Monterey

ESFMTR * WHAT...A series of storms over the next week will bring periods of light to moderate rainfall to the region. The first in the series of storms is a shortwave trough that will move into the North Bay this evening and slide south across the region tonight into Thursday. Confidence has increased significantly with this system and it is expected to bring light rain across the North Bay and the San Francisco Bay Area. The higher elevations of the North Bay will likely see around a half an inch of precipitation while North Bay valleys see around a quarter of an inch. Bay Area locations south of the Golden Gate, including the Santa Cruz Mountains, will see a tenth to a quarter of an inch. Less than a tenth of an inch of rain is forecast across the Central Coast. A stronger, more significant rainfall event is anticipated to impact the region Friday and Saturday. The Weather Prediction Center Day 3 and Day 4 Excessive Rainfall Outlook has the North Bay and a portion of the Bay Area in a Marginal (at least 5%) chance of exceeding flash flood guidance for this time period. This second system is significantly stronger low pressure system accompanied by a moderately strong cold front. The latest model guidance depicts rainfall beginning Friday evening in the North Bay and progressing southward across the Bay Area and Central Coast overnight into Saturday. While we expect these totals to change a bit, current solutions bring 3 to 5 inches of precipitation to the North Bay coastal range and 1 to 2.5 inches to the North Bay Valleys, 0.5 to 1 inch in the Bay Area, and Monterey Bay region, 1 to 2 inches across the Santa Cruz and Santa Lucia mountain range, and a trace to 0.25 inch over the interior portions of Monterey and San Benito counties. Unsettled wet weather will continue Sunday and into next week. Area streams and creeks will only see a slight to moderate rise with the first storm, and while streams are expected to stay below action/monitor stage with this storm it will prime the soils for quicker and more noteworthy rises with subsequent storms. The second stronger and wetter storm will result in greater and more rapid rises on small creeks, streams and rivers. Main stem rivers forecasts continue to stay below flood stage, however the exceedance probabilities (of rising above flood stage) have increased over the last 24 hours across Sonoma County with the Russian River at Guerneville - GUEC1 increasing to 20% (up from 10%). Napa County has seen minor fluctuations and the probability of exceedance remains low. SHEC1- Napa near Saint Helena (9%), and APCC1- Napa near Napa (5%) for Saturday. A few other rivers to keep an eye on that show higher probability of reaching Action/Monitor or Minor flood stage according to the latest CNRFC forecast are MWEC1 - Mark West Creek at Mirabel Heights now has a 77% probability of reaching Action/Monitor Stage (up from 70%) and a 57% probability of reaching Minor flood stage (up from 45%) on Saturday. CTIC1 - Laguna De Santa Rosa at Stony Pt Rd near Cotati has a 86% probability of reaching Action/Monitor Stage (up from 64%) and a 55% probability of reaching Minor flood stage (up from 41%) on Saturday. GEYC1 - Russian River at Geyserville has a 41% probability of reaching Action/Monitor Stage (up from 27%) and a 25% probability of reaching Minor flood stage (up from 14%) on Saturday. * WHERE...Sonoma and Napa Counties. Latest model guidance suggests the North Bay will receive the greatest accumulation of precipitation with the heaviest rainfall expected over the North Bay coastal range and mountains. * WHEN...Friday through Sunday. Light to Moderate rainfall expected over the North Bay Friday and Saturday. The heaviest rainfall accumulation is expected Friday and Saturday. Unsettled wet weather will continue Sunday into next week. * ADDITIONAL DETAILS...In addition to the moderate rainfall and localized ponding of water in low-lying or poorly drained areas, such as freeway offramps. Locally strong and gusty winds may result in downed trees, and potential power outages. Confidence is high that we will receive rainfall from this system however, confidence is moderate with respect to the exact location and timing of the most intense rainfall. Details regarding this storm will likely change as the system nears. Therefore, stay tuned to the latest forecast for the most up to date weather information.More