Monday, July 25, 2016

Nice Sunrise


I have to be away this morning and so will just have a cursory post. Very nice sunrise today - above looking north from campus and below looking east-northeast from house.

Another very down day for eastern Pima County - only 2 sites had rainfall across the ALERT network - 0.51" at Arivaca and .041" at another site.

Complex day today with much debris cloud and more outflows during night. The KEMX NWS radar has been down several days and that complicates things also. The 06 UTC forecasts from the WRF models at Atmo both forecast significant thunderstorms for eastern Pima County later today. However, neither run from 00 UTC forecast much in the metro area, so we'll see what the 12 UTC runs forecast.


Sunday, July 24, 2016

Another Outflow Across Southern Arizona

I have been out cleaning up tree and limb damage from the microburst event of four weeks ago and will just take quick look at the weather setting this morning.

Yesterday was another completely down day over most of southern Arizona, except for along the Borderlands and a storm in northeastern Cochise County. The 12 UTC WRF runs seemed better than those from 06 UTC. The plot of detected CGs below is from Atmo and Vaisala for 24-hours ending at 6:30 am MST this morning. There was no rainfall recorded across the entire ALERT network yesterday. Our really bad July continues.



There was significant thunderstorm activity in northern Sonora and IR image above was from 05:30 am. The storms have sent several moist outflows into southern Arizona. The current Doppler velocity image below is from Yuma at 1.8 degree tilt and indicates a fairly deep outflow with wind speeds of around 30 kt. During past few hours winds at Yuma have been from the south-southeast with gusts as high as 43 mph. Dewpoints there are running in the low 70s.




The morning TWC skewT plot above continues with about 1.5 inches of PW. The layer below 700 mb has considerable CAPE, but now has a capping, old elevated boundary above. So CAPE and CIN are doing battle again today. The 500 mb pattern is very chopped up and winds aloft are light and variable below 300 mb - not good, TS Frank has helped push high moisture into southern Arizona (below is CIRA blended PW analysis for 6:00 am) and values of PW are 1.5 inches and higher over a large portion of the area from Tucson west. However, other features just are not coming together well. Even though there is a weak inverted trough at 500 mb to our east, models continue to keep storm activity today along the Borderlands and into central Pima County - areas with higher elevations than the metro region. What steering flow there is would try to move storms from the Catalinas toward the metro - so that's a bit of a positive. Back to the yard mess.


Saturday, July 23, 2016

Very Suppressed Yesterday But Interesting Possibilities Today


Yesterday was the most suppressed day of the past few and was characterized locally by many orphan anvils with no associated precipitation by the time they were overhead. View above is from 6:00 pm MST last evening. The CG flash density plot below (from weather.graphics and Vaisala) shows the dearth of thunderstorms over most of southern half of Arizona yesterday and last night.

There was essentially zero percent coverage of rainfall at the ALERT sites during past 24-hours, as only 1 of 93 sites measured rainfall of 0.04".



However, the situation appears to be improving today. TS Frank is apparently going to pass close enough to southern end of Baja to push a surge of higher moisture into the Southwest - particularly tomorrow and Monday. The above graphic shows MIMIC PW analysis from Univ. of Wisconsin CIMSS for 6:00 am this morning. High values of PW are already into parts of Arizona, even though Frank is currently just south of 20 degrees north at 110 degrees west.

The morning sounding from NWS TWC on campus (below from NCAR RAP/RAL) has 39 mm of PW - up from yesterday's brief dry down. The steering winds are very good for organized storm events, as they would move storms toward the west-northwest, leaving the anvils trailing behind. Low-level moisture should continue increasing some during the day. If the boundary layer mixes out to a bit above 700 mb, I estimate CAPE at about 1000 J/kg, but with a layer of CIN requiring outflow help to get storms into lower elevations.



The WRF-GFS forecast from 06 UTC last night forecasts a large area of storms into the metro area around 8:00 pm (above). The GFS version did well picking up the nocturnal storms and near-severe outflow on Thursday night, so I'm showing that version here. The timing Thursday was too fast in the model forecast by 3 hours or so. The NAM version also forecasts nocturnal storms, but later than the GFS version and has them dissipate near the Pima/Cochise County line. The GFS versions 10-m wind forecast, below also valid at 8:00 pm, indicates the possibility of a very strong outflow impacting the metro area after dark.

Currently, the NWS forecast for TUS indicates a sunny, hot day followed by a 10% chance of thunderstorms after 5:00 pm through 5:00 am tomorrow. The forecast after that is for a 30% chance of rain at the airport every 12-hour period through the next six days. Seems like folks there couldn't decide which of the coming days will have a better chance of storms, thus the climatological type homogeneous forecast.


Friday, July 22, 2016

Near-Severe Outflow Event Early Morning Hours Today

Ron Holle sent the following:
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Bob-

There was a major wind event at our house I Oro Valley around 3 to 3:30 am this morning. The house was shaking and wind was whistling around the edges – sounded like Boulder! No lightning or rain.

The airport had gusts to 47 mph a little earlier, and D-M reached 38 mph. There was a power outage here at Vaisala around 1:30 am.

Was it an outflow?


Ron
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I hadn't looked at the surface obs when I did the morning post today. But the following stations had gusts over 40 mph early this morning:

Mt. Hopkins         G61 @ 2:19 am
Pioneer Airfield   G 54 @ 12:56 am
FHU                     G 51 @ 12:43 am 
TUS                      G 47 @ 0153 am

Basically, I found that all of the observing stations from FHU to Nogales to Sells to PHX to Muleshoe Ranch back to FHU had early morning gusts of 30 mph or more from the long-lived outflow. It developed as storms moved from Mexico into southwest Cochise County around midnight and passed Sky Harbor at 4:40 am MST, with the visibility reduced to 3 miles in dust. The only sites within the large area outlined that did not gust to 30 mph or greater were Sollers and Rincon RAWS sites at high elevations.

I could find no really strong, Boulder-like winds in the MesoWest data in Oro Valley, but these sites are further west than Ron, who is nearer the west end of the Catalinas, where there may have been some orographic enhancements.

I also took a look at the 00 UTC runs of the WRF models and found that, while there was nothing forecast by the NAM version, the GFS version did forecast a large, nighttime outflow.


The WRF-GFS radar forecast above was valid at 10:00 pm MST last night and the 10-m wind forecast below was valid at 11:00 pm. The location of the outflow event was very good, although the actual event occurred 2 to 4 hours later than forecast.


Graphics With Strange Color Schemes

Over past decades meteorologists have tended to use certain colors of contours and shading to denote the character of the fields shown. For example, moisture/precipitation fields have usually been depicted using greens for higher values and browns for lower. Temperatures have been shown in blues (cool colors for colder conditions) and reds (warmer colors for hotter conditions). For example, the standard depiction of cold fronts in blue and warm fronts in red. However, with the huge proliferation of graphics during recent years, these old approaches seem to be slip sliding away.


Graphics above are from the Tucson NWS webpage and relate to precipitation during the first third of the NWS defined monsoon calendar period from June 15 through September 30th. Upper left shows estimated rainfall for the period (June 15 through July 20) - source is unknown, but may be some combination of gauge observations and radar estimates. There is some green but low amounts are in cool colors. At lower right is percent of normal with the color scale completely reversed relative to upper left; a great way to cause some confusion.

Graphic below is also percent of normal, but for July 13 through 19. This plot uses more typical colors for dry and moist areas, and is from NWS Climate Prediction Center. The useful legend at bottom provides some quantitative information about what has been plotted and gridded. The week shown was certainly a grim one for the Southwest and most of northern Mexico.


Higher Elevations More Active Yesterday


Considerably more thunderstorm activity yesterday, as per detected CGs above from Atmo and Vaisala. Storms stayed mostly to higher elevations and avoided the metro area, except for one afternoon storm out to the west. Once again less than 20% of the ALERT sites measured rainfall, with amounts light except for 0.67" at Manning Camp in the Rincons.


Time-series of GPS PW from Atmo above, show values decreasing this morning over southeastern Arizona, which may reduce CAPE some for the afternoon. The WRF-NAM forecasts storms again sticking to higher elevations (forecast of composite radar echoes below is valid at 6:00 pm MST this evening).



Two new TSs this morning - NHC named the one closer to Mexico first, so the storm of interest for us is Frank (above). The morning NHC forecast for Frank is shown below. The forecast track is marginal for the storm to generate a strong GoC moisture surge and models seem to be trending further west with Frank's forecasts. So, it will be something to watch, but a more easterly track would definitely be more interesting.


Thursday, July 21, 2016

Play It Again


There was considerably less thunderstorm activity over much of Arizona yesterday versus that on Tuesday. For example, only 15% of the ALERT sites in eastern Pima County recorded precipitation yesterday, while 60% of the sites had rainfall on Tuesday. Amounts were quite light both days. Here at the house there was an early afternoon thunderstorm from a small cell to our south - but no rainfall.

With a bit more than a week left in July, we need a decent storm or this will be driest July here since I started my records.


This morning's skewT plot for TWC continues very similar to past several mornings. However, winds in mid-levels are southerly at 15 to 20 kts and winds above that are a bit chopped and have similar speeds - so anvil shading may not spread ahead of storm cells. Further, mid-level temperatures have cooled a bit, and with no mid-level inversion, thunderstorms should develop late morning over the mountains. What happens then? - we'll just have to watch. Several cells did form at low elevations yesterday - and getting a cell developing just to our south will provide the best chance for rain here.


There was apparently no 06 UTC run of the WRF-NAM. The WRF-GFS forecast for TWC skewT valid at 2 pm is shown above. Forecast wind profile is uni-directional from the south-southeast and model has mixed boundary layer out to 600 mb - perhaps a greater threat of downburst winds today. Although the model calculations indicate CAPE at 1400+, a more realistic estimate gives about 750 J/kg. 

The model forecast for 500 mb valid at noon today (below) shows the wide band of cooler air over eastern Arizona, as well as a very distinct anticyclone center east-northeast of El Paso.



The WRF-GFS forecast of composite radar echoes above is valid at 4:00 pm MST indicates a very stormy afternoon over eastern Pima County. However, the GFS version of the model has tended to overdo storms recently. The NAM version from 00 UTC last evening is much more subdued - so again we'll have to watch how things go later this morning.

The eastern Pacific continues very active, and there is a bit of longer-term hope in this morning's NHC outlook (below). The system that could become Georgette is forecast to head much closer to Baja than past storms - providing some possiblities for a serious GoC surge by early next week.


Wednesday, July 20, 2016

More Of The Same?


Yesterday brought two rounds of storms and some rainfall around eastern Pima County. The afternoon round stayed mostly out of the metro area as per post below. Storms after dark moved in from Cochise County and provided a lightning show, but only light rainfall, as these storms also weakened at lower elevations. 

Across the ALERT network 60% of the sites measured 0.04" for the 24-hours ending at 5:00 am MST this morning - greatest coverage for quite a while, but amounts were generally light except for a couple of sites in the Catalinas. Evening event brought thunder and 0.01" here at the house.


For contrast/comparison here are the morphed and blended PW products from CIMSS (above) at Univ. of Wisconsin and from CIRA at Colorado State Univ. (below). Both are for 11 UTC this morning. Very high PW remains not too far to the south, just waiting for a real push. Amounts over 50 mm are shown in amber tints at top, but in red tones at bottom. Highest values above are with Tropical Storm Estelle.




The morning sounding plot for TWC (above) remains similar to last couple of days. However, mid-level temperatures have warmed a bit and the wind profile has weakened in speed, and become even more variable wrt the directions. So, another day favoring the higher elevations of southeastern Arizona.


Finally, out of curiosity, I looked at the GEFS plumes for next few days. The plot above is for CAPE, indicating a dry-down around the 23rd and 24th. The QPF forecasts below seem unresponsive to the fairly large CAPE fluctuations - some members manage, somehow, to forecast light showers at TUS, even during the period of almost no CAPE. The GFS (blue) forecasts a CAPE spike on the 25th.

As I had mentioned before, within a stagnant, summer 500 mb pattern, these forecasts probably mean little beyond days 1 and 2. All of this leads to the no-skill, default forecast of mostly climatological POPs at TUS for next seven days.


Tuesday, July 19, 2016

Missed Again



I was out and about between 2:00 and 3:00 pm MST this afternoon, and there were storms and CG flashes all directions. But none of the storms really moved into the low elevation metro area. We had strong outflows of 30 to 40 mph and some dust. But net result for last several hours - shown above in plot of detected CG flashes last 3 or 4 hours (from Atmo and Vaisala) - appears to be another classic Tucson donut hole.

Severe Thunderstorm Hits Sky Harbor


Severe thunderstorm hit portions of the Phoenix metro area yesterday afternoon, with Sky Harbor measuring low visibility and gusts to 63 mph. Photo above is by Bruce Haffner - posted to Twitter (see either Mike Olbinski's or Bryan Snyder's Twitter links). Looks to be a fairly large downburst from a high-based storm.

Meanwhile, from far to the southeast, Mike Leuthold posted the photo below from Paradise in the Chiricahua Mountains.



There was a bit more storm activity over eastern Pima County yesterday - the CG FD for 24-hours ending at 6:00 am MST this morning (above from weather.graphics and Vaisala) shows high flash density on north side of the Catalinas. Also there is a bit of a donut hole over the metro Tucson area. The Catalinas sector of the ALERT network (below) shows heavy rain amounts on the north side of the mountains. We had a light shower here at the house after 5:00 pm that left 0.02" in the gauge. Most of the metro area had only light sprinkles yesterday.



This morning's sounding from TWC continues with about an inch and a half of PW and moderate CAPE. Steering winds are from the southeast at 10 to 20 kt, while upper winds are light. This looks to be a fairly decent sounding for more heavy storms this afternoon and evening. Mountain locations favored, but decent chance for outflow triggered storms in the metro area. 

The WRF-NAM forecast from 06 UTC for rainfall through midnight tonight is shown below. The GFS version is once again more active for eastern Pima County.