Monday, July 06, 2015

Storms In Town Yesterday Lead To Very Humid Morning

There were several strong thunderstorm cells in the metro area and Catalina foothills yesterday afternoon. Movement was slow and there were some locally heavy rainfalls. Campus webcam view at 2:44 pm MST yesterday shows storm along the foothills and also another rain shaft to the north of the west end of mountains. Development of storms in the metro was aided by an outflow from the south. The plot of CG flash locations below (from Atmo and Vaisala) is for 24-hours ending at 1:00 am this morning, and indicates most numerous storms were in central Pima County - relatively quiet again to the east of metro Tucson. Storms avoided Maricopa County until the early morning hours today, when a couple of storms moved west-to-east across portions of metro Phoenix.

Here at the house we were between cells to the south and the storm on the foothills shown above. We had considerable thunder but only a bit of rain from the nearby cells - total here 0.11". Across the ALERT network 63 of the sites measured rainfall, with a few heavy reports - 6 sites had half an inch or more while 2 sites measured over an inch. See second below for rainfall through 6:00 am for the metro west sector.

When I walked this morning the ground was damp for first time in quite awhile and rain was apparently a bit heavier just north of here. One large puddle area (which supports spadefoot toads) had enough water in it to perhaps bring them up out of the mud.

An interesting battle on tap tomorrow and Wednesday. The large and complex middle and upper level cyclone off of California (see water vapor image above from 1330 UTC) has brought upper-levl dry air well into the Southwest and across much of Arizona into New Mexico. However low-level moisture remains high (below is 1100 UTC blended MIMIC PW from CIMSS) indicating amounts of 50 mm or more covering almost all of the GoC. The battle will be in the vertical, as the dry air tries to mix down to low-levels.

This morning, the lower-half of the troposphere is very moist, while levels above 500 mb are dry - above is TWC skew-T plot for 12 UTC. Winds below 500 mb remain quite light and the only steering winds of significance are above and from the west - not a particularly good direction for this part of town. Anvils will also blow off toward east, another negative.  However, PW is high (1.62 in/41 mm) and CAPE is also substantial, with a low LFC. So storms should develop early today, once there is a bit of heating. Where they move after development will be more uncertain. If storms develop over the Tucson Mountains they could actually have some chance of making it this far east. The visible satellite image from 1330 UTC (below) shows pockets of clear skies this morning interspersed with middle-level cloud debris. There should definitely be more sunshine and heating today than there was yesterday.

Will there be a brief dry-out at midweek? We'll have to watch the dry air aloft and see how far it can mix down into the boundary layer.

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