Unfortunately I don’t have a ton of time for a full update this evening so I’ll save analysis of this weekend’s rain threat for tomorrow morning’s post. In this post I’ll look at tomorrow’s severe weather threat.
Today’s forecast worked out pretty well. Mostly sunny skies were reported across the area with only some high thin clouds to make a feeble attempt at blocking the sun. Temps soared as forecast into the 90’s almost everywhere. Even behind the sea breeze front, temps were near or over 90. Dew points dropped slightly, as forecast, as the atmosphere mixed out but it still felt quite stifling. Ready to do it again tomorrow except with even more humidity?
The plume of tropical moisture, believe it or not, was sitting just to our south today. The humidity you felt was mostly due to yesterday’s rain. Tomorrow, however, the full force of the tropical airmass will be pointed right at us and dew points will soar into the 70’s and stay there right on through the day (there is simply too much moisture in the air tomorrow to mix out like today). Meanwhile, a cold front will be approaching from the NW and an upper level disturbance will be moving into the area from the west (right black line on W edge of blue). The front and the disturbance will act as a trigger for some storms tomorrow. See those PWATs >2″ (blue colors) over coastal areas? Those PWATs, 3 standard deviations above the mean and in some cases never before seen in GEFS climatology, will provide plenty of fuel for downpours. Will there be any fuel for other severe weather? Absolutely.
As temps soar into the 90’s again tomorrow, the atmosphere will become quite unstable. CAPE values in excess of 1,500 j/kg will support strong storms, some of which could be strong enough for gusty winds. The atmosphere looks far too warm for significant hail but as a result of all the moisture, the atmosphere will be primed for a tornado or two. They look weak at this point but be prepared to seek shelter if you do come under a tornado warning. Also have a plan to be notified of that tornado warning if it’s issued for your area. Again, this is by no means a tornado ‘outbreak’ but one or two spinups are possible.
The final ingredient, the organizer, looks not fantastic but good enough for at least some severe storms. 0-6km shear between 20 and 40 knots isn’t fantastic but it does raise the isolated severe storm red flag. The most important thing to note about tomorrow’s storm setup is that the biggest threats will not be gusty winds or hail or tornadoes. The biggest threat will be intense lightning and very heavy rain that could lead to flash flooding. It’s been so dry that the soil has ‘forgotten’ so to speak how to absorb moisture. This means that any heavy rain that suddenly falls will run right off and into the nearest road/ditch, some of which won’t be able to handle the large volume of water at once. Remember, turn around don’t drown and when thunder roars, go indoors.
I’ll be back tomorrow morning with a full update on both the severe weather threat and the heavy rain threat this weekend.