textproduct: San Joaquin Valley

KEY MESSAGES

1. Hotter temperatures, including triple-digits for the San Joaquin Valley, are expected for today and Tuesday.

2. A Heat Advisory is in effect for the San Joaquin Valley and Lake Isabella area through 8PM Tuesday.

3. Moderate Heat Risk expected for the valley areas with a medium chance for Major Heat Risk.

4. Elevated fire danger Monday and Tuesday for the Mojave Desert and in the lee side of the Coastal Range in western Kings and Kern Counties due to low humidities and stronger winds.

4. Practice safety around area lakes, rivers, and streams as waters are running cold.

DISCUSSION

A ridge of high pressure passed over southern California this morning and is now centered over the Four Corners region of the desert Southwest. Subsidence aloft from this high combined with mid-level anticyclonic winds from the south-southeast are driving hot temperatures around 20 degrees above season averages into central California today. There is a 50 to 60 percent probability (via the NBM v5.0) for maximum temperatures this afternoon and Tuesday to exceed 100 degrees in the San Joaquin Valley; greater probabilities are found in the south valley areas. There is also a 60 to 70 percent probability for 100 degree temepratures in the Mojave Desert today, increasing to 80 to 90 percent for tomorrow. These temperatures bring widespread Moderate HeatRisk to the lower elevations of the region both days, with pockets of Major HeatRisk, especially where the thermal belt resides overnight. As such, a Heat Advisory is now in effect for the San Joaquin Valley and also extend into the Lake Isabella area through 8 PM Tuesday evening.

Late Tuesday into early Wednesday, the high pressure ridge is expected to erode slightly, allowing an open wave of a low pressure trough to push through the western United States. A slight cooldown is anticipated for central California as a result, though afternoon highs will remain above season averages by around three to five degrees. While the open wave will result in winds from the west-southwest, little moisture is associated with the low outside of the Sierra crests; though, this area has less than a 10 percent probability of precipitation.

After this low pressure area moves out of the region on Thursday, zonal flow will take hold as the dominant synoptic pattern over central California. This will continue warmer, above-average temperatures for the local area and cause dry humidities to prevail through this coming weekend.

AVIATION

VFR conditions will prevail for the next 24 hours over Central California. Winds approaching 10 knots at TAF sites around 03Z Tuesday.

FIRE WEATHER

Dry conditions with low relative humidities are expected to continue through this week, with minimums below 20 percent in the San Joaquin Valley each day except Wednesday when RHs are below 25 percent. This will continue the threat of grass fire development and spread across the region, especially with the prolonged drying of fine fuels during the early part of the week. Stronger wind gusts are expected along the west side hills in Kings and NW Kern County Tuesday afternoon into evening which has potential to spread any developed fires should they occur, but will coincide with an increase in RH as they begin to improve into the night. Elsewhere, in the Mojave Desert, minimum RH values are expected below 10 percent today and Tuesday, improve slightly to 15 to 20 percent on Wednesday before falling back below 15 percent for the remainder of the week. Stronger wind gusts will arrive in this area late Wednesday. Similar to the previous areas, low RHs below 20 percent will prevail across the Sierra Nevada through Tuesday, then improve between 30 and 40 percent for Wednesday and Thursday before falling below 25 percent again for the end of the week.

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

Heat Advisory until 8 PM PDT Tuesday for CAZ300>317-319-321- 332.