textproduct: San Joaquin Valley

DISCUSSION

A ridge of high pressure that was influencing our weather this weekend has moved out of the area. A closed low and a deep trough is expected to move into our area off the Pacific Ocean this week which will lead to cooler temperatures and precipitation. Today however, temperatures will be close to average with a cooldown after the warm weather this weekend. The probability of temperatures exceeding 85 degrees today across the northern San Joaquin Valley is low (10-25%), while the southern valley has a 50-70% chance of temperatures exceeding 85 degrees. Temperatures will cool significantly after today, and by Wednesday the probability of temperatures exceeding 75 degrees in the Central Valley will only be around 10-25%. Chilly overnight lows are likely, especially by late this week across the entire area including the valley. By Friday the chance of overnight lows below 50 degrees is around 55-70% across most of the valley.

In addition to the signficant cooldown in temperatures due to the influence of a deep trough, a closed low will bring in precipitation across the area by mid-week. Precipitation could begin as early as Tuesday evening or night in the mountains before likely beginning in the valley sometime Wednesday evening or overnight Wednesday. As of now, precipitation is likely to taper off sometime overnight Thursday or early Friday morning. In terms of precipitation totals, there is a 65-80% chance of at least a tenth of an inch of rainfall, and a 55-75% chance of at least a quarter of an inch of rainfall in the Central Valley and the Mojave Desert. The Weather Prediction Center (WPC) indicates a marginal risk for excessive flodding (at least 5% chance) in the southern portions of the Central Valley and the Mojave Desert within western Kern County. Many localized areas especially along the Mojave Desert and Tehachapi pass are especially vulnerable to flodding, and therefore the forecasted rainfall within that region is of particular importance. In the mountains above 8000 feet snowfall remains likely within a similar time period with a 50-75% chance of at least 4 inches of snow. Snowfall totals could potentially be even higher in the highest mountians slopes, with a 55-70% chance of at least 8 inches of snow in those areas.

In addition to the chances for rainfall, there is the possibilty of wind gusts along the Sierra Nevada slopes and within the Mojave Desert. The probability of wind gusts greater than 25 mph will be around 50-75% from Tuesday afternoon through at least Friday morning within localized areas. There is therefore the potential for gusty winds in addition to the rainfall, making travel more diffiuclt.

Looking at the long range conditions, the majority of ensemble members indicate that a troughing pattern will remain in place through at least this coming weekend across our area. There is also another chance of a very light rainfall early next week. However, confidence in this system is very low as of now given that there is a lot of model disagreement and this system is very far out. According to the Climate Prediction Center (CPC), we are looking at above average temperatures and precipitation over the next 6-10 and 8-14 days. In the 6-10 Day Outlook there is a 33-40% chance for above average precipitation and the same percentage chance for below average temperatures.

AVIATION

VFR conditions will prevail for the next 24 hours. Winds will be out of the northwest at KBFL and are expected to remain at or below 10 mph.

AIR QUALITY ISSUES

None.

CERTAINTY

The level of certainty for days 1 and 2 is high. The level of certainty for days 3 through 7 is medium.

Certainty levels include low...medium...and high. Please visit www.weather.gov/hnx/certainty.html for additional information and/or to provide feedback.

HNX WATCHES/WARNINGS/ADVISORIES

None.