EDITED AT 07:30 MST TO ADD - Just checked the rain gauge and total here so far is 0.12". At 06:00 am MST ~90% of the 92 stations in the ALERT network had measured rainfall, with amounts generally less than 2/10ths of an inch.
Woke up to rainfall here at 5 am MST (above composite radar plot from NWS TUS radar is for 6 am). The showers and rain developed with the first Pacific, middle and upper-level, short-wave that had been forecast by various models to cross southern Arizona during the past night. Models varied in forecasts of precipitation with this first wave. The water vapor satellite image below is also for 6 am. It shows that the short wave, in the upper half of troposphere, is already along the Arizona/New Mexico border. But there is a smaller-scale feature passing over eastern Pima County at the time of the image, and the showers seem to have developed with this feature. The next Pacific short wave is just off the coast of southern California.
A plot of detected CG lightning flashes through 5 am MST is shown above and indicates considerable thunderstorm activity over northern Sonora. There had been a couple of flashes just on this side of the border at the time of the plot.
Plot of the morning sounding from NWS Tucson is shown below from the Storm Prediction Center in Norman, Oklahoma. The tropopasue is nearly saturated through its depth (red line shows measured temperature along the track of the balloon and green line shows dewpoint temperature). The temperature profile indicates the top of the troposphere (topopause) is at about 350 mb (~ 8 km above the ground level at the NWS office). Winds observed along the path of the balloon are plotted vs height at the right, and are in knots, Precipitable water was calculated to be a bit more than 2/3rds of an inch (precipitable water is the total depth of water vapor measured through the atmosphere by the sonde instrument). It is the amount of PW and the profile of RH that help to determine the likelihood of clouds and precipitation. This is a general overview of what this graphic shows, in response to a question a few posts ago. So, the showers are not surprising given the very moist character of the atmopshere this early morning.
The SPC provides a nice interactive page to answer questions about what's plotted on the diagram as well descriptions of the parameters they calculate from the data. This can be found at:
http://www.spc.noaa.gov/exper/soundings/help/index.html
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