Models Forecast Huge Changes Next 12 to 24 Hours

At 500 mb this morning (above from SPC) gradual changes continue. There is now a weak anticyclone centered over eastern New Mexico. Winds are light and temperatures are warm to very warm, as per the -1 C at Amarillo, Texas. The IT of last several days has essentially sheared apart, with a bit of it remaining over south end of GoC. The pattern is better-defined at 250 mb (below also from SPC), with a distinct anticyclone over New Mexico. The jetstreak over the Great Basin will act to pull southern part of the western trough across Arizona tomorrow.

It appears that we will have a brief period of classic monsoon conditions next 18 to 24 hour, and then a change to Fall transition conditions with a westerly trough interacting with subtropical moisture.

The TWC skew-T plot (from SPC) above is little changed from last several mornings, with a bit of a moisture increase showing up in PW values. There is little CAPE this morning due to the ward temperatures above 500 mb and associated strong inversion.

I have looked at the WRF-RR for 12 UTC this morning and grabbed a couple of forecast soundings for TWC. Plot above is for 5:00 pm MST this afternoon. Model forecasts wind field to become better organized above 700 mb - PW is at 34 mm and mixed layer CAPE is about 350 J/Kg. However, very substantial outflow lift would be required to lift the BL air to its level of free convection (LFC).

But, the model forecast sounding for Sonoita indicates deep convection underway in that area by 5:00 pm. Strong storms to our southeast may generate an outflow into metro area this evening. This would further elevate PW, and perhaps have some chance of forcing deep convection. The TWC sounding forecast develops elevated, midlevel CAPE after midnight, indicating some chance of early morning storms.

All of the various versions of WRF model forecast a very active transition storm day tomorrow as short wave moves across southern Arizona. Forecast skew-T below is for TWC at 7:30 pm tomorrow evening - PW up to 49 mm with mixed layer CAPE over 1000 J/Kg. Possible severe storms and heavy rains indicated by model forecasts. Of course much of what the potential is tomorrow will depend upon how convection evolves later today and through the night. Certainly an interesting weather situation evolving, with much to watch.

Thundestorm Near La Paz Yesterday

The above plot of CG flashes (from Atmo and Vaisala) is for 12-hours ending at 03 UTC (8:00 pm MST) last evening. Although there were reports of light rainfall at higher elevation stations, I could find only one lonely Arizona flash down in the Santa Ritas. 

The convective system that went west to the GoC has triggered a strong, low-level moisture surge across the Yuma area this morning - between 4:00 and 5:00 am dewpoints jumped from the 50s into the 70s. The Yuma radar VAD indicates the surge reaches only to about 2,000 ft MSL. But, the thermal structure and inversion related to the surge has resulted in extreme ground clutter due to ducting - some of this is "fooling" operational rain-estimation, algorithms this morning.

Note the large cluster of detected flashes at the south end of Baja.

Luis Farfan sent these images yesterday evening. The huge storm in photo is west-southwest of La Paz at about 6:00 pm. Note that the rain appears to be extremely heavy and is producing a wet macroburst - definite outflow "foot" to left side of storm. An IR image of this event, below from about 5:00 pm, shows the intense convection was centered over the spine of Baja. Thanks to Luis for the images!

Isolated Storms Yesterday

Isolated thunderstorms hugged some of the higher elevations yesterday afternoon. Heavy storm above near Baboquivari  at 3:41 pm MST. Plot of detected CG flashes below (from Atmo and Vaisala) is for 24-hours ending at 1:00 am this morning. Most activity was out in central Pima County, as per WRF forecasts yesterday.

Four sites in the Pima County ALERT network had rainfall - two up on Catalinas and two in the far southwest part of network.

The BL over metro area yesterday afternoon heated out to about 600 mb in temperature but was not well-mixed in moisture. Result was a nearly well-mixed, surface-based BL that did not reach 700 mb, with almost no CAPE at lower elevations. The WRF runs available so far indicate a similar situation today, with isolated showers and thunderstorms hugging higher elevations. The 12 UTC morning sounding for TWC (below from SPC) shows that low-level structures remain similar to yesterday, but that warm inversion at 500 mb caps the lower elevations even more than yesterday. Note that the vertical wind profile remains a chaotic and weak winds mess.

Appears that mid-week may be more interesting as Pacific anticyclone is pushed westward and PW remains fairly high.

Moisture Returns

We have been away since early Thursday am to attend a family wedding in Marin County, California. Photo above shows the morning commuter (people and not cars) ferry for San Francisco departing the Larkspur Ferry Landing at 7:30 am Friday morning - conditions were foggy, cool, moist and great compared to long run of 100+ F days here.

However, storms in northern Sonora late yesterday (CG flashes below from Atmo and Vaisala for 12-hours ending at 10:00 pm MST last night) pushed cool outflows with higher moisture northward in to southern Arizona.

Morning skew-T plot for TWC sounding data above has PW up to about an inch and a quarter, and SPC analysis indicates  some mid-level CAPE. Wind field is, however, very chopped up. The WRF forecasts from last night indicate afternoon thunderstorms, mostly over central Pima County, where elevations are somewhat higher than here in Tucson area. The forecast soundings, however, indicate a deep and well-mixed BL. Not clear to me that afternoon sounding here will mix out to a single BL - may be lower BL with old, capping BL above.

The 500 mb analysis (also from SPC) below shows the messy 500 mb pattern. The old tropical disturbance that moved ashore in Texas has left behind a distinct inverted trough that is trying to inch westward against the trough - this could perhaps bring a more serious threat of storms by mid-week.

Tropics - Florence To Mangkhut And Between

Category 4 Hurricane Florence continues to head for the Carolina's this morning (above). Models now seem consistent in forecasting Florence to be blocked from turning north and to linger in the Southeast - this could result in extremely serious heavy rains and flooding.

Below is IR image showing TS Olivia heading west through the Hawaiian Islands - probably another heavy rain threat.

Super Typhoon Mangkhut above (currently with wind gusts approaching 200 MPH) is over West Pacific. This storm is forecast to clip the north end of the Philippines before heading toward Hong Kong.

Closer afield is a weak, middle-level cyclone (below) that is centered west of Cabo Corrientes, Mexico. This system is forecast to remain nearly stationary next several days. Second below is GFS forecast for Eastern Pacific at 850 mb level with PW valid at 00 UTC on Friday. The interaction between this feature at southern end of GoC and the nearly stationary West Coast trough, allows higher PW air from GoC to inch back into Arizona, with perhaps another transition pattern setting up over the weekend.

Tropics Very Active Edited To Add Olivia Track

Satellite IR image of east Pacific above shows what is left of Hurricane Olivia (now in central Pacific Basin. Tropical Storm Paul is at about 120 degrees west and is forecast to remain a TS and to stay well west of Baja. Below is track forecast for Olivia (graphic from the Joint Typhoon Warning Center), which is forecast to clip the Big Island as a Cat. 1 hurricane.

Three tropical storms are spread across the Atlantic - vis/sw image from 1345 UTC, below, shows the storms. Florence is of most concern, since current NHC track forecast (bottom) indicates significant strengthen and a track that takes ashore on East Coast toward end of week.

Summary For Meteorological Summer 2018 - Edited

I have summer rainfall data from Sister Pam Fletcher at Santa Rita Abbey (~ 5 miles north-northwest of Sonoita): June - 2.16"; July - 4.44"; August - 3.59"; TOTAL 10.19".

Photograph of CG flash taking out the NWS KEMX radar in the Empire Mountains - Friday, August 10th - photo by Caryn Hill (more details in August 17th post).
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Weather Summary for June – August 2018

Rainfall at our house:

June        0.93

July         0.62

August    2.81            TOTAL =  4.36 inches 

This made 2018 the seventh driest summer in 20 years of record here. For this short, 20-year period the average has been 5.41 inches with 10.81” in 2008 being the wettest summer and 1.51” driest in 2013.

There was measurable rain here on 18 of 92 days (20%). Thunderstorms occurred on 26 days (at least – records for hearing thunder are iffy for me because of near deafness).

No day had an inch or more rain – which is somewhat unusual (several summers have had a two inch event). Severe thunderstorms with strong winds occurred on July 5^th and August 1^st.

In contrast, the plots for summer for TUS (above and below for ASOS data from the airport) indicates a summer with above normal rainfall - from Mike Crimmins webpage at

https://cals.arizona.edu/climate/misc/monsoon/monsoon_summaries.html

Note that four significant events of around an inch hit the airport - providing the bulk of the summer rain (almost 6 inches) there.

The summer period was also quite moist after monsoon conditions began on July 8th - plot above (from NWS webpage) shows average daily dewpoint at the airport (remember, the more meteorolgical defintion was that monsoon began after 3 days with average Td of 54 F or higher). The daily averages stayed above 54 for most of summer, with only a few days drier than that. There was no extended dry period, or burst or big dry-out. The plot for August only (below) shows just 3 days with average Td below 54 F and 19 days with an average of 60 F or greater. So, it seemed like a very humid summer to many of us.

Lonely Thunderstorm Yesterday

North view from campus yesterday captures west portion of a thunderstorm that developed over the foothills of the Catalinas. Several small cells developed across metro area as outflow from initial storm moved southward. View and radar (below) are both from a bit before 3:30 pm MST. Here at house we had rumbles of thunder for nearly an hour and a tiny spit of rain - Trace.

Plot of detected CG flashes (above from Atmo and Vaisala is for period ending at 10:00 pm last night) shows the only storm activity in all of Pima and Santa Cruz Counties was with the foothills thunderstorm. The ALERT rainfall reports (below for 24-hours ending at 5:00 am this morning) show reports of 0.04" or more from 10 stations (one near Vail, not on plot, had 0.04"). Three sites had more than a quarter of an inch. Certainly surprised me when the thunder started rumbling!

Activity Continues To decrease

View of Catalinas at 6:00 pm MST last evening is interesting because of the thick anvil over the metro area that came from storms off to the southwest. There was no precipitation across the ALERT network during the past 24-hours, except for 0.04" at Tumacacori (the most southern site in network).

The plot below of detected CG flashes for 24-hours ending at 1:00 am (from Atmo and Vaisala) is quite interesting as it relates to yesterday's 06 UTC WRF forecasts. There were a few mountain flashes over the Catalinas and Rincons, but eastern Pima County was essentially suppressed. The WRF-GFS had forecast storms to remain mostly south and east of here, and that generally played out well. However, the NAM version had forecast an unusual propagation of heavy storms from higher terrain northwestward across the metro area - that of course did not occur. BUT, storms from just west of Nogales did propagate northwestward across central Pima County (reaching about to Gila Bend and producing the heavy anvil that moved overhead here). The unusual propagation forecast by the NAM version did occur, but was shifted southwestward from the forecast. Thus, aspects of both forecasts did verify.

The next few days look to be very quiet, since we'll be under the domination of the Pacific lobe of the subtropical anticyclone - sinking and drying. Perhaps some Cbs over mountains today. The above forecast is from 06 UTC WRF-GFS (on the 5.4 km grid) and is of PW at 11:00 am MST on the 9th (Sunday). Model forecasts local drying, but with southwest parts of state holding on to about an inch of PW. However, very moist air continues nearby over southern portions of the GoC. The forecast below (from same run but on 1.8 km grid) is for total precipitation through 11:00  am on 9th.

The big weather interest over the weekend will be focused on Hurricane Florence in the Atlantic - how strong will this storm be and will it impact the east Coast? Some model forecasts make it a significant event for US, while others keep it well offshore. Current NHC forecast track for Florence is at bottom.

Strange Day Today

Low-level moisture did persist yesterday and thunderstorms actually were bubbling up on higher elevations by 10:00 MST or so - very early start. I took these two photos around 11:00 am - storm on Catalinas above and mini-storm over Tucson Mountains below. The Tucson Mountain storms drifted our way with thunder before noon here, and a light shower produced 0.02". 

The plot of detected CG flashes (second below from Atmo and Vaisala) is for 24-hours ending at 1:00 am this morning. Storms mostly hugged the higher elevations, with the Tucson Mountain storms being the only activity within the usual Tucson donut hole. Across the ALERT network 23 sites (northern and southern portions of network) measured mostly light rainfall - but four sites had over an inch of rain (three in north end of Catalinas and one on west side of Santa Ritas).

Things are a bit strange today. For some reason there was no sounding available this morning from TWC. The PW appears to be continuing right around or a bit more than 30 mm. At 500 mb the last small trough within the chaotic large scale pattern will be moving across southern Arizona today, with southwesterly steering winds ahead of it. The 06 UTC WRF runs were available, and both versions forecast TWC mixed layer CAPE to be more than 1000 J/Kg around mid-afternoon. The GFS version keeps storms mostly to the east and south, with a couple of isolated storms in eastern Pima County. However, the NAM version forecasts significant storms over the metro area - above forecast of composite radar echoes is valid at 4:00 pm this afternoon. The model develops a large and strong outflow boundary that moves northwest from higher elevations in Cochise and Santa Cruz Counties - the outflow forces new storm development right over the metro area. Forecast below is 10-m winds, also valid at 4:00 pm.

The 12 UTC WRF-RR is also available, and it forecasts storms only across southern portions of Santa Cruz and Cochise Counties.

Depending on which model one chooses, our day today could be active, or have only some isolated storms in sight, or be very suppressed. My feel is that the NAM scenario is unlikely, and that GFS is probably more inline with what we'll see later today.

September 3rd And 4th

Early afternoon storms northwest of Kitt Peak yesterday (above).

Plot of detected CG flashes for 24-hours through 1:00 am MST this morning (below from Atmo and Vaisala) shows that low elevations, where heavy rains had occurred on Sunday were, as expected, totally suppressed yesterday. Cbs, however, were in clear sight off in southerly directions. Rainfall occurred (light amounts) at five ALERT stations in southern parts of network.

Graphic above shows GPS PW for past seven days on campus (top panel), with notable decreases since midday yesterday - currently down to around an inch. The morning sounding plot for TWC (below from SPC) is a mixed bag, with stronger winds and dry air above 600 mb and moisture confined to lower-levels where winds are L/V. There is more potential CAPE than yesterday and some storms are possible at lower elevations, but only IF moisture remains high below 700 mb during the afternoon.



Meanwhile, Tropical Storm Gordon is over northeast GoM heading generally toward New Orleans and vicinity. The morning outlook (below) indicates that NHC forecasts Gordon to become a hurricane a bit before landfall tonight. Current surface plots near and over Gulf waters don't seem to  be picking up Gordon's circulation, and will be interesting to see what comes out of the Gulf by nighttime.