As mentioned in the previous post, we were concerned about the potential of organized thunderstorm outflow creating favorable conditions for blowing dust, as well as previous heavy rain activity increasing the potential for flash flooding in portions of Southeast Arizona yesterday (Sep 2) and today. We have been trying to use LIS data as part of our process in determining the threat of both of these problems. Yesterday was a mixed bag as I briefly outline below with less than full cooperation from the atmosphere.
Convective initiation occurred in locations we expected (similar to the WRF output posted previously), however we were unable to get the chain reaction of outflows that we hoped for. We had problems in many valley locations (especially the Tucson Metro area) with early debris cloud and then anvils from early convection blocking solar insolation. We also underestimated the eastern extent of a modest low level drying trend filtering in from western Pima county.
Below is a loop of velocities with some observation and warning overlays early yesterday afternoon. The initial 45 kt outflow from the SVR southeast of Tucson attenuated rapidly as it approached Tucson. Readings from Davis-Monthan AFB on the southeast side of Tucson at 2137Z showed a gust out of the SE at 30kts, and shortly later Tucson International Airport (a couple of miles further west) registered 23 kts. By the time the outflow was west of Tucson it was difficult to detect. There was no additional activity along this outflow in Pima County and it certainly wasn’t strong enough on it’s own to generate any dust problems by the time it got to areas we were concerned about. The initial area that it started southeast of Tucson does have dust issues at times, but referring back to the soil moisture imagery from the previous post, things were pretty wet there.
It was an active day however. Below is a composite post of the Severe Thunderstorm (yellow) and Flash Flood (green) products we issued yesterday. When you compare to the 09z LIS output posted yesterday, the Flash Flood warnings were issued in an area with relative soil moistures above 70 percent (posted again for convenience).
We once again have a favorable atmospheric profile for strong storms today (Sep 3), but with a little more convective inhibition to overcome and continuing issues with cloud cover. We do have a stronger impulse embedded in the southwesterly flow that will push into our area late today and this evening. Most standard and mesoscale model output (including latest UofA WRF and national HRRR) show increased coverage and organization of thunderstorm activity by late afternoon, especially west of Tucson. This seems very reasonable, keeping the aforementioned caveats in mind.
A look at today’s LIS output shows that soil conditions are even more favorable in the areas of concern west and northwest of Tucson. Especially in eastern Pinal and Maricopa counties with widespread values below 15 percent:
Some of the special communications to our partners and the general public yesterday morning extended into mentions of issues for today as well. We will adjust our weather story and social media posts to reflect the latest information, but our message is similar to yesterday. We will again coordinate with Phoenix about any possible coordinated dust headline later this morning. An example of the partner email we sent yesterday below:
We continue to use LIS data to increase our awareness of potential flood prone areas, as well as potential problems with convective dust storms. An example below of interaction with the Phoenix office on 12Planet this morning where we discuss possible dust problems and inserting blowing dust in weather grids:
Below are this morning’s volumetric and relative soil moistures. It highlights 2 concerns for us today. The first is the area of heavy rain we saw 36 hours ago in the Tucson area and surrounding mountains is still very much reflected in soil moistures. This will be one of the main areas of concern for potential flash flooding today. The second concern is dust, with dry antecedent soil conditions a concern in favored blowing dust areas Pinal, Maricopa and central Pima counties.
Finally, below is a look at the University of Arizona WRF-NAM 10m wind showing some very interesting convective outflows. The first generated around the Tucson area this afternoon from the strong potential of our atmospheric profile today, and the second southwest of Tucson after 00z from the influence of an impulse embedded in the moist southwesterly flow early this evening:
So that will be what we’re watching closely for today. After a review of the 12z data, the day shift will coordinate with the Phoenix office on the possible issuance of an extended long fuse Blowing Dust Advisory. We will also be issuing a partner coordination e-mail to local and state officials on this potential, and a heightened awareness weather story for the web site and social media.
Just a quick initial note to show a few things we have been looking at with NASA SPoRT LIS and some of the satellite imagery so far.
1) We have had a limited sample size so far this year, but we have been looking at integrating LIS volumetric soil moisture and relative soil moisture into the Dust Storm decision making process (both short fused warnings and our longer term new “Watch”-like product). Here is the 0-10cm Volumetric soil moisture image from Wednesday, coincident with a moderate outflow (up to 20 kts) that pushed northward from Pima county into Pinal County. Not a strong outflow, but one that can generate enough dust for reduced visibilities (likely not to warning levels).
In this case, with percentages in the 18 to 21 percent range in the origin area and 12 to 14 percent in the path of the outflow, there were no indications whatsoever of reduced visibilities. We will be watching to see if the (relatively) elevated soil moisture in the origin area is any indication of limited potential and strength of blowing dust issues as the season progresses.
We are also trying to incorporate the more shallow volumetric and relative soil moisture levels into heightened awareness for flash flood threat areas daily. More on this later.
2) We have been impressed with the superior accuracy and versatility of the CIRA LPW products. Here is a recent comparison with the AMSU and SSM/I Blended Total Precipitable Water product:
About 1.3″ from CIRA versus 22mm (0.86″) for the Tucson area. 12Z sounding showed 1.76″. Add afternoon mixing in there and 1.3″ worked much better. With our typically deep boundary layer and elevated subcloud layer, the individual lower layers of the LPW have also been useful to help determine the threat of dry vs. wet microburst activity with initial convective development.
We continue to evaluate the NESDIS QPE and Passive Microwave Rain Rate imagery. More on this later as well.