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February 16, 2003  - Lander High Wind Event

On the evening of Sunday, February 16th a strong pacific cold front pushed through Lander around 6 PM MST.   A narrow line of rain showers along the front was followed by west winds at 20 to 30 mph and a 4 millibar rise in surface pressure.  The associated upper level circulation crossed over the Continental Divide just to the north of the Wind River Mountains (approximately over Togwotee Pass) afterwards around  9 PM MST.   Water vapor satellite imagery showed rapid drying on the east side of the Wind River Range behind this circulation at 930 PM MST.  This signature is an indication that much drier air from the stratosphere was being pulled downward by strong upper level winds near the boundary between the stratosphere and troposphere, or the tropopause.  This phenomena occurs as these straight-line upper level winds cross perpendicular to a large mountain range causing the winds to be initially pushed up (into the stratosphere) and then pulled back down on the east side of the mountain range in a wave-like pattern.   Occasionally, these winds will push down all the way to the surface resulting in sudden strong gusts of wind.   Note in the observations from 9 PM to 10 PM (2100 to 2200 MST) that the pressures fell suddenly (4 millibars) and the airmass dried out rapidly with the dewpoint bottoming out at 11 degrees F.    A maximum wind gust of 77 mph occurred around 10:05 PM MST or 22:05. 

D
a
t
e
Time
(mst)
Wind
(mph)
Vis.
(mi.)
Weather Sky Cond. Temperature (F) Pressure
Air Dwpt 6 hour altimeter
(in)
sea level
(mb)
16 23:53 N 17 G 28 10.00 Fair CLR 35 11 29.79 1011.1
16 22:53 W 48 G 68 6.00 Light Rain and Windy CLR 34 14 41 33 29.67 1007.2
16 22:37 W 53 G 66 4.00 Light Rain and Windy CLR 34 16     29.67 NA
16 22:28 W 56 G 70 2.50 Light Rain and Windy CLR 34 18     29.67 NA
16 22:19 W 48 G 64 3.00 Light Rain and Windy CLR 34 18     29.68 NA
16 22:12
 
W 43 G 77 1.75  Light Rain Squalls and Windy CLR 34 18     29.68 NA
16 22:04 W 44 G 70 6.00 Light Rain Squalls and Windy CLR 34 14     29.67 NA
16 21:53 W 43 G 60 10.00 Windy CLR 34 11 29.71 1008.7
16 20:53 W 13 10.00 Fair CLR 34 13 29.81 1012.3
16 19:53 W 18 G 25 10.00 Fair CLR 36 12 29.80 1011.7
16 18:53 NW 17 G 22 10.00 Partly Cloudy FEW055 SCT120 38 20     29.78 1010.8
16 18:17 W 31 G 38 10.00 Breezy SCT022 SCT043 39 25     29.71 NA
16 17:53 SW 21 4.00 Light Rain BKN020 BKN041 37 32     29.71 1008.4  

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water vapor image showing stratospheric intrusion

The water vapor image above (taken at 930 PM MST on February 16, 2003) shows moisture content at approximately 30,000 feet above sea level.  Light colors indicate higher levels of moisture, and darker colors show drier air.  The ( L ) over north central Wyoming is the center of an upper level circulation or low pressure center after it crossed the Continental Divide.  The blue arrow shows darker coloration indicating very dry air east of the Wind River Mountains over Lander.   This localized area of very dry air indicates that the dry, heavier air from the stratosphere is being pulled down into the lower levels of the atmosphere.  The yellow arrow shows the position of the main jet stream where the strongest upper level winds are occurring.     (Click on image to enlarge)

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