Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 281729
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1129 AM MDT TUE JUN 28 2016

.SHORT TERM...(Today through Wednesday night)
Issued at 529 AM MDT Tue Jun 28 2016

11-3.9um satellite imagery shows stratus and fog developing over the
S. Laramie Range and the Cheyenne Ridge early this morning. High
boundary layer moisture is progged by the majority of models through
mid-morning across this area, and even spreading up into  the
North Platte River Valley. Thus, maintained mention for patchy fog
through at least 15Z. A steady erosion of the stratus/fog will
give way to at least partly cloudy skies through early afternoon
and strong heating.

The next shortwave is still on track to round the upper level
ridge and across Wyoming today. A 65 kt H25 jetlet will move
overhead in conjunction with the shortwave, adding extra lift to
an already dynamic situation. At the sfc, expecting moist south-
southeasterly flow to persist through much of the day across the
eastern plains. A slightly more backed east-southeast component
to the winds will occur across our northern tier of counties ahead
of a developing sfc low over Wyoming. In particular, high res
models also show localized backing of winds vicinity of the North
Platte River valley and Pine Ridge. Instability progs remain very
high through the afternoon, perhaps up to 3000 J/kg in some areas
across the Nebraska panhandle where dews are progged to be in the
upper 50s/low 60s. 0-6 km shear will be on the increase through
the day as well due to the jetlet moving overhead. Both NAM and
GFS show shear values of 45 to 55 kts across the plains, and 25
to 35 kts out west.

With that said, expect thunderstorms to initiate over the mountains
mid-afternoon where convergence will be maximized, and also where
sfc winds begin to converge in response to the  developing sfc low.
Supercellular organization is likely as storms trek southeast across
the plains based on progged instability and shear, bringing the
threat for large hail and damaging winds for this area. WHere backed
sfc winds occur, could see an enhanced threat for tornadoes as
0-1 km SRH approach favorable values in these locations through
the late afternoon and evening. However, LCL heights are progged
to be fairly high in the afternoon due to deep layer mixing which
will reduce the overall threat. Still, can`t completely rule one
out. Upscale growth into an MCS still looks probable across the
Nebraska panhandle through the evening with increasing llvl jet.
Out west, dry boundary layer conditions will keep precip to a
minimum over the mountains, however 00/06Z models are producing
more QPF than previous runs so perhaps the threat for dry
thunderstorms will be less.

T-storms look quite probable once again on Wednesday as yet another
shortwave and higher midlevel moisture move in from the west.
Wednesday`s severe potential looks less tho due to scouring of
moisture from today`s activity, however some moisture return
across the panhandle could promote stronger activity here. Looks
to be more heavier rain produces and perhaps marginally severe
hail across Wyoming.

.LONG TERM...(Thursday through Monday)
Issued at 529 AM MDT Tue Jun 28 2016

Monsoonal-like flow pattern will hold across the area Thursday and
Friday keeping at least sctd showers and tstms in the forecast
both days. Most widespread activity looks like it will be on
Thursday as a decent upper shortwave moves across the area while a
cool surface high settles into the northern plains and provides a
surface upslope pattern over the CWA. Milder temperatures should
reduce the overall instability with more general showers and
storms expected that day. Subtle changes occur over the weekend as
an upper ridge drifts east and over the CWA which will act to
shunt the better moisture southward so should see less convection
for Sunday and Monday. GFS particularly dry those two days while
EC still paints some QPF mainly on Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1124 AM MDT Tue Jun 28 2016

Wyoming TAFS...VFR at Rawlins and Laramie with isolated
thunderstorms from 21Z to 02Z. At Cheyenne, VFR prevails with
isolated to widely scattered thunderstorms from 21Z to 02Z
producing wind gusts to 45 knots and localized MVFR. MVFR in
fog and low clouds at Cheyenne from 10Z to 15Z.

Nebraska TAFS...VFR prevails. Scattered thunderstorms, some
possibly severe, between 20Z and 06Z, with strongest storms
producing wind gusts in excess of 50 knots, large hail, heavy
rain and extreme turbulence under MVFR conditions. IFR in fog
and low clouds developing from 06Z to 15Z.

&&

.FIRE WEATHER...
Issued at 529 AM MDT Tue Jun 28 2016

An active pattern will continue through the week with chances for
showers and thunderstorms expected each day. Some storms may
become severe today across the plains with large hail and damaging
winds possible. Isolated dry thunderstorms remain a possibility in
the mountains, however current model guidance shows a better
chance for wetting rains today than previous forecasts, especially
in the higher elevations. Another round of scattered showers and
thunderstorms are expected on Wednesday, with an overall better
chance for wetting rains in the mountains. Similar conditions look
likely for Thursday.

&&

.CYS Watches/Warnings/Advisories...
WY...None.
NE...None.
&&

$$

SHORT TERM...RJM
LONG TERM...RE
AVIATION...RUBIN
FIRE WEATHER...RJM


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