Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 132046
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
246 PM MDT Thu Aug 13 2020

.SHORT TERM...(This evening through Friday)
Issued at 213 PM MDT Thu Aug 13 2020

Surface analysis at 18Z shows approaching cold front slowly making
its way toward the northern fringe of our forecast border near
Niobrara and Converse County, and the warm front further to the
east draped across central Nebraska to northern Colorado.
Satellite picking up on some diurnal afternoon Cu, even an
occasional lightning strike from towering Cu south of our CWA.
Temperatures have warmed up quickly from the morning period
timeframe. The warm temperatures, low dew points, and gusty
southwest winds have kept the region very dry for the day thus
far. This trend will continue through early evening, likely
verifying the RFW for today in all of the fire weather zone areas.
Low relative humidity recovery is anticipated in the overnight
hours for our western forecast zones, and potentially as far east
as the NE/WY state line. GFS short term guidance is hinting at
relative humidity values only recovering up to approximately
15-25 percent by 12Z. The cold front will advance overnight from
our northern zones toward the south, and become wedged up against
the lee side of the Laramie Range. This will not assist with the
western zones staying above RFW criteria, thus have issued the
product for tomorrow morning through the evening. It might be a
stretch for the zones east of the Laramie Range to verify in the
afternoon as the cold front advances southward, but gusty winds in
the morning with that tightened pressure gradient are certainly
possible. One last item to note is that behind the cold front,
700 mb temperatures are averaging 6-8 Celsius along the northern
zones by 18Z. Not expecting a stratus deck to keep temps too low,
but lowered the afternoon temperatures several degrees in this
forecast package for Niobrara/Converse county. Soundings show
about 22-24 degrees Celsius by afternoon at the surface, which
may be even lower than what is advertised presently for some of
the short term guidance. Went against the warmer solution that
initially advertised temperatures in the upper 80s, as the cooler
temperatures could easily mix down to the surface in that area by
afternoon time period and make for a pleasant day. The remainder
of the region looks to be dry and the region, with temperatures
easily making it near to above 90 degrees closer to the Colorado
state line and into the Panhandle region for Friday.

.LONG TERM...(Friday through Wednesday)
Issued at 245 AM MDT Thu Aug 13 2020

Areas west of the front though...will be dealing with critical
fire weather conditions Friday through the weekend as front really
never makes it over the Laramie Range. GFS 700mb winds across
Carbon...Albany Counties and the Laramie Range remain strong. GFS
forecasting 35-40kts at 700mbs Friday through noon time before
slowly easing. Previously issued Fire Weather Watch for FWZ 302
through 310 looking good and no changes were made.

Likely going to need fire headlines Saturday and Sunday. May not
mix as deep as we have been. GFS soundings showing mixing up to
just under 500mbs Saturday afternoon. Winds are fairly weak at
this level...so held off on a Fire Weather Watch for Saturday and
Sunday. GFS showing a surge of easterly winds across the Laramie
Range Sunday...another reason for holding off on fire headlines.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1134 AM MDT Thu Aug 13 2020

The main concern with this TAF issuance is the timing of the
frontal boundary moving through the area tomorrow morning.

Latest water vapor loop was showing a fairly strong shortwave
moving through the northern Rockies. This feature will continue to
move into the northern Plains by Friday afternoon. As a result, a
frontal boundary will surge through areas east of the Laramie
Range tomorrow morning. Once the frontal boundary surges through,
the wind will switch to the north at speeds of 15 to 25kts.


&&

.FIRE WEATHER...
Issued at 213 PM MDT Thu Aug 13 2020

Widespread critical fire weather conditions present for a
majority of the forecast area today. Red Flag Warnings in effect
for FWZ 301 through 312 through 8PM today. Gusty winds and low
relative humidity values will continue through this time. High
pressure will move south due to an advancing cold front. Westerly
winds will be present until this cold front passes through the
region, switching winds to northeast up against the Laramie Range
behind the front. To the south and west of the front...westerly
winds will stay strong with critical fire weather conditions
expected once again Friday. Critical fire weather conditions
expected to continue into the weekend.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning until 8 PM MDT this evening for WYZ301>310.

     Red Flag Warning from 9 AM to 8 PM MDT Friday for WYZ302>310.

NE...Red Flag Warning until 8 PM MDT this evening for NEZ311-312.

&&

$$

SHORT TERM...BW
LONG TERM...GCC
AVIATION...REC
FIRE WEATHER...BW



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