textproduct: San Joaquin Valley

UPDATE

Updated Aviation section.

KEY MESSAGES

1. Warm trend in temperatures as chances for triple-digits increases to near 80 percent on Monday and Tuesday. High chances for triple-digits will continue through mid-week.

2. A slight chance (10 percent or less) for thunderstorms over the Sierra Nevada and foothills this weekend.

3. Marginal (at least 5 percent) risk of flooding in the very high elevations of the Sierra Nevada due to the increasing potential for thunderstorms.

DISCUSSION

High Pressure Ridge now the dominate feature over the West as temperatures continue to warm. The ridge of high pressure is showing signs of amplification as it is expected to force a disturbance to ride over it into early next week. 24-Hour trend in temperatures is showing positive gains of 2 to 5 degrees over late morning on Friday. While the San Joaquin Valley has the potential of reaching triple digits today, the Probability of Exceedance (PoE) of reaching 100 degrees is still in the 40 to 60 percent range. Therefore, widespread triples are more likely on Sunday when PoE falls in the 60 to 80 percent range. Further amplification of the ridge will allow for highs well into the triple digit range as afternoon max temperatures reach for values of 103 to 105 degrees on Monday through Wednesday.

Ensemble moisture analysis is showing a return of the monsoonal that is currently being suppressed under the ridge pattern. Once the ridge is shifted by the off-shore disturbances, a southerly flow will allow for a northward surge of moisture that will see additional sources of moisture introduced from the tropics later in the week. Ensemble upper-air analysis shows a weak disturbance aiming at the Bay-Area as the flow becomes more southwesterly to southeasterly. Therefore, by Tuesday, Probability of Measurable Precipitation (PoP) along with instability analysis shows increasing percentages as significant moisture has the potential of entering the region. With PoP values reaching 40 to 50 percent, will evaluate if thunderstorms have the capacity of introducing heavy rain as guidance shows percentages reaching at least 5 percent of meeting excessive precipitation criteria on Tuesday and Wednesday across the Sierra Nevada and the Mountains and Desert of Kern County.

The ridge pattern is shifted east starting on Friday as the probabilities of cooling and drying increase across Central California. Thursday will be a period of transition as the heat and moisture linger as the significant ranges of Tuesday and Wednesday in terms of temperatures and moisture.

AVIATION

06Z Update:

VFR conditions will prevail across the central California interior for the next 24 hours. Less than 10% chance of Sierra Crest thunderstorms during the period.

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.