Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 181136
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
536 AM MDT Tue Jul 18 2017

.SHORT TERM...(Today through Wednesday Night)
Issued at 213 AM MDT Tue Jul 18 2017

In general, less coverage of showers/thunderstorms can be expected
today as the surface cold front pushes south into northern CO. The
placement of stronger convergence and drying low levels suggests a
limited risk for convection outside of the mountains. However, the
GFS/NAM both suggest a weak mid-level disturbance tracking near or
over the I-80 corridor later today, so will maintain isolated PoPs
for lower elevation areas between CYS-SNY. At this time, we do not
expect storms to be particularly strong, but gusty winds are quite
possible with deep inverted-v profiles. Southern plains ridging is
expected to shift east on Wednesday, likely promoting a good surge
of monsoon moisture across southeast WY and western NE. Models are
differing significantly w/ the placement of a weak mid level short
wave later in the day, but the GFS/NAM both suggest a feature over
northern CO which could possibly affect southern WY. Regardless, a
considerably higher risk of convective activity can be expected by
Wed afternoon and evening. Highs Wednesday should be quite warm w/
progged H7 temperatures averaging around +18 deg C for much of the
CWA.

.LONG TERM...(Thursday through Monday)
Issued at 242 AM MDT Tue Jul 18 2017

Somewhat better chances of rain still look to be setting up
Thursday into Friday as the large upper ridge shifts a bit east
and weakens allowing a bit more monsoonal moisture return in the
weak southwesterly flow aloft to move into the central Rockies.
Latest model consensus would put Precipitable Water values near 1
inch by thursday, which is fairly high for our area in mid
summer. Weak midlevel steering currents would also suggest slow
moving thunderstorms Thursday into Friday, so the abundant
moisture and slow moving storms suggest the potential for flash
flooding will be something that we will have to keep in check as
we progress towards late week. Otherwise...fairly zonal midlevel
flow continues into the weekend with diurnal formation of isolated
thunderstorms over the mountains in the late morning moving out
onto the plains in the afternoon.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 536 AM MDT Tue Jul 18 2017

In the very near term we are seeing LIFR ceilings at Sidney where
easterly moist upslope flow is resulting in a low stratus deck and
light fog (3-5SM visibility). Expect the ceilings to gradually
lift through mid morning at Sidney. Latest convective allowing
models showing isolated showers and thunderstorms developing from
Laramie to Cheyenne to Sidney in the mid to late afternoon moving
them southeastward through early evening. Given sparse coverage
not enough to pin down a prevailing mention for those airports
this afternoon...but would not be surpised to see a few
thunderstorms along and just north of the Colorado border by 22Z.
Otherwise...VFR with some passing morning light showers around
Rawlins and Alliance.

&&

.FIRE WEATHER...
Issued at 213 AM MDT Tue Jul 18 2017

Daily chances for showers/thunderstorms will persist over the next
few days, mainly over the higher elevations of southeast Wyo. Main
concerns with this activity will be lightning as well as gusty and
erratic outflow winds. Otherwise, warm/dry conditions prevail with
afternoon RH values in the 15-20 percent range. However, winds are
expected to be light which will mitigate fire weather concerns.

&&

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

$$

SHORT TERM...CLH
LONG TERM...JG
AVIATION...JG
FIRE WEATHER...CLH



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