Friday, September 22, 2017

Any Rain before September Ends?

Cloud band this morning led to a beautiful sunrise - above looking east from Tucson Blvd., and bottom Finger Rock highlighted by some color.

It was an interesting astronomical summer - the monsoon rains essentially fell from July 10th through August 13th, with hardly enough here the rest of summer to dampen the soil. Very dry conditions here with non-desert plants requiring attention nearly every day.

Large trough continues to deepen over the West - 250 mb analysis above from SPC - with a strong jetstream of  more than 100 kts crossing Arizona. But, this large system doesn't bring much moisture with it this far south, and subtropical moisture is shunted northeastward. 

Forecast below is from 00 UTC WRF-GFS last evening and is for total precipitation (on the 5.4 km grid) through 00 UTC on September 30th. Heaviest rains forecast for northeastern Mexico and southwestern Texas, but also wet for High Plains and Southern Plains.

Thursday, September 21, 2017

Last Day Of Astronomical Summer

At 500 mb a large, cold trough (below) is digging into the West - as has been well-advertised by the models for a week or more. The system is bringing snow to the High Country - as per Old Faithful above, as well as strong winds to much of the West.

By a week from now - GFS forecast below - the trough is still lingering, with a closed low over Arizona and New Mexico. Question is whether or not this system will tap-into any moisture to bring precipitation to Arizona. The tropical system's moisture down to the south will be shunted off toward Texas. Best chance will be wrap-around moisture coming westward from east of the Continental Divide. In the mean time we can expect dry, gusty winds, and a turn toward cooler temperatures for the weekend.

Tuesday, September 19, 2017

View Of Hurricanes - Continued Dry Here

Edited to add: Visible image of Maria at 2045 UTC this afternoon as she heads toward Virgin Islands and Puerto Rico at Cat. 5 intensity.

Although low-level moisture has inched upward here in southeastern Arizona, considerably more is needed to develop CAPE at low elevations. September has produced only 0.12" rainfall so far, and looks like this month may be turn out to be driest ever since my records started in 1999.

Visible satellite images from 1315 UTC this morning of Cat. 5 hurricane Maria above and Cat. 1 hurricane Jose below. Puerto Rico may be more seriously impacted by Maria than it was by Irma.

Below is from 00 UTC run of the WRF-GFS at Atmo and shows model forecasted precipitation, on 5.4 km grid, out through 5:00 pm MST on September 26th. Pretty grim for Arizona, while New Mexico has very wet conditions east of the Continental Divide.

Monday, September 18, 2017

Tropics Remain Very Active

Edited to add:

From the MAP List - the 12 UTC ECMWF operational forecast of 1000-500 mb thickness, valid at 180-hours. Storm to northwest is Jose, with Maria to his southeast. Same forecast from GFS (both are from operational versions of the models) below is very different.


Very pleasant this morning for walking, with clear, cool, and dry conditions. At 7:00 am MST it was 70 F on campus, 69 F at airport, and 58 F here along the Rillito.

Most weather attention during the coming week will be on the five named tropical storms - especially Jose and Maria. The current NHC status maps for this morning are shown here for both Basins - along with MIMIC TPW at 13 UTC. Here in the Southwest, as Norma pulls slowly away from the GoC, it appears that some low-level moisture will intrude into southern Arizona - so that will be something to watch locally. 

In the Atlantic the long-term future of hurricanes Jose and Maria becomes very complex in model forecasts, with the storms interacting with each other near the East Coast. There may be a Fujiwhara effect, as the storms could circulate around each other, since Jose is forecast to stall and loop to the south - the second time in the long-lived storm's history.

Saturday, September 16, 2017

More Of The Same

Several thunderstorms yesterday afternoon around the flanks of the Catalinas - stubby little Cb above was around 4:00 pm MST. The thunderstorms produced some showers and the heaviest of these stayed just north of the ALERT network stations - three sites on north end of network had very slight amounts of rainfall. Storms produced some CG flashes also - as per 24-hour flash density ending at 7:00 am this morning (below, from and Vaisala).

Edited to add: Turns out NHC named the easternmost system TS Lee and then the "X" system TS Maria.

Most weather action remains in the tropics, as per the morning updates from NHC. In the Atlantic (above) both Jose and the "X" east of Venezula pose threats to the mainland US (appears as if the  "X" spun-up rapidly during the night and is probably already TS Lee.

To our south (below) hurricane Norma is forecast to move toward southern Baja and then be pushed around by the deepening trough over the West.

At bottom is 00 UTC WRF-GFS forecast on 5.4 km grid for total precipitation through 5:00 pm on September 23rd. That model indicates the dry, trough to the north will preavil and keep Norma's impacts to the south.

Friday, September 15, 2017

Early Morning Miscellany

Above plot shows ALERT measured rainfall for past 30 days ending at 5:00 am MST this morning, indicating how miserably dry it has been for most of the metro area since mid-August.

Plot of detected CG flashes (from Atmo and Vaisala) below is for 24-hours ending at midnight last night. Models were right on, keeping most storms north of our area. There were some storms to the south affecting Santa Cruz County, with one storm off to southeast of metro area in Pima County.

Forecast above from 00 UTC WRF-GFS on 5.4 km grid shows precipitation through 5:00 am next Monday. The forecast indicates continued DRY. The heavy rainfall over Baja Sur is from forecast hurricane Norma (Max went inland over southern Mexico) - the nasty trough pattern over the Southwest shunts Norma off toward northern Mexico.

Forecast for 500 mb (from 00 UTC ECMWF) is valid next Monday at 5:00 pm - the western trough continues to amplify in the forecasts through at least the early part of next week.

Thursday, September 14, 2017

Mixed Signals Today

Have an appointment this morning and have only taken quick look at current situation. Photos top and bottom are from yesterday afternoon and evening, when some lonely Cbs developed.

Plot of detected CG flashes through 5:00 am MST (above from Atmo and Vaisala) indicates isolated activity around here yesterday afternoon, and considerable early morning thunderstorm activity over Rim Country, White Mountains, and northwest Arizona.

Morning sounding analysis at TWC from SPC indicates a bit of CAPE this morning , as well as deep southwesterly wind profile with PW of 1.25 inches. WRF-GFS forecast from 06 UTC of TWC sounding (below) is at 2:00 this afternoon, indicating some chance of storms in the area. The surface plot second below is for 7:00 am - Pacific front/dryline has moved into western Arizona. Timing may be an issue with the various models forecasting storms to stay north and east of Tucson this afternoon.

Wednesday, September 13, 2017

Transition Pattern Sets Up Tonight And Tomorrow

Running late this morning.  Of note was the record high of 106 F recorded at the NWS ASOS site at the airport.

The 500 mb cyclone is located just southwest of San Francisco this morning at 12 UTC (analysis above from SPC), and was again associated with widespread thunderstorm activity yesterday from central California  eastward across the Great Basin. Forecast models  finally kick this feature eastward and this morning's 12 UTC NAM forecast of the 500 mb below is valid at 5:00 pm tomorrow afternoon. By then the wind profile will have become southwesterly and strengthened considerably, producing a classic transition pattern for Arizona.

The key forecast question will be how much moisture and CAPE can develop ahead of the short wave. Above is this morning's 12 UTC WRF-NAM forecast of PW valid at noon tomorrow. With PW remaining near and just over an inch, some cooling at 500 mb could lead to CAPE and fast-moving thunderstorms over parts of southeastern Arizona tomorrow.

The morning outlook from NHC for next 5 days (below) indicates considerable activity over eastern Pacific, but long range forecast models are very divergent re where any tropical storms that develop might track.

Tuesday, September 12, 2017

Hot And Dry Run Continues

A few CG flashes yesterday afternoon were detected south to west of Tucson. Another day with no rainfall across the Pima County ALERT network, and with high temperature of 103 F at the airport.
The NWS is going for a near record high around 105 F today - see their web page (link to the right).

The plot of CG flash density above (from and Vaisala for 24 hours ending at 6:45 am MST this morning) shows the thunderstorm activity now stretching from the Pacific cyclone across California and well into the Great Basin. The 500 mb 12 UTC analysis below (from SPC) shows Irma cyclone over north Alabama and the Pacific cyclone west of San Francisco. Banana-shaped anticyclone in between is centered nearly overhead. Rest of week appears pretty dismal.

Monday, September 11, 2017

Quick Look September 11th

A sad day in history made even sadder for those suffering from the impacts of hurricanes Harvey and Irma.

High-based cumulus over the Catalinas yesterday at 3:00 pm MST (above) was about as active as it got yesterday, which was a seriously suppressed day. The plot of 24-hour CG flash density (below, ending at 6:30 am this morning - from and Vaisala) shows that all of southern Arizona had no thunderstorm activity yesterday. Unusual though is the degree of thunderstorms and lightning affecting southern California, which was associated with the persistent cyclone off-shore.

The TWC sounding plot above (from SPC) has PW around an inch, with perhaps a sliver of CAPE during afternoon. Some stronger easterly winds continue in low-levels, as dry air in New Mexico pushes against more moist air out to our west. The warm-air inversion just below 500 mb appears quite formidable also.

At 500 mb (above also from SPC) the huge cyclone, associated with now Tropical Storm Irma, has pushed the western anticyclone westward. this trend will continue as the anticyclone shifts toward the Four Corners and then is nudged southward as the Pacific cyclone shifts northeastward. The anticyclone eventually ends up over northern Mexico. This leads to a Fall-type pattern with a large trough over the West by 00 UTC on 16 September, as per ECMF 120-hour forecast below.

Sunday, September 10, 2017

Irma, Jose, and here

Irma and Jose are both Cat. 4 hurricanes this morning (image above from 1315 UTC). Irma has just passed through the Florida Keys headed northward. This morning's NHC forecast for Jose (below) is quite interesting, with a loop and then heading west again.

Finger Rock at sunrise this morning with both cumulus and lenticular clouds. Continued very dry at low elevations - CG flash density plot below (from and Vaisala) indicates little thunderstorm activity during past 24-hours from southern Sonora northward across Tucson, Phoenix, Grand Canyon and Utah. Storms our part of state were mostly over Sky Islands and higher elevations. Here at house we had a Trace on Friday and nada yesterday.

The 500 mb analysis for 12 UTC this morning (from SPC) shows that we're in a strange, weak flow zone between the Pacific cyclone and the anticyclone over Texas. With time the model forecasts indicate the cyclone to move northward, while an anticyclone consolidates over Sonora, not a good situation. Forecast below (from 00 UTC WRF-GFS 5.4 km forecast at Atmo) is for total precipitation through 12 UTC next Saturday morning. We'll to shift our hopes southward, where more tropical cyclone activity may head northward toward us.