Showers Out To The West Currently

At a bit past 6 am MST this morning there were light to moderate showers (composite radar from TUS above) out to the west and northwest of Tucson - from Sells to Marana and on north into the Phoenix area, where coverage was more substantial. The TUS morning sounding (below) has moistened considerably below 700 mb and deeper moisture will move into eastern Pima County as the front approaches this morning.

Quick Look At Tomorrow's Weather Event

As I had mentioned a number of days ago, the Winterhaven Festival of Lights seems to draw in several winter storms during its two week run. This year things are right on track, as the Festival kicks off tomorrow - Saturday, December 13th. This will be a quick-hitting frontal event, as the forecast models have been predicting for more than a week now.

There has been a pronounced atmospheric river (AR - aka the Pineapple Express) ahead of and along the Pacific front. This has brought a fairly warm and very wet storm to California, with snow levels at fairly high elevations. The above graphic (CSU CIRA blended PW analysis for 12 UTC this morning) shows that the AR may be losing some of its organization. But, PW values of an inch or so have nosed up the GoC and are a bit higher along west coast of Baja. So, the system will pull some decent PW northward at lower levels to feed showers and moderate convection along the front as it crosses southeastern Arizona tomorrow.

The forecast sounding for TUS (below, valid 11 am MST tomorrow) is from the WRF-NAM early run (both versions are fairly similar this morning) and indicates a bit less than 1 inch of PW that is mostly below 600 mb (there is also a bit of CAPE forecast, again below 600 mb).

The WRF runs forecast the front to cross eastern Pima County during the late morning/early afternoon. Graphic above is of WRF-GFS forecast composite radar echoes valid at 10 am Saturday morning. The WRF-GFS forecast below shows the models forecast of accumulated precipitation through 5 pm MST tomorrow afternoon. The model forecasts the event to just brush southern Arizona with light rainfall, keeping the main impacts to our north in eastern Maricopa County and the Rim Country, although the high elevations near Tucson pick up heavier amounts than the low elevations.

The WRF model has, for reasons that are not obvious, underplayed the forecasts for the last several precipitation events, and this will likely be the case again with tomorrow's event. I expect that the lower elevations of eastern Pima County will pick up some higher rainfall amounts than the model is currently forecasting.

Finally, to put this weather event into a regional perspective, the graphic at the bottom is the WRF-NAM forecast for accumulated precipitation through 5 pm tomorrow, on the 5.4 km grid. California continues to catch the brunt of this storm, with very heavy rains forced by both the southern coastal ranges and the Sierra Nevadas. 

Overview Of Current NWS Forecasts - Morning, Thursday 11 December

The following summarizes the current NWS forecasts for our area as the forecast Saturday storm for here is currently bringing winds and nasty winter weather to northern California.
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First - the forecast for the grid box that includes the airport, TUS:

Showers likely. Mostly cloudy, with a high near 62. South wind 10 to 15 mph becoming west in the afternoon. Chance of precipitation is 60%.

For perspective, the grid box POPs for Mt. Lemmon for Saturday are currently 90% for rain and snow during the day (note Saturday means between 5 am and 5 pm MST).

From the NWS Glossary - POPS means: The probability that precipitation will be reported at a certain location during a specified period of time. (Precipitation means an amount of 0.01" or more.)

Second - the broader area forecast for southeast Arizona:

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So, it appears that we will likely have our second rain event of the year, down here in metro Tucson, before we are even halfway through December.

Showers For Next Saturday?

There is a middle and upper-level cyclone/short wave crossing Arizona today, but this system remains moisture-starved. Main weather of significance today appears to be the dense fog over the northeastern quarter of the state.

The global models forecast a stronger, 500 mb short wave to cross the West next weekend. The GFS operational forecast of 500 mb (above) is valid at 5 pm MST next Saturday. The strongest part of this wave crosses southern Arizona, within a southern branch of the flow. The northern portions of the short wave are poorly organized in the current model forecasts.

Below is GFS forecast, again the operational member, of precipitation through 5 pm on Saturday. The southern edge of the precipitation forecast runs along the border - this indicates that, due to coarse terrain resolution of this model, upslope flow in the model is related to the precipitation. So the main forecast problem will again be lower-level moisture available ahead of the system. If moisture remains low, as indicated by current PW forecasts, then precipitation will stay over higher elevations to the north of us. 

Currently the NWS forecasts a 30% probability of rainfall over the low elevations of metro Tucson. In the GFS ensemble forecast from 00 UTC last evening 10 of 12 members forecast precipitation over southern Arizona, but again with the southern edge close to the border. The ECMWF appears less bullish for precipitation - but my access to output from the model is quite restricted.

November Summary

Nice colors on the Catalinas at sunset last evening.

Summary for November here at house is pretty short. Rainfall - NONE. Morning low temperatures in the 30s occurred on 8 days, while lows in the 20s occurred on 9 days. Freezing or below morning temperatures on 11 days, with the coldest morning being the 24th at a frigid 21 F.

The first week in December has already proved more interesting than the entire month of November, at least weather-wise.

Typhoon Hagupit Weakens

Once Super Typhoon Hagupit has weakened as it struck into the Philippine Island chain. The storm is now rated at about 90 mph as it heads toward a brush with Manila. The graphic below shows detected CGs during the 12-hours ending at 14 UTC this morning. There was little CG/W activity associated with Hagupit as the storm approached the Philippines. This was a marked contrast with Super Typhoon Haiyan of November 2013, which was very active electrically. I have a CG plot for last year's storm somewhere in my 2013 archives and will search it out later today for comparison.

Above graphic from Vaisala shows 24-hours of CG/Ws with Super Typhoon Haiyan during November 2013.

Weak Short Wave To Cross Arizona Today

A weak short-wave trough in middle and upper levels will cross Arizona today. However, even though this system brought some sloppy rains to California, it will bring mostly middle and high level clouds to Arizona with perhaps a few sprinkles. The 13 UTC IR image (above) does look impressive, with the wave very distinct to the west of Baja. However, the MIMIC loop of PW (image below is from 10 UTC) indicates the highest PW (light greens) is actually now retreating south and southwestward. The early WRF-NAM forecast of PW (second below valid at noon today - Saturday, December 6th) indicates PW values remaining near and below an inch as the system moves over Arizona. The WRF runs indicate a bit of precipitation at highest elevations only.

The GFS ensembles (above is 500 mb average and spaghetti plot) indicate a ridge dominating much of North America through Tuesday/Wednesday and beyond for the coming week. Only "spaghetti" in the 96-hour plot above is within a weak southern branch of the 500 mb flow that is of little consequence for the Southwest. So a good week for those folks over in Winterhaven, who will be putting up decorations for their Festival of Lights.

Showers Or Sprinkles Tomorrow?

Has become a dreary day with cirrus spreading over Arizona from the Pacific, as another weak short-wave approaches at middle and upper levels. View from Kitt Peak above is from 10 am MST. Visible satellite image below is from 9:30 am and shows deep convection west of California.

Graphic above shows detected CG flashes during the 12-hours ending at 9 am MST. The MIMIC PW from CIMSS at University of Wisconsin, below, shows a substantial blog of higher PW west of California and another broad plume of tropical moisture spreading northeastward west of Baja. Key issue for tomorrow will be whether or not this southern plume makes it into Arizona. The new run of the WRF-NAM this morning forecasts light showers and sprinkles across eastern Pima County late tomorrow morning - forecast of composite radar at bottom is valid at 10 am MST tomorrow (Saturday, December 6th).

Much Needed Rain Across Eastern Pima County

Rain had ended here at the house by 1 pm MST yesterday and by 3 pm (above) skies were mostly clear, clean, and sparkling, bringing a beautiful afternoon and evening to Tucson area. Here at the house our rain totaled up to 0.88".  Across the ALERT network amounts were heaviest over the Catalinas, reaching almost three inches at two stations. Across the low elevation metro area amounts were generally between a half and one inch. However, across the southern portions of the network amounts were lighter, generally less than half an inch. The rainfall sector plots from ALERT below are for the period midnight through 6 pm MST on Thursday, December 4th - top Catalinas; middle west Metro; bottom east Metro.

Meanwhile, on the other side of the Pacific, Super Typhoon Hagupit is approaching the Phillipines. IR image above shows the storm and graphic below is the current forecast for the storm from the Joint Typhoon Warning Center. Last year Super Typhoon Haiyan crossed the island chain in early November, causing massive destruction and thousands of deaths.

Rain Across Much Of Southeastern Arizona This Morning

Weak short-wave at 500 mb will move rapidly across Arizona today, interacting with the tropical moisture plume we've been following past few posts. The NAM 500 mb analysis at 12 UTC (above) shows the short wave approaching Arizona - current NAM forecast is for it to move to central New Mexico by evening. The plume of very high (for December) PW extends into much of Arizona with PWs of more than an inch - analysis below is blended PW at 13 UTC from CIRA at Colorado State with greens indicating PWs of an inch or more..

Composite radar (above) from NWS TUS at 7:18 am MST indicates rain and some heavier showers across most of Pima County - there have been lightning flashes and thunderstorms out to the west and northwest during the early morning hours.

So far (through 7:20 am) amounts over the city have been around 0.25 to 0.30", but with rains continuing. All but 4 ALERT stations had recorded rain through 7 am. Amounts were highest over the Catalinas (above). Graphic below shows rain amounts so far over the west central part of City and on out to west. So far, a nice and very welcome rain event - our first in many weeks.

Light Showers Across Pima County

There were light showers and sprinkles across the area last evening and during the night. Most places recorded only a Trace (as we did here at house). There were 10 of 92 ALERT stations that recorded 0.04" or more for past 24-hours. These were in the Catalinas and the southwest sector of the network - 3 sites measured just over 3/10 of an inch.

This morning the tropical moisture plume has reached into the Southwest, with PW greater than an inch (greens) over most of southwestern Arizona (29 mm here at TWC this morning). The GPS system on campus has been down for quite a long while. Above is blended PW analysis from CIRA at Colorado State valid at 12 UTC.

The early WRF-NAM forecasts the plume to move across southern Arizona tomorrow and also to weaken as it does. Forecast below is of PW on the 5.4 km grid and is valid at 5 am MST.

The best chances for area-wide rainfall occur tomorrow as what is left of the Pacific cyclone moves across Arizona as a weak short-wave. The WRF-NAM forecast above is for composite radar echoes and is valid at 9 am MST on Thursday the 4th. Below is the WRF-NAM forecast of rainfall amounts through 11 pm on Thursday night, with some decent amounts forecast for lower elevations. Last rainfall here at the house was back on October 19th - so some real rain would be very nice.

Tropical Moisture Plume Has Moved Directly Northward

EDITED at 9:30 am MST - have added the new NAM forecast of precipitation through 5 am on Friday, the 5th, since it is so different than the GFS. See below.

The moisture plume from low-latitudes that I showed in yesterday's post has moved northward, directly toward the LA Basin during past 24-hours. The graphic above is from CIRA (at Colorado State) and shows their blended PW analysis for 12 UTC this morning (December 2nd). This is a very impressive moisture intrusion and it will serve to increase the chances of rainfall across Arizona as the week progresses. Graphic below shows CG lightning flashes detected for 12-hours ending at 1:30 am MST this morning. There was considerable thunderstorm activity west and southwest of California during the night - both directly associated with the Pacific 500 mb cyclone and also within the tropical moisture plume.

The forecast models continue to weaken the cyclone rapidly as it begins to move toward the coast today, But the GFS has begun to again forecast rainfall over the Southwest, as the weakened short-wave moves across northern Arizona (GFS had gone dry for the last couple of days, after earlier forecasts that had indicated both the moisture plume and rainfall coming into Arizona). The GFS operational forecast from 00 UTC last evening (above)now forecasts a widespread precipitation event for Arizona for period ending 5 am MST on Friday the 5th. So, it appears that the most interesting weather for southern Arizona will occur from late tomorrow into Thursday. 

Below is the NAM forecast from 12 UTC this morning for precipitation through 5 am MST on Friday, i.e., for period ending at same time as GFS forecast shown above. Although NAM forecasts moisture plume to affect all of Arizona, it only forecasts precipitation for the higher elevations of northern Arizona - so two quite different model forecasts.

High Clouds from Pacific Over Tucson Area And Much Of Southwest

We've been away a couple of days but are now back after the Holiday and looking forward to a new month.

December starts here with a fairly wide-spread cloud cover, high clouds and some middle clouds, intruding into the Southwest. Visible image above is from 8 am MST this morning (December 1st).

The MIMIC PW analysis from CIMSS (Univ. of Wisconsin - below) is for 12 UTC this morning. The large closed low apparent to the west of California is forecast by current model runs to weaken rapidly as it moves eastward. This circulation has a narrow atmospheric river wrapping into it. However, a much more substantial and broad moisture plume from low-latitudes is pushing northeastward toward southern California and models indicate that this plume will also wrap into the weakening middle and upper level system. This moisture will spread over Arizona tomorrow, bringing an unsettled day with some winds, virga, mammatus, and some light showers.

The early run of the WRF-NAM at Atmo forecasts a fairly rapid moistening of the atmosphere as the moisture plume moves overhead tomorrow - above is the model's forecast of the sounding for TUS at 5 pm tomorrow. PW has increased from only 7 mm at initialization time to almost 30 mm. The model does not develop much in the way of CAPE, but the deeply saturated environment (assuming the forecast verifies well) should support some showers. The model's forecast of accumulated precipitation (below) through 11 pm Wednesday night keeps meaningful precipitation to our north. However, the forecast appears a bit conservative to me, given the forecast sounding, so tomorrow may be more unsettled than indicated by the forecast model.