Possible Convective Event Sat Night – Monday

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Extreme heat is expected across northern California through Saturday, with valley temperatures likely skyrocketing into the 108 – 114 degree range Saturday… which would set records across many locations.

To the south, a cutoff low meandering off the southern California coast will strengthen a bit over the weekend as a rex-block sets up and tightens it up. As it tightens… a very moist airmass to the west of the low will be forced into northern California Saturday night through Sunday and into Monday as it gets squeezed between a ridge up in the Gulf of Alaska and the cutoff low off the southern California coast. This small cutoff low will have a bit of a cool pocket aloft. Though not too significant, it will very well be enough in combination with the 1.0″+ precipitable water plume to support mountain surface CAPEs of 500 – 1000j/kg… though, in the valley, values are currently progged around 500j/kg.

The ECMWF and GFS are in decent agreement indicating the low pushing inland Sunday night into Monday, bringing inland the best lift, instability, and moisture to support convection… potentially into some of the lower elevations. It is possible that some convection could develop as early as Sunday, however it remains hard to pinpoint timing and where convection is possible, due to the shorter range models not being nearly as bullish as the GFS and ECMWF, with the SREF and NAM keeping the lower elevations completely dry. This is why I have waited so long to bring an update on this possible convective event, due to these model disagreements.

If the GFS/ECMWF solutions hold and are at least somewhat correct… initially, surface moisture will be very meager. If elevated does indeed develop Sunday,  75% of it would likely be at least partially dry. These types of setups, if they come together as the GFS and ECMWF indicate, can produce spectacular lightning events that continue through the overnight hours due elevated convection not really relying on surface based instability, which fades after sunset. The downside to the spectacular lightning, of course would be potential for fire starts from these strikes that occur with dry thunderstorms.

GFS/ECWMF model  derived graphic.

GFS/ECWMF model derived graphic.

By early Monday morning continuing through the rest of the day, the atmosphere should continue to moisten up, which will lower the dry lightning threat with time.

The portion of this update regarding the convective threat is nearly entirely based on the ECMWF and GFS at the moment. This is key to note, because if these models trend dryer to that of the NAM/SREF, this event will be confined to the mountains. If the event does occur like the ECMWF/GFS indicate, the entire area should be alert for convection (some of which potentially dry).

I plan to have updates nightly updates through Sunday if ECMWF/GFS trends continue. Stay tuned.

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