Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 192325

Area Forecast Discussion
National Weather Service Cheyenne WY
525 PM MDT Wed Sep 19 2018

Issued at 525 PM MDT Wed Sep 19 2018

Please see latest 00z Aviation Discussion


.SHORT TERM...(This evening through Thursday)
Issued at 237 PM MDT Wed Sep 19 2018

Quiet a plethora of weather hazards today as a stalled front and
gusty winds bring; low ceilings, fire weather concerns, and
potential for showers and thunderstorms this afternoon.

Visible satellite and regional METARS showed an area of broken
low clouds over the Nebraska panhandle. This band of clouds was
located on the cool side of a quasi stationary front draped along
the front range out through south central Nebraska. Pooled
moisture and cool temperatures will keep cloud decks low and the
potential for fog high this evening and tonight.

Scattered showers and thunderstorms will develop later this
afternoon and evening as the cool and moist post frontal upslope
flow develops. The Dewpoint at KCYS has held steady at 53 through
the early afternoon. With 2-6 km lapse rates in the 7.5-8.5C
range, 1000-1500 j/kg of MU cape should develop along the lee of
the Laramie Range this afternoon. There has been some signal for
marginal severe weather, but the limited shear profiles and
thermodynamics suggest this is not likely. Showers and storms
should continue overnight ending by 12z Thursday.

To the west, Clear skies and temperatures in the middle to upper
70s were mixing the atmosphere deep into the strong southwesterly
flow aloft. low teens to single digit RH values were noted across
western carbon county. Critical fire weather criteria were being
met and the current Red Flag Warnings look on track. Red Flags
continue until 8 pm this evening. Expect poor humidity recovery
overnight with another round of critical fire weather Thursday.

.LONG TERM...(Thursday night through Wednesday)
Issued at 237 PM MDT Wed Sep 19 2018

In the long term, a mostly dry period is expected after this week
and heading into the weekend. Southwest flow aloft will bring dry
downslope winds and once again bring the potential for fire
weather conditions. Temperatures will begin to rise Friday
reaching the middle to lower 80s by Saturday and Sunday.

There is good model consensus on a trough approaching western
Wyoming late Sunday and early Monday. This will bring rain chances
back into the forecast briefly Monday and Tuesday. A few storms
could also work their way in late Monday.

Behind the trough, cool northwest flow is expected with
temperatures overnight in the low 40s to upper 30`s. This cold
shot is likely the beginning of more seasonable air as a large
west coast ridge is expected to develop. This will keep the area
in northerly flow helping to keep temperatures down. The northerly
flow will also limit local moisture and will keep rain chances
low through the extended.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 525 PM MDT Wed Sep 19 2018

Persistent low ceilings and visibilities will continue to hamper
the NE terminal sites. Latest radar has showers and thunderstorms
forming off the mountains so expecting KCYS and perhaps KSNY to
see some vicinity storms in the first period. Once again, the late
evening and overnight period will see IFR to LIFR conditions of
low ceilings and areas of fog across the Panhandle with some low
ceilings into KCYS as well.


Issued at 237 PM MDT Wed Sep 19 2018

Critical Fire Weather conditions will continue this week as a dry
and wind period develops across southeastern Wyoming and western
Nebraska. Southwesterly winds aloft at 30 to 40 mph will mix down
through the afternoon hours and interact with RH values in the low
teens to single digits. Widespread critical conditions are likely
today with several area RAWS sites already hitting criteria.
Widespread areas of critical fire weather criteria will also be
met on Thursday. West southwest downslope winds of 30 mph are
expected which will dry the lower boundary layer even further.
Friday, very low humidity in the single digits is expected across
western carbon county. Deep mixing of the atmosphere will likely
produce a few wind gusts above RFW criteria even though sustained
winds will likely be just shy. A fire Weather Watch was issued
for Friday afternoon to cover the likely critical fire weather


WY...Red Flag Warning from noon to 8 PM MDT Thursday for WYZ302>310.

     Fire Weather Watch from Friday afternoon through Friday evening
     for WYZ303>308.

     Red Flag Warning until 8 PM MDT this evening for WYZ303-304-306.



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