Wednesday, August 23, 2017

Curse The Synoptic Pattern And What Happens?


Well I cursed the synoptic pattern yesterday and then saw isolated thunderstorms develop around the area. Image above from Kitt Peak looking south shows two of the storms at 5:35 pm MST. The plot of detected CGs below (from Atmo and Vaisala) is for 24-hours ending at 5:00 am this morning. We had thunder here from a small storm to the west, but only a brief spit of rain that wasn't enough to wet the the courtyard.

Around the ALERT network only 11 sites measured light rainfall amounts of 0.04" or more, with a couple of sites having around a quarter of an inch along east edge of network. Certainly more activity than I expected with yesterday's nasty inversion aloft. It was still present at 00 UTC but it had gotten hot enough during the afternoon to let storms build by it - highs around 103 F at TUS and Atmo.



The sounding this morning (above for 12 UTC) indicates a bit more CAPE today, even with the nasty inversion below 500 mb still overhead. The models have locked onto a weak short-wave that moves north from the huge data void of northern Mexico almost overhead by evening. Satellite loops this morning do indicate that this feature is down there, so a more interesting day on tap.

I've shown three WRF forecasts from Atmo below that all show forecast radar echoes at 3:00 pm this afternoon: Top - the 15 UTC WRF-RRx from yesterday; Middle - 06 UTC WRF-GFS ; and Bottom - the same from WRF-NAM version of model. There is reasonable consistency in the forecasts, with all forecasting strong storms in eastern Pima County. These storms also produce a strong outflow in each forecast.

The short wave, while quite weak, apparently brings some cooler air in mid-levels letting CAPE to increase substantially. This seems reasonable. But, I looked at the WRF-GFS 06 UTC forecast of the TWC sounding shown above - model had basically forecast no inversion as opposed to the actual observation. So, details of the thermodynamic vertical profile will be quite important as the day progresses.

Finally, the vertical wind profile is not very good, since anvils from storms to south and southwest will stream overhead, so the metro area may be close but anviled-out. Another day to watch what evolves.




Tuesday, August 22, 2017

Atmo Obs During Eclipse - Synoptic Pattern Miserable


Received the following email yesterday about Atmo observations during the eclipse. 
-----------------------------------------------------------
Hi Bob,

I saw something that you might be interested in.  I was looking at weather chart summaries from the Department of Atmospheric Sciences here at the university and noticed that when we had a partial eclipse this morning, the air temperature stopped rising momentarily (the measured dewpoint also has a drop around that time, not quite sure if that is coincidental though).  Doesn't seem like a big effect given the short duration of the eclipse but interesting nonetheless.

Thanks,

Patrick Broxton
Researcher
Arizona Remote Sensing Center
School of Natural Resources and the Environment
---------------------------------------------------------------
The incoming solar radiation was just what we'd expect (above), as was the temperature (just below). But what is surprising is the large drop in dewpoint temperature at the beginning of the eclipse - around 7 F (green below). The time series for RH is at bottom. This seems counter to what might be expected, i.e., with decreased mixing the dewpoint might even increase a bit during the eclipse.

I checked the observations at DM and TUS (note that observation time-series remain badly screwed up at TUS - this has continued for two weeks or so - not good) - and both sites experienced the drop in dewpoint also. So what was gong on? I also noted that winds at all three sites shifted to the west as the eclipse began. So, perhaps dry-air advection from west of metro caused the large drop in dewpoint. However, it is not clear to me why the winds shifted. Any other thoughts on this most appreciated.



As for August weather - the synoptic pattern remains miserable, with the dominant 500 mb anticyclone to our south and southeast and shifting only slightly north during next several days. The warm air, in the mostly southwesterly flow above 700 mb, is producing a nasty inversion just below 500 mb. Isolated storms likely to return to Cochise County but more grim here at low elevations. 

August has been a real bummer of a month, after the record setting character of July. Last and only significant rainfall here at house was on August 13th. With slightly more than a week left in the month, I am wondering if the pattern will change enough to bring another significant period of storms to the metro area. Most interesting thing in long-range models is forecast potential for a hurricane affecting south Texas by the weekend.

Monday, August 21, 2017

Serious Over-Forecasts Yesterday -Miscellany Today


Yesterdays forecasts (me, NWS, and models except for 15 UTC WRF-RRx) seriously over-forecast the likely hood of thunderstorms for all of southeast Arizona. I thought mountain storms would occur and inch westward, closer to Tucson, NWS had 30% POPs for measurable rainfall at the airport last evening, and most models also had rainfall over portions of southeast Arizona. The exception was the WRF-RRx which forecast absolutely nothing, which is what occurred. The suppressive impacts of the weak short wave that pulled northeastward toward Colorado were much greater than anticipated. So it goes in summer forecasting.

The 24-hour plot of detected CGs above ends at 1330 UTC this morning (from Atmo and Vaisala) - note that the lack of thunderstorms covered a huge area extending from southern California eastward across New Mexico. The WRF forecast shown in previous post was really bad across New Mexico. Luckily for most weather folks, today's eclipse is absolutely top news, allowing yesterday's lack of storms and rain to be totally ignored. 

Dry air encroaching from the west at lower-levels, and dry air already aloft, make it look a repeat for next day or two. This morning's sounding plot for TWC (below) is even more miserable than yesterday's.



As for the eclipse - the early morning visible image (above from 1330 UTC) shows most of the Northwest clear and only one band of clouds from south Idaho across northern Wyoming as a potential trouble-maker.  Things much more iffy from Nebraska eastward.

Mean while, far out in the Pacific, hurricane Kenneth has strengthened to a Category 4 storm - IR of Kenneth below also from 1330 UTC.


Sunday, August 20, 2017

Moisture Increase Continues Slowly


Nice view of Baboquivari in the sun at 7:07 am this morning - above - with dark cloud band and patches of light showers visible also.


The map of detected CG flashes above (from Atmo and Vaisala) is for 24-hours ending at 1:00 am early this morning. Thunderstorm activity stayed over higher terrain well to east and south east of Tucson area - distressingly little activity over Sonora to our south. There has been no rain detected across the ALERT network for past 5 days or so. 


Morning sounding from TWC (above) is quite dismal, with just a small layer with CAPE. The PW is up above 1.33" now, but there is little hope of mixing out the surface-based moist layer without a considerable increase in Td from 850 to 600 mb (note winds are southerly below 700 mb so we may see some increases. The wind profile is, however, quite nice with distinct steering flow form mountains toward the west.  I suspect that thunderstorm activity will move much closer today but still tend to remain over the mountains - perhaps some light sprinkle-showers moving out over lower elevations. A strong outflow form the east would also be helpful.

The WRF-GFS from 06 UTC seems a bit more optimistic for lower elevations of the metro area - so a wait and watch kind of day, which has been pretty much the story for August.


Saturday, August 19, 2017

Quick Look At WRF Forecasts From Last Night


View of Catalinas at 06:00 am MST this morning showing both middle and high clouds.

Two weak outflows moved into southeastern Arizona during the early morning hours increasing low-level moisture so that PW values have inched up to around an inch.


Shown here are the 06 UTC WRF forecasts, from Atmo, of total precipitation through 11:00 am next Tuesday, the 22nd. The GFS version (above) remains mostly dry through the period, while the NAM version (below) is considerably wetter.

There is a weak inverted trough at 500 mb moving westward along the Borderlands today and perhaps increased storm activity that area will help increase chances for storms here in eastern Pima County. 


Friday, August 18, 2017

Moisture Creeping Back


A number of contrails crisscrossed the morning sky just before sunrise this morning. It was cool and very comfortable along the Rillito Pathway - perfect for morning walking.


The daily average dewpoint temperature (above, from NWS) continued to fall here at Tucson yesterday, but it may start to recover some today, as convection creeps northward along the Mexican mountains of northeast Sonora. The diurnal circulations near the north end of the GoC have been bringing higher dewpoints northward into southwestern Arizona - as per Td time series below for Yuma. A large MCS moving into the central to north GoC would really help accelerate the slow, diurnal processes.



Above map (from Atmo and Vaisala) shows CG flashes detected over Mexico during the 12-hours ending at 07 UTC last night - note the very sharp delineation zone between considerable storm activity and complete suppression. The MIMIC map of TPW for 0600 am MST - above from CIMSS - shows a very strong PW gradient from south-to-north along 30 degrees north. The local area of higher PW along the Arizona/California border north of Yuma may be partly due to irrigation?


Wednesday, August 16, 2017

Harris Hawks Hunting This AM

There was a pair of Harris Hawks hunting through the Natural Resources Park by the Rillito this morning. First time I have seen these two - they were encroaching on the territory of two Red Tails that nest in large gum tree by the Rillito pathway. Four photos of pair shown below.