textproduct: San Joaquin Valley

KEY MESSAGES

1. Below average temperatures remain in place for the next several days with localized rain and snow showers (above 9,000 feet) across the area from tonight through the start of the weekend.

2. More substantial precipitation will move into our area by Saturday evening with a 40-65% chance of at least a half an inch of rainfall from Saturday evening through mid-day Sunday.

3. A Winter Weather Advisory has been issued for the higher elevations along the Sierra Nevada mountains with a 15-20% chance of greater than 4 inches of snowfall above 7,000 feet, and a 50-70% chance of greater than 10 inches of snowfall above 9,000 feet.

DISCUSSION

October is certainly going out with a bang! A low pressure system situated in the Pacific Northwest will interact with the trough that is currently over California and bring the rain and colder temperatures. Models are in good agreement that Sunday is when the San Joaquin Valley will see a majority of its rainfall. That isnt to say that we wont start seeing rainfall on Saturday. Currently, there is a 20-27% chance for Fresno up to Madera to see at least a wetting (0.1) rain by Saturday afternoon. This may make trick-or-treating just a tad bit wet in the northern CWA. As the low pressure system moves in, that chance for wetting rain will expand to encompass the entire CWA (yes including the desert). These 11 PM probabilities range from 30-40% in the Mojave Desert. The Valley has a 33-55% chance to see a 0.1 or greater of rainfall. Finally, the Foothills and the Sierra Nevada have a 70-90% chance to see a 0.1 or greater of rainfall. The projected time is around 11 PM, so hopefully those trick-or-treaters will either not mind getting rain on or begin to move the Halloween festivities inside.

Sunday is looking to be the day for most rain and snowfall. Models continue to be in good agreement that the trough will be digging in further south. However, there is a shortwave trough embedded within the larger main trough (trough-ception, woooaah) which will provide lift, cooling the moisture within the trough and bringing that sweet, sweet rain for the Valley and snow for elevations above 7,000 feet. There is a 15-20% for elevations above that 7,000 feet to see 4 or more of snow by Sunday morning. Areas above 9,000 feet have a 50-60% chance to receive 8 or more of snow by Sunday morning. These values may go up or down as we get closer to Sunday and the onset of the precipitation event. Down here at 250 feet above sea level (the elevation of the office), Sunday will be quite a wet one for us. The probability of exceeding half an inch (0.5) or more of rain by Sunday evening is 40-60%. As we move closer to the Foothills, that goes up to an 80-90% chance of seeing half an inch or more of rain.

This rain will be extremely short lived, unfortunately. The trough will be moving out by Sunday night. Ridging will take place almost immediately after. This will get temperatures up to a more normal range. Theres still a bit of spread, but there is a 10% chance that the maximum temperatures for Monday are above a few degrees above normal for the start of November (71-72 for the SJV). Based on office experience, when ridging sets up after rain, there is a potential for fog. We dont currently have the probabilities for the fog, but let this serve as your heads up that it may start soon.

Looking ahead with the Climate Prediction Center outlooks, the 6-10 and the 8-14 day outlooks both are hinting at warmer than normal temperatures. The 6-10 day outlook has a 33-40% chance of above normal temperatures, while the 8-14 day outlook ramps that up to a 50-60% chance of above normal temperatures. Precipitation for both of those outlooks remain at the near normal levels.

AVIATION

A reduction in visibility to around 4-5 statute miles due to haze is possible tomorrow morning at KFAT, KVIS, and KBFL. Otherwise, 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

Winter Weather Advisory from 8 AM Saturday to 7 AM PDT Sunday for CAZ323-326>328-330.