Extended Forecast Discussion NWS Weather Prediction Center College Park MD 207 PM EST Sun Feb 11 2024 Valid 12Z Wed Feb 14 2024 - 12Z Sun Feb 18 2024 ...Overview... Expect three main weather stories will develop over the coming week. These will include increasingly wet patterns for both the South and the West Coast along with the ushering of an Arctic airmass down through the central to east-central states. ...Guidance/Predictability Assessment... The WPC medium range product suite was primarily derived from a broad composite blend of generally compatible GFS/ECMWF/UKMET/Canadian model and GEFS/ECMWF ensemble mean guidance along with the 01 UTC National Blend of Models (NBM) and WPC continuity. In terms of the 01 UTC NBM, temperatures were again reduced across much of the north-central U.S. given the strong signal for an arctic surface high settling later this week. The unlikely much warmer temperatures of especially the 06 UTC GFS were mitigated with this manual adjustment. The QPF was also raised across the general vicinity of the Great Lakes Friday into the weekend from the NBM given the overall signal for light to moderate lake effect snows. Otherwise, NBM QPF seems mostly reasonable and consistent with guidance forecast spread that has now decreased across much of the lower 48 and adjoining waters, bolstering forecast confidence to a degree. Blending this QPF with some WPC continuity acted to lessen run to run product variance. ...Weather/Hazards Highlights... A relatively quiet period of time is expected across the nation on Wednesday with most areas remaining dry, albeit with some terrain enhanced snow across the northern Intermountain West/Rockies. No risk areas are warranted for the WPC Day 4/Wednesday Excessive Rainfall Outlook (ERO). 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 5 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. Guidance has slowly converged on a more similar solution for the focus and onset of organized precipitation development into the West Coast in an emerging and increasing wet pattern later this week and likely extending into next week to monitor. Multiple Pacific systems will struggle to work eastward, but do seem now to allow lead moisture fuel a moderate moisture/rain focus into the Pacific Northwest/Northern California mid-late week. Additional system approach should tend to allow activity to redevelop, possibly with greater intensity and focus gradually southward more into California into next weekend. 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 Midwest region on Wednesday and then across he Mid-South and Ohio Valley region 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 Minnesota through the end of the week, perhaps up to 25 degrees below average across portions of Montana, but not as cold as the previous Arctic blast back in mid-January. Expect a period favorable for moderate upslope fetch snows will dig down through the north-central Rockies/Plains mid-later week with frontal advance. Cold temperatures with this front will gradually modify with subsequent digging through the central the eastern U.S. later week into next weekend. Accordingly, the prospects for lake effect snow are increasing 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. However, it is notable that latest 12 UTC model guidance is more variable with flow amplification. 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 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