Central/North Valley Thunderstorm Threat Today

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A band of stratiform precipitation sagging south through the Sacramento area this afternoon may give way to some breaks in the clouds in the north/central Sacramento valley this afternoon into the early evening. Though clearing likely won’t be widespread… increasingly cooler upper level temps above surface temperatures in the low to mid 60s will contribute to some slight instability.

Band of light to locally moderate rain sagging south into the southern Sacramento valley.

Band of light to locally moderate rain sagging south into the southern Sacramento valley.

Though instability is meager… the HRRR indicates bands of stronger convergence pushing into the valley… potentially enough to aid in the development of convection. Usually the HRRR has 60 – 70% accuracy with the development of convection, just not individual placement of storms. Though the HRRR has been consistent with the development of convection… it has not picked up on the band of precipitation pushing southward. Because of this… it may be underestimating evaporation cooling from precipitation and thus lowering surface temperatures a bit (weakening instability). Then again, it has been noted that regions with wet grounds are more conductive for convective development due to increased low level moisture availability.

Overall, I give the highlighted region below a 30 – 50% probability of a thunderstorm developing. Thunderstorms today would be most capable of some gusty winds and very heavy rainfall given a 1.2 – 1.4″ precipitable water plume working its way inland this afternoon/evening.

Best thunderstorm threat region.

Best thunderstorm threat region.

The HRRR indicates much stronger available helicity than other short range/high resolution models… with upwards of 200 – 500 M2/S2 values possible near convection due to mesoscale wind changes and strength increases in the storms. If the HRRR were to be correct… thunderstorms could potentially rotate and become more capable of hail and possibly a funnel cloud or tornado. Will keep an eye on this through the afternoon and evening to see if any convection that develops does attempt to rotate like the HRRR suggests.

17z HRRR indicating a few not-so-weak showers and thunderstorms in the north valley around 4 - 5pm.

17z HRRR indicating a few not-so-weak showers and thunderstorms in the north valley around 4 – 5pm.

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