textproduct: San Joaquin Valley

UPDATE

Updated Aviation section.

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

Upper low (disturbance) moving across over Southern California Today. Based on Satellite and Doppler Radar imagery, wrap-around moisture has already intruded into Central California with scattered showers already being picked-up. Due to the nature of the flow around the Upper Low, the best influx of moisture will exist over Southern California, with lower moisture levels reaching Central California. Yet, enough moisture is expected to exist over the area to produce measurable precipitation this afternoon. Currently, the best instability and lift will exist over the Sierra Nevada (with a focus on the Crest) where a 40-70 percent chance of receiving a quarter of an inch (0.25) will exist today. The storm exits the area on Tuesday as precipitation potential diminishes going into the remainder of the week. Yet, temperatures will become more of a concern as we go through this week.

Ensemble analysis is showing an increased Probability of Thunder (PoT) across the Sierra Nevada Today. With percentages of 10 to 20 percent across the Crest of the Sierra Nevada, confidence is high that thunderstorms will be confined to the mountain. Yet, because of the subtropical nature of the moisture, a thunderstorm over the San Joaquin Valley can not be ruled out. By Tuesday, the flow aloft becomes more northwesterly and stable. Therefore, will expect todays convection to shift east and away from Central California.

A closer look at temperatures has the Probability of Exceedance (PoE) of reaching 90 degrees below 50 percent on this Monday and Tuesday. Wednesday is looking like a transition period as PoE of reaching 95 degrees breaks above 50 percent. At that point, confidence is high that a warming trend will occur and peak out on Thursday. By Thursday, PoE of reaching 100 degrees rises to above 50 percent for areas in the San Joaquin Valley from Fresno County, southward. In addition to the PoE percentages, ensemble 90th percentiles is showing widespread 100 degrees across the San Joaquin Valley on Thursday. A cooling trend will than be expected going into this weekend.

AVIATION

MVFR visibility due to smoke in the vicinity of the Dome Fire in Yosemite NP through at least this evening. There is a 10-20% chance of thunderstorms along the Sierra Nevada crest through 04Z Tuesday. 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

Lake Wind Advisory until 5 AM PDT Tuesday for CAZ300.