Warm temperatures and afternoon mountain thunderstorms

April 23, 2018 – Mainly dry and warm most of this week except for a chance of a few showers or thunderstorms over the mountains each day starting Tuesday.

Discussion

Other than a few high clouds, skies are clear across interior NorCal early this morning. Temperatures are showing little change compared to 24 hours ago except across the northern Sacramento Valley where light northerly winds have developed. Current readings range from the 30s in the mountain valleys to the 50s to mid 60s across the Central Valley.

Ridging will remain over the area through the middle of the week as a low pressure system deepens off the coast and becomes cutoff from the jet. Temperatures will be running well above average (10- 15 degrees) through Wednesday. North winds today may provide some local enhanced warming at the north end of the Sacramento Valley and portions along the western edge of the valley.

Some moisture advects northward over the Sierra Nevada on Tuesday and may bring a few showers or thunderstorms, mainly near the crest.

The models are mixed on Wednesday with the convection over the mountains with the GFS indicating greater activity while the NAM has a dry forecast. Have left in a mention of showers and thunderstorms over the mountains for now.

The cool down is forecast to commence Thursday depending on whether the cutoff low edges close enough to the coast. Most of the shower and thunderstorm activity will be to the north and east of the forecast area, though storms may initiate along the northern Sierra crest.

Extended discussion (Friday through Monday)

Extended period will be characterized by large closed upper level low. As is typical with this type of pattern, there’s still a lot of run-to-run model variability and differences in solutions for the end of the week into the weekend. Therefore, not much confidence in exactly how widespread precipitation or convective chances might be heading into next week. At this point, the best chances will be over the mountains and during the afternoon/evening hours as instability is diurnally enhanced. May see a few showers in the valley during the period but again, confidence is low. Regardless, should see cooler temperatures for Friday into the weekend with valley highs back down into the low to mid 70s.