Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 200106
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
706 PM MDT Sun Mar 19 2017

.UPDATE...
Issued at 706 PM MDT Sun Mar 19 2017

Fire weather conditions are improving overall with a steady
decrease in winds and increase in humidities, so allowed the Red
Flag Warning to expire at 7pm. Winds on the whole are diminishing
quite nicely with sunset and expect wind gusts in the wind prone
areas to remain 30 mph or less through the night. There may be a
brief period of higher gusts to 40 mph shortly before sunrise near
Arlington.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 300 PM MDT Sun Mar 19 2017

Another very warm and dry afternoon across the region with breezy
to windy conditions. The Red Flag Warning is working out well with
RH values of 13-15 percent and winds gusting to 30-40 mph over
areas to the east of the Laramie Range. With deep mixing in place,
have seen gusts to 50-60 mph in the Arlington area over the past
few hours. Current thinking is winds should begin to decrease
later this afternoon as the gradient weakens some. The 850 mb
CAG-CPR gradient is around 40 meters currently and comes down to
20 meters by 00Z. Will handle with an SPS as gusts above high wind
criteria have been sporadic. Weak backdoor front will move into
the Nebraska Panhandle by late tonight into Monday morning. Not
going to see a whole lot of cooling with weak cold air advection
behind it. SPC has introduced an elevated fire weather threat
across Laramie county (in the vicinity of CYS) on Monday
afternoon as west winds will gust to around 25 mph and RH values
fall to 15-20 percent.

The models continue to show a chance of rain showers developing by
late Monday afternoon across far western zones as a weak shortwave
approaches WY. Added a slight chance of aftn thunder as both the
GFS/NAM show 50-150 J/kg of MUCAPE. The best isentropic lift over
the llvl front stretches from Carbon county eastward to the
northern Nebraska Panhandle by late Monday night. Better cooling
will occur across the plains by Tuesday as sfc winds become
southeasterly and low clouds persist through early afternoon.
Although much of the plains will be capped through the day, there
will be at least a slight chance of showers/tstms along the
Laramie Range with the llvl convergence.

.LONG TERM...(Wednesday through Sunday)
Issued at 300 PM MDT Sun Mar 19 2017

Very unsettled pattern in the long term. Could be looking at a
significant winter storm Thursday night into Friday and another
storm late in the weekend.

Starting off Wednesday...Upper ridge axis shifting east during the
day Wednesday. Leeside low located over the northern Panhandle,
with a frontal boundary extending south from the low into eastern
Colorado. Westerly winds at 700mb over southeast Wyoming. GFS
showing 30-35kts 700mb winds over our western CWFA, so gusty winds
could be widespread.

A Pacific low pressure system moves into northern California
Wednesday afternoon and is forecast to be near the 4 corners area
Thursday afternoon. Fairly large diffluent flow at 500mb over the
CWFA and both the GFS and ECMWF show showers developing across our
western zones Thursday afternoon. By Thursday evening, upper low
centered over south central Colorado. 700mb temperatures Thursday
night on the ECMWF range from -6C over our northwestern zones to
+2C over the southern Nebraska Panhandle. GFS 700mb temperatures
colder across much of the CWFA with -2C to -6C. In both solutions,
precip will fall as snow across southeast Wyoming and a cold rain
in the Panhandle.

ECMWF showing a TROWAL feature over southeast Wyoming much of the
day Friday. Total QPF through Friday close to an inch. Could be
looking at a fairly widespread heavy snow event. Even an 10:1
ratio would put 10+ inches of snow along the east slopes of the
Laramie Range and over the Laramie Range. Believe guidance is way
too high on temperatures Friday and did lower over guidance 3-5
degrees. Should the ECMWF solution come true, with 700mb
temperatures -8C, we are likely to see snow all day Friday and
thus daytime highs only in the 30s for highs.

Low ejects out of the area into Nebraska Friday afternoon with a
relatively dry forecast Friday night into Saturday. A second low
forecast to move into the area Sunday. Trajectory similar to the
Friday one, so another snow event possible Sunday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 543 PM MDT Sun Mar 19 2017

Gusty winds early this evening will diminish with sunset and will
remain relatively light tonight. A cold front will drop south
across the plains on Monday, and may stretch from KDGW to KSNY by
midmorning. This will keep winds at sites to the north and east of
the front light and out of the north-northeast, while winds at
sites south and west will likely be gusty and out of the west once
again Monday afternoon. Expect gusts of 25 to 30 kts late morning
through the afternoon.


&&

.FIRE WEATHER...
Issued at 706 PM MDT Sun Mar 19 2017

For this evening, winds are on the steady decrease with sunset
and humidities are improving. Expect this trend to continue
through the remainder of the evening, therefore will allow the
warning to expire at 7 pm. It will not be as windy on Monday,
however an elevated fire threat will exist across Laramie county
as minimum afternoon humidity values drop to 15-20 percent and
winds gust to around 25 mph. Cooler temperatures will occur by
Tuesday.

&&

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

$$

UPDATE...RJM
SHORT TERM...ZF
LONG TERM...GCC
AVIATION...RJM
FIRE WEATHER...RJM



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