Minor to moderate HeatRisk today with cooler weather Tuesday and beyond, high temperatures falling below normal by Wednesday. Monsoon thunderstorm chances each day in the mountains through Wednesday, with best chances and heaviest rain today and Tuesday. Deepening marine layer through the end of the week with breezy winds in the mountains and deserts.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, UPDATED AVIATION DISCUSSION,
Mid level water vapor shows troughing to the northwest with the ridge in place over the Four Corners region, poised to weaken into Tuesday as the trough becomes more pronounced. Minor to moderate HeatRisk continues today for much of the region, although temperatures begin a cooling trend today, reaching near normal by Tuesday afternoon. High clouds will continue to move into the region today as southeasterly flow shunts moisture northward, but these clouds shouldn't meaningfully limit storm potential in the mountains this afternoon. The morning sounding indicated decent CAPE and increasing PWs of 1.3-1.6", with models signaling a wide swath of instability to set up today stretching from southwestern Arizona into southeastern California. This instability, along with the ample moisture in the mid and lower levels, will be key for more widespread monsoonal thunderstorms today, likely kicking off as early as noon. While much of the convection today will be anchored to the mountains, a few storms may migrate into the deserts and/or far eastern valleys with brief, heavy rainfall. Rain rates in the higher terrain will be a bit more impressive today, with 1"/hr or higher not out of the question for the San Diego and Riverside county mountains. Further north in San Bernardino, there will be a significant cut off of the moisture near the border with LA County. Therefore, lesser max rain rates closer to 0.5-0.75"/hr can be expected, with the strongest storms likely on the eastern/northeastern slopes of the SB County mountains. While widespread flooding isn't expected, some localized spots, especially near the peaks or eastern sides of the mountains, could see some brief flooding both today and tomorrow. As always with any thunderstorm, frequent lightning, gusty winds, and small hail will be possible. Ensure you are prepared to take shelter in a sturdy and enclosed structure should you hear thunder.
The ridge continues to weaken on Tuesday with some models now indicating a weak easterly wave may move across Tuesday morning, which could allow for some morning rainfall for the deserts and far inland areas. Should this come to pass, a rumble of thunder or two cannot be ruled out. This will be something to closely watch as any morning convection could limit afternoon storms in the mountains. As it stands now, additional moisture will be pushed into the region on Tuesday with a slight decrease in the instability, allowing for another round of monsoonal thunderstorms Tuesday afternoon. Conditions look conducive for a rince-and-repeat of Monday, but with the potential for slightly higher rain rates/localized flooding as PWs peak above 1.5". Again, much of this will depend on what occurs Tuesday morning with any easterly wave, but for now, will continue to message widespread mountain thunderstorms for Tuesday afternoon.
After Tuesday, the aforementioned upper level trough will encompass much of California as the state experiences a significant cooldown, with temperatures falling to 3-10 degrees below normal Wed-Fri and the marine layer deepens each day. This will be the first time in nearly a month that highs will be below normal, so take advantage of the cooler weather! Monsoonal moisture will linger in the region which could allow for some abnormally warmer mornings, but with limited forcing, afternoon thunderstorm chances will be falling through the end of the week. Still, models continue to push for a few storms over the San Bernardinos Wednesday afternoon as the trough begins to move in. Otherwise, quieter weather for the end of the week and weekend with cooler weather/a more robust marine layer and afternoon breezy winds in the deserts and mountain passes.
101945z. Coast, VFR conditions expected this afternoon and evening. Patchy low clouds to gradually develop overnight, increasing in coverage and duration, with best chances of cigs between 11-15Z Tuesday. Bases around 700-1000 feet MSL. Scatter out of any cigs Tuesday by 17Z.
Valleys/Mountains/Deserts, SCT-BKN clouds mostly above 15000 feet through 18Z Tue. Scattered TSRA over mtns with an isold TSRA or two in the High Desert to 02z Tue with bases around 9000 feet MSL with tops to 50000 feet. Any TSRA could produce lightning, strong up/downdrafts and associated vis reductions.
No hazardous marine conditions are expected through Saturday.
High tides will exceed 7 feet during evenings today through Wednesday between 800-930 PM, resulting in minor tidal overflow of low-lying areas along the beach. Surf will be low and is not expected to add much to the flooding potential. Check the Coastal Flood Advisory for details.
Ca, Coastal Flood Advisory from 6 PM this evening to 11 PM PDT Wednesday for Orange County Coastal Areas-San Diego County Coastal Areas.
PZ, None.
