Few Storms Yet Again

Yesterday's early WRF GFS forecast the down trend to continue and was quite accurate again. Lightning strikes for 24-hours ending at 7 am this morning are shown above - very little thunderstorm activity in all of southeast Arizona, except for some parts of Cochise County. More activity in far southern California and some severe storms in the Central Sierra Nevada. There were some warm rain showers again in eastern Pima County. During past 24-hours 21 (23%) of 92 sites had rain - mostly before 5 pm yesterday and with mostly very light amounts (two high elevation sites had more than 1/2"). Phoenix Sky Harbor did pick up over 8/10s of an inch just before noon yesterday, for its first decent rain of the summer.

Little change today - 12 UTC TUS skew-T plot below shows: slight CAPE, high moisture, warm mid-level temperatures, and a very chaotic wind field (essentially light and variable through the troposphere). So, not a good setting for organized storms here in southeast Arizona. Showers again at higher elevations and showers at low elevations at places where they might develop nearly overhead.

The early WRF forecast of composite radar echoes valid at 6 pm MST today is above (this is the most activity in the model forecast for today). Forecast of rainfall through midnight is shown below - model forecasts a little bull's eye of heavy rain up on the Catalinas and also heavier rain amounts in Cochise County.

Above is this morning's NAM forecast for 500 mb valid at 5 pm MST on Wednesday afternoon. Very large anticyclone covers much of the US from south Florida to west of California. Note that winds are quite weak over about the southern 2/3rds of the anticyclone - so we will continue to see a moist atmosphere but with little steering flow. CAPE will probably remain low until cooler mid-level air comes around the high and combines with warmer boundary layer temperatures. Seems very similar to the pattern we fought with for much of last summer.

Heavy Storms Over Parts Of Metro Yesterday

This morning activity continues over southwest Arizona (above is 1230 UTC IR image) and also southern California. Heavy storms yesterday moved across the metro along the I-10 corridor and then on westward. Below is the central and west sector of the ALERT network showing 24-hour rain through 6 am this morning. Across the entire network there were 64 sites with rain (~70 %) coverage with the rainfall occurring mostly in mid-to-late afternoon. Here at house we had only 0.08" inches, as the storm cores stayed to the south. The airport, however, had 0.81" and gusts to 54 mph. There were several reports of wind damage along the I-10 corridor also. Nogales reported 1.51" of rain, along with two ALERT sites with over an inch of precipitation west of the airport. Lightning strikes through 6 am MST this morning are shown in second graphic below.

Conditions remain very wet this morning - PW values from morning soundings are Yuma 60 mm; Phoenix 52 mm; Tucson 47 mm; and El Paso 30 mm. The early WRF GFS forecasts PW to stay at similar values through the day today. Winds aloft are a bit chopped up at Tucson (12 UTC skew-T plot above) from yesterday's storms. Heavy clouds cover much of southern Arizona, with the exception of Cochise County - so heating will be an important factor this afternoon. The early WRF GFS forecasts heaviest storms and rain out to the west again, with strongest activity across the southeast staying over the mountains - below is the total rainfall forecast through midnight tonight. Note that the heavy amounts are over-done west of Phoenix, where the model forecast a significant, sunrise MCS that did not develop.

Outflow Approaching From South

Heavy storm off to south with outflow arc approaching rapidly - taken looking south-southeast at about 3:10 pm 20 July 2013.

Heavy To Severe Thunderstorms Moving Into Metro Tucson

Heavy to severe thunderstorms are moving into the metro Tucson are - much as forecast by the WRF-GFS this morning - but the timing is earlier than forecast by the model this time. around.

Quick Update - Re WRF-GFS

As per Mike's comment below - WRF-GFS from 06Z is running. It forecasts a big day over much of Arizona, including all of Pima County. Composite radar echoes valid 7 pm above and 10-m winds valid same time below. Later in the evening outflows from all directions converge on Phoenix area.

Wet Atmosphere Yesterday But Suppressed Again Southeast Arizona

Yesterday was an active over much of Arizona - above plot shows 24-hour lightning strikes for period ending at 5 am MST this morning. Note that again there were almost no thunderstorms over all of southeast Arizona. Severe thunderstorms hit parts of the Phoenix and Las Vegas metro areas with damaging winds. The 5 am water vapor image below indicates an MCS over the lower Colorado River Basin. Here in eastern Pima County there were isolated showers - we had a brief shower and 0.04" of rain here at house during mid-afternoon. These were low top storms with warm rain and no lightning. Across the ALERT network there only 10 reports of light rainfall - so past three days have had ~10, 0, and ~10 % coverage of rainfall, hardly what one would expect with such a wet pattern.

Phoenix metro finally had some storms with rain - better amounts across the north part of metro - above is the Phoenix Rain Index (PRI) for 24-hours ending 7 am this morning. The PRI is accessible at: http://www.wrh.noaa.gov/psr/PRI/  The morning 12Z skew-T plot for Tucson is shown below - high PW but limited CAPE. Wind profile remains easterly with directional shear. But steering winds this afternoon may be stronger than upper-levels, letting storms leave their anvils trailing some to the rear. Better wind profiles for organized severe storms again will be toward northwest and west parts of state. Yuma has extreme PW this morning of >2 1/4 inches!

The early WRF-GFS run failed at Atmo - and Mike Leuthold is away this weekend. The crude resolution NAM model indicates a stormy and wet day for all of Arizona - rainfall amounts here in the southeast are greatest along the Borderlands, extending northward into Tucson area. The sounding indicates good potential for heavy rains and wet downbursts today - so the three days of suppression appear are ending today.

Moisture Surge Into Lower Colorado Basin

Yesterday (Thursday, July 18th) was very suppressed across southeast Arizona, much as the early WRF-GFS forecast indicated it would be. Rainfall across the ALERT network was zilch (0 % coverage) during the past 24-hours ending at 6 am MST. Graphic above is detected CGs for the same 24-hours. Thus, the significant tropospheric cyclone/inverted trough has produced little weather in this area for three days now - certainly hope for an improvement next couple of days.

There has been a significant surge of low-level moisture from the GoC into the lower Colorado Basin after about 11 pm last night. This morning VAD data from the Yuma Doppler radar (above) show strong south-southeast winds up to about 3,000 ft MSL. As easterly winds have weakened, PW values have increased across all of southern Arizona and values range from around 1.5" east to 2" or more out west. Below is early WRF-GFS forecast of PW valid at 5 pm MST this afternoon - model forecast indicates little change from conditions this morning.

The model forecasts a fair amount of CAPE (>1200 J/kg) at Tucson at 5 pm this afternoon (see forecast skew-T above), but with a unidirectional wind profile, that is not particularly favorable for much of Tucson metro area, unless storms develop nearly overhead. If storms develop, they will try to propagate toward the west but anvils will tend to spread out ahead of the cores - not good for lower elevations. The early WRF-GFS forecasts an upturn in storm activity today (forecast of total rainfall through 5 am tomorrow morning shown below). Rain amounts are not large and best amounts are in Santa Cruz and central to western Pima County (as well as along the Colorado River out near Parker). It also appears that the model forecasts storms forming over the Rincons and Santa Ritas, but these do not propagate very far to the west. However, the model does forecast much more activity for all of Pima County tomorrow and the next day, with very heavy storms forecast for the lower Colorado River Basin.

NOAA ARL HYSPLIT Trajectories

Given the strong easterly winds at low-levels, I thought it would be interesting to take a look at some trajectories using ARL's HYSPLIT interactive web page. The above shows backward trajectories from TUS beginning at 10 am this morning. The trajectories begin at 500, 1000, and 1500 m agl over Tucson. Model data used in these computations are from the NAM 12-km run at 12 UTC this morning. As one would suspect, the air parcels reaching Tucson have all been sinking, more or less from the Continental Divide westward. Hopefully these ugly, downslope winds will diminish as the afternoon progresses.

18 July - Easterly Downslope Winds Continue

Looks to be another difficult weather day here in the Tucson area. The downslope, easterly winds continue this morning and have been gusting 25-30 mph along the Rillito wash. The CIRA blended PW product for 6 am MST is shown above (light blue - dark green indicates PW values from 25 to a bit over 30 mm) and indicates a dry region over southwest New Mexico and southeast Arizona, generally west of the Continental Divide. Higher PW is currently pinched into a narrow zone from south-central Arizona north-northwestward to the Lake Mead region. The early run of Mike Leuthold's version of the WRF-GFS model forecasts the east winds to continue through most of the day - graphic below shows forecast of 10-m winds valid at 4 pm MST this afternoon. These winds are strongest from along the Continental divide westward across Cochise County. A confluent zone is again forecast across western Pima County. From late evening on the model forecasts increasing PW and conditions becoming more favorable for storms and rain.

The skew-T plot of TUS upper-air data for 12 UTC this morning is shown above and indicates warm temperatures and drier air below 700 mb. The SPC diagnostics indicate a small layer of CAPE that is limited by an ugly inversion centered at 500 mb. The forecast skew-T for TUS at 4 pm this afternoon is shown below - the inversion has vanished in the forecast, which is good if it actually does shift westward. Deep easterly flow is forecast and the atmosphere over Tucson is totally devoid of CAPE. In contrast, east of the Continental Divide, and also east of the long-watched inverted trough, winds are southerly to southeasterly and the troposphere is very moist.

The WRF-GFS forecast of total rainfall through midnight tonight is shown above - forecast rainfall is very sparse except east of the Continental Divide and south in Sonora. A check of the new morning forecasts from Atmo will be very helpful today. The new NAM forecast this morning appears similar to the early WRF-GFS, with most activity suppressed today but chances for storms and rain improving during the night.

July 17th - A Seriously Down day

Yesterday's early WRF-GFS forecast a down day and that is essentially what most all of southeastern Arizona experienced. The PW decreased (above is two day time-series of GPS derived PW at Univ. of Arizona ending at about 5 am this morning) as the model forecast, stabilizing things while the east winds continued. Some deep convection developed around dusk - below is TUS radar composite at about 7 pm MST. So, slightly more convection than the model indicated. The evening convection produced some locally strong outflows - about 30 mph from south here at the house. I went out just a bit after dark but could see no lightning flashes in any direction.

The plot of 24-hour lightning strikes (below) ending at about 5 am MST emphasizes what a suppressed day it was. Not a single strike detected in Cochise, Santa Cruz and Pima Counties and only some strikes out in far western Pima County. As for rainfall - no rain was observed across the ALERT network yesterday afternoon through 6 pm last evening. There were 10 sites (~ 10 %) with light rainfall after 6 pm. Nothing, of course, here at the house.

Early WRF-GFS Forecasts Down Day For Southeast Arizona

Storm activity was on the wane yesterday across eastern Pima County. The plot above shows detected lightning strikes for 24-hours ending at 5 am MST this morning (July 17th). Most significant lightning was out in central Pima County and with a strong cell to the south of metro Tucson, near Green Valley. At 6 pm yesterday evening only 19 of 92 ALERT sites had reported any rain. During the night 14 additional stations recorded rain - so, about 20% coverage during both yesterday and last night - much lower than expectations, which had very high POPs forecast. The south sector of the ALERT network (below, 24-hours through 6 am this morning) had the only rain reports of significance, with two stations reporting over an inch.

The early WRF-GFS forecasts continued easterly winds below 700 mb (forecast TUS skew-T valid at 4 pm MST shown above), along with a drying trend. The model forecasts PW, which is at 41 mm this morning, to decrease to 30 or below during the mid-afternoon. Forecast composite radar echoes, below - also valid at 4 pm - indicate almost no storm echoes over southeastern Arizona and very little precipitation is forecast. The low elevations will have little to no CAPE and my main question re the model forecast is whether the drying will be significant enough to shut down convection over the mountains. Will watch the mountains this afternoon and also the evolution of the upper-low from New Mexico toward northern Sonora (what's left of the circulation is forecast to be located just south of Nogales at 5 pm MST tomorrow afternoon).

Another Unusual Day On Tap

The 500 mb cyclone is centered over northeastern New Mexico and the Texas Panhandle this morning (above is 12 UTC analysis from NCAR RAL). Water vapor loops indicate the upper-cyclone is currently moving toward the northwest, while there is a tiny, upper-level anticyclone centered over eastern Arizona. Heavy clouds cover much of the Southwest and northern Mexico this morning - 7:15 am MST visible image shown below.

This morning's Tucson sounding (above is 12 UTC skew-T plot) shows an unstable and moist atmosphere, with unusual northwesterly steering winds and strong easterlies near the surface. The early WRF-GFS forecasts the northwesterly steering winds to continue through most of the afternoon, while the morning NAM forecasts them to become more northerly. Rain chances here along the Rillito would be much increased with more northerly steering winds. The early WRF seems to clear out the clouds rather quickly this morning, so I haven;t looked at its forecasts in detail.

The NAM forecasts the 500 mb cyclone to move slowly southwestward, underneath the Great Basin anticyclone - above forecast is valid at 60-hours or 5 pm MST on Thursday afternoon. The NAM forecast of total rainfall from this morning through 5 pm Friday is shown below. The models forecast a continued wet and stormy week for most of the Southwest!

Edited to add: Rillito now flowing as per USGS current data below.

Severe Thunderstorms And Heavy Rains

There were many thunderstorms around southeastern Arizona yesterday afternoon and evening (above graphic shows lightning strikes for 24-hours ending at 6 am MST). Many of these storms were terrain-locked and movements were extremely variable. The morning papers report wind damage at at least four spots spread across the general Tucson area and severe reports at SPC extend up to parts of Maricopa County - widespread severe storm reports for out here.

The rains were somewhat fickle yesterday, with many places completely dry while the nearby Catalinas received torrential rains - across the ALERT network 57 stations had rainfall (62%) with much of the rain falling with storms after dark (only 17 sites had rain up to 6 pm last evening). The map above shows 24-hour rain amounts over the Catalina portions of the ALERT network - note the 4+ inches at Mt. Lemmon. The Rillito was not flowing this morning, which I found surprising. A check of the data for the USGS gauge at the Dodge Street bridge shows only a brief spike of 60 cfs a bit before midnight. The fickle nature of the coverage is shown by the reports in the Rincons/east metro section of the network - below. here at the house there was a storm a bit after 9 pm MST that left 1/10" in the gauge. At many places along my walk this morning the ground remained bone-dry.

Comment On The Unusual Pattern This Week

David Blanchard - of NWS Office in Flagstaff - has left a new comment on your post "Miscellany - Sunday July 14, 2013":

"...A very similar evolution of the large-scale pattern occurred back in the second week of August 2003 - that ended with a widespread outbreak of strong storms across most of Arizona..."

In fact, there were numerous supercells -- some of which produced funnel clouds and tornadoes across northern Arizona. I documented this system and it appeared in Weather and Forecasting in 2011.
http://journals.ametsoc.org/doi/abs/10.1175/WAF-D-11-00012.1

Edited to add: This is a very interesting paper. Below are two figures from it.

Models Continue To forecast Significant Rain Event

Yesterday afternoon storm activity was confined to the mountains primarily - above shows lightning CGs for 24-hours ending at 5 am this morning (Monday 15 July). Only 15 of the ALERT stations (~16%) reported rainfall and amounts were generally light. Exceptions were 0.79" at Samaniego Peak and 2.28" at Mt. Lemmon. Storms were essentially over by dusk. Total rainfall here at house for July so far adds to 0.42" - no rainfall here in June.

The 500 mb low over central U.S. continues to move toward the southwest and is located over Oklahoma and north Texas this morning (12 UTC analysis above from NCAR RAL). The morning NAM forecasts the low to move slowly westward today with a secondary vorticity maximum near the New Mexico boot heel by 12 UTC tomorrow morning (below). This western lobe of the system is associated with significant convection overnight in the model forecasts.

The NAM forecasts a significant nocturnal MCS over eastern Cochise County tonight and this results in a large area of forecast heavy rainfall, with a secondary maximum along the Borderlands (above is forecast NAM total rainfall through Wednesday morning). The early WRF-GFS forecast of 48-hour total rain valid at midnight tomorrow night (below) keeps heaviest rains on the mountains of Santa Cruz and eastern Pima Counties. Will be important to compare the models once the 12 UTC runs of the WRF are completed.