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FXUS66 KSTO 252125 AFDSTO

Area Forecast Discussion National Weather Service Sacramento CA 225 PM PDT Thu Apr 25 2024

Synopsis
Light rain and mountain snow this afternoon through Friday with thunderstorm chances today and tomorrow. Highest precipitation amounts and thunderstorm probabilities will be over the foothills and mountains. Dry weather and a warming trend returns over the weekend and into next week.

Discussion
Pesky and patchy low stratus continues to hang out over the central Sacramento Valley as seen on GOES-West visible imagery this afternoon as scattered showers begin to trickle over the Coastal Range and into the northern Sacramento Valley. Shower coverage and cloud cover are expected to increase as a weak weather system moves through the area today and tomorrow.

Thunderstorms will be the main threat as we close out the work week with a 15 to 20% chance of isolated thunderstorms over the mountains/foothills this afternoon/evening. Thunderstorm chances and coverage increases on Friday with a 15 to 30% chance over the eastern Valley in addition to the Sierra foothills/mountains.
High resolution models depict storms developing by mid-morning and persisting through the evening hours.

Overall precipitation amounts will be minimal and low impact, with the bulk of the moisture staying over the mountains and foothills.
The National Blend of Models depicts under a 0.25" of rainfall over most of the Valley, the exception being the northern Sacramento Valley where the NBM has roughly a 20% chance of 0.25" or more. The highest probabilities are over the foothills/mountains where the NBM has a 20 to 40% chance of 0.50" or more of rain. Due to the warm nature of this system, snow levels will be around 7000 feet through this evening before lowering to 6000-6500 feet on Friday. Highest snow totals will be along the highest peaks south of HWY 50 where the NBM has a 40-60% chance of 2.00" or more of snow. Winds will be breezy out of the west-southwest with strongest gusts of 25 to 30 mph through the Delta and over the mountains today and tomorrow, gusts will be 15 to 25 mph through the Valley.

By the weekend, dry weather returns as heights begin to increase and weak ridging moves in. Temperatures will gradually start to increase with Valley highs in the 70s and 80s. Over the foothills/mountains, high temperatures will be in the 60s and 50s, respectively. Winds will be light and breezy out of the north as this weather system exits the region.

//Forrest



.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
As we start off the work week, zonal flow and dry weather continues with Valley highs in the 70s & 80s and 50s & 60s over the foothills/mountains. Cluster analysis and ensemble guidance depict zonal, onshore flow over NorCal as a high pressure ridge hangs out over the Pacific and a low tracks eastward just north of the Pacific Northwest. This pattern continues along with a warming trend and above normal temperatures through Wednesday before variability in the clusters appears in regards to a trough potentially digging down over NorCal by late week. Uncertainty remains in the forecast, so be sure to check back frequently for updates!

//Forrest




AVIATION
VFR conditions expected over the next 24 hours with isolated areas of MVFR/IFR due to showers/thunderstorms (15 to 20%) over the foothills/mountains (thru 12Z Fri) as a weak weather system moves through the area today. West-southwest surface winds gusting 25 to 30 mph through the Delta and over the mountains (20Z Thurs to 14Z Fri) with Valley gusts 15 to 25 mph (thru 07Z Fri). Snow levels will be between 6000-7000 feet. Tomorrow, there is a 15 to 30% chance of isolated thunderstorms in the Valley & Sierra foothills/mountains from 18Z Fri to 05Z Sat.

//Forrest



STO WATCHES/WARNINGS/ADVISORIES
None.

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