A Dreary Sunday Morning

Sunrise yesterday (Valentine's Day) painted the eastern sky an appropriate red. Photo above was from Santa Rita Abbey northwest of Sonoita, looking toward the east.

This morning, skies are dreary with a overcast of middle-level clouds (view of Catalinas below from about 7:30 MST) associated with the 500 mb closed low off of central Baja. That feature will pull eastward and weaken later today and tonight, while brutal winter weather continues over much of the central and eastern U.S.

Precipitable water (PW) has increased to around an inch over lower elevations of southern Arizona. The 13 UTC blended analysis from CIRA at Colorado State (above) indicates values well over an inch over the northern GoC and along the Borderlands. The sounding below (fromTWC at 12 UTC this morning) indicates little resistance to vertical motion above 700 mb. So sprinkles and light showers will be the weather word for today and tonight. Some spots may get measurable amounts, especially along the Borderlands, perhaps as far north as eastern Pima County. 

Check On Long-Range Verification

In an earlier post I had highlighted the 168-hour global model forecasts that were valid at 00 UTC on today, Friday the Thirteenth (i.e., at 5:00 pm MST yesterday). Forecast above is the GFS 500 mb 168-hour forecast and below is the NAM 500 mb verifying analysis. Both the GFS and the ECMWF forecasts were certainly good approximations of the large-scale features present last evening. But the weather is in the details, and both models over did the size, intensity, orientation, and location of the small 500 mb closed low that is currently over southern Baja. So, close but no cigar for the models. The accumulated precipitation forecast in the GFS for period ending at 5:00 pm MST yesterday was extremely over done and was mostly a no show in the Southwest.

The small, digging system did bring strong winds from southern New Mexico westward to the Pacific. Ron Holle was driving from San Diego back to Tucson yesterday and reports winds estimated at 60 mph as he crossed the coast ranges on I-8. Mt. Hopkins RAWS station measured 84 mph at mid-morning yesterday and is still gusting around 50 mph this morning. So it goes.

Strong Winds This Morning

Gusty winds impacting southeast Arizona this morning with a number of observation sites reporting gusts of 30 to 40+ mph. Here at house winds seem to be about 30 mph. Douglas hit 46 mph last evening and Mt. Hopkins RAWS is currently reporting winds of 62 with gusts to 81 mph! 

Mike Crimmins noted yesterday:

I just came across this interesting paper a couple of weeks back...
http://journals.ametsoc.org/doi/abs/10.1175/MWR-D-11-00203.1
I didn't realize that digging troughs were such a common feature across the SW this time of the year. Too bad we didn't have some more moisture to work with today.
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I think that short waves that dig both southward and westward are more rare than those reported in the paper linked above. Currently models close the 500 mb low off and eventually move it west of Baja before it starts back toward the Borderlands. Latest WRF forecast runs indicate moisture and showers late Saturday and Sunday moving across most of Pima County. But, we'll have to wait and watch to see how much moisture this system eventually picks up.

Short Wave Digs Southwestward Today

This morning's (11 February) analysis of the 500 mb level from the NAM (above) places the short wave across the Four-Corners Region at 12 UTC. This feature is forecast to dig south-southwestward, close off,  be south of the border by tomorrow morning, and over the east Pacific west of Baja by late Friday. As this happens, winds will pick up from the east to northeast tonight and tomorrow across our region. The midnight run of the WRF-NAM at Atmo forecast of 10-m winds at 11:00 am MST tomorrow morning is shown below. The model forecasts strongest winds to occur over the California coast ranges and Baja, as well as southeastern Arizona.

The possibility exists that, as the two closed, 500 mb cyclones over the east Pacific consolidate, subtropical moisture may make it into Arizona for shower activity Sunday and Monday. At this point in time it remains a coin toss as to what might actually happen. The GFS keeps precipitation south of the border, while the ECMWF brings showers into southeastern Arizona.

Latest Model Forecasts

A quick update based on the WRF models run at Atmo. There has been little change since yesterday, except that the model (NAM version) has really kicked up the winds blowing in from the east late Wednesday night and Thursday. Forecast above is from the 00 UTC forecast run of the WRF-NAM on the 5.4 km grid and is for 10 m winds valid at 9:00 am MST on Thursday the 12th. Strong winds now forecast from southern New Mexico and northern Mexico westward across the the coast ranges along the Pacific coast. Forecast below is from the 1.8 km grid and is valid at 1:00 pm MST on Thursday afternoon - speeds are quite strong in eastern Pima and Santa Cruz Counties. The current NWS grid forecast for the airport (TUS) is for:

• Wednesday NightPartly cloudy, with a low around 55. Breezy, with a north wind 14 to 19 mph becoming east 23 to 28 mph after midnight. Winds could gust as high as 41 mph.
• Thursday Mostly sunny, with a high near 76. Breezy, with an east wind 24 to 29 mph, with gusts as high as 44 mph.

By 5:00 am MST the WRF-NAM forecasts a distinct cyclone at 500 mb to be located west of central Baja (above), with low-level subtropical moisture extending northward up the entire Gulf of California - setting the stage for possible weekend showers/rain extending into President's Day.

Winter Storms In The Northeast

Winter continues to hold sway over the northeastern quarter of the country. Moderate to heavy snow piling up again today in Boston area - above image is of Marsh Plaza at Boston University about 7:00 am MST this morning. Model forecasts indicate a couple of more nasty storms during the next 10 days or so back there.

As for the Southwest, the models continue exhibiting considerable run-to-run variability for the end of week through the weekend.  The GFS 500 mb spaghetti plot above valid at 96-hours (00 UTC 13 February) from last evening again indicates maximum uncertainty for North America continuing over the Southwest and Pacific west of northern Mexico. There will likely be some showers around late in the week but details very nebulous at this time. The WRF-NAM forecast from last evening forecasts strong easterly winds after midnight on the 12th - as per forecast below that is valid at 5:00 am MST Thursday morning.

Keeping Focus On 00 UTC Feb 13th

This is just a quick update to yesterday's post.

The global model's forecasts have changed fairly markedly after just 24-hours and here is very quick look. Graphic above is the 500 mb spaghetti plot (average of the ensembles left and spaghetti right) from the GFS with valid time of 00 UTC February 13, a Friday. The dominant feature over North America is the strong ridge positioned from the Great Basin northward. The only bowl of spaghetti present at low to middle latitudes sits over the Southwest and eastern Pacific - so maybe it's too early even for a coin flip. 

Only a couple of the ensemble members have precipitation near the Borderlands in this run. Graphic below is from the operational GFS for 48-hour precipitation ending at 00 UTC the 13th (i.e., the latest version of the forecast shown at bottom of previous post). Quite some change. All of this says something about the logic of the NWS issuing high-resolution (time and space) grid-point forecasts out through seven days!

Look Ahead To Late Next Week

The long range forecasts by the ECMWF and the NWS GFS have become very similar toward the end of next week. So, here's a quick look. Above is the ECMWF forecast for 500 mb valid at 5 pm MST Thursday, February 12th (or 00 UTC on Friday the 13th). Below is the same forecast from the operational GFS. Both models forecast a Rex block configuration, with a closed low sitting beneath a strong ridge and closed anticyclone.

Since Rex blocks are, as the name implies, fairly stagnant, they don't produce strong vertical motion due to vorticity advection (note that at 500 mb there is very little vorticity advection indicated by either model). But, if the closed low portion of the block picks up substantial moisture and some convective instability, then things can become interesting (again due to slow movement or evolution of the large-scale pattern).

At the bottom is the GFS forecast of precipitation for the 48-hours ending at the time of the two 500 mb forecasts. The precipitation forecast indicates an apparent influx of moisture from low latitudes and substantial precipitation for the Southwest. All of the 12 GFS ensemble members forecast some precipitation for southeast Arizona at the end of next week. However, we need to keep in mind that in the last two similar situations (re: agreement among the ensemble members), one event fizzled while the other became a serious, record breaker. So, out at seven days we're essentially looking at a coin-flip, but one that could become interesting.

Beautiful Days

I meant to do a post yesterday about what a great day it was, but day got away from me. So, view above is from 10:00 am MST yesterday morning (Tuesday, February 3rd). View below at 5:00 pm shows some high, thin cirrus to the north and northwest.

This morning I took a quick look at the forecasts from the Atmo WRF-GFS run initialized at 00 UTC last evening - the evening forecast runs include an expanded domain on the 1.8 km grid that includes much of New Mexico.

First, the above graphic shows the forecast of Global Horizontal Irradiance (GHI in W/m2) valid at 1:00 pm MST this afternoon. Model forecasts another very bright and sunny day. From Vaisala here is definition of GHI:

The radiation reaching the earth's surface can be represented in a number of different ways. Global Horizontal Irradiance (GHI) is the total amount of shortwave radiation received from above by a surface horizontal to the ground. This value is of particular interest to photovoltaic installations and includes both Direct Normal Irradiance (DNI) and Diffuse Horizontal Irradiance (DIF).

There is a strong cold front pushing down the High Plains and Front Range this morning, and I was curious as to how the WRF would handle this front. By 10:00 pm tonight (10-m winds above) the front has intruded deep into Texas with strong and cold east-northeasterly winds gusting across the Big Bend Country. The east winds weaken during the night but the model does forecast a period of easterly winds across southeast Arizona late tomorrow morning (forecast below of 10-m winds valid at 11 am). And that's about it for short-term weather - enjoy!

Groundhog Day 2015

Phil says six more weeks of winter.

Sister's deck, yesterday in Batavia (west of Chicago), Illinois.

Harvard campus this morning.

Finally Some Bright Sunshine

Today began with heavy fog (second fog event of the winter here) through much of the morning. The fog has broken with stratus now hanging on the mountains. Views above are just before 2:00 pm MST looking north from campus and from Kitt Peak. The sunshine is most welcome after the heavy clouds and rain of the past several days.

The end of month event here at the house left us with 1.97" of rain, making the total for January 2.48". This was the second wettest January during my records here at the house (16 years) with the 2.96" of January 2010 being the wettest. Looks like we'll now have at least a week of fair weather for things to dry out. I pulled up the ALERT data for the month and the totals for the three northern sectors are shown below. The January range for those sites was from 1.46 to 9.41 inches. Note that the gauge with over 9 inches appears as somewhat of an outlier and there may be problems with that particular gauge.

Record Rains At Many Points In Southeast Arizona

Here at the house it is still raining and all I know for the event total is that it stands at well over an inch. The TUS composite radar echoes at 6:20 am MST above indicates substantial areas of light to moderate rain occurring currently over and west of Tucson. There have not been any thunderstorms within this event so far (nearest lightning down south in central Sonora) and snow levels have stayed quite high. The NWS observation site at the airport observed a daily record high rainfall amount yesterday at just under an inch. Amounts in the Catalinas and Redington Pass area have been prodigious, with some ALERT stations reporting 5 to 8+ inches of rain! Flow in the Rillito peaked at a bit over 4000 cfs around midnight - not a large flow, indicating that the ground has been soaking up much of the rainfall.

Below are rainfall amounts for the 36-hours ending at 6:00 am MST this morning (January 31st) for all the sectors of the Pima County ALERT network.

Very Heavy Rains In Nearby Mountains Already

Regional surface plot for 7 am MST this morning (above) indicates rain or snow extending from west Texas and northern Mexico northward into southern Utah and southwestern Colorado. The 12 UTC skewT plot for the Tucson sounding (immediately below) shows a mostly saturated atmosphere in place, with more than an inch of Precipitable Water, but only a touch of CAPE at this time - which fits with the lack of any detected CG flashes so far. Tucson radar composite reflectivity, also at 7 am (2nd below), indicates moderate to heavy rain mostly east of metro area at this time.

Rainfall amounts so far (through 7 am MST) over the ALERT network are very heavy in the high elevations of the Catalinas and also across Redington Pass area - note two stations reporting amounts over 3 inches. There is no flow yet in the Rillito at Dodge, but I suspect washes on all sides of the Catalinas will soon be flowing, so caution is advised for morning commuters.

Quick Look At WRF This Morning

Mike Leuthold did a much more detailed discussion last evening and it can be found here

http://www.atmo.arizona.edu/products/models/forecasts/wrf_disc.pdf

The day has dawned heavy, dark, and damp and precipitation may begin a bit earlier this afternoon than the models are indicating. Already sprinkling here at the house.

Satellite products continue to show a very broad plume of subtropical moisture moving northward into the Southwest. The IR image above and the CIRA blended PW analysis below are both from 13 UTC (6:00 am MST) this morning.

All of the various models available to forecasters continue to indicate a major precipitation event for the Southwest, with a focus continuing to emphasize large rainfall amounts over southeast Arizona. Forecast below is from the WRF-NAM forecast run at 06 UTC this morning. The forecast shows accumulated precipitation through 11 pm MST on Saturday night (the 31st).

The WRF models continue to keep the most significant snowfall up in the White Mountains, since this is another relatively warm system. The WRF also tries to backdoor a Plains front across the Continental Divide, bringing a complicating surge of strong easterly winds into parts of southeast Arizona. The latest runs weaken this front to our northeast as precipitation begins in earnest. But yet another feature to keep and eye on.