Area Forecast Discussion
Issued by NWS Cheyenne, WY

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576
FXUS65 KCYS 201130
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
530 AM MDT WED JUL 20 2016

.SHORT TERM...(Today through Friday)
Issued at 243 AM MDT Wed Jul 20 2016

The main concern with this timeframe is how hot temperatures will
be in the panhandle today, and where the best chances of precip
will be.

Today-Tonight:
Latest water vapor loop was showing the monsoonal flow continuing
to stream through southeast Wyoming and the Nebraska panhandle.
This should set the stage for another round of afternoon
thunderstorms mainly near the mountains and the high plains of
Wyoming. Not expecting anything severe...due to limited
instability and lack of shear.

Otherwise, hot temperatures will be the rule especially in the
panhandle. We did decide to go ahead and issue a heat advisory for
the northern panhandle today and tonight, since the current
temperatures are still in the mid to upper 70s as of 3 am. In
addition, it appears like we should mix out much the drier air
this afternoon in this region which should allow temperatures to
climb well above the century mark especially in Chadron where they
could see 105 to 107. The downslope flow may also persist through
much of the night which may aid in keeping temperatures in the mid
to upper 70s once again. Even though heat indices will only be 95
to 100 this afternoon felt like this was going to be a hot one
regardless especially with the drier air in place which may cause
more heat stress due to lack of moisture.

Thursday-Friday:
Models are showing the upper level ridge in the plains retrograding
a bit to the west on Thursday. This will tend to flatten the upper
level flow in the Northern Plains which may cause the surface low
to track east of the forecast area. This will also cause cooler
air to filter into areas east of the Laramie Range on Thursday.
In fact, afternoon highs may drop about 5 to 10 degrees in
portions of the panhandle which will be a welcome relief from the
day before. However, dewpoints may be a bit higher. Convection
chances will also be nil due to lack of forcing.

The models are still in agreement in bringing a stronger
shortwave through the Northern Rockies and skirts it east along
the U.S./Canadian Friday. The consensus models are trending
towards better precipitation chances. However, we are still
favoring rather limited precipitation amounts due to lack of low
level moisture which will result in more high based thunderstorms.

.LONG TERM...(Friday night through Tuesday)
Issued at 243 AM MDT Wed Jul 20 2016

A shortwave moving across Montana and into the Dakotas on Saturday
will turn the midlvl flow westerly.  A cold front will push across
the region on Saturday morning, ushering in drier air at the sfc.
Thus, with PW values falling, kept tstms out of the fcst.  Llvl
winds across the plains become southeasterly by Sunday, bringing
moisture advection and increasing instability.  Both the GFS/ECMWF
suggest some possibility for strong to isolated svr storms with CAPE
values rising to 1000-1500 J/kg.  Weak upper level impulses will
move overhead on Sunday/Monday which will promote isolated to
scattered convection.  The subtropical ridge builds westward over
the Great Basin by Tuesday into the middle of next week.  Highs
through the extended will be around seasonal normals for late July.
Although RH values will fall to around 15 percent for areas to the
west of the Laramie Range each aftn, winds should be below critical
levels.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 528 AM MDT Wed Jul 20 2016

VFR. Southwest winds will gust to 20-25 kts at RWL from late
morning through 00z. Isolated to scattered thunderstorms will be
possible in areas near the Laramie Range this afternoon. Included
vcts at CYS with gusty winds and brief heavy rain being the main
threats.

&&

.FIRE WEATHER...
Issued at 243 AM MDT Wed Jul 20 2016

Wind speeds aloft are expected to be quite low this afternoon
which will result in much lower spread rates. However, relative
humidities this afternoon will certainly be low enough in zones 311
and 312 to make conditions flammable. Wind speeds will continue to
be light Thursday due to the influence of the upper level ridge
along with low relative humidites around 15 to 20 percent mainly
in zone 301 and 303. The more critical fire weather day could be
on Friday due to stronger winds aloft and better mixing especially
in zone 301.

&&

.CYS Watches/Warnings/Advisories...
WY...None.
NE...Heat Advisory from noon today to 6 AM MDT Thursday for NEZ002-
     003-095-096.

&&

$$

SHORT TERM...REC
LONG TERM...ZF
AVIATION...ZF
FIRE WEATHER...REC



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