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Nowcast

• 

• Now as of 10:40 PM MDT on May 23, 2012

  Isolated showers and a few weak thunderstorms will gradually diminish across portions of east central Wyoming and the northern Nebraska Panhandle through midnight. Additional rainfall will be a few hundredths of an inch.

Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Thursday
• 
• High: 70 °
• Low: 41 °
• Chance of Rain

• Friday
• 
• High: 68 °
• Low: 46 °
• Chance of T-Storms

• Saturday
• 
• High: 86 °
• Low: 50 °
• T-Storms

• Sunday
• 
• High: 73 °
• Low: 46 °
• Partly Cloudy

• Monday
• 
• High: 79 °
• Low: 36 °
• Clear

Area forecast discussion 
National Weather Service Cheyenne Wyoming 
1115 PM MDT Wednesday may 23 2012 


Aviation...06z tafs 


Mainly VFR conditions expected next 24 hours. Could see some MVFR 
conditions with showers this afternoon...mainly across the 
northern Panhandle. Upsloping winds look to set in Thursday night 
that may lead to IFR and below conditions across the Panhandle and 
airports east of the Laramie range. 


Claycomb 




&& 


Previous discussion... /issued 850 PM MDT Wednesday may 23 2012/ 


Update...water vapor imagery and 00z sounding data showed a long 
wave middle/upper level trough over the western Continental U.S. This evening. 
A 130-knots 300 mb jet extended from the eastern Pacific through the 
central Great Basin and central rockies... with northern Colorado 
and southern Wyoming on the left exit region. Upper level 
diffluence was enhancing large scale lift with widespread 
precipitation over much of the County warning forecast area. Marginal instability in the 
middle levels was contributing to convective nature of precipitation... 
with scattered showers and isolated thunderstorms across central and 
eastern Wyoming. More stratiform banding with embedded thunderstorms 
prevailed in region of middle level frontogenetical forcing over 
northern and northeast Colorado. Rainfall amounts thus far have 
generally been light... from a trace to around a tenth of an inch. 
Heavier/steadier rain with tenth to quarter inch south of I-80 
corridor from east of Cheyenne to Sidney was indicated. 


Expect a gradual decrease in coverage and intensity of precipitation 
as the frontogenetical forcing shifts southeast with the upper 
level jet overnight. It will be cold enough for some light snow 
for the mountains as snow levels drop below 8500 feet. 
Accumulations will be minimal and confined to grassy surfaces. 


Based on radar trends...have raised probability of precipitation for extreme southeast 
portion of County warning forecast area and expanded the coverage of isolated thunderstorms 
this evening. Low temperature forecast generally on track. 


Previous discussion... /issued 332 PM MDT Wednesday may 23 2012/ 


Short term...tonight through Friday night... 
radar imagery is currently showing a band of light rain showers 
over portions of Laramie County and the southern Nebraska 
Panhandle. The models have done a good job at moving this band 
southeastward during the day along an axis of 700-500mb 
frontogenesis. The frontogenesis is prognosticated to be in northeastern 
Colorado by 00z. The GFS and NAM both show a quarter to one half inch of 
quantitative precipitation forecast just across the border in Weld County through tonight. Went 
with a tenth inch of quantitative precipitation forecast along the border...as the heaviest 
showers should remain south of the County Warning Area with the forcing. Thursday 
will be a cool day with 700mb temperatures around -3c and broad cyclonic 
westerly flow over the area. With the 300mb jet positioned over 
Colorado...the northern part of the County Warning Area will be in the left exit region 
through the afternoon. This will create enough lift for scattered 
showers mainly in that area. Cannot rule out some isolated thunderstorms 
with the cold middle level temperatures producing some weak instability. 


The models continue to show a strong middle level trough digging into 
the Great Basin on Thursday night and closing off over Nevada on Friday. The 
surface pressure falls over the Great Basin will result in increasing southeast 
winds on Friday...which will transport low level moisture into areas east of 
the Laramie range. High temperatures on Friday will be tricky over the plains 
due to the low level stratus that will likely develop in the moist 
upslope flow...however leaned toward the warmer GFS. The GFS...due 
to its warmer boundary layer...shows a narrow axis of 500-1000 j/kg 
of cape along and just east of the Laramie range on Friday afternoon. 
Should any storms develop...the favorable environmental shear 
profile could produce a few stronger storms. The storms would 
weaken as they move out of the instability axis and into a much more 
stable airmass over the plains. Expect a persistent stratus deck 
over the plains on Friday night...with some of the soundings indicating 
drizzle or light rain possible with deepening saturation in the 
low level. 


Long term...Saturday through Wednesday... 
a sharp and negatively tilted upper-level trough will dominate 
the western Continental U.S. Early in the extended period as a significant 
closed low lifts northeast through the Great Basin. Medium range 
model guidance continues to trend northward with the track of this 
feature...and the prospects of convective precipitation across our County Warning Area 
continue to diminish as a result. Nonetheless...strong southwest 
flow aloft and a strengthening surface low over northeast Colorado should 
continue to promote low-level moist advection over east central Wyoming 
and the northern NE Panhandle. This scenario along with steep middle- 
level lapse rates would result in sufficient instability in the 
presence of very strong deep layer vertical shear to support 
organized thunderstorm activity over those areas on Sat. A fire weather 
risk would exist over southeast Wyoming...where a middle-level dry slot is 
expected to lift rapidly northeast that afternoon. Beyond 
Saturday...dry west to northwesterly middle-level flow will tend to 
limit chances for showers and thunderstorms to the mountainous terrain. A 
few disturbances should traverse the flow toward the end of the 
period...resulting in additional chances for precipitation over the High 
Plains. However...no significant precipitation events appear to be in the 
offing. 
&& 


Fire weather... 
no fire weather concerns through Friday as temperatures have 
cooled and relative humidities have risen behind the cold front 
that passed over the area last night. Scattered showers will 
continue over portions of Laramie County and the southern Nebraska 
Panhandle through early tonight. Dew points will increase on Friday 
especially for areas east of the Laramie range as southeasterly 
winds transport moisture into the area. There is the potential for 
elevated fire weather conditions to develop on Saturday afternoon 
mainly in areas near the Colorado border as increasing south winds 
produce a warmer and drier airmass. 


&& 


Cys watches/warnings/advisories... 
Wyoming...none. 
NE...none. 


&& 


$$ 


Short term/fire weather...Finch 
long term/aviation...hammer