Saturday, July 04, 2015

Quick Look At Today

More serious challenges for all forecasters - humans and models - on tap today. The 06 UTC run of the WRF model at Atmo forecast the MCS activity in southeast corner of state. However, the WRF-NAM moved the precipitation northward too fast, while the GFS version moved it too fast also, and to the northwest over eastern Pima County. This is illustrated above (WRF-NAM) and below (WRF-GFS) by the WRF forecasts of accumulated rainfall through 7:00 am MST this morning.

Cloud cover and outflows appear to be real Catch-22s for today. Above is visible satellite image for 7:00 am, while below is IR image for same time. Arizona is covered by heavy clouds, but the clouds extend far to the south because of several MCSs over western Mexico. The 5.4 km grid forecasts from the WRF did not forecast these more southern MCSs and their forecasts move away the clouds much too quickly today. So, outflow cooling and limited solar radiation will hold down CAPE during much of the day.

The morning sounding from TWC continues to be a mixed bag. The skewT plot of the 12 UTC data (above, from SPC) indicates only a sliver of CAPE, warm mid-level temperatures, L/V winds below 400 mb, and southerly winds at anvil levels. Most of this is negative for significant storm developments at lower elevations later today.

I took a look at the latest run of the NWS HRRR (High-Resolution Rapid Refresh) model to see what that model might be forecasting.The forecasts look fairly reasonable through the day. The forecast of composite radar echoes below is valid at 11:00 am MST this morning. The forecast area of light sprinkles and a few showers over southeast Arizona and the metro area looks reasonable, as all the MCS debris moves northward and a bit westward. For the afternoon hours, the HRRR forecasts little activity as the negative impacts of the thermodynamic structure, wind fields and MCS debris dominate.

Another Morning MCS For The Fourth

Edited to add: The 6:45 am plot from MesoWest (above) shows surface winds with gusts (red). It appears that an outflow with east to southeast winds is approaching the Tucson metro area. Outflow associated with one or both of the MCSs mentioned below, will bring in cooler and more moist low-level air.

The IR image above is from 4:30 am MST this morning - July 4th 2015. A morning MCS is ongoing for the second consecutive day - this time it is focused on Cochise County and northern Mexico, with a second, weakening MCS, to its southwest over Sonora. The composite radar chart below is from a bit before 5:00 am. Looks like the strong storm south of Sierra Vista was close to Art Douglas' place in Ash Canyon.

Two different views of thunderstorm activity from Vaisala data are shown here. The CG flash locations for the 24-hours ending at midnight (above, from Atmo) does not cover the period of the current MCS, but does show, in black, the flashes associated with the pre-dawn storms yesterday. In contrast, the CG flash density map (below from Weather.Graphics) covers the 6-hours ending at 6:00 am MST. The most frequent CG flashes have occurred just south of the border, in the northeast corner of Sonora. There'll be more fireworks this evening.

Friday, July 03, 2015

Chopped-Up Setting Today

The CG flash density maps shown here (for last 24-hours above and for last 6-hours below - both ending about 6:30 am MST - illustrate that thunderstorm activity was concentrated along the Arizona/New Mexico into Mexico yesterday afternoon. During early morning hours storms extended rapidly eastward from Cochise County across Pinal and Maricopa Counties - as per post below. The flash densities are from Weather.Graphics/Vaisala.

Heavy cloud cover (visible satellite image above is from 6:45 am), as well as easterly outflows, prevail this morning across southeastern Arizona, setting up a difficult forecast situation. Clear skies and/or thin cloud cover are off to the southeast and are moving this way. But it is likely that temperatures will not warm nearly as quickly as current model forecasts indicate. The 00 and 06 UTC WRF-NAM forecasts suggested the early morning MCS, but moved the cloud shield away too quickly, so Mike's discussion of the 12 UTC WRF runs will be the more up-to-date word.

The 12 UTC TWC sounding below (from SPC) indicates a very deep cloud layer at sounding time, quite high PW, and some possible CAPE even with the warm temperatures in middle levels. However, the wind profile below below 300 mb is chopped-up, with mostly light speeds, so things are a bit of a mess. The MCV mentioned below is an unknown in the current mix, and latest NAM forecasts indicate the weak, 500 mb short-wave, also mentioned below, evolves into a small cyclone north of here during the afternoon. It may absorb the MCV and be stronger than the model forecasts. Very many "ifs" at play today and will be interesting to watch how this all sorts out.

Finally, at bottom activity has resumed in the eastern Pacific, as per the morning outlook from the NHC - however, the current disturbances of interest are well west of 110 W.

Sunset Photos From Art Douglas - Early AM Storms And Rain

A storm near Naco, Mexico, spewed anvil and mammatus northeastward over the Borderlands at sunset last evening (2 July), and Art Douglas sent some very beautiful photos, two of which are shown here. The radar image second below (03 UTC on the 3rd) shows the storm and also the anvil echo heading toward Sierra Vista.

It did not dry out nearly as much as some of the model runs indicated yesterday and an early morning MCS has developed over southeastern Arizona. The activity apparently resulted from interacting outflows, as well a 500 mb, weak short-wave moving southward around the east side of the anticyclone. The IR image above is from 1130 UTC and the composite radar below is from 12 UTC. There is a distinct MCV spinning south of Wilcox that may be a player later today, as the current storms move off toward the west-northwest. Rains have been moderate to heavy and have reached to the Redington Pass area just east of town - during last 6-hours 4 sites there have more than a quarter inch of rain, with Italian Traps reporting 0.71". Perhaps a few light showers from this system's debris clouds during next hour or two, especially for eastern portions of the metro area.

Thursday, July 02, 2015

Fireworks On Hold Currently

Strongest thunderstorm activity shifted to northeast Arizona yesterday evening. The IR image above from 03 UTC shows a large storm complex over the Navajo Nation, where there were reports of severe hail. Unusual to see such a large complex up in that part of state, but the WRF seemed to predict it fairly well yesterday.

Locally, we saw a return to more typical summer frustrations, as storms on the mountains and to south produced heavy anvil cloud that shut down all storm development over lower elevations. The CG flash plot through midnight last night (above) shows very much reduced thunderstorm activity across all of southeastern Arizona.

This morning the 500 mb anticyclone over the West has two distinct circulation centers - one over northwestern Nevada and the other near the Four Corners. Flow and subsidence around the southeast portion of the Four Corners anticyclone center is bringing warm and drier middle-level air across much of New Mexico and Arizona. The 13 UTC water vapor image below shows that upper-tropospheric dryness is spreading over Arizona from the southeast.

The TWC 12 UTC morning sounding (above) remained moist with PW at 40 mm (which was a bit higher than the concurrent GPS estimate). The 06 UTC WRF-NAM forecast sounding for TWC at 12 UTC was too dry, with PW at 34 mm. By 5:00 pm MST this afternoon the WRF-NAM forecast sounding (below) has dried out (PW down to 28 mm) and stabilized tremendously. In response, the WRF variants forecast virtually no thunderstorm activity today across most of southern Arizona. One question will be whether or not the large-scale drying and subsidence can completely shut down convective development over the highest mountains, where small-scale, orographic-forced vertical motions will be stronger than the large-scale fields. I would suspect that there may be some isolated, mountain storms this afternoon.

Wednesday, July 01, 2015

Nasty Anvil Overhead

The poor vertical wind profile, mentioned in post below, has led to thick anvil and mammatus over the Tucson area this afternoon. Storms over the Santa Ritas threw out the anvil and then dissipated as they tried to move toward Tucson - a more typical situation of the small details complicating things.

Visible image above is for 2:45 pm MST and radar below is from 3:00 pm. The temperature at airport has fallen 3 F since 1:00 pm - so it goes.

Very Quick Look At Today

Had other obligations this morning and have just now had a chance to look at the observations and latest WRF-NAM forecasts - I'm sure Mike L will be sending a much more comprehensive analysis of what today might hold in store. Below is Fitzsimmon's carton for July from his 2015 calendar - very appropriate for last few days.

The morning sounding from TWC is shown above. There will be an afternoon BL again today that reaches only to about 750 mb, but that has considerable CAPE when lifted above 700 mb. Once again outflows from higher terrain will be needed, as per yesterday. There is warmer air upstream at 500 mb, so that may reduce CAPE during the afternoon, but skies are clearing and we should have full sun for several hours to heat up BL. The sounding below is from the 12 UTC WRF-NAM and has considerable CAPE at 3:00 pm MST, even though 500 mb temperatures have warmed some. Steering winds are forecast to become more southeasterly during the day and anvil shading could be a problem for lower elevations, since there is little speed or directional shear in the wind forecast. So, a bit of a mixed bag for today. The WRF-NAM forecasts strong storms again for parts of the metro (forecast at bottom of composite radar echoes is valid at 5:00 pm) as a strong outflow moves in from earlier storms off to southwest of Tucson. Will again be an interesting day to be a weather watcher.

Severe Thunderstorms To End June - II

The NWS current product map from yesterday afternoon was very colorful and included a Severe Thunderstorm Watch and Warning, among other products. The graphic below (from Atmo/Vaisala) shows detected CG flashes for yesterday through 1:00 am MST this morning. Another very active day, especially over south-central and west-central Arizona. The storm featured in post below left a distinct track across the metro area, stretching southwestward from the Catalinas. A very active storm area was off to the southwest of Tucson.

The SPC plot of severe thunderstorm reports for yesterday is shown above. Again, another very active day, especially for June. Looking at the specific reports for southeast Arizona, I found 7 reports of severe winds with 6 in Pima and 1 in Cochise Counties; and there were 12 reports of severe hail (1 inch or more in diameter) with 9 in Pima, 2 in Santa Cruz, and 1 in Cochise Counties.

The reports of severe hail during the past two days have been somewhat amazing - storms producing severe hail seem, at least in my experiences, to occur most often in the September transition period. Large hail at lower elevations during the core of summer is rare. I wonder if any readers have thoughts about what has caused the plethora of hail events the last two days - I did not feel that the soundings exhibited unusually large CAPE wrt to many summer severe storm days.

Finally, rainfall from the storms was again mostly light. Here at house the storm off the Catalinas left behind only 0.03" in the gauge - above is ALERT sector for the west metro area and the visually spectacular hailstorm did not produce much rain. However, heavy storms impacted the southwest sector of the network where several sites had over an inch of rain. For the entire network, 52 sites had rainfall, but only 13 sites had more than a quarter of an inch, with 5 of these having over an inch (see below).

Severe Thunderstorms To End June - I

Too many things to talk about today, so will need to do several posts. First will just show some storm and hail photos.

There were numerous reports of hail yesterday afternoon mainly in eastern Pima County and also around Sierra Vista. Above is from Jim Toth, who lives a bit northwest of here. He has scaled the hail relative to his big toe - take note SPC, could this become a new standard? - which he says is a bit over 1.25 inches wide. Hail fell here at the house also, and I grabbed the largest stone I saw on the courtyard (note many of the stones shattered on impact) and it is shown below relative to a quarter.

The view from the campus looking north above is from a bit after 5:15 pm MST. Heavy rains obscures the west end of the Catalinas, while a new updraft has formed to the southeast of the heavy rain - it is only partly shown on the east side of photo above. Jim Toth's view from north of River looking almost directly east is shown below - his photo captures both the heavy rain shaft and the south portion of the new updraft.

Two photos here are from the house at about 5:15 pm. Photo above - looking northeast - shows the horizontal extent of the updraft, which appeared to be rotating. Photo below zooms on the west side of the updraft, plus the heavy rain to its north and west. The storm moved southwestward off the mountains crossing a large part of the western metro area, while producing heavy rains, strong outflow winds and abundant hail.  Outflow winds here at the house, from the western cell on higher elevations, was from the north at about 45 mph and occurred before these photos were taken.

Finally, from Jim Means east of San Diego, a photo of an elevated funnel cloud that formed as rare June thunderstorms were building west off the coast ranges.

Tuesday, June 30, 2015

TWC Special Sounding Today

First - a storm chase photo from Mike Olbinski
taken last night. Specifics of where and when exactly not known.

The NWS Forecast Office did take a special sounding at 18 UTC today - above. The sounding shows a new BL developing with considerable low-level moisture and CAPE. But it appears that the new BL will also have considerable CIN (Convective INhibition). Note that at 2:00 pm the surface ob for TUS is 96/54 versus 104/54 at this time yesterday. So, it will probably take a considerable convergence zone to force storm development at low elevations locally. The PW has also been falling since the early morning max. The 18 UTC analysis of blended PW from CIRA (below) shows a pocket of drier air sneaking into southeast Arizona. 

The GPS estimates of PW (above for Bisbee and below for TWC) have been showing the drops also.

It appears that once again it will be a duel between the drier air and very moist air to the west. The added hitch for today is that substantial low-level convergence will have to develop to get storms in the low elevations of eastern Pima County. Plot below (from MesoWest for 1:00 pm MST) shows most light winds currently in play.