textproduct: San Joaquin Valley

KEY MESSAGES

1. Minor Heat Risk through Tuesday as temperatures remain at or below seasonal normal values.

2. A disturbance will cross the region on Monday and Tuesday with a slight chance of showers and thunderstorms across the Sierra Nevada Monday afternoon.

3. A warming trend in temperatures starts on Wednesday as the region will see the return of heat during the latter part of the period. Thursday looks to be the hottest day with a greater than 70% chance of a Moderate Heat Risk. Friday also keeps a 40 to 60% chance of a Moderate Heat Risk.

DISCUSSION

Looking outside, you may have noticed some high clouds apparent this morning. This is because the low pressure system off the coast of California has slowly begun to make its way in. Current models show that the low is off the central coast. With that, the clouds will stick around all day, acting as a blanket, and keeping temperatures slightly above normal, which is 90 degrees. Todays Probability of Exceedance (PoE) of 90 degrees ranges from 40-70%, with Merced being at that 40% and the probability increasing to 70% in the south San Joaquin Valley. However, PoE of 93 degrees is 10-40%. This is a parting gift, if you will, from the weak ridge who brought slightly warmer temperatures these past few days.

The low pressure system should move on-shore throughout the day and with impacts noticeable tomorrow. Temperatures will be cooler and dropping to below normal once more. Currently, the PoE of 85 is 70-80% for the San Joaquin Valley. As for potential warmer temperatures, the PoE of 89 is 25-45%. So, much of the San Joaquin Valley can expect high temperatures between 85 and 89 degrees tomorrow. This trough will also bring a 5-17% chance for thunderstorms along the Sierra Nevada, particularly along the Crest. Rain cannot be ruled out either, as most of the Crest has at least a 50% chance of a wetting (0.10) rain. The high end (a 10% chance of happening) of models want to put a smattering of different values. The highest points (upwards of 45,000 feet) of the Sierra Nevada could receive up to an inch of rain, while elevations of up to 12,000 feet could see up to a 0.5 of rain. Again, this is the very high end scenario. Unfortunately, no rain is forecasted for the valley. The trough wont be sticking around for long, as temperatures will start to increase once more. Summer is attempting to get one last shot in, as ridging will build towards the end of the week as the trough moves out. Theres 90% chance of being above the low 90s. Thursday looks to be the warmest day, as there is currently a 25-40% chance of seeing triple digits.

AVIATION

MVFR with local IFR conditions will exist across the Sierra Nevada and adjacent foothills as smoke from the Dome Fire in Yosemite continues through 08Z Sunday. After 08Z, MVFR visibility in the vicinity of the Dome Fire. Otherwise, VFR conditions prevailing 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.