Sticky and Stormy?

Well, in case you didn't notice, it was really hot today. Downtown Los Angeles got to 98 F and many inland locations were well over 100 F. With dew points on the rise, expect a sticky warm night; I'll be surprised if many locations get below 73 F for the low.

Dew points are on the rise because a massive plume of tropical moisture is surging northward out of Baja. Last week all the models were forecasting this plume to nail Los Angeles with rain and thunderstorms. More recent runs now have the bulk of this moisture moving to our east; Phoenix is forecast to get 2-3 INCHES of rain tomorrow and Tuesday. In fact, even San Diego and OC are likely to see much more action than LA proper.

That said, I do think LA will see some showers and thunderstorms - especially tomorrow. An upper low spinning off the coast will wrap some of this tropical moisture into its weak circulation. Because the moisture is so abundant, I expect that the limited dynamics will be enough to wring out a thunderstorm somewhere ... chances are much higher in eastern portions of LA county (and the I.E.).

Orange County and San Diego are also likely to have increased chances of a thunderstorm and heavy rain, especially on Tuesday. 

Below I've attached two images of forecast CAPE - "Convectively available potential energy" - that is, the higher the CAPE, the greater the likelihood of a thunderstorm. The left image is for 4pm Monday and the right image is for 1pm Tuesday. As you can see, there is forecast to be a little bit of CAPE in our area (in LA tomorrow evening and in OC/SD on Tuesday).

This CAPE combined with weak mid-level dynamics and 99th percentile Precipitable Water values (for this time of year) is very likely to wring out a thunderstorm somewhere. Where and when is anybody's guess. For LA, I'd say tomorrow night is our best bet.

WHERE IT RAINS, THE RAIN COULD BE HEAVY! (And there could be lightning).

This is a very tricky forecast. For one - the models really underperform with these situations - namely, moisture surging up from the South. For two - the flow around the upper low will be offshore at first, turning northerly - and both of those directions are unfavorable for thunderstorm activity in the basin.

As always, stay tuned.

Mika ToscaComment