Dry and warm today, weak systems bring cooler temps to start the week

April 22, 2017 – Dry today then several Pacific storms move through bringing cooler temperatures and mainly light precipitation.

Discussion

A narrow band of showers continues to move through parts of the area this morning and weaken. The showers should be ending by 11 am. High clouds spreading into the region will help to cool temperatures today into the low to mid 70s for the valley. Another weak wave will spread through the region tonight and may bring some brief showers to some locations over the northern end of the valley and surrounding foothills and mountains.

Previous discussion (Today through Tuesday)

High amplitude upper ridging shifting east into the Great Basin as Pacific frontal system approaches. 88-D Mosaic showing some associated frontal precip along the NW CA coast attm. While negatively tilted upper trough lifts into the PacNW today, associated surface boundary over NorCal undergoes frontolysis. Thus not expecting any measurable precip to reach into Interior NorCal today. Main impact will be some cloudiness and about 5 to 10 degrees of cooling.

Additional vorticity maxes move across northern portions of Interior NorCal tonight into Sunday morning, leading to a slight chance of a few light showers mainly over the mountains of Shasta and Western Plumas counties. Dry Sunday afternoon into evening with northwesterly flow aloft. Minor cooling expected tomorrow as heights and thicknesses decrease slightly.

Next frontal system spreads into the PacNW Sunday night into Monday. Associated 130+ kt jet becomes quasi-stationary over Southern Oregon as NorCal remains under unfavorable right front quadrant. IWVT showing extensive moisture plume along south side of jet but also indicates some weakening of the plume as it moves into Interior NorCal. Thus given weak dynamics but available moisture, expect mainly some light precipitation possible over portions of the forecast area late Sun and Mon. Heights increase in the EPAC Tuesday but deep moisture plume will keep a threat of some light precip over portions of the CWA Tuesday. Remaining on warm side of jet, snow levels will generally be near to above pass levels with limited travel impacts.

Extended discussion (Wednesday through Saturday)

Mainly dry northwesterly flow expected across interior NorCal during the extended period as models are in general agreement with upper ridging building across the eastern Pacific. A couple fast moving weather systems are forecast to move over the ridge and may bring a few showers to the northern mountains and northern Sierra Wednesday and Thursday followed by breezy north winds at the end of the week. Temperatures will remain a little below average for late-April.