Cold And Rainy Early Morning

Edited to add webcam image from Mt. Lemmon at about 7:30 am. Break in rain here at 7:30 am let me peek at rain gauge which has caught 0.34" so far.

Rains moved into eastern Pima County around 4 to 5 am MST this morning. By 6 am 100% of the stations in the ALERT network had already measured rainfall - with snow apparently falling at the high elevation sites. Too ugly to go read the rain gauge here at house. Above is Tucson composite radar echoes a bit after 6 am and below is the metro and west sector of the ALERT network showing rainfall through 6 am. More later.

Kitt Peak web cam at a bit before 7 am shows that snow level has fallen below their elevation (6875 ft MSL).

End Of Day Look At Morning WRF Forecasts - 19 December

By 4 pm MST this afternoon some clouds were starting to come in from the southwest - above.

Forecasts of total precipitation through 8 am MST on Saturday the 21st - WRF-NAM above and WRF- GFS below. The GFS version appears to be wetter than the NAM version, particularly over eastern Pima County and across north-central Arizona.

 The QPF forecast from NWS Tucson this morning appears a bit wetter than either of the model forecasts - below.

Finally, below is the surface forecast from the WRF-GFS valid at 10 am MST tomorrow morning - looks like a fairly dismal start to the day.

End Of Week Storm

First - the diurnal temperature swing yesterday was around 55 F - low here at house was again 28 F and high at airport reached 83 F - which was a record high for the date.

The short wave at 500 mb that will dig southward during the coming 48 hours is currently over western Canada and the Pacific. Upper-air data this morning indicate that temperatures in this wave are currently quite cold - at minus 39 C or colder. The early WRF-GFS model run from Atmo this morning extends through 11 pm MST Friday night the 20th of December.

Above is WRF-GFS forecast of composite radar echoes valid at 1 pm MST on Friday afternoon, while graphic below shows the model's forecast of total precipitation through 11 pm Friday night. The model forecasts a broad maximum of precipitation (through late Friday night) to occur from north of Phoenix, southward across central and western Pima County, and into northwestern Sonora.

This morning's run of the NWS NAM model is considerably different than the midnight run of the WRF-GFS. That model forecasts very light rainfall through 11 pm MST Friday night across most of southern Arizona except for the far southwest and the southeast corner.

The surface plot forecast by the WRF-GFS for noon on Friday indicates a cold, rainy, and dreary day for metro Tucson.

Final note is that the 500 mb spaghetti plot from the GFS model ensembles (below) valid at only 72-hours continues to show largest uncertainty from the east Pacific across the Southwest. This means that timing and duration of the coming weather event may be a bit difficult to forecast exactly.

Large Diurnal Temperature Range On December 16th

The low here at the house yesterday morning was 28 F, while the high at TUS (the Tucson airport) reached 78 F. A diurnal range over some parts of the city of about 50 F. Looks like more of the same today.

For the weather event coming at the end of the work week, I'll again concentrate on the 500 mb forecasts from the global models. The ECMWF (above is 500 mb forecast valid at 5 pm MST Friday afternoon the 20th of December) continues to be very progressive with the short wave, moving it to west Texas by that time and also continues with a weaker, trailing short wave. The GFS has become somewhat similar in the model runs last evening. Graphic below shows one of the GFS members (valid times are all the same here) that is similar to, and even a bit faster, than the ECMWF.

Three of the GFS ensemble members continue to be distinctly different, forecasting a deep, closed low holding to the west along and off the coast of northwest Mexico - see above. The GFS 500 mb spaghetti plot valid at this time is shown below. The spread of the forecasts is greatest from west of Baja northeastward across the Central Plains. The height differences between the two GFS members shown here is as great as 250 to 300 m west of Baja.

Regardless, 10 of the 12 GFS members forecast precipitation over southeast Arizona for the 12-hours ending at 5 pm Friday. So the models indicate a decent chance for a second December precipitation event before the year comes to an end.

Bit More Re End Of Week

The longer-range global models continue to have considerable differences. I've been able to take a look at the 144-hour, 500 mb ECMWF forecast from 00 UTC last evening, valid at 5 pm MST on Saturday, December 21st - above. The ECMWF forecasts a progressive short wave across the Southwest, with a weaker trailing wave. The same forecast from the GFS operational member - below - is similar, but with the leading short wave digging deeper into Mexico.

However, a number of the GFS ensemble members close the system off, dig it to south toward or west of Baja, and move it much more slowly. Forecast below is from one of those ensemble members and is quite different than the two shown above. At this time 5 of the GFS members forecast a progressive short wave and 7 members forecast a deep, closed and lingering low at 500 mb.

It has been a difficult fall and early winter for the long-range global forecasts with many cases of low predictability. The ECMWF has appeared to keep its advantage over the GFS, but not to a very high degree as has been the case in some winters. We will have to watch as this interesting scenario evolves this week.

Back From San Francisco

Sunset colors on the Catalinas the evening of Sunday, December 15th.

We have been away in San Francisco for several days and are now back in Tucson. Interesting trip with perfectly clear and dry skies on flights on the 10th. Have never before seen the lights of both Los Angeles and San Francisco so bright and clear on the landings. Delays coming back on flight from Los Angeles to Tucson.

Looks like the week before Christmas may have an interesting few days as the global models predict a significant closed low off of northern Baja by Thursday and Friday. The GFS ensembles are forecasting precipitation in 9 or 10 of 12 members for several periods late Thursday into the weekend.

Last Of Stranded Travelers May Escape DFW Today

The last round of the great ice storm that began last Thursday has moved into the Mid-Atlantic region and the Northeast this morning (Monday, December 9th).

North Texas was hit hard on Thursday and Friday - CBS photo above was on Friday afternoon and shows de-icing efforts at DFW. Photo below had no details as to which day and where in Texas - but it shows an agave encased in ice.

Thousands have been stranded and last night about 650 travelers were still sleeping in the terminals at DFW. Morning headlines on the local CBS station indicate that these folks may finally escape today from their forced visit at DFW. Very glad not to have been one of them - during my NOAA career I flew through DFW hundreds of times, but was never stranded - some long, long delays but never overnight.

Cloudy And Fairly Dreary Sunday

Skies have been mostly cloudy today as the broad trough at 500 mb continues to affect southern Arizona (current view of Catalinas above). The surface observations for TUS (below) indicate that low clouds and overcast skies have prevailed since about 4 am this morning. The clouds kept low temperatures about 10 F warmer than were observed yesterday (34 F here at house this morning compared with 23 F yesterday morning). Bottom graph of solar radiation at Atmo shows the dramatic difference yesterday to today.

Quick Look At The NAM

First - another frosty morning here along the Rillito in north Tucson - the low temperature has again dropped to 23 F this morning, with moderate frost.

Shown above is the NAM analysis of 500 mb heights, winds, and vorticity for 12 UTC this morning. There are several vorticity maxima associated with the short wave over the Northwest, with the strongest being just north of San Francisco. (Note that when NWS forecasters refer to "energy" in Forecast Discussions they are probably talking about the vorticity structures of features aloft.) The NAM forecast valid at 24-hours tomorrow morning (Sunday, December 8th) is below. Two vorticity maxima are forecast to move quickly by just to the north of the Arizona/Utah border, while a long vorticity tail develops over the Pacific from northern California westward. The longer range forecasts for this system, particularly those of some runs of the ECMWF, took this short wave too far south, with substantial height errors over southern Arizona.

The NAM forecast of total precipitation through 12 UTC tomorrow morning is shown below. The event is forecast to produce snow over the Rim country and along the northern border lands of Arizona, with amounts maximized over Utah and Colorado. So it goes.

Frosty Morning - Friday, December 6th

It's a frosty morning here on the north side of the City of Tucson. Photo above is of frost on neighbor's roof at a quarter to 9 am. Looks like the low here at the house was 23 F - far and away the coldest morning of the Fall/Winter so far.

Brief November summary - two rain events during the month with 0.11" on the 3rd and 2.09" from late 21st to around noon on 23rd. so, total of 2.20" - more than double that for September (1.04"), which had been the rainiest month of the year.

There were 10 days here in November with morning lows in the 30s, but only the 1st, with 30F, was freezing or below.

Damp And Dreary Morning - 5 December 2013

NOTE - edited to add this morning's TUS upper-air sounding plot.

Light rains and cool conditions prevail across Tucson early this morning. The event early this morning has again exceeded expectations, especially mine based on yesterday morning's WRF forecast runs - I will come back to this later in this post. Below is Tucson NWS radar composite chart for 5:30 am this morning, indicating light showers continuing to the west and southwest of the metro area, as well as over town.

It is very hard to evaluate the ALERT data this morning. There are 10 sites that report no precipitation during the 24-hours ending at 5 am MST. However, the event has produced a mix of rain and snow and snow is not captured by the network. Two of these sites obviously received snow (Mt. Lemmon and Manning Camp) but the 8 others are at higher elevations in the east and southeast part of the network. If I had to guess, I'd say that precipitation coverage was essentially 100% during the early morning hours. For stations with rainfall, there were 40 sites with more than a quarter inch of rain and 9 with more than half an inch. The two sectors of the ALERT network that cover the metro area are shown above and below. Here at the house we had 0.13" through 5 am, while the airport had 0.34" and DM had 0.41". This was a more widespread event than expected, and one that was similar to several other light events this Fall.

If I recall correctly, the WRF under-forecast several of the light events this Fall because the PW available exceeded what was forecast. This may be the case again with this event. The time series of GPS PW above indicates that PW has increased over south-central Arizona to values around 3/4 of an inch. The 6 am WRF forecasts yesterday generally kept PW forecast values in the range of 0.5 to 0.6 inches. The Tucson skew-T forecast (from WRF-NAM) valid at 4 am MST this morning (immediately below) had 15 mm (0.59") of PW. The area forecast of PW (bottom) indicated considerable drying across almost all of Pima County by 5 am. I will try to take a look at the earlier events this fall to determine if my memory is correct.

Note - I added the morning sounding plot for TUS just below the forecast - observed temperatures are considerably colder than the forecast sounding and RH is high to saturated through a very deep layer.

Quick-Hitting, Moisture-Starved System Tonight

I've shown two total PW products here - above is from CIMSS at Univ. of Wisconsin at 18 UTC today and below is from CIRA at Colorado State Univ. at 2013 UTC today. Both products show the moisture-starved character of the system that's about to cross southern Arizona - for example, the light blue maximum area in southern Arizona (below) is just over 1/2 inch PW.

The forecasts from the 6 am morning run of the WRF model also show little in the way of precipitation with this event. The WRF-NAM forecast of composite radar echoes valid at 1 am MST tonight (above) shows little in the way of showers with the front and the total precipitation forecast through noon tomorrow (5 November 2013 - below) shows only very light amounts of rainfall. These occur during a short period of a few hours during the early morning hours. The WRF-GFS forecasts even less precipitation than does the WRF version.

The trailing system that will affect southern Arizona this weekend seems a bit more interesting (at this time), and will bring very cold thicknesses to our area, so that what snow might fall could affect quite low elevations.

Tuesday Morning 3 December Quick Look

At 500 mb this morning there is a cold, closed low over the Montana/Idaho border - above is NCAR RAL analysis and below is NAM analysis both at 12 UTC this morning. The low has a long, curved tail that extends west and northwest into the Gulf of Alaska. This tail will swing southward and cross the Southwest during the next several days. At issue is what its impacts will be across southern Arizona.

The early run of the WRF-NAM from midnight last night forecast minimal precipitation across southern Arizona through midnight Thursday night (above, on 5.4 km grid). The focus in this forecast was across the Great Basin from the Sierra Nevadas to the Colorado Rockies, with a second maximum along the Continental Divide in Mexico. However, the latest run of the NAM now forecasts considerably more precipitation over southeast Arizona for same period (below). So, we will watch to see how much moisture attends the trough across this region.

A Strange Trip To Winslow

We took a quick trip to Winslow this weekend - left Friday am and returned about dark on Saturday. Mild and warm here when we left, but with a band of Pacific cirrus overhead. Up on the Rim north of Payson there was still about 6 to 8 inches of snow cover from the previous storm - snow was generally above 6500 ft MSL. Skies were clear and temperature was up to 48F, so it was sloppy and the snow was melting and sublimating. However, when we headed down into the Little Colorado drainage the temperature dropped markedly and we drove into low clouds and fog. Temperature when we pulled into La Posada Hotel in Winslow was a damp and cold 35F. It had been as low as 33F as we approached the town across the grasslands to its south. Photo above was taken from Highway 87 about 15 miles south of Winslow, looking toward mesas to the west. Apparently the high basin was filled with saturated, cold air draining north from the snow fields on the Rim.

On Saturday morning there was cold fog in Winslow and temperature was stuck at 33F, although the low had been down to 29F. There had been ice on a couple of small bridges along the front entry way to the hotel and they had scattered salt. As we headed south at mid-morning we drove into colder air and by the time we reached the forested areas the temperature had dropped below freezing and the fog was depositing rime ice on the pines - photo below taken at about 7,000 ft MSL where the temperature was 28F. When we checked out of the hotel the forecast for Saturday, noted on a white-board at the desk, was for cloudy skies and a high of 50F. Not to be - high in Winslow was 37F, after the early morning low of 29F (on Friday the high had been 37F after a low of 28F). In a few places on the rim the weather was about W0X0F - was really quite something. The satellite visible image, just below, from 7:45 am MST shows widespread low cloud and fog continuing over northeast Arizona and beyond this Monday morning.

After we drove through the highest terrain along the highway the cloud and fog dissipated almost instantly. Was warm and sparkling in Payson, but as we drove south to lower elevations the skies were increasingly dirty.

We stopped at Boyce Thompson Arboretum which is just east of Superior off of Highway 60. Skies were dirty and we were back under the Pacific cirrus again - so not a very good day for photos, but I took some anyway above and below.

The Tucson business leaders who support the development of the proposed Rosemont copper mine should all be forced to drive slowly from Globe to east of Superior. It is difficult to look at the terribly ravaged and ugly landscape that has resulted from the copper mining in that area!