Sunday, September 23, 2018

Dry And Warm Rest Of September


Yesterday was very suppressed, WRT to thunderstorms, across the entire Southwest. Flash density above (from weather.graphics and Vaisala) is for 24-hours ending at 9:00 am MST this morning - as quiet as I've seen the entire Southwest in a very long time.

Forecast below is from the 06 UTC WRF=GFS (on 5.4 km grid) and is for total precipitation through September 30th and is very dry forecast for most of the Southwest. 

Little chance of rain or thunderstorms, along with very warm highs in the 90s seem likely to prevail here until October.


Friday, September 21, 2018

Backdoor Front With Gusty East Winds - Edited 22 September

Update re gusty east winds - airport has gusted briefly to 31 mph and we had gusts along the Rillito from mid-morning to early afternoon of 30 to 35 mph. Mt. Hopkins RAWS site has gusted as high as 61 mph (below), showing how well the WRF forecasts can be used to predict high wind events there.




A Plains cold front is moving southward across west Texas and northeastern New Mexico this morning - surface plot above from NCAR RAP at 7:00 am MST this morning. The front will backdoor across southern Arizona tonight and tomorrow bringing gusty winds from the east.


Forecast above of 10-m winds is from the WRF-GFS at 06 UTC and is valid at 4:00 am tomorrow morning. This forecast indicates possible gusts around 30 mph for the metro area after midnight and into the morning tomorrow.

The forecast skew-T for Sonoita (below from same run and valid at 7:00 am on 22nd) indicates east winds below 700 mb of 20 to 30 kts - this forecast, if it verifies, would bring an east wind event to Mt. Hopkins during the night with gusts in 45 to 65 mph range. 

Thursday, September 20, 2018

Significant Rains Yesterday


Yesterday's widespread heavy rains left behind very moist air that led to fog and stratus fractus this morning. Above photo from about 6:30 am MST along Rillito - Finger Rock through the fog. Below is view from campus at 7:15 am.



The event yesterday (somewhat similar to the June event) resulted from a tropical moisture intrusion interacting with an advancing trough in the westerlies. Also playing a role was TD-19 (as per NHC); however, Art Douglas sent along observations from Mexico that indicate the system was likely a tropical storm in the lower third of GoC. 

Plot of detected CGs above (from Atmo and Vaisala 24-hours thru 10:00 pm last night) shows that thunderstorm activity with the event was quite limited and mostly occurred before noon yesterday morning.


Significant amounts of rain fell across the entire ALERT network - plots ending at 5:00 am for north portion above and south portion below. There were 45 sites that recorded over an inch of rain and 16 had over two inches. The two reports of more than three inches came from Samaniego Peak in the Catalinas and from Altar Wash at Highway 286. Here at house we had 0.65", while airport had 0.76", as did Atmo (DM ASOS has been out of service a couple of days). The Rillito was flowing this morning and apparently had reached bank-to-bank levels at a couple of spots between USGS gauge at Dodge and the Campbell Ave. bridge. Plot second below shows the flow peaked at about 2700 cfs around midnight.



The WRF forecasts indicate a quiet day today, with perhaps some storms over mountains off to east. While low-level moisture persists, dry air is intruding across Arizona at middle and high levels and this will cap deep convection. The MIMIC plot below is from 6:00 am and is the analysis of PW in the layer 700 to 500 mb - very dry air west of the 500 mb trough.

The longer-term global forecasts indicate some hope for another intrusion of tropical moisture before the month closes out.

Wednesday, September 19, 2018

Rain Today? How Much?


An unusual sunset last night with lavender hues (above), while there was a more distinct orange to purple sunrise this morning (bottom).



Thunderstorms yesterday were mostly southeast to southwest of Tucson (as per detected CG flash plot above for 24-hours ending at 12:30 am MST this morning - from Atmo and Vaisala). The interesting sunset colors were in the anvil clouds coming from Santa Cruz and a tiny corner of Pima Counties.

Four ALERT sites had rainfall of 0.04" and more last evening between 5:00 and 10:00 pm - these were the southern stations with very slight amounts, except Arivaca at 0.47". Nogales reported 0.45".


This morning Arizona is increasingly under the influence of the approaching West Coast trough - analysis of 12 UTC 250 level from SPC. A piece of that trough appears to extend down the GoC and will likely be an important player in today's weather events. Also of interest is the distinct Rex block over south-central U.S.

The morning skew-T plot of TWC upper-air data (below, also from SPC) indicates PW up to 1.75" in a very wet atmosphere. Winds aloft are better organized, veering from southeast at 600 mb to southwest in upper-levels. The old, surface based BL appears to have over 1000 J/Kg CAPE, but with considerable lift required to reach the LFC a bit above 700 mb.



The upper-tropospheric water vapor image above, for a bit after 7:00 am, shows the huge plume of moisture from south end of GoC north to southeastern Wyoming. Looks like very little solar heating during the day, so the approaching trough from GoC will be important for our local rainfall.

The model forecasts agree on rain today at TUS but possible amounts have large range. The 12 UTC WRF-RR (below) forecasts 1.2" through 6:00 am tomorrow morning (06 UTC NAM version forecasts 0.3" and GFS version is at 0.8"). This version of the model forecasts extreme amounts of up to over 6 inches on the mountains of Santa Cruz and Pima County. The 06 UTC GEFS plumes for Tucson indicate a QPF range from 0.2" to 1.25" through 6:00 am tomorrow.

Thus, a wide range of possible scenarios for the day - will sit and watch now. - I see that current radar indicates that a large thunderstorm has already developed west of Tubac - an interesting start. 


Tuesday, September 18, 2018

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!

Monday, September 17, 2018

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.

Sunday, September 16, 2018

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.


Wednesday, September 12, 2018

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.


Sunday, September 09, 2018

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.


Friday, September 07, 2018

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).
---------------------------------------------------------------------------------
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 5th and August 1st.



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.