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March 28, 2019 – Unsettled weather continues today with showers, mountain snow showers, and possible thunderstorms. Drier weather Friday into the weekend with more unsettled weather returning early next week.

Discussion

Nearly vertically stacked system with low center near 42.4 N 132.5 W is progged to slowly track ENE as it gradually fills. Multiple embedded vort maxes will track across NorCal today in cyclonic flow to keep unsettled weather. Scattered showers this morning will become more widespread this afternoon as lapse rates steepen.

Highest model CAPE is depicted over the Southern Sac/Northern San Joaquin Valleys invof of channeled vort maxes. Isolated afternoon thunderstorms will be possible with main threat being heavy downpours and small hail. Snow showers will continue in the mountains today with local accumulations up to 6 inches. Snow levels will be around 4000 to 5000 feet today.

Low pressure system continues to slowly fill and migrate towards the PacNW coast tonight into Friday as heights begin to increase over NorCal from the SW. Models keep some lingering showers over mainly the Shasta, Coastal, and Western Plumas mountains Friday invof of additional weak vort maxes moving through in WNW flow aloft. Remainder of interior NorCal expected to see mostly dry conditions Friday as subsidence increases.

Upper level ridging amplifies off the West Coast Saturday with dry NWly flow aloft over the CWA. AMS warms as heights and thicknesses increase. Above normal high temperatures expected Saturday with max temps around 70 in the Central Valley with mostly 40s to 60s for the mountains and foothills.

Models differ with amplitude of upper ridging by Sunday with GFS suggesting some overrunning light precip possible over the northern third of the CWA. EC keeps precip off the CA coast through 00z Mon. Forecast leans toward the GEFS which is a compromise between the two deterministic models. So some light precip advertised mainly over the Coastal range and western Shasta mountains by Sunday afternoon, spreading down to around I-80 Sunday night.

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Extended Discussion (Monday through Thursday)

Operational models consistent with fairly flat upper ridge over the western U.S. on Monday but also light overrunning precipitation over nearly all of the CWA. This warm sector precipitation and high snow levels will precede the passage of a Pacific cold front Monday night and Tuesday. Models indicating that this will be a moderately strong storm system producing moderate rain and snow and breezy south winds. Snow levels should remain below pass levels so mountain travel impacts are likely once again. Precipitation threat shifts northward by Wednesday as somewhat flat upper ridging builds slightly.

Forecast Confidence drops significantly for the end of next week with operational models showing big discrepancies developing by the end of the extended period Thursday. ECMWF dries things out Thursday amplifying the ridge over the west coast. GFS brings in a much wetter solution digging in a trough closer to the coast while projecting a cold frontal passage with rain and snow during the day. Have kept some precipitation chances in but not hitting it hard at this time due to large uncertainty.