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Area forecast discussion 
National Weather Service Cheyenne Wyoming
1042 am MDT Thursday Aug 21 2014

Update...
issued at 908 am MDT Thursday Aug 21 2014

Current forecast for today looks on track. Made some minor
adjustments to precipitation probabilities and tstorm coverage today.
Convection will struggle to develop this afternoon further south
due to subsidence and drier air aloft. However...model soundings
show this warm/dry layer aloft eroding by this evening. Can not
rule out an isolated shower or thundershower along i80 late this
afternoon and this evening as a weak disturbance aloft will move
across the region. Still expect most of the activity to remain
across central and northeast Wyoming as a frontal boundary
gradually drifts southward and stalls across north-central Wyoming
today.

&&

Short term...(today through Saturday night)
issued at 426 am MDT Thursday Aug 21 2014

Flow aloft remains southwest. Isolated to scattered late day
showers and thunderstorms on tap west of a Laramie to Chadron line
where moisture and instability will coincide along with best upper
forcing.

Tonight...cold front moves west to east across the counties with a
few showers possible late north of a Lusk to Sidney line.

Friday...next negatively tilted shortwave trough aloft moves across
western Colorado...with middle level shortwave trough over northern
Colorado combined with adequate low and middle level moisture to
produce scattered late day showers and thunderstorms...most
numerous east of a Cheyenne to Lusk line.

Friday night...shortwave trough aloft rotates northeast across
eastern Wyoming and western Nebraska...with at least scattered
showers and thunderstorms developing...likely most numerous across
western Nebraska.

Saturday...unsettled pattern continues over our counties as the
dominant upper trough prevails over Montana and Wyoming...with the
next shortwave trough aloft rotating across western Wyoming...
producing at least scattered showers and thunderstorms near the low
and middle level Theta-E ridge axis.

Long term...(sunday through thursday)
issued at 426 am MDT Thursday Aug 21 2014

00z medium range deterministic models continue to paint a fairly
similar picture for Sunday and Monday...but deviate dramatically
on Tuesday through Thursday. Saturdays front will be south of the
County Warning Area for Sunday...with the associated shortwave energy lifting
northeast across the Dakotas. Looks like a relatively cool and
stable day shaping up...which will suppress most convective
chances. The GFS does paint some moisture along the i80 corridor
from Cheyenne to Sidney as the warm front lifts back north late
Sunday evening. Southwest flow will persist on Monday as the next
shortwave dives southeast into Montana/Idaho. Increasing moisture
and ascent with the approach of the upstream trough will increase
thunderstorm chances west-east Monday and Monday night. It as at this
time when model solutions begin to diverge. The 00z GFS and
Canadian maintain a progressive pattern for the Tuesday-Thursday timeframe.
Meanwhile...the Stalwart European model (ecmwf) shows this shortwave trough beginning
to elongate into northern California late Monday...eventually cutting
off over the Great Basin mid-week. The downstream impacts are
many...pending which solution is correct. Have largely discounted
the 00z European model (ecmwf) given its deviation run-to-run as well as from other
global models. Of course...any addl support both run-to-run or
amongst other global models in future output would add credence to
this outcome. In the non-European model (ecmwf) solution...another front would
slice through the County Warning Area on Tuesday... ushering the coolest temperatures of the
week and another good chance for precipitation. Precipitation will exit quickly
Tuesday nt...with drier and warmer conditions expected for Wednesday and
Thursday.

&&

Aviation...(for the 18z tafs through 18z Friday morning)
issued at 1039 am MDT Thursday Aug 21 2014

Convection looks to be confined to extreme southern Wyoming and
the southern Nebraska Panhandle today. Used timing from latest
hrrr forecast that shows kcys and possibly kbff and ksny seeing some
convection late this afternoon. VFR conditions otherwise outside
of thunderstorms.

&&

Fire weather...
issued at 426 am MDT Thursday Aug 21 2014

Minimal concerns as the winds and humidities remain below
critical thresholds.

&&

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

$$

Update...tjt
short term...Rubin
long term...Hahn
aviation...claycomb
fire weather...Rubin

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