textproduct: San Joaquin Valley

KEY MESSAGES

1. Slow but steady warmup this week, with widespread Moderate Heat Risk by the weekend and isolated areas of Major Heat Risk.

2. Hot, dry, and windy conditions will create elevated fire risk today and tomorrow, particularly in eastern Kern and Tulare Counties.

3. Increased chance for Sierra Nevada thunderstorms late this weekend into next week with monsoonal moisture pushing into our region.

4. Practice safety around lakes, rivers, and streams, as water is still running cold.

DISCUSSION

The high pressure ridge that sat over California today and caused triple digits in most of the lower elevation areas of our CWA is expected to shift east and be more centered over the Four Corners by Sunday into early next week. This will initially cause slightly lowered 500mb heights and lower the high temperatures by a couple degrees, keeping them in the triple digit range throughout the weekend, but further into the work week, highs are expected to rise again and remain in the low to mid 100's through at least Thursday.

The pattern arrangement will also lead to an influx of monsoonal moisture up from the Gulf of California and this will likely lead to thunderstorm development along the Sierra Nevada and into the Tehachapi Mountains as well as the Mojave Desert. Current chances for said thunderstorms are about 15-25 percent on Sunday, but will ramp up on Monday to 20-35% as both temperatures and humidity increase. The rest of the week will see thunderstorms chances similar to Sunday showing up each afternoon through the rest of the week as the ridge over the Four Corners remains in place.

As a consequence of the incoming moisture, low temperatures are expected to increase into the low 70's for much of the rural areas of the Valley while the cities are expected to be in the mid 70's at night, which combined with the mid 100's during the day means there will not be as much relief at night after the heat of the day. This increases the Heat Risk from a mix of Minor and Moderate to all Moderate throughout the Valley and Mojave Desert mixed with areas of Major Risk, which affects much of the population, especially those without sufficient cooling methods. The overall probability for Major Heat Risk on Wednesday (likely the hottest day for both highs and lows) in the southeastern portion of the Valley is 45-65% while other areas are in the 15-35% range. These low temperatures are expected to come down again by this Friday, and even as highs remain in the triple digits, the overall Heat Risk is expected to decrease.

AVIATION

VFR conditions expected across the area 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.