Wednesday, September 17, 2014

Odile Remnants

The above is composite radar from NWS Tucson radar at about 2:15 pm MST this afternoon. The organized rain areas associate with the remnants of Odile are moving across northern Mexico and the Arizona Borderlands at this time. Radar loops indicate that heaviest additional rains will stay east and south of Tucson metro area. Further, dry air in the upper troposphere (water vapor image below is from 2:00 pm) is pushing eastward across Pima County. So it appears that whatever additional rain we might get will be from any local convective storms that can develop. Here at house we have managed a total catch in the gauge of only 0.29". Heaviest rain amounts have fallen during last 24-hours over the Catalinas and Redington Pass with only light amounts over lower elevation portions of metro area - so it goes. Bottom three graphics are current amounts across three sectors of the ALERT network showing this, with one amount over 3 inches recorded in Redington Pass area.

Remnants Of Odile To Move Into Southeast Arizona Today

So far Odile has not produced much in the way of heavy rainfall in eastern Pima County. This morning 87 of 92 ALERT stations had measured rainfall in past 24-hours, but only 6 sites in the Catalina Mountains and Redington Pass area had more than half an inch. I did find two stations in southeast Arizona with just over an inch so far - Sells and a new ob site called Pioneer Field (northwest of Sierra Vista). Here at the house the total for Odile event stands at 0.18".

Heaviest storms yesterday were out in the lower Colorado River Basin and also in the San Diego metro area - quite something. Many severe thunderstorm reports out there. Some heavy rains also occurring over in southwestern New Mexico.

There is considerable media frenzy going on with Jim C. of the Weather Channel setting up yesterday along the Rillito Wash trails, where I usually walk. I was half expecting to find Al Roker broadcasting from the Campbell St. bridge when I walked this morning, but he was a no show. I've seen people sandbagging residences - a first for me since I've been out here.

Odile is currently somewhere in the northern GoC, but with deepest cloud masses to east and northeast of the storm center. Visible satellite image above is from 7:00 am MST and does not show the center of the TS clearly. Below is the current NHC forecast for Odile and her remnant depression. This forecast brings the depression across central Pima County west of Tucson tonight, which would put us in the region of heavy rainfall.

Composite radar image from NWS TUS above is from 6:40 am and shows the first large rain band directly associated with Odile approaching metro Tucson from the south. This band is now moving across the metro area and it is raining lightly here at house. The radar shows nothing to its southwest where there should be lots of echo. This is because the precipitation echo tops are low, and there is a huge sector of terrain blockage to the lowest radar beams in that direction. Below (from College of DuPage weather page) is the lowest, 0.5 degree, base scan radar image. This shows clearly where the blockages are - the large one to the southwest is due to a small peak in the Empire Mountains just southwest of the radar and a designed blockage to the west by Mt. Fagan (at north end of Santa Ritas) that is meant to "protect" Kitt Peak from the lower radar beams.

I looked at the early WRF forecast runs. The NAM version is not reliable since it can't get Odile moving out of the GoC (I think that Mike Leuthold has been mentioning this in his discussions and updates). In contrast, this morning's early WRF-GFS moves Odile rapidly (faster than forecast by the NHC) northeastward right across eastern Pima County. Several intense rainbands accompany the circulation, producing very heavy rains in the model forecast. These basically are past the metro area early in the night and graphic below shows the very heavy rains forecast by that model through midnight tonight. Obviously this is a day for extreme caution and careful weather watch.

Tuesday, September 16, 2014

Odile Impacts Have Begun

Tropical Storm Odile is partially over the warm waters of the GoC this morning and moving toward southeastern Arizona. While far to the south a new storm has formed - TS Polo. Above is morning overview from the NHC, while below is an IR image from 1230 UTC.

Some light showers moved across eastern Pima County durng the early morning hours (about 0.01" here) and there is currently a long band of light rain extending across the metro area and well to the east and west of Tucson (composite radar image above is from about 6 am MST). The high PW associated with Odile now covers the low elevation areas of southern Arizona with values of 1.75 to over 2:00 inches.

Mike Leuthold did special model runs and a discussion last evening highlighting the heavy rain and flood threats though the next couple of days - however, it does not seem to show up at the link to the right.

The models are all zeroing in on southeast Arizona  as the remnants of Odile move directly notheastward across our area. The rainfall forecasts shown here emphasize the need for weather alertness and caution through Thursday. Amounts are valid for period ending at 5 am MST on Friday morning the 19th. Graphic above is from the NAM and below is from the GFS.

Monday, September 15, 2014

Phoenix Summer Rainfall 2014 And 1970

From Mike Crimmins - two summers at Phoenix from his webpage. Top is this summer which was very dry until Norbert event in September. Below is 1970 which was dry until Norma event in September - interesting in that it was the "N" tropical storm in both years that changed the character of the entire season.

Surface Observations From San Jose del Cabo

Jack Hales sent along these observations from San Jose del Cabo that he grabbed from MesoWest before the power was lost down there a bit after midnight. This site is up the coast northeast of Cabo San Lucas (see map below). Winds gusting well over 100 mph and note the six-hour rainfall of over six inches in six-hours - although, the gauge catch can not be very accurate with such wind speeds.

Hurricane Odile Stays To Right

Hurricane Odile has proven to be difficult to forecast and illustrates that much progress remains possible for hurricane forecasting. Shown here are 4 forecasts from NHC of Odile's anticipated track. Top is from 8 am on September 10th; just above is from 8 am on September 11th; just below is from 5 am yesterday morning; and bottom is from 5 am this morning - Monday September 15th. Note that the first forecast was extremely close to the path Odile has followed so far. The next two forecasts shown were off to the left of the actual track by varying distances.

Unfortunately, the storm moved fairly rapidly once it started moving and made nearly a direct hit to Cabo San Lucas during the early morning hours today. The situation was apparently chaotic yesterday in Cabo, as flights were cancelled and tourists were stranded. We hope that the town weathered the storm as well as possible. This morning the storm is moving up Baja, and current NHC forecasts indicate it will slip east again, ending its life in the northern GoC. It's exact path will determine to a large degree how the week plays out in southeastern Arizona.

High values of PW continue to extend north to the lower Colorado River Basin (above is MIMIC analysis for 12 UTC from University of Wisconsin CMSS). With pressures lower near the weakening storm, highest PW values will tend to track with the storm, making the situation quite different than was the case with Norbert.

The exact details of how things will play out can not be forecast very accurately at this time. The day-to-day evolution of the thunderstorm activity across southeastern Arizona will modulate the next day's activity and etc. I have shown below the early WRF-NAM forecast of rainfall on the 5.4 km grid for the period ending at 11 pm MST on the 17th (Wednesday). Through that time, the heaviest rains have spread northward with Odile, but are still confined mostly to Mexico in the model forecast.

Sunday, September 14, 2014

Javelina Herd And Miscellany

There is a small herd of urban javelina that lives somewhere along the Rillito, or up a side wash, near the end of Country Club. In their nocturnal wanderings they have some times come up our circle and I have encountered them a number of times on my morning walks. They have paid two visits to our back yard during the past few weeks, coming in through a small break in the ocotilla fence back in the far corner of our lot. The first visit they made quite a mess, eating up all the plants that appealed to them, breaking a large pot, dumping the trash bin, and leaving muddy nose prints on the front porch, full-length windows. Their visit on Thursday night this past week was less damaging; however, neighbor John Ferner had set up a surveillance camera and caught several shots of them back where the break in our fence is. Above photo is apparently of a juvenile digging along the neighbor's side of the fence

The storms on Friday afternoon and evening avoided our rain gauge, but above photo is of a rainbow with a dissipating storm just to the east, with a more distant storm off to the southeast. We were at Santa Rita Abbey Friday evening and Saturday (about 5 or 6 miles northwest of Sonoita). The storms that were scattered around southeast Arizona and northern Mexico put on a nice show of fireworks after dark. A storm out there hit at a bit before 9 pm with strong winds from the east - could not see enough to even estimate how strong the gusts might been. Storm produced 0.33" of rain, and left behind enough low-level moisture for low clouds to hang on the Santa Rita mountains at sunrise Saturday. Photos below are looking west at the mountains just before and after sunrise. If you look close, the summit of Mt. Wrightson is sticking just above the clouds.

Hurricane Odile A Category 4 Storm

Category 4 Hurricane Odile is the 7th major hurricane of the season in the eastern Pacific this season. Above is visible satellite image of Odile located south-southeast of the southern end of Baja. Located to the southwest of Odile is TD Sixteen-E. The forecast track for Odile, from NHC, this morning (Sunday, September 14th) is shown below. Odile poses a serious threat to southern Baja, since it is forcast to track very close to Cabo San Lucas as a major hurricane.

The 12 UTC blended PW analysis from CIRA at Colorado State is shown above. Values of of PW from 35 to 50 mm are already in place over all of the GoC. I expect that higher values of low-level moisture will return to southwest Arizona late tonight or tomorrow morning. The forecast of PW from the WRF-NAM early run this morning is shown below on the 5.4 km grid. Valid time is noon Tuesday and forecast indicates deep moisture with Odile to be entering the lower Colorado River Basin at that time - model timing is likely a bit slow. There is also a stream of high PW air into southeast Arizona with east-southeasterly flow up the Rio Grande - this is similar to the situation with Norbert. It is far too early to anticipate the details of how the week may unfold, except that there will much to watch weather-wise during coming days.

Friday, September 12, 2014

Strong Cold Front Over Plains And Northern Rockies

An unusually strong, early season cold front is pushing southward along the Front Range and into the Southern Plains. This front brought the first snow of the season to some locations in Wyoming and along the Colorado Front Range. The NAM analysis at 12 UTC for 850 mb (above) shows the strong temperature gradient along the front, which extends into northeastern New Mexico. Visible satellite imagery from 7:15 am MST (below) shows the extensive cloud mass along and behind the front. The 850 mb analysis also indicates that there is a tropical disturbance over the western GoM and that a band of strong easterly winds along the northern periphery of this disturbance reaches westward to the New Mexico Boot Heel. A broad and amorphous inverted trough stretches along the west coast from southern Mexico north to Washington state - certainly a very complex large-scale pattern.

Graphic above shows detected CG flashes for 12-hours ending at 7 am MST this morning. Of note is intense storm activity over the southern GoC; widespread thunderstorms with the GoM disturbance; and thunderstorms along the Plains cold front. The early run of the WRF-NAM at Atmo continues to forecast an extended period of strong easterly winds in southeast Arizona, as the Plains cold front backdoors westward across the Continental Divide. The WRF forecast of 10-m winds below is valid at 9 pm this evening.

The NAM model from this morning forecasts the frontal zone to be nearly to the Colorado River by tomorrow morning (above); and the WRF-NAM forecasts strong winds to continue through the day tomorrow and to affect all of southern Arizona.  The WRF also forecasts isolated thunderstorms for parts of Pima County today, with more extensive coverage across Cochise County - forecast below is for total precipitation through 5 am MST tomorrow morning.

To the south, Tropical Storm Odile has remained nearly stationary during the past 24-hours. The NHC forecast for Odile, once she decides to begin moving northward, is similar to yesterday's forecast. So, many interesting weather features over and near Arizona for the coming few days.

Thursday, September 11, 2014

Early WRF Forecasts Strong East Winds Tomorrow And Saturday

A backdoor cold front from New Mexico is forecast to bring strong easterly winds to southeastern Arizona by tomorrow both early versions of the WRF model run at Atmo. Even with the east winds, the model forecasts some thunderstorms in southeastern Arizona (above is WRF-NAM forecast of composite radar echoes valid at 4 pm MST on September 12th).

Both models forecast the east winds to become quite strong and to continue through Saturday the 13th. Above graphic shows WRF-NAM forecast of 10-m winds valid at 10 pm on the 12th. The winds have apparently been given an added kick by the MCS that the model forecasts over Cochise County and the New Mexico Boot Heel - below is radar forecast valid at 11 pm on the 12th. So, there is some possibility of winds reaching severe thunderstorm levels - but a closer look will need to be taken tomorrow.

Finally, a quick look to the south. Tropical Storm Odile is meandering slowly around near 105 W. The system to Odile's west is also likely to become at least a depression. Additionally, two large, northward moving MCS were present this morning (image is from 6:30 am MST) near the south end of the GoC. This morning's forecast from NHC for Odile (below) indicates that the storm will become a major hurricane and begin moving northwestward by Saturday morning. There is undoubtedly large uncertainty in the forecasts at this time, given the current stagnant motion of the storm. The forecast track of the storm, if it were to verify, is ideal for causing a Gulf Surge of more mT moisture into the Southwest.

Wednesday, September 10, 2014

Some Preliminary Thoughts About September 8th

In comments below Russ Scott and Mike Crimmins have asked what I think the forcing for the early morning storms that developed over metro Tucson might have been.

First, I want to point out that similar events have occurred before. Darren McCollum (forecaster at Flagstaff) studied an event (July 23/24, 1990) that began with a late night MCS over the Phoenix metro area, followed by development of a second MCS over the Tucson area around sunrise. Both metro areas received rains of 4 inches or more during the storms. In the Tucson area there were over 50 high water rescues and 1 flood fatality. The Abstract from the paper reporting results of Darren's MS research work is:

The reference for this paper is: McCollum et al., 1995: Case Study of a Severe Mesoscale Convective System in Central Arizona. Weather and Forecasting, September issue - available at AMS web site.

As for the event this week, the upper-air charts show that any large-scale forcing for vertical motion was very weak. The only hint that such forcing was present is in difluent flow in the upper-troposphere. There were, however, several weak outflows providing low-level convergence across much of eastern Pima County. The largest of these was from the Phoenix MCS. The surface observations from TUS, DM, and other nearby stations indicate that there may also have been weaker outflows from the southeast and also the west that also moved into eastern Pima County. None of these features had strong or obvious signatures by the time they reached the metro area, and more careful analysis of the surface data is needed. I hope to also access MesoWest surface plots for the period of the event.

However, the thermodynamic setting by sunrise on the 8th was very potent - 12 UTC sounding from TWC is below.

There is a fair amount of CIN for the 50 mb mixed parcel shown on the Univ. of Wyoming skewT plot. However, the parcel at 850 mb has almost no CIN, if lifted to saturation. Further, there is a shallow layer above 800 mb which appears to be a Moist Absolute Unstable Layer (MAUL). The relevant reference here is: Bryan and Fritsch, 2000: Moist Absolute Instability: The Sixth Static Stability State. Bull. Amer. Meteor. Soc., June issue - also available at the AMS web site. Thus, deep convection appears to have been likely given only the slightest of forcing.

The WRF-GFS (both from midnight and 12 UTC) forecast the thermodynamics very well - forecast sounding for TWC valid at 6 am on the 8th is shown above. The forecast has developed a MAUL centered at about 800 mb, with no convective inhibition present. The model also forecast the outflow (10-m winds below) from the Phoenix MCS to be into the metro area at 6 am. 

So one of the key issues that need to be researched are just exactly how, and why, do such MAULS sometimes develop during the night over southern Arizona? I have noted this happening a number of times during the past several summers and have mentioned it here on the blog before. Hopefully, I'll find time to do a more careful examination of the record flood event we're now cleaning up from.

Eastern Pacific Continues Very Active

First, there is a band of middle clouds and higher PW values strung out across Arizona this morning from north of the northern end of GoC east-northeastward across the White Mountains. There is some CAPE with this feature especially out to the west-northwest of the Tucson area - so there may be isolated thunderstorms to the west and north again today.

Tropical Storm Odile has developed rapidly off the southwest coast of Mexico - Odile is currently centered near 15 N 105 W. There are three tropical disturbances lined up from Odile to one at about 10 N 127 W. The middle disturbance is expected to move northward, while Odile (current NHC forecast below) is forecast to move north-northwestward. Odile is also expected to rapidly become a hurricane.

The situation is again quite complicated. Odile may interact some with the Mexican land mass to its east. The NHC track forecast also takes the hurricane very near the mouth of the GoC. Storms that track southwest of southern Baja, west of 110 W generally produce surges of low-level moisture up the GoC well ahead of them, as did Norbert. Hurricanes near the southern GoC initially produce pressure and wind fields that favor northerly winds down the GoC, hindering the advance of low-level moisture northward. So, a continued complex tropical regime and, I think, very unusual situation over the eastern Pacific.