Monday, January 25, 2021

Wintry Start Last Week Of January

Snowy vistas this morning at Mt. Lemmon General Store and downtown Flagstaff (bottom).

Precipitation from ALERT network (north above and south below) for 24-hours ending at 8:00 am MST. Amounts across main metro area ranged from around 0.20" to about 0.50". Only 0.21" here at the house this morning.

Powerful, cold 500 mb trough (above at 12 UTC this morning) continues over the western half of country.  A variety of watches and outlooks for hazardous weather cover much of the country (below). Heavy snow/winter weather advisories stretch nearly continuously from California to Washington DC.

Detailed NWS forecast for the airport (above) includes snow tonight and tomorrow, but with little accumulation expected at lower elevations.
Precipitation amounts at airport average around 0.60" inches in the GEFS forecasts, but only 0.10" in the 12 UTC WRF-RR this morning - note the WRF forecasts the donut hole effect. So quite a difference again between the models.

Sunday, January 24, 2021

An Extended Winter Storm


Damp morning on the East Mall at Campus - assume that the setup and tents are for virus vaccinations. Some snow at the airport in Prescott shown at bottom. Showers here have been light, and I haven't had chance to see if amount was just measurable or a Trace. First tilt radar echoes below from 7:32 am MST.

Morning upper-air charts from Univ. of Wyoming - 500 mb above and 250 mb below. Second morning in a row with missing stations in California. (Note that the bad heights are still being reported at Chihuahua, Mexico, - about 30 m too low for many months now.)  The shading on the 250 mb chart does not have explanatory legend - my eyeball says light purple 75 kt; grayish purple 95 kt; and white greater than 115 kt - whats impressive is the HUGE area of the country with very strong upper-level winds. Probably will be a bumpy day for air travelers.

Surface plot above is from 7:38 am - note heavy rain report at PHX and snows in the Rim Country.
Forecasts from the 06 UTC GEFS here. Plumes above are for QPF at the airport, indicating break from tonight into tomorrow afternoon, and then a heavy continuation of precipitation Monday night and Tuesday. The plumes below are for snow accumulation at the airport - more than a bit mind boggling. Note official forecast is for little or no accumulation, which seems much more reasonable. This snow forecast assumes a 10 to 1 ratio of snow depth to water equivalent. Any snow around the extended metro area would be much wetter with considerably lower ratios.

The WRF-GFS forecast above from 06 UTC shows total precipitation amounts for period though 11:00 am on Wednesday morning. Below is the WRF forecast of snow on the ground valid at 11:00 am on Tuesday morning. The WRF has some snowfall across much of metro area - will be interesting to see how this verifies!

Morning Forecasts

Some new snow this morning at Forest Lakes in the Rim Country.

This morning's forecast from NWS Forecast Office - an active three days on tap. Note that the airport is under a winter weather advisory starting tomorrow. The two graphics below are a bit confusing, since one has Tucson in the advisory area and one does not. Consider the above as the current situation.

Morning charts and model forecasts in next post.

Saturday, January 23, 2021

First Significant Storm This Winter

Bit of morning sun hitting campus about 7:40 am MST today. Down at bottom is snow stake in Forest Lakes, Arizona, which is in the Rim Country east of Payson.

GFS forecast (from 00 UTC last evening) above valid at 11:00 am MST tomorrow indicating sharp, 500 mb trough approaching southern Arizona. As this system, and following short wave, impact Arizona, models continue to forecast a significant precipitation event. Plumes below from GEFS are for QPF at the airport. The members indicate measurable precipitation at airport tomorrow and then again Monday morning continuing through the day on Tuesday.
The plumes for temperature at the airport above indicate falling temperatures tomorrow through Wednesday, with drops of 30 F or more - given our fairly mild January to date, this will be a very pronounced turn toward more wintry weather.

In fact, the ensembles forecast a high probability of snow mixed with the rain at the airport (below) Tuesday night into Wednesday morning.

The 06 UTC runs of the WRF-GFS at Atmo are indicating very strong winds at the airport Monday afternoon (above), as second short wave approaches. The same forecast runs indicate light snow accumulations in the far east and south portions of the metro area during Monday night (below), which could bring some hazardous driving conditions, especially on two lane highways such as 83 south toward Sonoita, and 86 west toward Sells, as well as 90 south toward Sierra Vista. Will follow up re these possibilities tomorrow.

Friday, January 22, 2021

Waiting For Next "Event"

Sun breaks through to highlight the University a bit after 5:00 pm MST yesterday. Denver (bottom) had a very fiery sunset yesterday.

Showers yesterday totaled mostly less than a quarter of an inch, except on west side of Tucson Mountains, with much of the main metro area mostly missing out. Couple of sprinkles here but nothing measurable. ALERT (above) and MesoWest (below) observations are for 24-hours ending at 6:00 am this morning.

Now I'll wait for next system and hope for a better outcome here at the house. At 500 mb another closed low is forecast to cross Arizona Sunday (above) with trailing system re-enforcing the Southwest trough by Tuesday (below).

Models (GEFS above, and 00 UTC WRF-GFS below) again forecast a significant precipitation event for Arizona, although amounts were biased considerably too high by last event's forecasts. We'll wait and see how the situation evolves, beginning Sunday. Wouldn't take much to beat the meager 0.05" here so far in January.

The 06 UTC GEFS plumes for temperature are shown second below. Cold Sunday through Tuesday but then a rapid warming rest of week. Looks like another morning here with temperatures down in the 20's Wednesday.

Thursday, January 21, 2021

Overview Of Event So Far

Chaotic skies this morning before sunrise, after light showers that occurred a bit before and after midnight. Here at the house there was rain, but as of now it totaled only 0.05". Barley enough to wet our bone-dry ground. Radar (2nd tilt) from 0635 am MST (below) shows heaviest showers off to our southeast and some light showers/sprinkles out to the west.

Both the 06 UTC plumes for QPF (above) and 06 UTC WRF-GFS precipitation forecast through 6:00 am (below) had amounts for airport that were too large (airport has recorded 0.07"; Atmo had 0.03"). Models indicate that our event is mostly over and that we'll now have to look forward to Sunday and early next week for next rain chances.

Rainfall reports through 6:00 am: ALERT north above; ALERT S below; and metro area (bottom, from MesoWest). Amounts were heaviest to our south and southeast - only one report of half inch (0.51") down near Madera Canyon. All-in-all somewhat of a fizzle given the forecasts of past few days.

Wednesday, January 20, 2021

First Precip Event Of 2021

Another great sunrise here in Tucson.  Our first precipitation event of 2021 is imminent and much anticipated, since there has only been 0.01" of rain here at house since December 11th.

Happened to catch a view of a BurlingtonNorthernSantaFe train clipping through Flagstaff this morning (bottom).

Time series of TUS observations above shows dewpoint temperature rising slowly, but steadily since the strange blip yesterday (reasons for that not clear). The east-southeast winds have been quite gusty all night at the airport, with a max of 40 mph a bit before midnight.

Yuma has had a thunderstorm during the night and now has about 0.40" of rainfall. Plot of detected CG flashes for about the last 6 hours (below, from Atmo and Vaisala) shows quite a bit of activity north end GoC into southwest Arizona, and also with the closed low west of Baja.

The 500 mb low (above) has moved about as forecast yesterday and is currently well southwest of San Diego. The 1430 UTC GeoColor image below (from CIRA at Colorado State) shows considerable middle and high clouds (gray shades) from the low across Baja and into western Arizona and California deserts. The blue shades are low clouds and the orange areas are the city lights of Arizona and California.

Model forecasts from the GEFS (above) continue to call for a significant rain event to begin at the airport later today and extend into tomorrow morning. Forecast amounts today are a bit lower than they were yesterday. The morning forecast for the airport - below from NWS - indicates 100 percent POPS, as well as heavy rain amounts, tonight into tomorrow morning.

Second below is forecast rain amounts from the 12 UTC WRF-RR run this morning - WRF amounts are down by around an inch relative to yesterday. Note that the WRF picks up the ominous Tucson donut hole, probably due to downslope, low-level winds. 

Regardless, I look forward to seeing what the gauge out in our yard catches!