Two More Interesting Emails

Mike Leuthold sent the above summaries of Temp and Precip for 2015 through April 25th - of note is the extreme precipitation over much of Mexico. This is probably related to the weak El Nino of this winter. Art Douglas had pointed this out to me a couple of months ago and noted that NWS CPC seemed totally focused on the US and was ignoring this strong signal south of the border. Amazingly dry across most of the US so far for 2015.

Art sent these two recent forecasts from the CFSv2 that is run by NWS CPC out through very long ranges.The model is run, apparently once per day, out to as long as nine months - which seems like a bit of model overkill to me. Regardless, the precipitation forecasts (for what they are worth) for the months of July and August (above and below) indicate southeast Arizona in a near normal situation during July and a bit wet during August. This will be a long wait and see situation.

The View At Brainard Lake Colorado

Ron Holle was at Brainard Lake, Colorado, yesterday and sent along this photo, showing heavy new snow on the pines. The lake is west of Boulder, off the Peak-to-Peak Highway, and is a bit above 10,000 feet elevation.

Look Ahead For Next Seven Days

First - it is a mild and windy morning here along the Rillito, with winds from the east to southeast. Quite a contrast to yesterday morning, when the low temperature here was a chilly 37 F.

The long-range, GFS ensemble forecasts (00 UTC run last evening averages and spaghetti plots shown here, above valid at 84-hours and below at 168-hours) indicate that weak troughiness will continue to persist in the southern branch of the 500 mb flow which is affecting the Southwest. The GFS forecast (operational member, at bottom) for accumulated precipitation for this period keeps Arizona mostly dry, except for the White Mountains. So continued quiet for much of the Southwest.

Event Summary Through Early AM, Sunday April 26th

Edited to add a couple of things at 09:40 am.

Above is from General Store web cam up in Summerhaven on Mt. Lemmon this morning.

There was widespread rain, and some snow, across eastern Pima County during the night. Yesterday's models and POPs proved to be conservative at lower elevations for the night. Composite radar image above is from 4:00 am MST. However, the WRF-NAM forecast of the TWC soundings (shown in yesterday's post) was probably quite good for the  period of rain and thunderstorms. Below is plot of CG flashes detected through 3:00 am MST (from Vaisala) - indicating considerable thunderstorm activity over and west of the metro area. Both TUS and DMA reported thunderstorms on their observations. Not sure if there was thunder here (at least two rumbles of thunder here at the house!), but there is 0.18" of rain in the gauge this morning.

There was essentially 100% coverage for measurable rain across the ALERT network, with heaviest amounts occurring in the Catalinas and Rincons (as yesterday's WRF-NAM forecast). Mt. Lemmon and the Rincon RAWS appear to have received mostly snow, accounting for their low totals for rain. The heaviest precipitation occurred over the northern Catalinas and Redington Pass, where the strong west winds were running upslope.

There may be enough lingering moisture and instability for some morning showers.

Tough Forecast For System This Weekend

First, much of yesterday was quite cloudy and some light showers developed mid-morning and moved across parts of the Catalinas. The northern sector of the ALERT network recorded light rainfall from these showers (above, 24-hours through 6:00 am MST this morning). Not even a sprinkle here at house.

As a strong, 500 mb short wave digs southward toward northern Arizona, forecasting exactly what might happen across lower elevations of Pima County has been quite a challenge. The fairly crude resolution of the NWS NAM and GFS models result in a smearing of forecast precipitation southward toward the border. This is due to the coarse resolution of the terrain in those models.

The high-resolution WRF model variants run at Atmo, forecast the precipitation event with this system to remain mostly in the mountains and higher elevations to our north. Here are two forecasts from that model for comparison. The WRF-NAM forecast above is from the 06 UTC run and shows the forecast of accumulated precipitation through 11:00 pm tomorrow night (Sunday, April 26th). Over eastern Pima County the focus is over the Catalinas and Rincons, with little forecast for low elevations of the metro area. The similar WRF-GFS forecast below is from the 00 UTC run and is even more restrictive with it's forecast, indicating just a touch of precipitation in the nearby mountains.

However, the WRF-NAM forecasts of the evolution of the vertical profiles over the campus, sounding-release site (TWC) indicate that conditions briefly become fairly favorable for convective showers, as the strongest portion of the Pacific cold front comes by. The forecast sounding below, valid at 1:00 am MST tonight, has almost an inch of precipitable water and CAPE of over 500 J/Kg.This is the most favorable sounding I've seen in the model forecasts for quite some time.

The sounding indicates to me that there is a better chance for showers in the metro area than the WRF models are indicating above. However, the most favorable conditions last only for a brief period - so we'll have to hope for the best as this event unfolds. Note that current NWS forecasts of POPs for precipitation are: 40% tonight and 30% tomorrow for the airport grid box; but only 60% tonight and 50% tomorrow for the grid box that Mt. Lemmon is within.

Overview - Friday, April 24th

Heavy clouds around this morning, with a smell of moisture in the air, but no rain here. Very light rains in southeast Cochise County yesterday (Douglas reported a thunderstorm with 0.01") and some lightning strikes in southeast corner of the state. Plot below is of detected CG flashes through 11:30 pm MST last evening (from Vaisala). Most thunderstorm activity was out to the west along the Colorado River Basin.

Yesterday afternoon was quite windy across southeastern Arizona with many stations reporting gusts of 35 to 40 mph - Sasabe, Pioneer Field and Guthrie RAWS reported gusts just below 45 mph. So, lots of pollen blowing around yesterday.

At 6:00 am this morning there was a single report of rainfall across the ALERT network. That report was 0.35" from the gauge at Arroyo Chico and Randolph (near Reid Park). A look at the data from that gauge indicates the "rain" fell during 15 minutes right before 2:00 pm yesterday afternoon, when skies were basically clear. Perhaps this was a sprinkler event, or perhaps the gauge has gone awry, or?  

The next system comes in from the northwest Saturday night and Sunday with strong west winds and a chance for some showers at low elevations. Forecast of composite radar echoes above is from 06 UTC run of the WRF-NAM and is valid at 03:00 am MST on early Sunday - best shower activity will stay off to the north. However, the forecast sounding for TWC (below, valid at 10:00 am Sunday morning) indicates a bit of CAPE at low elevations. So, a bit of hope for rain in gauge here before end of April.

Unsettled Conditions Through The Weekend

At 500 mb a vorticity maximum west of central Baja will swing northeastward across southern and eastern Arizona during the next 24-hours. Currently there is sparse moisture and no CAPE ahead of this system (above is TWC 12 UTC sounding from SPC). So development of convective showers this afternoon into early tomorrow will depend upon whether or not there are slight increases in low-level moisture, coupled with a bit of cooling at 500 mb. Regardless, precipitation with this system will likely be as sparse as the moisture. The 06 UTC run of the WRF-NAM at Atmo forecasts some very light precipitation on the mountains of eastern Pima County through 5:00 pm MST tomorrow afternoon. The model forecast may be a bit dry, since PW at TWC was already over 3 mm higher than the model forecast at 12 UTC. We continue with no measurable rainfall here at the house for April.

By Sunday morning a much stronger, closed low at 500 mb will be digging south-southeastward across the Great Basin - 500 mb forecast below is valid at 12 UTC on the 26th and is on the 5.4 km grid from the 00 UTC forecast run. Moisture with this continental system will be mostly what it drags along with it. Thus, it remains to be seen whether this system will bring wind and dust only, or if there will be a chance of some showers this far south.

Earth Day 2015

Southern Arizona is a land of extreme contrasts some of which are shown below - no commentary needed as we celebrate Earth Day, which began back on April 22nd 1970.

A Look Around This Morning - April 21st

Several short waves in the southern branch of the flow will cross the Southwest during the coming week. The system on Thursday will probably produce some light showers around southeastern Arizona. But like so many systems so far this year, it will be struggling to pick up moisture. The 500 mb forecast above is from last evening's run of the ECMWF and is valid at 5:00 pm MST on Thursday the 23rd.

Meanwhile a look around at some web cam views this morning - one month into astronomical spring.

 Joe's Lodge near Bemidji, Minnesota.

El Paso, Texas.

Some of the power grid in Havana, Cuba.

The Panama Canal.

Cold Morning In Spots

Another morning illustrating the difficulties in forecasting low temperatures across a region with complex terrain. Above plot is from MesoWest and shows some of the reported 24-h lows ending at 8:00 am MST this morning - the range in the lows on plot spans 27 F. Here at the house the low fell to 28 F (second coldest morning since back in January). At the observations page on the NWS site I found an additional 6 stations with lows of 32 F or colder - coldest at the RAWS site on Mt. Graham (Columbine) with 19 F. The NWS grid box forecast for where the house is was for 45 F - pretty good for spots a km or 2 north and south of here but way off for the Rillito Wash. I suspect that the algorithms used to adjust the model forecast temperatures for the grids are not very sophisticated - but it's hard to find any technical details.

BBRRRRR!

Very chilly here this morning - low was 36 F and northwest wind felt cold to me when I walked between 8:00 and 9:00 am. If winds are calm tonight along the Rillito, we'll have a late, hard freeze here in north part of the City tomorrow morning.

Meanwhile, things turning back to winter in Colorado today. Image above is up at Eisenhower Tunnel on I-70 west of Denver and view below is down at Boulder Creek near downtown.

Ugly Skies This Afternoon

Certainly nothing like Salt Lake City yesterday, but ugly, dusty skies prevail here this afternoon. Very appropriate for April 15th - Tax Day.

Rest Of Week Stormy Over Parts Of West

A cold, 500 mb low is centered just northeast of Salt Lake City this morning, with temperatures within the core of the system colder than -30 C. Although this system roared into the West yesterday, it is now forecast to take a somewhat long, strange trip before it exits onto the Plains. I show here a sequence of 500 mb forecasts from the 06 UTC run of the WRF-NAM at Atmo - times are in upper right corner and temperature color bar is at bottom. A trailing piece of the short wave digs south-southwestward, giving the system two circulation centers through much of the period covered here. By 0600 UTC on 18 April the closed low has only advanced to north-central New Mexico, with a strong vorticity maximum brushing through southeast Arizona late on the 17th.

Shown here are WRF-NAM precipitation forecasts for the period ending at 11:00 pm MST on the 17th. Precipitation produced by this system maximizes in Colorado, with the model forecasting a very significant event. Above is model's forecast of total precipitation, indicating the focus of the event over northeastern Colorado, north of the Palmer Divide. The model forecast of snowfall through the same period (below) indicates  maximum amounts of heavy snow remaining over the northern Foothills of the Rockies. Interestingly, the current morning forecasts from the Denver/Boulder NWS Office indicate a maximum precipitation probability of only 70% for both DIA airport and also west Ft. Collins on Thursday night - with snow accumulations of just 1/2 to 1 inch. Details of where the heavy, wet snow falls will be modulated by the surface to 500 mb temperature profiles - 500 mb temperatures of -30 C most always bring snow east of the Foothills, across the major megalopolis along the Front Range.

Thunderstorms In Eastern Pima County

Yesterday afternoon provided a reminder that summer thunderstorm season is slowly approaching, as there were buildups and some thunderstorms around late in the afternoon. I took these photos right around 5:30 pm MST - top is looking north toward the Catalinas and below is looking toward the southeast, where thunderstorms were developing and moving eastward.

Jack Diebolt sent the above radar image that was from a bit after 6:30 pm. Graphic below shows detected CG flashes during the evening through 11:00 pm MST (from Vaisala). The storm that moved eastward, south of I-10, was fairly strong during portions of its life. Pioneer Airfield (located southeast of the strongest cell) reported a NW wind gust of 54 mph at 8:03 pm. It is quite probable that the storm moving across the Cienega Grasslands north of Pioneer Field produced some wind gusts that reached severe levels (>56 mph). Two ALERT stations, impacted by the echoes shown above, recorded rainfall - Sahuarita had 0.35" and Davidson Canyon reported 0.24". So, an interesting afternoon.