Dreary Or Sunny?

Edited to add: Now that the sun's up, the webcam view of Catalinas above shows that it's definitely a dreary start to the day. The north edge of the cirrus is visible at left side of the view.

This morning (15 February) a large area of high cloudiness from west of Baja is intruding into southern Arizona (above is water vapor image from 5:30 am MST). Thus, one forecast issue is how cloudy it will be and when during the day. The "when" question is probably easiest, since thin cirrus is already overhead. The how cloudy (i.e., how dreary) issue is more difficult.

I have examined the early WRF-GFS forecast from Atmo and show above total outgoing long-wave radiation and below total incoming solar radiation (both in watts per meter squared). Both forecasts are valid at 10 am MST this morning. the northern edge of the clouds is fairly sharp both in the forecast and in current satellite imagery. So, the model forecast indicates dreary along the Borderlands this morning but mostly sunny up in Phoenix. However, by 2 pm the model forecasts sunny skies across all of southern Arizona except the far southeast corner, near Douglas.

The forecast is tough re the timing, since flow in the upper-troposphere is quite strong. The timing is quite important for a number of practical reasons. This time of year solar in put is highest from around 10 am to 2 to 3 pm. If thick cirrus is overhead during this time of day, then the output from solar panels will be way down. The standard NWS ASOS observations won't shed any "light" on this issue, since clouds above 12,000 ft agl are not detected and automated surface observations will report "clear" even when it's quite overcast.

Valentine's Day Miscellany

The last five mornings have been quite chilly here at the house. The low temperatures from the 10th of February through this morning, the 14th, have ranged from 24F to 28F. Down at the airport the official lows have ranged from 29F to 34F, so it's been about 5 to 6F colder here along the Rillito. This week will

continue with fair and mild weather. However, the professional golfers will be in town next week for their unusual match-play tournament. This event has seemed to be a magnet for wintry weather, with the start of the last day delayed by snow either last year or year before. The course they play is out north in the Tortolita Mountains and at elevations around 4,000 ft MSL. Photo above shows tents and stuff at the course. Note the widespread, invasive, non-native grass out there. Tucson is down in the dirty air in the distance (photo is looking south with the downtown buildings just showing in the murk).

The long range forecast models bring the spell of nice weather to an end during the golf tournament. The above is the operational ECMWF 500 mb forecast valid at 5 pm MST on Wednesday the 20th (tournament runs from the 18th to the 24th).

As for the GFS, it too forecasts substantial change next week. The ensemble-average 500 mb forecast (above) for 5 pm MST on Tuesday the 19th indicates a deep trough along the west coast. It is interesting how little spread there is in the GFS ensembles at 144-hours (below). All the members have about the same forecast for North America. Will be interesting to watch how this evolves.

Frosty Morning - February 12th

Yesterday's precipitation event ended here at the house around dark - total was only 0.15". Looks like 100% coverage across the ALERT network again. Amounts were light, but somewhat better than Saturday's event. There were 7 sites that measured rain amounts of more than 0.25", but no amounts of 0.50". snow amounts unknown, but roads to Mt. Lemmon and Madera Canyon were closed yesterday afternoon. Once again Atmo's WRF-GFS provided excellent forecasts. Actually, some school delays and closings today across southeastern Arizona! Photos of the Catalinas and Kitt Peak at sunrise today are above and below.

This was the second event this winter where I wanted to check on what the observed 1000-500 mb thickness was. But once again the NWS RSS sounding system failed here at Tucson and there were no upper-air data. So it goes.

Look At Model Forecasts From 06 UTC

The system that will affect much of southeastern Arizona this afternoon has been digging south-southwestward across the Great Basin during the past 24-hours. I have looked at the NWS NAM and the Atmo WRF-GFS model forecasts that were initialized at 06 UTC (midnight). There are several interesting aspects to the forecasts. First, the 500 mb vorticity maximum is forecast by the NAM (above forecast is valid at 5 pm MST) is forecast to move across southern Arizona during the afternoon, so forcing for upward motion will be significant. This is another cold and relatively dry system, and temperatures aloft are again very cold. The NAM forecast of 1000-500 mb thickness (below) valid at midnight tonight brings thicknesses less than 5340 m across southeastern Arizona. Meaning the snow levels will drop very low late this afternoon - perhaps into the metro area, if precipitation lingers late enough into the evening.

The midnight run of the WRF-GFS has precipitation moving out of eastern Pima county by around 9 pm, so there may be some flurries around the area. The surface plot forecast for 2 pm is shown above, indicating a pretty raw afternoon here in Tucson. The WRF forecast for total precipitation through midnight tonight (below) is quite different than those for the last two event. The model is squeezing out more precipitation over the lower elevations of eastern Pima County, indicating that key ingredients come together nearly overhead. An interesting forecast, we'll have to keep an eye on the situation and take a look at the new forecasts from the morning data.

Couple Of Photos

Katie shot these photos of snow along Highway 83, south of I-10, yesterday at mid-day. Top shows the NWS Doppler radar atop the Empire Mountains, and bottom shows the west-east ridge that is highest point along the highway between I-10 and Sonoita.

For contrast, below was taken in Boston on Friday evening.

First Rain Band On Saturday AM

Am writing this at 7 am on Saturday morning, 9 February 2013. At this time the first rain band has moved on to the east of the house. Between about 5:30 and 6:45 am MST there was 0.07" of rain here, and I see that the snow level was very low on the foothills. I show two radar products here from the KIWA radar (these have come from the College of DuPage - CoD link to right - weather site). The top image is precipitation type at about 6:35 am - this is one of the products available from the dual polarization upgrade. The CoD radar page has many of these polarization products available, which is a real plus, since they are not shown at the NWS radar pages. Precipitation type indicated in the image is DS (dry snow). But wait, it was raining here. Unfortunately, the NWS KIWA radar is sited at over 5,000 ft MSL out in the Empire Mountains. So, the radar beam is always substantially above the low elevation locations here in the metro area, thus the radar indicates only snow. This illustrates one of the problems of siting the radars at high elevations (there is a separate set of problems that would occur were the radar down here in the low elevation areas).

The product below is the VAD winds aloft time-series, another product that can be examined at the CoD web page. This product shows the strong west-southwesterly winds aloft over eastern Pima County. Note that the lowest winds are obtained at 6,000 ft MSL. Regardless, the CoD site is one that I go to if I want to examine radar data in more detail than I can at the NWS web pages.

Moisture-Starved System Approaches

A quick look at the approaching system. This morning's 12 UTC NAM analysis at 500 mb (above) indicates a cold and complex system - center of circulation is near San Francisco but a strong vorticity maximum is approaching Las Vegas. A stronger vorticity maximum is over the ocean west of San Francisco. Temperatures at 500 mb, near the core of the system, are below -30C, so definitely a cold event.

As per the last several systems, this one is also starved for a decent moisture feed. Both the Mimic (above from CIMSS for 09 UTC) and CIRA (below for 11 UTC) blended PW products show an inflow plume near San Diego, but with values only reaching to around 20 mm.

The early run of the WRF-GFS forecasts best band of precipitation (above is the forecast, composite radar image valid at 8 am Saturday morning) across eastern Pima County tomorrow morning. The surface plot forecast for the same time (below) indicates a raw morning with northwest winds, temperatures in the 30s and light rain showers. It will be quite a change! Total WRF-GFS forecast precipitation through midnight Saturday night is at the bottom, indicating light amounts, except in the mountains and higher elevations east and southeast of Tucson. Snow levels will come quite low along parts of I-10 and Highway 83, but ground and pavement will start out very warm. Some driving caution may be needed.

A Look At WRF-GFS For Friday And Saturday

This morning the 500 mb analysis for 12 UTC indicates that the next system to impact the Southwest is currently off the coast of British Columbia. The temperatures in the core of this system are currently around -35C, fitting with the forecast for a serious cool down on the weekend. Most weather attention remains centered on finding Nemo. However, there will be interesting weather out in this part of the country also.

I have just taken a quick look at the forecasts from the early run of Atmo's WRF-GFS model. The forecast surface plot (above) for 4 pm MST on Friday afternoon, indicates warm temperatures but with strong and gusty south-southwest winds. The front moves through quickly during the night and by 9 am on Saturday morning the forecast radar echoes (below) indicate a post-frontal band of showers moving across eastern Pima County - this is the first of several bands forecast during the day Saturday.

The surface conditions forecast at 10 am on Saturday (above) indicate damp and much cooler temperatures - note that there are some temperatures down in the 30s on the north and east sides of the metro area. The forecast of total precipitation through midnight on Saturday night is shown below. This event is currently forecast to be a light precipitation situation, except over the higher elevations of the Catalinas and Rincons..

Northeast Storm Named Nemo by TWC

The Weather Channel has named the forecast big Northeast storm Nemo. The cyclone, assuming it comes together as forecast by the models, will bring a serious snowstorm to much of the Northeast. This naming of winter storms is something the Weather Channel is doing for the PR hype.

Below is the 8 am MST surface analysis from the NWS HPC. Where is Nemo if you want to track him? Too soon - Nemo's not on the map yet. The storm is expected to develop on Friday as short waves in the southern and northern streams merge and a deep low develops rapidly along the East Coast.

Next Weather System

The first weather system of February struck over the past weekend and brought an extended period of thick middle and high clouds, and that was it. However, the next system looks a bit more interesting (but nothing like the major storm forecast for the Northeast). There are also significant differences in the model forecasts

at 96-hours (i.e., valid at 5 am MST on Saturday morning 9 February). The NWS GFS forecast at 500 mb valid at that time (above) indicates an elongated short wave that stretches from southern Canada to southern California. The ECMWF forecast valid the same time, however, predicates a significant closed low over the Great Basin with a strong vorticity maximum over central Arizona. The ECMWF forecast would bring a strong Pacific front through southeastern Arizona late Friday afternoon with wind, dust, and possibly showers along the front. The GFS forecasts a less distinct front and no precipitation for southeast Arizona. Both of these forecasts are from the operational members of the two models.  Both models forecast much colder thicknesses by Saturday and it will be interesting to see if the faster and stronger ECMWF forecast verifies better than the GFS forecast. The ECMWF heights at 500 mb are about 120 m lower than the GFS over central Arizona on Saturday morning.

Dr. John Jeffries

John Jeffries, a Boston physician and scientist, is sometimes said to be the country's first “weatherman.” He was born on February 5th in 1744, and, in his honor, today is National Weatherperson’s Day.

However, more people are probably aware that this is also National Pancake Day. For the eighth year, IHOP restaurants are offering a free stack of buttermilk pancakes today from 7 a.m. to 10 p.m.

More News Re The NWS RRS Sondes

Back on July 18, 2012 I reported that:

The efforts to replace the the problem-plagued Mark IIA sondes of the NWS RRS program are moving ahead, after the testing reported above. A Technical Implementation Notice indicates that 5 more NWS upper-air sites will begin using the Vaisala RS92 GPS sondes on or about March 1st. The sites are Morehead City, NC, (72305); Santa Teresa, NM, (72364); San Juan, PR, (78526); Gaylord, MI, (72634); and Medford, OR, (72597).

Apparently, while the transition to the the RS92 sondes is occurring, other NWS upper-air sites will be using the Sippican LMS6 (rather than the MarkIIA) sonde. The LMS6 uses an improved humidity sensor.

Pacific Moisture Inches Northward

First - brief January summary: TUS had 12 days during January with lows of 32F or colder. Here in the Rillito Bottoms we had 20 such days, with 4 mornings down in the teens. Rainfall at TUS was 0.81" and here at house we had 0.76". Not an exciting month, except for the cold snap.

Very chopped up setting this afternoon in upper-troposphere, with several weak short waves moving different directions along and off the U.S. and Mexico west coasts - above water vapor image is from 3 pm MST. The MIMIC blended PW (below from 2 pm MST) shows that higher values of PW have moved northward, with values of over an inch nearly reaching San Diego.

As a weak middle-level short wave affects Arizona during the day tomorrow, the models forecast a bit of precipitation. The 5 am forecasts from the WRF-GFS indicate widespread radar echo coverage at noon tomorrow (below - Sunday 3 February). These are mostly mid-level echoes with light showers and virga.

The forecast for total precipitation through 5 pm tomorrow (below) shows widespread coverage of very light amounts, with the mountains doing slightly better.

And least I forget, it's a special day today!

From Mike Leuthold

Bob,

    I've returned to astronomy after almost 30 year hiatus so I'm much more interested in the WRF cloud forecasts than I was previously.  It does a pretty good job normally.  Last night, it was forecasting clearing in the early evening thus I set up my equipment.  By about 8:30 the high clouds did move off to the east and I was able to take these images.
    The forecast for the next few days looks really bad as you have pointed out-WRF is forecasting frequent high clouds.  Too bad as the moon has just left the evening sky so it's perfect for astro-photography and observing. It will make for nice sunsets though.

Mike

High Clouds In The WRF-GFS Forecast

The Outgoing Long wave Radiation (OLR, in watts per square meter) product can be used to evaluate the model's forecast of cloudiness. The model keeps skies mostly clear today until late afternoon and evening, and then brings a large patch of high clouds in from the Pacific during the night (below is OLR forecast valid at 6 am tomorrow morning) with gray-scale indicating watts per square meter. Low OLR indicates increased cloudiness, while high values indicate clear skies. So the model is forecasting significant high-cloudiness during the night tonight. If this verifies, it will keep low temperatures mild (the early WRF-GFS forecasts lows next two mornings at TUS to be in the 50s, i.e., considerably milder than this morning).

During the day tomorrow the clouds move away and the forecast for OLR at 3pm (above) indicates mostly clear skies again. But, by midnight tomorrow night (below) the model has forecast an even larger area of cirrus across southern Arizona. Timing and duration are everything with these patches of cloudiness wrt both high and low temperatures.

First day Of February In Tucson

February dawns with beautifully clear skies here in Tucson and southeast Arizona. Low temperatures here in the north part of the city are again in the upper 20sF, so it's quite chilly out right now. Low at house was 28F and there is frost out there on roofs and cars, but it will warm up quickly.

The main forecast problem today and tomorrow will be the timing of high-level cloudiness coming by from west and southwest of Baja. Above is the water vapor image from 6 am this morning, showing a very large area of middle and upper-level cloudiness from south of 10 degrees north to about 30 degrees north.

The MIMIC blended precipitable water (above, from CIMSS in Madison, Wisconsin) for the eastern Pacific shows that PW values are low north of 20 degrees latitude (except far to the west). This means that the clouds of interest for the Southwest are high and that low-levels are dry. So, the main forecast impacts today and tomorrow will be the timing of cloudy periods and their impact on temperatures. Will look at the WRF-GFS forecast of OLR in next post.