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Area forecast discussion 
National Weather Service Cheyenne Wyoming
1132 PM MDT sun Apr 26 2015

issued at 927 PM MDT sun Apr 26 2015

A vigorous upper low continues to spin over central New Mexico at
this hour. The associated middle level deformation axis has allowed
moist upslope flow to persist over the High Plains of southeast Wyoming
and the western NE Panhandle through much of the evening. Do not
expect this to change much in the near term. Regional radar mosaic
indicates precipitation is starting to regenerate within this
have opted to keep at least likely...if not categorical probability of precipitation going
through the night. Surface observations suggest the environment is
quite moist...with dewpoints still in the 40s over the Panhandle
at 03z. With continued east-southeast will be hard to
cool things down. Increased dewpoints and minimum temperatures for
tonight for areas along/east of the Laramie range. Fog and/or low
stratus will be an issue tonight with the moist blyr. Decided to
increase snow levels a bit with such warm thermal profiles. A mix
of rain and snow may occur at elevations as low as 5500-6000 feet
but accumulations are unlikely. Greatest impacts from snow should
be at elevations above 7500 feet. Will make no changes to ongoing
winter advisories for the i80 Summit and Snowy Range.


Short term...(this evening through tuesday)
issued at 410 PM MDT sun Apr 26 2015

Convection has overspread much of Carbon County and the Cheyenne
Ridge this afternoon as the shortwave moves up from Colorado.
Thunderstorms are most prolific out over southern Carbon County and
are quite the lightning producers. Temperatures are holding in the
upper 30s to low 40s in the lower elevations in this area...with
low to middle 30s in the mountains as storms move overhead so think
that snow levels may be a bit higher than 8000 feet overall. The
strengthening inverted surface trough is keeping the cold front at Bay
while aloft...water vapor imagery depicts a sort of zonal
shortwave ridge overhead. It would appear that both features are
keeping the significantly colder temperatures from invading the forecast
area for now. Still expect the cold front to drop south late
tonight through Monday morning while the upper level deformation
zone moves overhead...which will bring in colder air and maintain
precipitation chances across the forecast area through tonight especially
alongthe Laramie range and Wyo plains. Will see snow in the
higher elevations above 7500 feet this evening dropping to 6500
feet overnight...and should mix down even lower as the cold front
moves north to south overnight. Will leave the Winter Weather
Advisory for now as there is plenty of time for convection and
deformation band to accumulate snow in the southern Laramie and
snowy ranges through tonight. With the combination deformation
band and also some meridional jet energy sneaking in from the west
overnight...could also see up to 5 inches in the Sierra Madre and
northern Laramie range mountains tonight...with an inch or less of
accumulation possible in the lower elevations of S/east Wyo with the
cold front by Monday morning. Likely to see fog overspread the
plains in this pattern again as will keep mention of
widespread areas of fog in the forecast through Monday morning.

For Monday...the upper jet will weaken as it shifts north with the
midlevel trough moving overhead. Will see showers continue on and
off through the day with the favored locations along northeast
facing slopes of terrain features. Not looking at significant cold air advection
behind the cold front overnight so temperatures should moderate with
daytime heating enough to keep snow confined to the mountains. It
is not out of the question to see snow mix with rain at times
though even across the plains as 700mb temperatures will be around minus
4c through the day.

Conditions will dry out Monday night through Tuesday as the upper
level ridge moves in from the west in the wake of the departing
upper low. Highs should return to the 50s/60s by Tuesday.

Long term...(tuesday night through sunday)
issued at 330 PM MDT sun Apr 26 2015

Upper ridge building into the area Tuesday night with drier
conditions continuing. Looks like dry weather should stay with US
through Thursday before another shortwave moves into the area from
the northwest. Pretty warm temperatures expected as 700mb
temperatures climb to around +6c Thursday afternoon.

Next chance for precipitation looks to be Thursday night into Friday as
an upper shortwave and associated cold front moves into the area.
Both the GFS and European model (ecmwf) bring the front into the area around 06z
Friday (thursday night) with showers developing over the snowy and
Sierra Madre ranges.

Frontal boundary looks to stall near the Wyoming/Colorado border
Friday and persists into the weekend. Both the GFS and European model (ecmwf)
painting fairly widespread quantitative precipitation forecast along the north side of this front
over southern Wyoming Saturday into Sunday. Freezing line well
north across northern do think most of this
precipitation will fall as rain next weekend.


Aviation...(for the 06z tafs through 06z Monday night)
issued at 1131 PM MDT sun Apr 26 2015

Abundant available moisture along with persistent easterly upslope
flow will continue to produce poor aviation conditions at most
terminals through at least the morning hours. Widespread LIFR/IFR
conditions anticipated at southeast Wyoming terminals through 18z.
Stratus should lift some by midday...but did add some additional
-shra after 18z. Conditions will be slightly better at western
Nebraska sites where some MVFR conditions can be expected. The one
exception may be kcdr...where some lower conditions may sneak in
around daybreak. Expect little if any chance for shower
development at these sites on have lifted them back to
VFR between 16-18z. Mountains will be obscured through much of


Fire weather...
issued at 410 PM MDT sun Apr 26 2015

No fire weather concerns through the middle of this week as a
period of unsettled weather will continue across southeast Wyoming
and western Nebraska. Periods of rain showers and high elevation
snow are expected into Monday. Much drier conditions will return
by midweek with daytime relative humidities trending lower towards
the 20 percent range on Wednesday.


Cys watches/warnings/advisories...
Wyoming...Winter Weather Advisory until 6 am MDT Monday for wyz114-116.




short term...rjm
long term...gcc
fire weather...rjm

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