Tuesday, August 14, 2018

Totally Suppressed Yesterday

The newspaper this morning reports the first drowning due to flash flooding this summer in metro area. The heavy storm Sunday afternoon/evening that moved from Vail toward I-15 (see previous post) flooded washes in that area. One car was washed away and the driver perished.


The southern half of Arizona was as suppressed yesterday as it has been in many weeks. Appears there was one lonely thunderstorm off in far southeast corner of the state. The plot of detected CG flashes above (from Atmo and Vaisala) is for the 24-hours ending at 7:00 am MST this morning.

The outlook for storms that would be marginally severe yesterday was definitely a bust. The TWC 00 UTC skew-T plot below shows that the well-mixed surface BL only built to about 800 mb - very shallow, and requiring considerable lifting to release the sliver of CAPE that was present. The PW held steady at about an inch and a quarter through the day. The thermal profiles seem to indicate several layers of subsidence above the BL, which led to the abrupt dissipation of mountain buildups during the mid-afternoon.



The strange upper-air pattern continues, as the mid/upper-level cyclone remains blocked over Kansas. Here in the Southwest the 500 mb anticyclone center has migrated to near the Four Corners (12 UTC analysis above from SPC). However, up at 250 mb (below) the center of the anticyclonic circulation is shifted far to the southeast, i.e., near Del Rio, Texas.


The TWC sounding, below, for this morning (skew-T and analysis from SPC) shows an increase during the night of PW, up to 1.65 inches, leading to considerably more potential CAPE than the evening sounding displayed. But the thermal profiles indicate that several layers of weak subsidence remain aloft. The BL will likely build to a deeper height today, but considerable lift will still be required to produce thunderstorms at low levels, because of very warm temperatures just above 700 mb. The wind profile is quite favorable for storms to propagate into the deserts.

The various WRF model forecasts available at this time indicate considerable and heavy thunderstorm activity over much of southeast Arizona - a better chance today for those marginally severe thunderstorms. Several of the forecasts continue storms well into the night, with MCSs reaching the Colorado River. 

Should be a much more interesting afternoon today for storm watching.

Monday, August 13, 2018

Interesting Blog Posts

Just a heads up - couple of blog posts worth a visit today.

Jim Steenburgh's post this morning: 

"Deep Convection and Haboobs" provides interesting commentary on his last few days in Tempe, Arizona.

David Blanchard's last two posts have some stunning weather photography:

"Arizona Monsoon Clouds - July 2018"

"Storm Chasing and Photography - Spring 2018"

Links to both at the right.

A Metro Tucson Donut Hole Day


Storms on and north of Catalinas at 6:20 pm MST yesterday afternoon. During the day yesterday PW plunged significantly - reaching values around 30 mm before thunderstorms moved across portions of the metro area (time series of GPS-PW below from Atmo).



The classic Tucson donut hole is quite evident in the plot of detected CG flashes above - from Atmo and Vaisala for 24-hours ending at 1:00 am this morning. The ALERT map below (for 24-hours ending at 5:00 am this morning) presents a much diminished rainfall picture relative to Saturday. There was one heavy storm that moved westward from near Vail toward I-15. Here at house we had thunder, brief gusts to around 40 to 45 mph, but no rain at all.

Once again the Phoenix area was hit by severe thunderstorms with damaging winds and numerous reports of damage.



This morning skies are more clear across southern Arizona than they have been for many days - visible image above from 6:45 am this morning.


The strange large-scale pattern continues - above shows 12 UTC 500 mb analysis from SPC. An extended trough extends from south of Baja northward to a closed cyclonic circulation over eastern Colorado. The main anticyclonic circulation in West is over southern Utah, with heights now around 5900 m. The strong cyclonic circulation at 250 mb (the culprit that brought us the significant drying above the BL yesterday) has shifted well to northeast and is also over eastern Colorado.

The morning sounding has potential CAPE, but a new BL will be developing today and main question for afternoon will be whether a deep, well-mixed layer can set up with the very clear skies and abundant sunshine. The various WRF forecasts I looked at kept things quite suppressed locally. However, of additional interest is the strong gradient in PW across southern Arizona from east to west (below is MIMIC total PW analysis from 12 UTC this morning). Westerly flow in the BL could increase PW considerably during the afternoon. Many factors at play as the day evolves.


Sunday, August 12, 2018

Direct Hit



View at top from campus captured developing storm cell along the foothills - this cell moved directly over this part of town producing some winds and heavy showers. The CG plot above (from Atmo and Vaisala) is for 24-hours ending at 3:00 am MST this morning. Limited thunderstorm activity in southeast Arizona, with most action occurring over eastern Pima County. The other very active area was in northwest Arizona and southern Nevada. There were numerous reports of severe wind gusts from the Las Vegas area. Radar below is from 5:10 am this morning and shows early morning showers continuing west of Tucson. 

WRF forecasts yesterday were quite accurate for the severe storms in the northwest part of state, while some runs were better than others for the storms in eastern Pima County. Across the ALERT network about 75% of the sites had measurable rainfall, with generally light amounts and only a few sites had over half an inch. TUS had no rain and DM recorded a Trace. Here at house the direct hit by the small thunderstorm cell produced 0.61" between 6:00 and 7:00 pm. Late night showers provided another 0.06" before midnight - total here of 0.67" was most significant rain since the unusual June event.



This morning skies are clear, or clearing, across much of southeast Arizona as the shower area moves westward - visible image above from 6:45 am.

The morning sounding data is again a mixed bag. At TWC (skew-T below from SPC) there is an onion like low-level thermal profile and steering winds have become very light. However, to the northwest (Phoenix skew-T second below) there is much more CAPE and a considerably better vertical wind profile for organized storms. Various WRF forecasts have not captured the early morning activity well, so the model world for this afternoon is quite uncertain. Some versions forecast storms over the metro area late afternoon well into the night, but other versions keep storms mostly to south and west. Storms in our area will depend on heating and outflows to help. Severe storms appear likely again for the greater Phoenix area.



Saturday, August 11, 2018

Active Day Yesterday Continued Through Night


Thunderstorm on Catalinas at 3:36 pm MST yesterda,y trying to move into north part of city. Photo down at bottom of post is sunrise over Thimble Peak this morning.


Plot of detected CG flashes (above from Atmo and Vaisala) is for 24-hours through 7:00 am this morning. Thunderstorms around Tucson stayed mainly on the mountains. There was widespread activity across Phoenix area again, and storms continue active this morning out west near and along the Colorado River (as per the WRF forecasts yesterday).

The ALERT rainfall plot below is for 24-hours ending at 6:00 am this morning. The heaviest amounts were on and west of Catalinas (large hail reports just west of Catalina); however, one strong cell built southward across the city from the east end of Catalinas - DM reported 1.03" from this storm, but it missed airport where only 0.06" fell. Here at house the early morning shower plus afternoon storm totaled 0.21". Note that the most southern sites in ALERT network had rainfall also, with amounts up to around half an inch.



The Phoenix area received another significant rain event during the night - composite radar chart above is from 04:30 am. The rainfall plot of various network reports below (from Maricopa Flood Control District) shows how widespread the nocturnal event was (there were a couple of reports of severe winds out in the western suburbs). Second below shows composite radar from Yuma at 7:00 am this morning.




The morning skew-T plot above (from SPC) for TWC shows a bit of drying; however, significant steering winds continue from the northeast, while upper winds have become northerly - anvils over city from storms on Catalinas possible. The CAPE analysis for surface parcels by SPC is a considerable over-estimate, and mixed layer CAPE this afternoon would likely be around 500 J/Kg or so.

The 500 mb pattern (below) is very chopped up with three centers of anticyclonic circulation present with several troughs separating the centers. The trough over Colorado and northern New Mexico may try to move our way today. Most significant aspect of the analysis appears to be the cold temperatures across the Southwest - I've shaded temperatures of -9C and colder. The two 06 UTC variants of the WRF forecasts (from Atmo) are somewhat similar for today - severe thunderstorms this afternoon across parts of western Arizona. Both forecasts indicate storms for eastern Pima County near and after midnight tonight.

The sounding plot for Flagstaff (second below) was launched into an unusual, early morning thunderstorm, accounting for the bizarre data up there.



Friday, August 10, 2018

More Of Same


There was light rain across parts of the metro early this morning, leaving behind a nearly saturated atmosphere. Photo above just after sunrise shows stratus fractus and fog hugging the lower foothills of the Catalinas.


Afternoon storms yesterday again produced both hail and severe winds across the Southwest from New Mexico to California - above plot shows SPC reports for August 9th. The tornado report at Eagle Nest, New Mexico - east-northeast of Taos - occurred at an elevation of over 8,000 ft MSL. The hailstorm in the Flagstaff area was probably the most significant severe thunderstorm event in Arizona.


During the early morning hours a large MCS developed between Tucson and Phoenix and moved southwestward - NCAR regional base-scan radar chart above is from 2:00 am MST. The system brushed the metro area with light anvil rain and some nocturnal lightning displays. The ALERT rainfall plot below is for 24-hours ending at 7:00 am - the heavy amounts from Oro Valley westward across the northern Tucson Mountains were produced by an afternoon storm that moved off east end of Catalinas - we had thunder here but no rain from that storm. The early morning rain showers here amounted to 0.03" in the gauge.



While things are very moist and a bit more unstable in this morning's upper-air data, the overall situation remains very chaotic. A weak short-wave at 500 mb hangs, within the larger anticyclone, across southeast Arizona - with Tucson just on the south side of this feature. The sounding was taken very near the storms and MCS that were occurring, so its representativeness  for the day is at question also. Southeast Arizona is again covered by heavy debris cloud this morning - visible satellite image above is from 7:00 am. Nice wind profile again for organized storms, but heating uncertain place to place and role of short-wave unclear.

The two versions of the 06 UTC WRF forecasts from Atmo are again quite different for eastern Pima County. I'll illustrate this below, using the forecasts of total rainfall through 6:00 am tomorrow morning. Below at top is GFS version and at bottom is NAM version. Both versions do end up with a severe MCS/line of storms moving all the way west to Colorado River.

Another day to watch things evolve and to hope for a bit more rain here at house.


Thursday, August 09, 2018

Back From Wisconsin

We've been away on trip to Wisconsin since early Saturday am and returned early this morning. We had a late connection through Denver and that was delayed 2 1/2 hours - finally back here at house at 3:00 am MST. Many Southwest flights were seriously delayed yesterday, and there were a lot of grim travelers crowding the C-Concourse at Denver International (DIA). An airline employee told us that golf ball hail at DIA on Tuesday had taken 12 planes out of service, causing the flight chaos that continued yesterday. However, I see no severe report of hail right at DIA on Tuesday - so I'll investigate a bit further.

In Wisconsin our travels took us a number of places - Milwaukee, Waukesha, Madison, Mt. Horeb, Cross Plains, and Mineral Point. Weather was unsettled - showers and thunderstorms Sunday evening and night through mid-morning Monday, light showers and sprinkles Tuesday, and thick morning fog yesterday - very nice change.


Just a quick look at the local situation. There were severe thunderstorms in the Phoenix area yesterday with many reports of severe winds at and east of the airport. The radar above (from NCAR RAP - base scan only in the NCAR products) is for about 7:15 pm last evening. Scottsdale reported gusts to 59 mph, along with 0.54" of rain. Sky Harbor had gusts to 63 mph, blowing dust and low visibility, along with 0.08" of rain. Sounds like a real "mud storm" in parts of Phoenix.

Here at house there was 0.11" in the gauge this morning. After examining ALERT data and radar (below is also from NCAR at about 10:00 pm last night), my guess is that we had thunder and a Trace on Tuesday, and then a repeat last evening with the measurable rainfall.



This morning there is heavy residual cloudiness over southeast Arizona and northern Mexico - as per 7:00 am visible satellite image above. Obviously, BL heating will be a problem today.

The morning sounding from TWC (skew-T below from SPC) is very moist and with almost a thousand J/Kg of potential CAPE. The wind profile is excellent for organized thunderstorms moving into the deserts. However, there has been considerable cooling through multiple residual BLs, and that will also cause problems. Soundings like this have often been associated with severe storms in the metro area, but also as well with no-go donut hole type events. Since a new and relatively shallow BL will be trying to re-build today, significant outflows and storms from east will be needed to trigger storms later today.

My very quick look at 06 UTC WRF forecasts revealed that the NAM version forecasts a donut hole day, while the GFS version forecasts afternoon and evening storms, particularly in northern portions of eastern Pima County. Yet again, another difficult forecast situation.


Friday, August 03, 2018

In The Donut Hole Yesterday


Storms south of Kitt Peak at about 2:30 pm CST yesterday afternoon - above. Considerable severe thunderstorm activity over Southwest yesterday - mostly strong winds but with a couple of large hail reports also - SPC report map below for August 2nd. Many of the reports were in the western suburbs of Phoenix.



Only six sites in the entire ALERT network reported rainfall yesterday, with four of those up in the Catalinas. Pretty miserable day, but several of the WRF forecasts for yesterday afternoon/evening definitely had metro Tucson in its well-known donut hole. Plot of detected CG flashes for 24-hours ending at 1:00 am this early morning (below from Atmo and Vaisala) shows the void over us and also another over eastern Maricopa County.



The 500 mb analysis for 12 UTC this morning (above from SPC) shows that a weak trough has moved across the state during night, leaving us in a non-monsoonal flow regime, with parts of the anticyclone pushed south over Sonora and also east to the southern Plains - ugh.

Sounding plot for TWC (below for 12 UTC from SPC) indicates westerly winds through entire troposphere, but with abundant moisture below 500 mb and considerable potential CAPE. However, subsidence and drying will likely be occurring above 500 mb, putting a serious damper on storm activity except over higher elevations. 

Only chance we have here at house for a storm in this type pattern is if something develops over the northern Tucson Mountains or the Tortolitas - i.e., immediately up-wind and close. Both 06 UTC WRF forecast runs at Atmo forecast a couple of isolated thunderstorms for eastern Pima County this afternoon, but with a bit more activity on to the east.