Significant Weather Report From Neighbor John Ferner

                                                               11 am today

                                                                  2 pm today

Summary Yesterday Plus Latest Look Ahead To Christmas

First, the NWS posted snowfall information for reports yesterday (Thursday) morning. (Note - having some text formatting problems this morning.)

PUBLIC INFORMATION STATEMENT
 NATIONAL WEATHER SERVICE TUCSON AZ
 1140 AM MST THU DEC 18 2014
 
 ...STORM TOTAL SNOW AS OF THURSDAY MORNING...
 
 LOCATION          STORM TOTAL     TIME/DATE   ELEVATION                  
                      SNOWFALL           OF 
                      /INCHES/   MEASUREMENT
 
 ...GRAHAM COUNTY...
    MOUNT GRAHAM           6.0   900 AM 12/18  10600 FT                
    3 S MOUNT GRAHAM       3.5   900 AM 12/18  9000 FT                 
 
 ...GREENLEE COUNTY...
    HANNAGAN MEADOW        6.0  1100 AM 12/18  8900 FT                        
    6 NE HANNAGAN MEADOW   1.0  1100 AM 12/18  8000 FT                        
 
 ...PIMA COUNTY...
    3 SE SUMMERHAVEN       9.0   900 AM 12/18  7900 FT                 
    MT LEMMON SKI          8.0   900 AM 12/18  9100 FT                 
    SUMMERHAVEN            8.0   900 AM 12/18  7800 FT                 
    2 SE SUMMERHAVEN       6.5   900 AM 12/18  8200 FT                 
 

Although there was more snowfall during day yesterday, I 

have not seen any updated information.

About 60% of the ALERT network stations measured additional

rainfall yesterday. Two mountain sites had 0.31", 7 sites 

had 0.20" or more, and other reports were light. Here at 

house we had mid-morning showers that produced another 

0.04". 

This morning it is cold and frosty here and some spots in 

Arizona are reporting thick fog this early morning.

---------------------------------------------------------

Christmas is now within seven days and here is update on 

what ECMWF and GFS global models are forecasting for North America.

These 168-h 500 mb and sfc forecasts are again valid at 5 pm MST Christmas afternoon (as per the earlier post showing 240-h forecasts). Top forecasts are from the ECMWF and those below are from the GFS, 

The ECMWF continues to forecast a strong, winter storm system over the West. It is now forecasting a considerably stronger storm just northeast of the Great Lakes Region that would bring lake effect snows and general snows for much of New England. Features in the ECMWF forecast continue much stronger than similar features within the GFS forecast.

The GFS forecasts seem to be trending toward the ECMWF solutions. The GFS now forecasts a wintry, upslope storm from Colorado to Montana. The storm impacting the Great Lakes and New England is shifted north over Hudson's Bay, with mostly lake effect snows within its forecast.

Will check back a couple more times as the Holiday approaches. Air travel could be snarled the day before Christmas in Chicago and the big Northeast Airports. Travel after Christmas could be difficult through Denver and Chicago, so stay alert if you're heading those directions.

More Light Showers Moving In

More showers approaching Tucson early this morning - December 18th. Composite radar chart above is from a bit before 6:00 am MST. These showers are quite light compared to some of the moderate to heavy showers that passed through the area yesterday afternoon. There were also a few CG flashes in eastern Pima County, so there were isolated thunderstorms mixed in with the showers. Here at the house we ended up with 0.51", which was a fairly typical amount at the lower elevation ALERT stations. Heavy precipitation on mountains with snow occurring at highest elevations. Web cam from Summerhaven below is from early afternoon yesterday. Couple of stations on Redington Pass had over an inch of rain. So quite a nice event.

Light Rain Across Tucson Area Before Sunrise

EDITED AT 07:30 MST TO ADD - Just checked the rain gauge and total here so far is 0.12". At 06:00 am MST ~90% of the 92 stations in the ALERT network had measured rainfall, with amounts generally less than 2/10ths of an inch. 

Woke up to rainfall here at 5 am MST (above composite radar plot from NWS TUS radar is for 6 am). The showers and rain developed with the first Pacific, middle and upper-level, short-wave that had been forecast by various models to cross southern Arizona during the past night. Models varied in forecasts of precipitation with this first wave. The water vapor satellite image below is also for 6 am. It shows that the short wave, in the upper half of troposphere, is already along the Arizona/New Mexico border. But there is a smaller-scale feature passing over eastern Pima County at the time of the image, and the showers seem to have developed with this feature. The next Pacific short wave is just off the coast of southern California.

A plot of detected CG lightning flashes through 5 am MST is shown above and indicates considerable thunderstorm activity over northern Sonora. There had been a couple of flashes just on this side of the border at the time of the plot. 

Plot of the morning sounding from NWS Tucson is shown below from the Storm Prediction Center in Norman, Oklahoma. The tropopasue is nearly saturated through its depth (red line shows measured temperature along the track of the balloon and green line shows dewpoint temperature). The temperature profile indicates the top of the troposphere (topopause) is at about 350 mb (~ 8 km above the ground level at the NWS office). Winds observed along the path of the balloon are plotted vs height at the right, and are in knots, Precipitable water was calculated to be a bit more than 2/3rds of an inch (precipitable water is the total depth of water vapor measured through the atmosphere by the sonde instrument). It is the amount of PW and the profile of RH that help to determine the likelihood of clouds and precipitation. This is a general overview of what this graphic shows, in response to a question a few posts ago. So, the showers are not surprising given the very moist character of the atmopshere this early morning.

The SPC provides a nice interactive page to answer questions about what's plotted on the diagram as well descriptions of the parameters they calculate from the data. This can be found at:

http://www.spc.noaa.gov/exper/soundings/help/index.html

Very-Long Range Model Forecasts For Christmas

The short-term forecasts have considerable fluidity as the model forecasts are a bit volatile. So, I thought I'd look all the way out to Christmas Day, just out of curiosity. By 240 hours out, the GFS ensemble spaghetti plots do indeed look like a bowl of the same.

So here goes. Above are the ECMWF 500 mb and surface forecasts valid at 5 pm MST on Christmas Day. Below are the same two forecasts from the GFS. Both are from the operational versions of the models. The ECMWF is shown "on the top" for obvious reasons.

The ECMWF forecasts the most significant weather action to be over the West with a strong cold front crossing the Southwest, a strong low pressure system over Colorado, and nasty upslope snow from eastern Colorado north to Montana.

The GFS patterns are generally similar but considerably damped. The model forecasts an east-west cold front across the U.S., no significant low pressure systems in the interior, and scattered areas of light snow across the northern half of country. The small area of heavier snow forecast southwest of Chicago seems to be right where the ECMWF forecasts the greatest 500 mb height rises that would likely be accompanied by considerable downward motion. 

In eight to ten days, or so, we'll know how these forecasts actually played out. Cheers.

Unsettled Weather To Continue This Week

The weather here in the Tucson area and southeast Arizona will continue unsettled as we head toward Christmas. This is well indicated by the current NWS forecast probabilities of precipitation (POPs) at the airport - Wed 50% Wed Night 70% Thur 70% and Sun 30%.

However, the global forecast models (GFS vs ECMWF) have considerably different details within their respective forecasts. Shown above are the 500 mb forecasts valid at 5 pm MST on Wednesday (GFS top and ECMWF bottom). The short wave and vorticity maximum forecast by the ECMWF to be over the Texas Panhandle is much weaker and faster in the GFS forecast. However, the short wave over the Southwest is essentially similar in both forecasts, although the GFS has considerably more small-scale structure and a more complex vorticity field. So, the exact timing and details of what will happen here is not well-defin, even for the short term.

The forecasts below are longer-term and are valid at 5 pm MST next Sunday, December 21st. The closed low forecast to be over the Southwest by then is slower and considerably stronger within the ECMWF forecast. The ECMWF forecast, were it to verify, would lead to a stormy, wet and cold day for us next Sunday. The ECMWF also forecasts a significant coastal storm to impact the middle Atlantic coast next Sunday; whereas, the GFS forecasts much higher heights and zonal flow over that region. So, considerable uncertainty about the details of the weather for much of country persists through the week - keep a close eye on things if you plan to be travelling next weekend.

Brief Overview - Sunday Morning

When it rains in desert people sometimes lose their grip on reality (photo by Mike Christy, Arizona Daily Star).

Graphics here show 24-hour precipitation amounts across the ALERT network (for sectors covering the Catalinas, Rincons, and metro Tucson) at 7 am MST this morning. Coverage over eastern Pima County was 100%, but with a large range in amounts, as the figures illustrate. If there was snow, it was at the highest elevations of the Catalinas and Rincons. The highest rainfall measurement was just over two inches at the Mt. Lemmon ALERT station. One site southeast of here indicates only 0.04". If that's a good measurement, then gradients were over 2 inches across a fairly short distance. Here at the house we got 0.41", thanks to several fast moving, moderate showers that seemed to develop just upstream on the Tucson Mountains and then come right across our location. Art Rangno out in Catalina reports about 2/3rds of an inch. This has been yet another event where the skill and accuracy of the model predictions was very impressive, out to and just beyond 7 days!

Also a damp and frosty morning here at house with the temperature a couple of degrees below freezing - too early though to know exactly the low will come in at.

The details of the global models (at least ECMWF and GFS) are considerably different in our area, but both models forecast another event in the Wednesday/Thursday time frame and then another around next weekend. I note that the GFS ensemble members all seem to forecast precipitation over southeast Arizona for Wed/Thur, and the current NWS for the airport reflects this with 50% POPs Wednesday and 60% Wednesday night.

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).