Extended Forecast Discussion NWS Weather Prediction Center College Park MD 154 AM EST Fri Mar 08 2024 Valid 12Z Mon Mar 11 2024 - 12Z Fri Mar 15 2024 ...Strong storm exiting the Northeast on Monday will continue a threat for high winds... ...Unsettled weather along the northern-central West Coast will continue into early next week... ...Overview... Strong low pressure will be exiting the Northeast by the start of the period on Monday, but the threat for high winds will continue on the backside of this system at least through Monday. Meanwhile, a couple of shortwaves will move through the West Monday-Wednesday, bringing some unsettled conditions across much of the region before a strong upper ridge builds over the coast next Thursday-Friday. This should allow for amplification of the system over the West late week, with guidance all suggesting an eventual deep upper closed low over the Southwest/Four Corners. This would support a possibly heavy rainfall threat by next Thursday across parts of Southern Plains/Lower Mississippi Valley. A mean upper ridge shifting from the Central to Eastern U.S. next week will bring an expanding area of above normal temperatures, with the greatest anomalies likely to be over the northern Plains/Upper Midwest early-mid week. ...Guidance/Predictability Assessment... Latest model guidance shows very good agreement on the large scale pattern through the entirety of next week, and a general blend of the deterministic guidance worked well for the first half of the period. Some typical differences in the details, most of which will take until the short range period to fully resolve. Given a briefly quiet pattern to follow behind a departing deep surface low from the Northeast on Monday, these differences shouldn't have huge implications for sensible weather impacts anyways. After Wednesday, there are some more notable differences which arise concerning the timing of a northern stream shortwave which amplifies over the Great Lakes late in the week. And while guidance is in excellent agreement on a deep closed low over the Southwest next Thursday-Friday, there are some subtle differences in placement of that feature and the resulting track of a surface low/front through the Central U.S to Midwest, and of course, late period QPF distribution across the South. A look at the new 00z guidance (which was available after forecast generation time) shows continued uncertainties for both the northern and southern stream systems late next week. The WPC blend incorporated more of the ensemble means late period to tone down the detail discrepancies, but was still able to maintain 60 percent deterministic guidance through Day 7 allowing for better system definition overall. No major changes were needed to the new day 3 to 6 progs and QPF forecast compared to previous WPC continuity. ...Weather/Hazards Highlights... As the strong surface low exits the Northeast by Monday, much of the precipitation will be well offshore by then, with the exception of some light to moderate snow showers continuing into the day across Maine and the higher terrain on the backside of the low. Gusty to high winds will also continue into Monday and maybe Tuesday across much of the Northeast. Behind this, weather across the Eastern and Central U.S. should trend quieter for the first half of the week, but the Western U.S. remains unsettled as a couple of shortwaves bring rounds of rain and higher elevation snow. The Day 4/Monday Excessive Rainfall Outlook highlights a marginal risk along the coast from northern California through Washington. Guidance continues to show some uncertainty for details of magnitude/distribution of moisture and higher rain totals, but wet ground conditions following heavy rain the prior day (Sunday) may lower the threshold for localized runoff issues in some areas that see overlapping heavy rain/high rates. As the final upper shortwave in the series amplifies and moves inland, the best focus for rain and mountain snow should shift into the central Rockies by Wednesday, with rainfall beginning to increase in coverage and intensity over the Plains and Mississippi Valley as well. Moisture streaming ahead of a closed low developing over the Southwest should increase the threat for another round of heavy rain across the Lower Mississippi Valley and vicinity next Thursday shifting more into the Gulf Coast/Southeast by next Friday. Some threat for locally heavy rain/mountain snows across the Southwest as well in association with that system. Mean ridging aloft over the central/east-central U.S. will support an expanding area of above normal temperatures to the east of the Rockies. The core of warmest anomalies should cover parts of the northern Plains and Upper Midwest Monday through Wednesday, with highs potentially reaching 20-30 degrees above normal. Above normal temperatures will gradually expand into the South and East mid to later next week week. Over the West, the wet/snowy pattern over northern-central West Coast and eventually into the Rockies will maintain moderately below average highs and near/above average lows through early next week. Upper troughing that amplifies inland by Wednesday-Thursday should spread a broader area of cool daytime highs across the West with temperatures beginning to rebound again along the immediate coast next Friday as strong ridging builds in aloft. Santorelli 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