Update And Monsoon "Start"

View looking toward the Rincons at around 4:30 am MST this morning.

There is an article in the the morning paper that states the 2026 monsoon has arrived, right on time. However, this is based on the NWS definition of a "Monsoon Season" running from June 15th to September 30th. This definition ignores the actual meteorological conditions that might be prevailing.

Yesterday's 0.19" of rainfall presents an example of the problems of the seasonal definition.

The rainfall was associated with a weak shortwave that sneaked in from the Pacific - consider the 500 mb charts from the 06 UTC GFS forecasts.

The 500 mb chart for this morning (above) shows the weak disturbance over Arizona. The 7-day forecast (below) shows the typical monsoon high at 500 mb situated across central Baja, with a weak trough still across Arizona. The fourteen day forecast (bottom) indicates a large trough dominating the western US at 500 mb. There is no indication in the forecasts of the typical Four-Corners anticyclone that defines the summer monsoon circulation at 500 mb. So, if the forecasts are accurate, the start of the summer monsoon, from my perspective, remains several weeks away.

Stormy

Skies clearing at 11:00 am MST. Current rainfall reports across eastern portions of the ALERT Network (below) indicate amounts up to just over an inch. Here at house there is currently just 0.19" in the gauge.

Several periods of showers and some thunder beginning yesterday evening and continuing this morning. At 6:45 am (view above) there was only 0.06" in the gauge but more rain has fallen since. Will update things later today. Plot of detected CG flashes (below - from Atmo) shows considerable activity over eastern Pima County through 1443 UTC.

Mysterious Radar Echoes

Map above shows the Goldwater Range and the Army's Yuma Proving round, with I-8 stretching through a narrow corridor from Gila Bend to Yuma.

Tuesday afternoon (June 9th) I noticed some radar echoes out northeast of Yuma around 3:45 pm MST (above and below). The echoes were only present in the lowest two tilts of data and were moving north-northeastward. Skies were, however, perfect clear - see concurrent visible satellite image - second below. Note that bird and insect migrations usually occur in the evening and during the night. So what was going on?

I assume that some exercise or activity at Yuma Proving Ground injected chaff into the near-surface atmosphere. Below is some kind of big armament out at Yuma Proving ground. The echoes dissipated after an hour or so. There was no similar activity yesterday afternoon. There was also no mention of the strange echoes in either the Tucson or Phoenix NWS weather discussions covering the relevant times. This event was also reminiscent of the high-level chaff releases that the Air Force used to do over the Goldwater Range. 

Moonrise and Sunrise

Rising quarter moon, looking toward the Rincons about 2:30 am this morning. View at bottom is a bit before sunrise.

Plumes from GEFS rins at 06 UTC this morning. Above shows QPF amounts at the airport, indicating chances for light showers around the weekend.

The plumes for PW exceed and inch over the weekend (above); and POPs for the airport (below) stay under 30 percent. Will have to watch how the plume forecasts evolve as weekend approaches.

Tropical Storms Boris and Cristina

 

Tropical Storm Boris has developed early this morning over the eastern Pacific. As the NHC graphic (above) shows, Boris is just south of the coast of southern Mexico. The storm is forecast to be  short-lived and to move ashore this afternoon. 

Updated at 1800 UTC today 8 June: The NHC has upgraded the second disturbance in the eastern Pacific to Tropical Storm Cristina. Current track forecast shown below.

Summer Outlook

View toward the Rincons at 5:30 am this morning - a bit after sunrise.

This spring (Mar, Apr, and May) was relatively dry here with only a total of 0.66" of rain. Since 1999 this was the 11th driest spring. The wettest spring here was 2004 with 2.71", while the driest was in 2018 with only 0.03" for the three months.

The current NWS Climate Prediction Center (CPC) outlook for this summer is below - they expect the warmth over the West to continue, along with a slight chance for above normal rainfall. Of course, one big storm day here can determine the character of the entire summer - so we will watch to see how things evolve.

Eastern Pacific Tropical Storm

The eastern Pacific is fairly active as we head into June - above. Tropical Storm Amanda is the first of this season.

Her center is just to the east of the stroger storm cluster in the 1350 UTC IR image above. The storm is far southwest of Baja and poses no threat to land. The forecast from NHS early this morning is shown below. It keeps Amanda at TS levels as she drifts generally westward.

Storms Yesterday

View of heavy storm over the Catalinas and foothills at 5:45 pm MST yesterday afternoon.

Plot of CG flashes detected during 24-hours ending at 7:30 am this morning. Note the abundant activity across eastern Pima County.

Rain from the ALERT network (above) for 24-hours ending at 7:00 am this morning, and for same period from CoCoRaHS at Atmos Science page CSU, Ft. Collins CO, across low-elevations of the metro area (below). Here at house we had two brief showers between 3:00 pm and 6:00 pm yesterday afternoon. There was thunder and wind to around 30 to 35 mph with the second shower. Total rainfall was only 0.07" here.

Very Isolated Showers

 Update - only four ALERT sites had rainfall yesterday of 0.04" or more (one of these had 0.08"). Sites were in the Catalinas, plus one at far southwest corner of network.  In sum, a very quiet day across the metro area.

Widespread Rains

Showers on Catalinas and foothills at 6 pm MST yesterday afternoon.

There were widespread rain reports across the ALERT Network yesterday (above and below) for 24-hours ending at 7 am this morning. A couple of the null reports look a bit suspect. Here at the house we had 0.31"; the airport had 0.23"; DM AFB reported 0.32"; and Atmo had 0.16". This was first significant rain here since March 10th.

The 09 UTC SREF plumes for QPF at TUS (above - from SPC webpage) show several  members indicating very light amounts after 12 UTC at the airport, but with a few showing over a quarter on an inch. The current morning forecast from the NWS for the airport (below) indicates slight chances for showers and thunder today. We shall see.

A Dry April

It looked promising late yesterday afternoon - view of the Catalinas above from 5:45 pm MST.

However, measurable rain stayed to east and south of the metro area. ALERT observations (above) are for 24-hours ending at 9:00 am this morning. There was no rain at the house during all of April, making this one of 8 Aprils with no rain here since 1999.

The plumes from the 06 UTC runs of the GEFS (below) indicate slight chances for light showers around the 5th of May. 

Chance For Showers Mid-Week

Clear skies over the Rincons pre-sunrise this morning (note - sunrise was at 5:42 am MST).

The 06 UTC GEFS plumes for temperature (above) indicate a distinct cooling at mid-week, as April draws to a close.

Plumes for QPF at the airport (above) indicate chances for measurable rain on the 30th and 1st of April and May. There's a large range in both the timing and amounts among the various ensemble members.

The GFS forecast from the 06 UTC run (below, for 500 mb) indicates a distinct shortwave from Wyoming south-southwestward across the Four Corners, Tucson, and central Baja at 00 UTC on May 1st.

The GEFS POPs for the airport (bottom) reach above 50 percent on the 30th. So far, April has been rain-free here at the house, so Thursday and Friday will be interesting.

Earth Day 2026

 

Thanks to Walt Kelly and Pogo for this graphic.

And also to Charles Schulz' Snoopy.

Windy And Slight Chance For Showers

Note added Tuesday - several sites northwest of the Catalinas had sprinkles and a Trace yesterday afternoon. Nothing here at the house.

Clouds and a bit of virga overhead at 7:30 am MST this morning, but with some blue sky off to the north.

NWS graphic shows forecast wind gusts for southeast Arizona (above) - gusts at the airport yesterday reached 32 mph.

 Plumes for QPF (from 09 UTC runs at SPC) shown above indicating chances for light showers into tonight. Current NWS forecast for the airport below. There has been no rain here at the house since the end of March.

Isolated Showers End March

View of the Catalinas at 2:00 pm MST yesterday afternoon, March 31st. Reports across the ALERT Network are shown below for 24-hours ending at 8 am this morning. Here at the house we had 0.01" a bit before 2 pm. Monthly total for March was 0.28", with rainfall on only two days. I did note a thunderstorm on the 9th. The month closed out with considerable winds and dust.