Friday, September 08, 2017

Complicated Day Today

Yesterday first - view of the Catalinas at 4:00 pm yesterday afternoon. We had just had thunder from a dissipating Cb coming off the Catalinas - but not a drop of rain. Note the dirty air that has been around for quite a few days now. Art Rangno has discussions and photos regarding the cruddy air - link to his blog to right.

Plot above is 24-h rainfall across the ALERT network through 5:00 am MST this morning - classic case of isolated thunderstorms with light showers (see 24-h plot of detected CG flashes below ending at 1:00 am this morning - from Atmo and Vaisala). Locally rain reports of 0.04" and more were mostly at low elevations - somewhat unusual. Here at house we had brief, but fairly heavy shower around 7:00 pm - small cell developed nearly overhead - did not note any thunder or flashes - but got 0.11" in the gauge. The lightning plot also shows that most significant storm activity was to our west and northwest, as forecasts by models. There were a number of severe wind gusts reported along the lower Colorado River, and PHX had thunder with gusts to 54 mph last evening.

Today the situation is quite complex - 500 mb analysis above (from SPC) is for 12 UTC and shows Irma just coming into the domain. The trough along the West Coast has nudged the huge ridge eastward. There appear to be weak anticyclonic circulations over northern Idaho, near the Four Corners, and most notably over Texas. The sounding from Empalme seems to indicate a weak short-wave coming northward toward Arizona from low-latitudes, which would be quite favorable for our area.

Have taken a quick look at WRF forecasts from Atmo - shown here are composite radar forecasts - above is from 00 UTC WRF-GFS and is valid at 4:00 pm this afternoon; while below is from 06 WRF-GFS valid at 2:00 pm today. The NAM versions are a bit less active. The 12 UTC WRF-RRx seems a bit out of whack, with heavy morning storms coming north from Mexico and crossing metro area around noon. This version of the WRF seems to be bringing an MCV (see the IR image at bottom from 2:30 am this morning) from the Mexican storms right across us.

Very much to watch today - including the possible large outflow that 06 UTC WRF forecasts to move northward across Pinal into Maricopa County with severe winds late afternoon.

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