textproduct: San Joaquin Valley

KEY MESSAGES

1. A warming trend will continue this week with afternoon temperatures approaching 10 to 15 degrees above average today and even warmer Tuesday through Saturday.

2. Daily and monthly record high maximum temperatures will be challenged this week.

3. Practice cold water safety, as waterways will be running cold and fast over the next several days.

DISCUSSION

An exceptionally strong ridge will build into the southwest this week, bringing potentially record-breaking heat to the entire region. Temperatures in the San Joaquin Valley are likely to reach 90 degrees by Tuesday, with much of the Valley seeing a 60-80% chance for that temperature. The heat is expected to peak on Friday, with chances for 95 degrees in the Valley at 40-60% that day. This heat starting on Tuesday is around 10 to 15 degrees above normal, while the temperatures expected on Friday are about 20 to 25 degrees above normal. The Mojave Desert will likely see a similar degree of above normal temperatures, likely reaching into the upper 90's by Friday, with a 20-30 percent chance for hitting triple digits.

In tandem with these record temperatures, rivers will likely see increased run-off from the Sierra Nevada due to rapid snow-melt as low temperatures consistently remain above freezing at higher elevations. This will lead to rivers running much colder than the outside air, which can be dangerous to swim in. Use caution while swimming in the rivers during this time, and always wear a life vest.

Ensemble models for the long range forecast are indicating the ridge flattening out into zonal flow by mid next week, leading to decreasing temperatures, but these are likely to remain above normal. Current CPC outlooks continue to put the southwest in likely above normal temperatures and likely below normal precipitation for days 6-10 and 8-14.

AVIATION

VFR conditions are expected for the next 24 hours.

FIRE WEATHER

Warming air temperatures and steady dew point temperatures will lead to a decrease in minimum relative humidities, especially for the Mojave Desert, high Sierra, and Coastal Range. This will coincide with a sharp decrease in 100- and 1000-hr dead fuel moistures and an increase in ERC in these areas. Rapid curing of fine fuels will bring about some risk for isolated grass fires. However, live fuel moisture remains below critical thresholds and significant wild fire potential remains at little or no risk.

AIR QUALITY ISSUES

None.

CERTAINTY

The level of certainty for days 1 and 2 is medium. 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.