Extended Forecast Discussion NWS Weather Prediction Center College Park MD 141 PM EST Mon Feb 12 2024 Valid 12Z Thu Feb 15 2024 - 12Z Mon Feb 19 2024 ...Increasingly wet pattern across California this weekend into early next week... ...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... Models continue to show good agreement through most of the period across the U.S. on the large scale, with some lingering uncertainties in the details of individual systems. Models have trended stronger off the Pacific Northwest coast on Thursday with a compact upper low which should weaken and lift northward by Friday as the next trough moves towards the region. Also some timing differences with shortwaves through the Great Lakes/Northeast but minor and could be handled with a general model blend. The CMC is noticeably slower with troughing across the Gulf Sunday-Monday. There are also uncertainties with the next trough/upper low into the West Coast, with the CMC weaker with the overall trough vs the GFS and ECMWF (with support from the ensemble means) show a closed low breaking off from the larger scale flow and moving in towards Southern California. The WPC blend for today was based on a general model compromise through day 5, replacing the CMC and UKMET with the ensemble means days 6-7 to help smooth out the later period differences. Overall, this maintains good continutiy with the previous WPC forecast as well. ...Weather/Hazards Highlights... Looking ahead to Thursday and Friday, a weak low pressure system is expected to develop over the western Gulf in advance of an approaching southern stream upper trough energy and advect increasing moisture northward and over a developing warm front. 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, but given an overall decreasing trend in amounts and high flash flood guidance across that region, did go ahead and remove the Marginal Risk on the Day 4/Thursday ERO. The heavy rainfall signature quickly increases across parts of 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. For Friday, did maintain the Marginal Risk area along the Texas Gulf Coast region on the Day 5 ERO 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 some moisture also extending 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. Santorelli/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