Tuesday, December 06, 2016

Interesting Weather This Morning But Far From Here

Dreary morning as heavy middle cloudiness has moved in from the northwest, as per view from Kitt Peak looking north. Little shows up for the Southwest on long-term forecasts through next 10 days - below is operational GFS forecast of total precipitation through 5:00 pm MST on December 15th. The reds to yellows are amounts of 3 to 10+ inches.

A slow moving blizzard has shut down much of North Dakota this morning. Above view is predawn Bismark, while below is along I-94 (which is closed) near Jamestown. First really cold air mass of winter moving across much of Wyoming and Montana and down the central Plains. So, enejoy what we've got here.

Monday, December 05, 2016

High Wind Forecast A Bust For Mt. Hopkins

The forecast for a high wind event this weekend at Mt. Hopkins was the first to fail (see earlier post below). All that occurred at the RAWS site was brief period of winds gusting over 40 mph. Not at all what the WRF-GFS forecast sounding on the 1st indicated (below from 06 UTC for Sonoita valid at 00 UTC 4 December).  Had the sounding forecast been accurate, there would have been an extended, high wind event event. However, the GFS forecast that was driving the WRF went seriously awry over the weekend. The closed low at 500 mb that was forecast to cross northern Sonora actually dug far to the south, ending up over the southern end of the GoC before turning eastward. Quite a significant bust by the models, given the fairly short time range.

The model forecasts did trend downward wrt wind speeds at Sonoita as time went by and the models tried to catch up with the misbehaving, closed low. The forecast that is second below was for Sonita at midnight on the 3rd - but from the WRF-GFS run at 12 UTC on 3 December. Finally, at bottom is observed TWC sounding for 00 UTC on 4 December - going with the models continues, at time, to be dangerous!

Saturday, December 03, 2016

Precipitation Events Swings By South and East of Tucson

Views to north from campus (above) and to south from Kitt Peak (below), both at a bit after 7:00 am MST, captured sparse cloud cover, as bulk of clouds with this event are off to distant south to east this morning (see 8:00 am visible image second below).

The 500 mb closed low dug farther south than some model forecasts and is located over the GoC this morning (12 UTC analysis above from NCAR). Precipitation reports from past 24-hours plotted at MesoWest (below) show that this marginal event affected mainly Cochise Couthy with light showers. Greatest amount of rainfall I saw in observations this morning was 0.38" at the Rucker RAWS site , north-northeast of Douglas.

Friday, December 02, 2016

Mixed Signals For Tonight and Tomorrow

Morning forecast for the airport from NWS is above, indicating 30% chance of 0.01" or more at airport tonight.

GEFS QPF plumes above from 06 UTC last night indicate measurable precipitation forecasts at TUS from all members, plus the operational GFS. However, amounts are very light as the system has become even more moisture starved. Plumes for PHX and YUM have all members forecasting zero rainfall. However, the plumes for El Paso, below, are very impressive. 

Finally, the 06 UTC WRF-GFS forecast from Atmo indicates little precipitation for the Tucson metro area (forecast below is for total precipitation through 11:00 pm MST tomorrow night. So models say nothing, or some light showers around, or a general but light rain event - things can be tough even when forecast is for less than 36 hours.

Thursday, December 01, 2016

Low Temperatures and Possible Rain Event

Yesterday the low temperatures, as per MesoWest observations, hit hard freeze levels well to the north of the Hard Freeze Warning area. Hard freeze temperatures occurred over the Las Cienegas grasslands, up the Santa Cruz Valley almost to airport, and over a northeast portion of the metro toward Redington Pass.

This morning high and middle clouds before sunrise kept temperatures a bit warmer - the web cam views from campus are at 7:00 am MST top and 8:00 am down at bottom. Low here at house was only 29 F today.

A closed, cold 500 mb low will be developing to our west today and tomorrow - 06 UTC WRF-GFS forecast above is valid at 8:00 pm tomorrow - and then moving southward into northern Sonora. As this happens, the model forecasts PW to increase from the east to the south with shower activity developing. The model forecasts a fairly significant precipitation event, especially in Cochise County. Forecast below is of total precipitation forecast by the GFS version of the model valid through 11:00 am on Sunday, December 4th.

However, the NAM version of the model is much drier for both the 06 and 12 UTC runs this morning - so the models present quite a coin toss for the Tucson metro area.

Extended High Wind Event At Whipple Observatory

Photo showing the entrance gate to the Whipple Observatory on Mt. Hopkins. The large structure at the top of Mt. Hopkins is the MMT facility, and the nearby weather station is the Mt. Hopkins RAWS site, which often observes extreme wind speeds from the east.

I am exploring ways to forecast the high wind events at the observatory, with Mike Leuthold's help. Mike is extracting forecast soundings for Sonoita from his WRF forecasts. The location, along Highway 83 just north of Sonoita, is directly upwind of the massif of the Santa Ritas Sky Island. Shown here are skewT forecasts from the 06 UTC run of the WRF-GFS last night - top is valid at 5:00 pm on Saturday, December 3rd, and the bottom is valid at midnight that night on the 4th. Deep easterly flow impacts the Sky Island beginning during the early am hours on the 3rd and reach maximum speeds during Saturday night. 

The skewT speeds of 40 kt, and a bit higher, below mountain top indicate that wind speeds at the RAWS station could exceed 70 to 80 mph during this extended event - assuming of course that the forecasts are accurate this far out. This WRF forecast cycle provides an excellent case for examining how far ahead of an event the model can be used to forecast same.

Wednesday, November 30, 2016

Hard Freeze North Part City of Tucson

Above is web cam view of Grand Canyon this morning, looking west-northwest from the Yavapai Point Geology Museum - temperature at the Canyon South Rim fell to at least - 5 F. The NWS web site observations link is broken now for the third day, so details regarding lows at ASOS sites are sketchy this morning.

Here at the house we had a morning low of 23 F - a hard freeze for this part of the City along the Rillito. Other lows - TUS about 32 F and Douglas about 14 F. Sasabe RAWS hit 18 F, while Empire RAWS dropped to 21 F.

There were two freezes here during November - 32 F on the 18th and now 23 F on the 30th. Rainfall amounted to only 0.37 inches, which was near the median for my period of record.

The QPF plumes from the 00 UTC run of the GEFS ensemble models (above for TUS) illustrate how, at times, the ensembles can actually confuse the forecast, with different members forecasting rainfall on three different days through the 7th of December. Certainly no convergence or consensus at this time.

Meanwhile the 00 UTC WRF-GFS (on the 5.4 km grid, below) forecasts little precipitation for Arizona and northwestern Mexico through 5:00 pm MST on December 7th. Cold morning temperatures will prevail, but with little chance of rainfall here.

Monday, November 28, 2016

Fast-Hitting Nighttime Winds and Light Rain

Bit of snow at higher elevations early this morning. Above shows a couple of inches at General Store in Summerhaven and below shows just a dusting at Kitt Peak. 

Here at house we had 30 to 40 mph winds as the front passed and some rain both before and after midnight. Total ended up at 0.11" and the GEFS average from 06 UTC yesterday morning was quite good - 06 UTC WRF versions were a bit dry for the metro.

Several issues noted this morning. First, the Pima County ALERT map (above for 24-hour precipitation though 7:00 am MST) no longer fits my screen well, and I can't do a proper snip to show the entire array. Rain amounts were generally quite light, but one site on Redington Pass reports over half an inch.

Sadly, the old version display of the data (metro west sector below) is no longer updating. This is distressing to me, since the old version is (was) extremely versatile wrt examining precipitation across varying time periods and also for looking back to past events. Serious loss for those interested in using the ALERT data for research.

Finally, the radar/gauge product from WDT (below, which is my preferred product of this type) illustrates some beam blockage artifacts this morning - below is 24-hour estimate and sectors where lowest beams are blocked show clearly. Reason for this is that the precipitation echoes with this event had very low tops - thus, if gauges not available then radar estimates were too low where lowest tilts weren't available. Radar-based precipitation estimates remain a difficult product to evaluate or use in research where terrain is complex and substantial beam blockage is present.