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First, brief summaries of yesterday and a look at this morning's situation. Yesterday forecasts and expectations again exceeded what the environment could produce. Thunderstorms were mostly restricted to Santa Cruz County, The Santa Rita Mountains and the flanks of the Huachuca Mountains. Model forecasts were significantly overdone for northeastern Sonora and Cochise County. Very blah and down days here in eastern Pima County for both Saturday and Sunday. Across the ALERT network only 3 sites on the north side of the Santa Ritas had rainfall and only amount worth mentioning was 0.35" near Elephant Head Butte.
This morning light showers have developed over a fairly large area to our west and northwest - visible image below is from 7:00 am MST. These are moving northeastward and were forecast in the 06 UTC run of the WRF-GFS, which is interesting, since the WRF-GFS forecasts for Cochise County yesterday were seriously out-of-whack. Neither version of the WRF forecasts much in the way of thunderstorm activity this afternoon. However, the morning TWC sounding has high PW and afternoon CAPE of 1000 J/kg or more, so a look at the morning model forecasts would be prudent.
Yesterday I mentioned that Hurricane Linda, which is moving fairly rapidly north-northwestward, might move close enough to south Baja to force a GoC moisture surge This morning I took a closer look at the moisture situation over the eastern Pacific, which led to the question posed in the heading for this post. The 09 UTC MIMIC PW analysis (above from CIMSS at Univ. of Wisconsin) shows that PW values are already very high across the entire GoC region and into the lower Colorado River Basin. The GPS time-series for PW at Yuma (below) shows that PW has been increasing gradually for the past five days - this increase was associated with the southerly flow to the east of TS Kevin (which has completely dissipated).
My basic perception of what a Gulf Surge is goes as follows - after a period of hot and dry conditions over northwest Sonora and the lower Colorado River Basin, an impulse of much increased low-level moisture, cooler temperatures, and distinctly stronger low-level winds pushes rapidly northward up the GoC into the Southwest. So, according to my subjective definition, we can't have a GoC surge due to Linda because high moisture is already in place. However, there are differing perceptions of what exactly a surge is. Since Jack Hales (who was at the Phoenix Forecast Office) first identified the phenomena in 1972, there have been continuing publications about GoC surges in the formal literature, but I don't think there is a generally accepted, quantitative definition of the phenomena - putting it somewhat in the category of "I know one when I see it!" I'll do a quick literature survey to see what I can find - more later.
Finally, a Thomas Hart Benton mural for Labor Day -
So far this late afternoon and evening the WRF-NAM forecasts have been closer to reality than have those from the WRF-GFS. Most storm activity has been in Santa Cruz County. Storm cores have dramatically weakened recently - composite radar above is from 8:10 pm MST. An outflow is moving northward into eastern Pima County, and the main question is whether nocturnal storms will develop in our area - there have been hints in the high-resolution models that some storm activity may develop/persist past midnight.
TS Linda has been upgraded to a hurricane by the NHC, and current predicted track for Linda is shown just below. The storm is forecast to move close enough to the south end of Baja that it could trigger a Gulf Surge. The 7:30 pm IR image at bottom shows that Linda has a very large cloud and shower pattern associated with it, so it will be interesting to see how this new tropical system affects us here in Arizona.
Yesterday brought another round of morning showers and rain to eastern Pima County. It was dreary and damp much of the day, as per morning view of Catalinas above. Widespread morning rains are usually the kiss of death for afternoon storms and that was certainly the case yesterday. Plot below (from Vaisala and Atmo) shows CG flashes through midnight last night and almost no thunderstorm activity over all of southern Arizona - there might have been two flashes in Cochise County.
The rains, however, were widespread across eastern Pima County - 90 of 93 ALERT stations measured 0.04" or more. so virtually another 100% event - the second in four days. But, amounts were very light with nothing recorded over 0.20", except 0.55" at Mt. Lemmon site and 0.28" at Manning Camp. Here at the house we had 0.09".
Today has dawned bright and sunny, with just some middle cloud around (above). The forecast for today will be a bit difficult. There may be a weak short moving moving toward southeastern Arizona this evening - or the feature forecast by the NAM model this morning may be a mesoscale response to significant, heavy thunderstorms over north Sonora. The NAM forecasts very heavy rainfall over the borderlands of northeastern Sonora and southeastern Arizona during coming 24-hours. The 06 UTC forecasts from Atmo were a bit of a mixed bag - the WRF-NAM forecast isolated storms over higher elevations of southeast Arizona, with heavier activity along the border; while the GFS version forecast more widespread thunderstorm activity over eastern Pima County and Cochise County - definitely something to keep an eye on.
The morning sounding from TWC (below from SPC) indicates substantial moisture with slight to moderate CAPE. However, low elevations need to heat and mix to about 700 mb, and it may not get that hot. However, the higher elevations will be much more unstable, but storms that develop in the strong southwesterly winds will be heading away from metro Tucson.
Finally, the NHC expects to declare the TD south of Baja has become Tropical Storm Linda this morning. They forecast Linda to become a hurricane during next few days, but to stay well southwest of Baja.
It was a very suppressed day wrt thunderstorm activity across southeast Arizona yesterday, as was well-forecast by the WRF model runs at Atmo. Mike Leuthold noted in his morning discussion - "It looks like the only chance for activity is out west where the
higher CAPE is forecast." This is how things played out and is well-illustrated by the CG flash density map above (from Weather.Graphics and Vaisala for 24-hours ending at 5:00 am MST this morning).
Only 10 ALERT sites across the southeast corner of the network measured rainfall during past 24-hours and amounts ranged only from 0.04 to 0.12 inches. There was a light sprinkle here during the afternoon - Trace.
This morning residual moisture from TS Kevin continues to stream across our area, producing light showers as shown by 5:00 am composite radar below. Kevin has been sheared apart with moisture plume continuing to advect northeastward, while the residual low-level circulation weakens and turns off toward the west.
It was a very dry summer here at the house - total June through August rainfall was only 2.44", which was the third driest summer since 1999. There was measurable rain on 26 days, which is about average for a summer here. But, there were only two days all summer with rainfall of 0.20" or greater. There was 0.33" here on August 11th, as well as estimated wind gusts of 60 to 65 mph (only severe thunderstorm day of the summer). The 0.63" on August 23rd saved the summer from being totally dismal. Also of note was 3/4 inch hail on June 30th.
Monthly totals June July August Summer
House 0.37 0.60 1.47 2.44
Near Prince and Country Club
Ron Holle 0.30 1.64 2.85 4.79
Oro Valley Near Naranja and La Cholla
Carl Hergenrother 1.12 1.56 4.88 7.56
Near Houghton and Catalina Highway
Sister Pam @ 4.27 3.09 4.51 11.87
Santa Rita Abbey 5 miles NNW of Sonoita 82/83 intersection
Finally, the five panels below show summer rainfall for the sectors of the Pima County ALERT network. Note that the gauge at I-10 and Cienega Creek was out of service until the last couple of days of August.
The models forecasts got back on track yesterday as there was rainfall at almost all stations across southeast Arizona. While thunderstorm cores mostly avoided the metro area, an MCS developed nearly overhead bringing light to moderate, stratiform rain and rumbles of thunder for much of the afternoon. Above is view from campus at 4:00 pm MST looking toward the nearly obscured Catalinas. First below is an IR image from 2:30 pm and second below is the composite radar chart for 3:35 pm. It was very nice event, except for some spots that were hit by intense storm cores.
The plot of detected CG flashes (above from Vaisala and Atmo) for the 24-hours ending at 11:00 pm MST last night shows that activity was focused over the eastern 2/3 rds of Pima County and north into Pinal County. There was little activity over much of Cochise County.
The ALERT network had 100% of stations measuring rainfall - above is the metro-W sector for 24-hours ending at 5:00 am this morning and below is same for the metro-E sector. Over the main part of the City amounts were generally around a quarter to a half inch. Here at the house we had 0.31". There were six sites that reported over an inch, and these stations were off to the far east and west sides of the array. Rincon Creek at X-9 Ranch had 2.09" and Rancho Del Lago (1.8 miles northwest of Vail) reported 3.46" The time plot of the rainfall for that site at bottom shows most of the heavy rain fell with a storm core that hit between 1:30 and 2:30 pm. Off to the northwest side of the network Picture Rocks had 0.94" (above) and that fell before noon with the morning storms that stayed off to the west of the City. Outflow from those storms moved eastward across much of the City, converging with outflows from the south helping to force the wider rain event.
Today the 00 and 06 UTC runs of the WRF models at Atmo forecast minimal activity for this afternoon, which would be the most common scenario, following such a widespread, summer rainfall.
First - I'll be posting a meteorological summer (June, July, and August) summary tomorrow and will use rainfall amounts for those months from anyone who wants to share their location and observations.
The metro area's see-saw pattern of up/down days ended yesterday, with the second down day in a row. The negatives mentioned yesterday beat down a favorable large-scale pattern and kept storms to the east and also south of the Tucson metro area, mostly in Cochise and Santa Cruz Counties. The plot of detected CG flashes (above from Vaisala and Atmo) for the 24-hours ending at 11:00 pm MST last night shows the dismal storm situation that prevailed yesterday for most of southern Arizona. I also snipped the color bar which shows the age of the flashes (violet most recent to dark blue oldest).
Today is starting out similar to yesterday, with considerable cloudiness from south Baja and Sinaloa into southern Arizona (high temperatures yesterday struggled to reach the mid-90s as morning clouds gave way to thick anvils). Visible satellite image above is from 7:00 am, as is radar composite below. There is an east-west band of light to moderate showers moving northeastward toward portions of eastern Pima County. I suspect that these are high-based showers feeding on some elevated instability present in this morning's sounding - I see a couple of CG flashes have been detected, so there is a bit of thunder embedded. The evolution of these showers will be critical to how the rest of the day goes, The models forecast significant thunderstorms activity for eastern Pima County this afternoon, but that may be optimistic again.
Tropical Storm Kevin is far southwest of Baja (the morning forecast from NHC is below) and not forecast to intensify much, while moving northward and then turning west. Kevin itself won't be a direct player wrt the Southwest, however the continuing northward flux of clouds and moisture to the northeast of Kevin will keep things interesting over southeastern Arizona for the Labor Day weekend.
Thunderstorm activity was very much diminished yesterday, as expected. Plot above shows CG flashes for 24-hours ending at 3:00 am MST this morning (from Vaisala and Atmo). Storms stayed around the periphery of the area, occurring primarily in regions where there had been no rain early Monday morning. Only 13 sites around the edges of the Pima County ALERT network reported rainfall. Couple of late afternoon sprinkles here - Trace.
This morning dawned gray, dreary, warm, and humid under heavy middle and high cloudiness, which has had a long fetch from low-latitudes The visible image below (for 7:30 am) shows the widespread cloud cover over much of Arizona and all of northwest Mexico. The degree to which the clouds keep temperatures down will be one aspect of the forecast puzzle for today - although the low temperature at TUS was a warm 83 F.
The morning sounding from TWC (12 UTC above from SPC) indicates moderate CAPE this afternoon, but with some CIN above the top of the boundary layer (BL). Although upper winds are missing in this plot, other sources show that they are south-southwesterly at 30 to 35 kts, giving a somewhat uni-directional profile above the BL - except for the layer with weak westerly winds between 500 and 300 mb. Not a particularly favorable profile for parts of the metro area, since it favors anvil shading.
The larger-scale environment indicates weak upward motion, indicating a background environment favorably conditioned for storms. Temperatures are cool at 500 mb (chart below is 06 UTC WRF-NAM forecast of the 500 mb level valid at 5:00 am MST this morning). The forecast agrees well with the morning observations (note that Guaymas - much needed today - is again missing). The upper-level winds are very difluent over Arizona due to the Pacific trough. A weak short-wave over central Baja at 12 UTC is forecast to move northward across southeastern Arizona today. So there is a bit of a mixed bag today.
The 06 UTC WRF forecasts from Atmo both indicate a big storm day for the eastern half of Pima County (drier low-level air has inched eastward to around Organ Pipe National Monument). The models appear to heat things up too quickly, and the evolution of the cloudiness will be an important factor in the development and evolution of storms today.
The model-predicted upturn did indeed occur yesterday, although by mid-afternoon it was looking like it could be another doughnut hole day. Storms began developing just to the west of here, probably over the Tucson Mountains, around 5:00 to 6:00 pm MST. A heavy storm moved by just to the north of house (see photos previous post) producing considerable lightning and thunder, but only about 0.08" of rain. Another round of storms affected much more of the metro area around midnight to 2:00 am, resulting in some very heavy 24-hour rainfall amounts.
The plot of detected CG flashes above (from Vaisala and Atmo for 24-hours ending at 12 UTC this morning) shows most storm activity concentrated in the northern part of eastern Pima County and northward. The minimum area of flashes on the northern side of the Catalinas is quite puzzling, since heavy rains fell in that area. The MCS activity during the night mostly avoided us here also - my partitioning of the rain, based on nearby gauges, indicates that August ended with 0.10" and that September has begun with 0.26". There were strong west-to-east gradients in the rain amounts - for example, the ALERT gauge less than a mile to the east of had almost twice as much rain as the gauge here.
The ALERT plots below are for the 24-hours ending at 5:00 am MST this morning - note 4 sites were over 2 inches in the Catalinas and Redington Pass areas, with Mt. Lemmon recording 4.72". Areal coverage across the network was almost 80%, with only southern and far western sites missing out on the rain.
The Tucson sounding for 00 UTC (skewT above from SPC) indicated moderate CAPE, but considerable lifting needed for low-elevation storms. However, the mountain storms that had been forming off and on several times, beginning during midmorning, did produce outflows that moved into lower elevations. The wind profile remained very light here in the lower half of atmosphere but was changing as 500 mb trough was inching eastward from the coast. The time series of T and Td and wind and gusts below from Atmo indicate that 4 or 5 outflows moved across campus, beginning a bit before 4:00 pm MST.
There were numerous severe wind reports up in the Phoenix area, with the SPC list showing 26 separate reports of wind damage. Only one of these was in our area - tree damage in Oro valley.
The 00 and 06 UTC runs of the WRF-NAM model at Atmo did quite well with the late night/early morning activity. Not surprisingly, the models forecast much diminished activity today, continuing the seesaw pattern of day-to-day storm activity for yet another day.
We are currently in a classic transition pattern, with westerly winds associated with the Pacific trough dominating above 600 mb, but with southerly flow and subtropical moisture remaining up to 700 mb or so. The trough is forecast to move little and tropical storm activity may continue the fetch of mT into parts of the Southwest, so an interesting few days ahead.
Below are some photos from storms yesterday afternoon - some of the storms were very nice visually with back-lighting from the west. Times are on photos except the bottom, which was taken at 1846 MST.
