Saturday, March 16, 2019

Bit Unsettled Today

Old Bisbee webcam view at 6:40 am MST this morning. There have been some thunderstorms, with light showers, this early morning over far southeast Arizona. 

The culprit is a weak, closed 500mb low over southwestern Arizona - see 12 UTC 500 analysis below from SPC. Low is centered somewhere north of Yuma, with coldest 500 mb air over eastern half of state.

WRF models forecast storms and light showers this afternoon over Santa Cruz County, extending northward over parts of metro area. Radar composite forecast above is from 12 UTC WRF-RR and is valid at 7:00 pm this evening. Forecast Tucson skew-T below (from 06 UTC WRF-GFS) is valid at 5:00 pm this afternoon - model forecasts a sliver of CAPE at that time. Any showers/storms would be based fairly high (reflecting the low moisture levels) and any showers around here would be very light, due to strong, downslope easterly surface winds. 

Wednesday, March 13, 2019

Event Rainfall Totals - AM 13 March

There are some lingering, light showers still around this morning - composite NWS radar above is from 7:00 am MST.

Event total rain amounts ending at 7:00 am - ALERT data above north portion and below south portion. General rains of half to around an inch occurred across Tucson metro area. Here at house gauge shows 0.82", with perhaps a bit of that occurring this morning. Four sites at higher elevations recorded over an inch.

The 12 UTC 500 mb analysis (from SPC) shows a powerful, negatively short wave heading into Plains. Fast-moving, trailing wave will cross Arizona this morning - affecting mainly north portions of state, but leading to continued chance of some showers here locally.

The deepening surface cyclone has triggered widespread NWS watches and warnings. Blizzard conditions expected today and tonight from northeastern Colorado to the Canadian border. Image at bottom is from 7:30 am MST along I-80 west of Cheyenne, Wyoming.

Tuesday, March 12, 2019

Event So Far

Above shows light snow so far at Summerhaven General Store (7:30 am MST). At bottom is webcam view looking north from campus. Here at house it is raining lightly, with 0.42" in gauge so far. ALERT plot below (for northern 2/3rds of network) indicates widespread rains, with totals generally around a third of an inch. Four stations coming in at over half an inch.

Morning 500 mb analysis from SPC (above at 12 UTC) shows that south-to-north elongated, closed low is centered somewhere west of Yuma, with considerable cold air still coming our way. So far CG flashes (24-hours through 7:00 am this morning below, from and Vaisala) have been centered mostly over in Cochise County.

The TPW analysis (second below from MIMIC at 13 UTC) indicates a narrow band of low-latitude, high PW air trying to curl northward into southern Arizona. MIMIC has been down  much of last 48-hours, so it was not possible to follow the advance of subtropic air northward.

More later.

Monday, March 11, 2019

Latest Afternoon Radar 11 March

Latest NWS composite radar displays from Tucson (above) and Yuma (below). Showers out in western Pima County and also southeast of Tucson over northern Mexico and Douglas areas. Widespread rains moving into far western Pima County as per the Yuma radar.

Sunday, March 10, 2019

Look At Our Impending Weather Event

Current Sunday morning NWS forecast for event total rainfalls.

Above is the 12 UTC GFS 500 mb analysis. The large trough off West coast is forecast to come across the Southwest early this week, with southern portion closing off and moving eastward along the Borderlands while northern portion shears away rapidly to the northeast. Satellite water vapor image (for upper-levels, below) is from 11:00 am MST this morning. There appears to be a dominant  southern circulation west of northern Baja, with the weaker circulation to north near San Francisco. Second below is 12 UTC GFS 500 mb forecast valid at 5:00 pm Tuesday afternoon (the 12th),

The GEFS QPF plumes for TUS (above) are from 12 UTC forecasts this morning - event occurs mostly Monday night into early Wednesday. Forecast amounts for airport range from 0.3 to 1.2 inches, with average amount coming in at 0.6 inches.

Wild card in this event is moisture advection from lower latitudes (12 UTC WRF-NAM forecast this morning - below) is for 700 mb RH and is valid at 11:00 pm tomorrow night, the 11th. The model forecast indicates moisture from low-latitudes reaches into southeastern Arizona - will have to watch this aspect of event tomorrow.

Friday, March 08, 2019

Short Wave Coming By Today

A weakening, positively tilted, short wave from the Pacific will be moving across the Southwest today into tomorrow (morning 500 mb analysis above from NCAR RAP).

It is another dreary morning here, with high-cloud overcast - water vapor image (from 13 UTC) shows a long plume of upper-level moisture from south of Hawaii eastward across the Southwest. However, webcam image from Kitt Peak a bit after 7:00 am MST this morning (second below) indicates that there is lower cloudiness out to our west.

None of the GEFS or WRF runs from last night forecast precipitation at the airport (plumes above from 06 UTC GEFS forecasts for TUS) do indicate a much better chance for rainfall at the airport next Monday night/Tuesday.

Main concern today is how strongly winds will break through to surface. The 06 UTC WRF-GFS (below from Atmo) is for 10-m winds valid at 3:00 pm this afternoon. Quite strong winds forecast by that model - especially for Cochise County and southwestern New Mexico.

Wednesday, March 06, 2019

End Of Week "Event" Fizzling

Webcam view at Mono Lake, California, this morning (from Jack Hales CamWall). Snow falling as weak short wave moves across the area. The next short wave (which was threatening a light precipitation event in our area) comes in much stronger and threatens much of California with another significant event, with heavy rains and mountain snows extending inland across the Great Basin and Colorado.

The 09 UTC SREF ensembles for end of week here (TUS QPF - above) are all over place, but with only a third of members forecasting even a Trace here. The 06 UTC WRF-GFS forecast of precipitation through 11:00 am MST (below) now indicates only a slight event for northern portions of Arizona. 

However, the next system, which will threaten our area on Monday and Tuesday (see four panels with precipitation forecasts at bottom - from 06 UTC GEFS forecasts) seems to have some chances for actually picking up some moisture from low latitudes (forecasts are valid at 5:00 pm Monday afternoon). So our attention will mostly shift out to this time frame.