Scientific Forecaster Discussion
000 FXUS66 KSTO 202329 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 329 PM PST Wed Nov 20 2019 .SYNOPSIS... Breezy winds and isolated mountain showers in to the overnight. Quieter weather to end the week into the weekend. && .DISCUSSION... The upper level low is currently located over SoCal and is slowly pushing off to the east. The current SAC to MFR gradient is around 12 mb and we are seeing breezy winds with gusts up to 45 mph down the Valley and in some of the higher elevations. The breezy winds will continue for the next few hours but we will start to see them let up some this evening as the gradient weakens. Easterly flow and upper level energy are bringing some light showers to the east slope of the Sierra and the Sierra crest south of I-80. The majority of the showers will stay off to our east but some light activity will continue to be possible into the overnight mainly along the crest. Quieter weather will set in by Thursday afternoon as a ridge builds in. Highs will be near to a bit above average the next few days. -CJM && .EXTENDED DISCUSSION (Sunday THROUGH Wednesday)... A broad east-west oriented ridge will remain overhead for Sunday ensuring another day of mild, dry conditions. High temperatures across the Valley and Delta should reach the mid/upper 60s with even a couple low 70s toward Red Bluff and Redding. This is approximately 6 to 12 degrees above typical late November climatology. At night, high pressure will ensure calm winds which supports optimal radiational cooling effects. This will take lows into the 30s and low 40s over the Valley, foothills, and Delta. Global ensembles continue to advertise a pair of systems to impact the region during the Monday through Wednesday (November 25-27) timeframe. To start the week, another amplified shortwave is expected to move from the Pacific Northwest into the central Rockies. This setup would enhance height/pressure gradients allowing for a period of dry, northerly winds on Monday into early Tuesday. Given extremely dry fuels, elevated fire weather concerns will need to be monitored. Moving into the Tuesday/Wednesday period, model guidance continues to advertise an upper trough tracking into the West Coast. With the stagnant ridge over the east Pacific retrograding west, this may allow the trough to bring well needed precipitation back to the region. Ensemble spread is around average with some dry members keeping the precipitation to the north. Based on the latest models, have maintained cooling temperatures along with increasing precipitation chances. This includes mountain snows which will continue to be monitored given busy Thanksgiving travel over the major thoroughfare. ~BRO && .AVIATION... VFR conditions expected the next 24 hours with gusty winds continuing into the evening. KRDD and KRBL can expect the strongest northerly wind gusts, generally around 25-35 knots through 03Z Thursday, with breezy conditions into the Sacramento area. The northern San Joaquin Valley TAF sites could see gusts of 15-20 knots through 00Z Thursday. Lighter overnight winds may bring local MVFR visibilities after 14Z to KSCK and KMOD. ~BRO && .STO WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 7 AM PST Thursday for Central Sacramento Valley in Glenn, Colusa, Yuba, Northern Sutter, and Butte County Below 1000 Ft-Eastern Mendocino NF-Eastern Portion of Shasta/Trinity NF-Lake County Portion of Lake-Napa-Sonoma Unit- Northern Sacramento Valley to Southern Tehama County Line Below 1000 Ft-Northern Sierra Foothills from 1000 to 3000 Ft. Includes portions of Shasta-Trinity and Butte Units-Northern Sierra Including Lassen NP and Plumas and Lassen NF/S West of the Sierra Crest (West of Evans Peak-Grizzly Peak-Beckworth Peak)- Southeast Edge Shasta-Trinity NF and Western Portions of Tehama- Glenn Unit-Southern Sacramento Valley in Yolo-Sacramento Far Western Placer, southern Sutter and Solano County Below 1000 Ft. Wind Advisory until 10 PM PST this evening for Central Sacramento Valley-Clear Lake/Southern Lake County-Mountains Southwestern Shasta County to Northern Lake County-Northeast Foothills/Sacramento Valley-Northern Sacramento Valley-Shasta Lake Area / Northern Shasta County-Southern Sacramento Valley- Western Plumas County/Lassen Park. Winter Weather Advisory until 7 PM PST this evening for West Slope Northern Sierra Nevada.