Sunset Behind The Santa Ritas

Two photos of sunset on Friday, 13 September 2013, looking west toward the Santa Rita Mountains.

Morning Storms To East Of Tucson - Sunday, 15 September

Thunderstorms the last two afternoons have stayed to the east and north of the Tucson metro area. Some moisture and CAPE lingers from Tucson eastward. Storms at sunrise were affecting northern Cochise County, roughly from Benson over toward Wilcox.

Products from NHC this morning are shown above and below. Above is forecast for Hurricane Ingrid, which is in the Gulf of Mexico. Below is forecast for Tropical Storm Manuel, which is near the southwestern Mexican coast. Envelops expected for TS force winds is at bottom. Both storms threaten central Mexico with heavy rains and flooding.

Low-Level Moisture Inches Upward

CG data from past 24-hours ending at 5 am MST (above) shows that thunderstorms stayed off in Cochise County yesterday - much as forecast by WRF models. The CIRA blended PW product for 7 am (on Friday the 13th) shows below that PW has inched up some - from both the east and the southwest - over southeast Arizona..

Water vapor imagery (above from 7:30 am) indicates that the upper-half of the troposphere is very dry over almost all of Arizona. The morning sounding from TUS, below, also indicates this. However, there is considerable CAPE now for parcels from below 600 mb. So buildups will be fighting dry entrainment (especially given the wind profile) at higher levels. There should be increased chances for storms, especially over higher elevations, across the eastern half of Pima County today.

Heavy Rains New Mexico And Colorado

Was tied up this morning taking a look at the setting that has produced 8 to 10+ inches of rain near Boulder. Had some similarities to the Big Thompson flood event of July 31st 1976. However, this event has been longer-lived and more tropical (warm rain processes) in character. Above is web cam shot of Boulder Creek running out of its banks at 2:30 pm MST this afternoon. I guess that the models were not very far off yesterday - I should have taken a closer look at the larger-scale setting before downplaying yesterday's WRF-GFS.

Locally, the forecast models continue to keep the west edge of the convection across Cochise County, just to our east. Below is this morning's WRF-NAM forecast of radar echoes at 10 pm MST this evening.

Rillito At Dodge ALERT Site

Back on August 21st I posted the above photo of the ALERT gauge called Rillito at Dodge. My post was about what effects the over-hanging tree might have had on rain measurements at the gauge the day before. I was alerted by Andy Wigg (Pima County Regional Flood Control District) yesterday that the gauge shown above is no longer in service. It had been replaced several months ago by a new ALERT station. I had actually noticed this new station and wondered about it. It is located about 700 ft to the east (upstream) and is just west of the Alvernon bridge and on the south side of the wash. The new site is shown below (I took a photo of it on my early morning walk today). Obviously my post back in August was just meaningless babble.

End Of Summer Storms At Low Elevations?

After mid-morning yesterday, it was very suppressed and all the variant WRF forecasts were quite good in predicting the total downturn for eastern Pima County. Rainfall coverage across the ALERT network fell from 100% Monday and Monday night to 0% for Tuesday and last night. Lightning plot of CGs for 24-hours ending at 5 am this morning (above) shows only a couple of isolated storms across all of southern Arizona. The morning 500 mb analysis (12z from NCAR RAL below) shows a Rex Block over the western US and a large anticyclone off east edge of the map. The long-range forecasts gradually evolve this pattern into one with westerly flow dominating across the US.

The early WRF forecasts (above WRF-GFS and below WRF-NAM) for rainfall through 8 pm MST on 13 September indicate precipitation over the higher elevations, particularly over Cochise County. The GFS version goes a bit crazy over New Mexico, forecasting some amounts over 10 inches and the NAM version seems more realistic. Little is forecast for low elevations of Pima County - thus, right now the models are indicating that storm season is over for most of southern Arizona, and we'll have to await some transition situations during last half of September and October.

Situation Has Really Gone South

The morning forecasts from both versions of the Atmo WRF model are similar to the early versions. The models all forecast a significant downturn, with little recovery from the drying that set in early this morning. So very much decreased chances for light showers this afternoon. See Mike Leuthold's discussion and model output at:                http://www.atmo.arizona.edu/products/models/forecasts/wrf_disc.html

Widespread Rains Over Eastern Pima County

An area of thundershowers moved across most of eastern Pima County around 11 pm to midnight last night, producing rains at some spots of 1 to 2 inches. Regional radar at midnight shown above from NCAR RAL - this product shows base reflectivity and tends to down-play the intensity of echoes because of clutter problems. The Rillito was flowing at 1000 cfs a bit after midnight at the Dodge gauge. Across the ALERT network 100% of the reporting gauges had rainfall during the past 24-hours. (Note that there were only 90 sites reporting - the Picture Rocks rain gauge has apparently been out of service for at least two months.) There were 50 sites with more than half an inch and 10 of these had over an inch. The max reported rain was 2.01" at the site at Altar Wash and 286. Here at the house we had 0.15" during midmorning showers and then another 0.15" around midnight with thunder - total rain for past 24-hours was only 0.30" here.

Skies were mostly clear this morning and PW was down quite a bit - above is time series of GPS derived PW at the Univ. of Arizona site. The CIRA blended PW product for 13 UTC this morning (below - Tuesday, September 10th) shows a distinct pocket of drier air over southeast Arizona - indicated by the darker green shades. So a key issue for the afternoon is that of how much will PW recover? There are considerably higher amounts of PW across the southwest third of the state. The early WRF forecasts from Atmo tend to keep the metro area PW low and afternoon storms decrease rapidly as they move toward eastern Pima County. It does appear that warm and dry air above 300 mb will limit CAPE this afternoon, but I suspect that things will recover a bit better than the midnight model runs forecast. It will be interesting to see what the morning forecasts from the WRF indicate for later today.

Light Showers Continue

Continuing periods of light showers with more extensive coverage during the nights across eastern Pima County. It has been a continuing cloudy and dreary period, with quite light rain amounts over most of the metro area. The TUS sounding (above) from 5 pm MST yesterday (Sunday, September 8th) indicates that there was at best a very shallow boundary layer. The lowest levels had decent CAPE but would have required lifting to about 700 mb to realize it. Up at 750 mb or so there was no parcel CAPE available, thus we've had stable, light showers, while areas that had more sunshine and heating have experienced deep convection and some thundershowers. Southerly winds were quite pronounced from 500 to above 300 mb, but winds below 500 mb continued very anemic.

At 5 am MST this morning (radar from TUS above) there was a large area of weak, low-topped showers covering Santa Cruz and much of Pima and Pinal Counties. here at the house we had only 0.03" in the gauge at dark last evening and showers during the night had added an additional 0.05" during the night - so not much of a two day event. At 5 pm yesterday only 25 ALERT stations had recorded rain during the past 6-hours. But rainfall was more widespread during the night and 73 sites (almost 80%) report rain during past 24-hours.Amounts were generally light and only 13 stations had 1/4" or more and 4 sites had over 1/2". Best rain amounts and coverage were across southern parts of the network - below is 5 am sector plot for the southern-most part of the network showing rainfall at every site and 3 of the sites with over 1/2"..

The plot of CGs through 5 am this morning (above) shows large portions of Santa Cruz, Pima, Pinal, and Maricopa Counties with little or no lightning during the past day. there were some active storms during the early morning hours (the pink to red colors) in southern California. Another dreary morning with heavy cloud cover and continued light sprinkles - as per north view from Kitt Peak, below at a bit after 6 am.

A Day With Light Showers

Sun did come out late yesterday but it was not enough heating, or CAPE, for thunderstorms to build - note the significant lack of CGs over a VERY large area of Mexico and Arizona  for 24-hours ending at 4 am this morning (above). The evening Tucson sounding indicated an extremely shallow boundary layer that only reached to 850 mb and indicated that the showers were based up at 600 to 700 mb. Thunderstorms got going mainly to the east in Cochise County and northward into the White Mountains. Across the ALERT network this morning 44 of 92 (almost 50% areal coverage) sites had light rainfall during past 24-hours. Only 5 stations had 0.25" or more and these were all in the Catalinas and Rincons - both Green Mountain and Manning Camp came in with 0.43". Sector plots below illustrate that the showers stuck to the east and mountainous parts of the network. Here at the house we had only a Trace through midnight and have picked up 0.02" from early am showers.

The early runs of the WRF model at Atmo indicate a somewhat similar day today. Atmosphere is moist but not very unstable, due to clouds and little in the way of a deep boundary layer. It is a damp and dreary morning across the metro area (Sunday, Sep. 8th). The PW values from Tucson west across southern Arizona are around 1.75 inches. The WRF-NAM appears to have forecast the morning shower coverage a bit better than the GFS version. Above is WRF-NAM forecast of radar echoes valid at 2 pm this afternoon and below is the forecast of rainfall totals through 5 am MST tomorrow morning. Models again forecast most significant showers to stay to the east and north. High temperature yesterday reached only 88F at TUS and WRF forecasts only 84F at the airport for today. So the dampness continues but CAPE will remain limited, unless we get some more serious sunshine this afternoon.

Saturday Afternoon 7 September

Finally, some sunshine broke through around 3:30 pm - too little too late or will it get things rumbling by evening?

Very Moist Again

Have been busy with other things and haven't been able to post much. The storm that hit here at house yesterday with 0.66" of rain was quite a small cell (house is under the "D" in Wetmore RD). The ALERT sector above shows that most sites here in north part of metro had little rain yesterday. At 5 pm yesterday afternoon only 24 ALERT sites had measured rainfall. However, light showers during the night have brought that number up to 54 at 6 am this morning. Heaviest amounts were in and near the Catalinas, with two sites reporting just over an inch.

At sunrise this morning there are light showers continuing over parts of southeast Arizona and skies are heavily overcast, as view of Catalinas shows below.

Morning TUS sounding (above) has PW back up over 1.60 inches - showing an important role of moisture recycling from yesterday's storms. There is some CAPE and good southeasterly steering winds. However, the dilemma for the day will be sunshine and surface heating - how much will there be? Only the early WRF-NAM forecast model has the morning clouds and shower activity forecast. This version of the model keeps things mostly suppressed during the day today, due to clouds and limited heating. So, a good day to keep an eye on the morning model forecasts and also on the skies.

Finally Some Meaningful Rainfall Here

The rain shaft on the right side of this 3 pm image scored a direct hit on the house. Some wind (not severe) and 0.66" of rain in 10 minutes or less. Note that rainfall for entire month of August totaled only 0.68". So there are finally some serious puddles around the neighborhood.

Tropical Depression 12E Forms

Tropical Depression 12E developed yesterday and is now forecast by NHC to move northward toward the south end of Baja. The 1330 IR image above shows a large area of disturbed weather associated with the TD - should help spread mT air northward again. The NHC forecast below indicates a short-life for this system, but it is forecast to become a brief tropical storm - would be TS Lorena. Meanwhile in the Atlantic TS Gabrielle is moving near Puerto Rico today and is then forecast northward well east of the mainland.

Very suppressed over much of Arizona, New Mexico, and northern Mexico yesterday. The forecast models indicate storm activity returning to the borderlands of Santa Cruz and central Pima County as early as late afternoon today, and then increasing in coverage into the weekend as moisture gradually increases.

Some Wind Damage Yesterday Afternoon

Storms erupted early yesterday and impacted the higher elevations and the far south side of the metro area. Lightning strikes through 6 am MST (above) show the increased activity in the southeast part of the state. A severe storm produced wind damage and took down some power poles between the airport and Green Valley. During the past 24-hours 43 (~45% areal coverage) of the ALERT sites reported rainfall and amounts were mostly light as yesterday's model runs had indicated. However, 10 sites did have over 1/2" of rainfall, particularly in the Redington Pass area - see sector plot below. Here at the house we had a couple of outflows and some light anvil sprinkles, for another Trace day. Activity decayed rapidly by evening.

The Rillito was running some at sunrise for the second time in less than a week. During the night someone with 4-wheel drive vehicles had been running in the flow in the stream bed, making for an ugly mess this morning that included littered beer cans. Quite disgusting.

Dry air has moved into the southeast part of Arizona, from the east yet again, and the models forecast only some weak afternoon showers for the next two days. The blended PW product for 13 UTC this morning (above, from CIRA at Colorado State University) shows values of less than inch (the light blues) intruding into eastern Arizona, while the highest values hold out in the southwest part of the state.

First Round Of Storms

Storms have moved off to west rapidly and weakened some, while new cells have formed over the Rincons. Radar above shows composite reflectivity at 3 pm MST. Two panels from the ALERT network below show rainfall for 6 hours ending at 3 pm. Most of the rain stayed on south side of metro and further south. Coverage has been only 26 sites (28% coverage) with rainfall so far. Wind and a couple of slight spits here so far. Hopefully there is still decent, elevated boundary layer air that can feed additional storms, since surface has been cooled and stabilized.

More Storms Than Early WRF Indicated!

Heavy storms already moving through Tucson metro arae as per 1:20 pm MST radar above. Outflow passed here already at 30 to 40 mph. The morning model runs were mush more active than the midnight runs. See Mike's discussion (if you haven't already) at:

http://www.atmo.arizona.edu/products/models/forecasts/wrf_disc.html

Big Bend Inverted Trough Will Brush Southern Arizona Today

Yesterday was very suppressed after the early morning storms and MCS moved off to the northwest. There were 8 stations in the ALERT network that had rainfall from the morning storms and then coverage was zero though the afternoon and last night. There was one thunderstorm over in Cochise County that moved from near Benson toward the south end of the Rincons and then dissipated. Here at the house there was a morning sprinkle or two as the MCS passed by - so another Trace day.

                                              

This morning at 500 mb (above is 12 UTC NAM 500 mb analysis) there is an inverted trough over central Mexico that extends northward into the Texas Big Bend. This feature brushes southern Arizona late this afternoon and tonight, primarily in the upper-troposphere. Two main impacts, from the 12 UTC NAM forecasts this morning, are that winds at 500 mb increase some in speed and become more easterly, and that significant difluence in the upper-troposphere impacts northern Sonora and the Borderlands.

This morning's skew-T plot for Tucson (above) indicates mostly southeasterly flow with strongest speeds above 500 mb. When I modify this sounding for late afternoon, I estimate only a sliver of CAPE available at low elevations (similar to yesterday's situation). However, the early WRF-NAM sounding forecast for Tucson at 6 pm MST (below) indicates substantial CAPE (routine within the the model often over-forecasts available CAPE).

The early WRF-NAM (note that early WRF-GFS went seriously awry early in its forecast with a large, sunrise MCS forecast over southwestern New Mexico) keeps storm activity mostly west of Tucson area and along the Borderlands. However, the model forecasts a cluster of storms across the metro area just at dark (above forecast of composite radar echoes valid at 8 pm). Total rainfall forecast through midnight is shown below, indicating a nice swath of rain across southern metro and also a separate storm off the west of Catalinas into Oro Valley area. Will watch to see how things actually evolve.