textproduct: San Joaquin Valley

KEY MESSAGES

1. Dry conditions with a brief warm up will continue into Monday before a cooling trend sets up starting Tuesday.

2. A disturbance dropping south from Alaska is expected to result in the next favorable chances for precipitation across the region beginning Friday.

DISCUSSION

A stable atmospheric pattern has set up over central California today in the wake of the disturbance from the latter portion of last week. The shortwave region of high pressure will result in dry conditions and seasonable temperatures through Monday and generally clear skies across most of the region. Also present today is a low pressure system centered over the Pacific Northwest, which will transport weak amounts of moisture over the Sierra Nevada, resulting in some partly cloudy skies between 15-25 kft overnight into Monday morning. The weak influence of the trough will erode the aforementioned ridge of high pressure into Tuesday as the low progresses eastward. A second area of low pressure is projected to develop into Tuesday morning over the PacNW, causing a localized mid-level jet streak to push through northern California and into the central Sierra Nevada. The cold, dry origin of the entraining air from the northwest will cause a sharp drop in minimum relative humidities across the higher elevations of the Sierra: falling from 20 to 30 percent on Monday to 10 to 20 percent on Tuesday. However, with sufficiently saturated soils from recent precipitation, there are not significant fire weather concerns in this area.

Temperatures across the region will gradually cool through the week as the prevailing flow continues from the west-northwest. By Friday, there is less than a 30 percent probability for valley temperatures to exceed 70 degrees, with near-zero chances for next weekend. This can be attributed to the presence of a robust low pressure system developing over the Pacific Northwest which will push moisture into the region from the southwest and resulting in the next best probabilities for precipitation across the region. On Friday, there is a 40 to 50 percent probability for daily measureable precipitation (0.01") at the highest elevations of the Sierra, with just a 20 to 30 percent probability in the Sierra Foothills. However, these probabilities ramp up into Saturday, approaching 70 percent for the Sierra, and 40 to 50 percent in the San Joaquin Valley and Sierra Foothills; similar chances exist on Sunday. Ranges for snow levels are rather broad still this far out, with the ensemble 25th percentile (75 percent prob to be above) around 4500', and the 75th percentile (25 percent to be above) around 7500'. Though, there is a 70 to 80 percent probability for at least a trace of snowfall for the weekend for elevations above the ensemble mean around 5500'.

AVIATION

VFR conditions will prevail for the next 24 hours.

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.