5 (Friday) where the model signal is strongest for heaviest QPF. Guidance has slowly converged on a more similar solution for the focus and onset of organized precipitation development across the West Coast in an emerging and increasing wet pattern later this week and likely extending into the beginning of next week. Multiple Pacific systems will initially struggle to work eastward given the upper ridge axis in place over the Intermountain West, but there should be enough moisture advection to fuel a moderate rain event into the Pacific Northwest/Northern California to close out the week. There will likely be additional rounds of precipitation across this region going into the weekend and beyond based on latest model guidance. A Marginal Risk of excessive rainfall is planned for portions of the Washington/Oregon coastal ranges and the west facing slopes of the Cascades on Thursday, and for coastal areas of northern California on Friday. Expect snow for the higher terrain, especially for the Sierra, with diminishing support farther inland across the Intermountain West and Rockies. Temperatures are expected to be generally 5 to 15 degrees above mid-February averages across much of the east-central U.S. on Thursday. Meanwhile, a strong cold front dropping south from western Canada is expected to herald the arrival of an arctic airmass across the Northern Plains and bring a return to below average temperatures from Montana to the Dakotas and Nebraska through the end of the week, perhaps up to 20 degrees below average across portions of Montana, but not as cold as the previous Arctic blast back in mid-January. Cold temperatures with this front will gradually modify across the central to eastern U.S. going into next weekend. There will likely be some lake effect snow to close out the work week into next weekend with the much colder airmass crossing the Great Lakes. The prospect of northern stream flow amplification next weekend and frontal wave development offers at least modest snow potential from the Ohio Valley through the Northeast. 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 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