Weather Service Report


829 
FXUS65 KCYS 202102
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
302 PM MDT Fri Jul 20 2018

.SHORT TERM...(This evening through Saturday)
Issued at 247 PM MDT Fri Jul 20 2018

Main hazard focus will be on the strong thunderstorm potential
Saturday afternoon and early evening across the southeast Wyoming
High Plains and into far southern portions of the Nebraska 
Panhandle. Pea to quarter hail and winds of 40 to 60 mph could be 
possible in the strongest of storms during this time frame.
Outdoor activities should be closely monitored for possible
impacts from 2pm to 8pm near the Cheyenne area Saturday. 

Weak H5-H3 ridging aloft resides across the four-corners region as
monsoonal moisture slowly shifts farther north on the western
periphery per water vapor channel imagery. A very low chance of
isolated showers could occur this afternoon as this moisture
attempts to reach the area during diurnally peaking instability
time frame. However, these two factors look to not be temporally
coincident enough for more then just isolated coverage (if any)
late this afternoon to early evening. A quiet overnight periods is
expected. 

For Saturday, greater moisture will be present through the
vertical atmospheric column and combined with strong diurnal
heating, increased instability will result. These factors combined
with a weak shortwave trough rotating around the periphery of the
ridge will set the stage for scattered showers and thunderstorms
to develop. With 30 knots of deep layer shear, some storm semi-
organization could occur in the weak west to northwest flow. Pea
to quarter sized hail and wind gusts of 40-60 mph winds could be
possible in the strongest of strums from 2-8pm tomorrow. Activity
will diminish through mid-evening hours. 

.LONG TERM...(Sunday night through Thursday) Issued at 315 AM MDT
Fri Jul 20 2018

Similar to yesterday, 00z models and ensembles are in reasonable
agreement with the overall pattern across Wyoming and Nebraska,
showing northwest flow aloft prevailing across the region as a
cool front stalls along the Front Range. However, the timing and
coverage of showers and thunderstorms are still up in the air due
to timing difficulties with FROPA and an upper level trough moving
east near the Canada/US border. 

For Sunday night and Monday, all models show a pretty strong cold
front for this time of the year sliding south along the Laramie 
Range and stalling across the Front Range by early Monday morning.
Depending on the timing of this cold front, Sunday night may be 
pretty active with nighttime thunderstorms in addition to another
round of thunderstorms with heavy rainfall later in the day.  
Model difference appear after Tuesday with significant deviations 
in frontal position. Will need to closely monitor Tuesday and 
Wednesday for strong to severe thunderstorms as convective 
parameters are still favorable for severe weather across the 
eastern plains. There appears to be a good chance for some very
heavy rainfall across the mountains and eastern plains as well,
mainly next Thursday and Friday. 

&&

.AVIATION...(For the 12Z TAFS through Friday night) 
Issued at 345 AM MDT Fri Jul 20 2018

VFR conditions will prevail through tonight with a few high res 
models showing brief fog and low VIS around KSNY and KAIA this 
morning. For this afternoon, a few isolated showers and 
thunderstorms are possible near the mountains and perhaps across the 
southern Nebraska panhandle this evening. Coverage will be very 
limited, so will keep out of the regional TAFs for now. Winds should 
be lighter compared to the last few days across southeast Wyoming 
with surface winds shifting into the east through this evening. 

&&

.FIRE WEATHER...
Issued at 247 PM MDT Fri Jul 20 2018

Elevated fire weather conditions are ongoing this afternoon for portions
of the mid and higher terrain of the Sierra Madre and Snowy Mountain 
ranges in Carbon and Albany Counties, WY. Relative humidity values 
have fallen into the lower teens but winds have remained near 10 
to 15 mph with periodic gusts to near 20 mph at times. Similar 
conditions are expected Saturday and Sunday but with greater rain 
chances over the higher terrain and adjacent high plains in WY. 

Scattered wetting rain and thunderstorms will occur through much
of the upcoming week as well with no large wind signals and slightly
higher monsoonal moisture. 

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&

$$

SHORT TERM...JSA
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...JSA

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Western Regional Climate Center, wrcc@dri.edu