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Area Forecast Discussion (AFD)

Issued by Cheyenne, WY (CYS)

                            
000
FXUS65 KCYS 171734
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1134 AM MDT Wed Jul 17 2019

.UPDATE...
Issued at 1126 AM MDT Wed Jul 17 2019

...Please see latest 18Z aviation discussion...

&&

.SHORT TERM...(Today through Friday night)
Issued at 514 AM MDT Wed Jul 17 2019

Forecast challenges with this mornings package deal with severe
thunderstorms once again today...followed by very dry/windy
conditions through Friday...leading to increased fire weather
concerns.

Currently...Pesky frontal boundary remains over the northern
CWA...roughly along a line from Chadron to Guernsey to Rawlins
this morning. Mid to upper 50 dewpoints north of this front...with
upper 30s along the Colorado/Wyoming state line. Still observing
some thunderstorm activity early this morning along that front
with storms moving northeast. 80kt jet max currently analyzed over
Carbon County aiding in lift along the front as well.

Fronts takes its time this morning to shift east and northeast and
may hang up for a time over the northern part of the CWA. By
18Z...it looks to be roughly along a line from Alliance to Lusk
with very dry air for points west. MUCAPES around 3000 J/KG over 
the northern Panhandle up into Niobrara County this afternoon...so
can not rule out a few severe thunderstorms once again today for 
areas along and north/east of a line from Douglas to Alliance this
afternoon. HRRR and HiresNMM showing this happening this 
afternoon through roughly 02Z.

For our western Counties today...winds and very dry conditions 
are the main concern. GFS 700mb winds 35-40kts and afternoon
humidity down near 10-12 percent. Fortunately...fuels are not
receptive yet west of the Laramie Range...so fire weather
headlines are not warranted out there for today.

Dry/breezy conditions shift east for Thursday with downsloping 
winds off the Laramie Range. GFS soundings showing 30-35kts mixing
down to the surface at Rawlins and Laramie...while Cheyenne mixing
25-30kts down to the surface. FWZ 310 fuels are being reported as
YES for rapid fire spread...so went with a Fire Weather Watch for
late Thursday morning through early evening.

Backdoor cold front begins to move into the area Thursday night
into Friday from the northeast. This front will oscillate from
southwest to northeast through the afternoon Friday...which may
impact afternoon humidity levels. For now...do not expect fire
weather issues for FWZ 310 on Friday. But very low humidity
along/west of the Laramie Range continues Friday. Fuels out there
are really going to dry out. WOuld not be surprised to see some
zones fuels turn over to YES over the next couple days.
 

.LONG TERM...(Saturday through Tuesday)
Issued at 514 AM MDT Wed Jul 17 2019

A fairly typical mid/late July weather pattern over the region
with an upper high centered over the southern Rockys. Some
subtropical moisture will move around the western periphery of the
high and over this are especially Sunday into early next week
returning daily chances for showers and tstms for that time. Some
cooler air will also filter down Saturday with temperatures
being close to seasonal averages into early next week. 

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1126 AM MDT Wed Jul 17 2019

IFR and MVFR ceilings continue to hang on this morning at KCDR,
KAIA, and KBFF. Daytime heating is slowly eroding the cloud layer
likely removing it completely by 21Z. VFR conditions will prevail
for the rest of the period though there is the possibility of 
lowering visibilities and ceilings between 8Z and 14Z depending 
on the retainment of surface moisture overnight. Not enough 
confidence yet to note it in the TAF, but may be updating it with 
the later TAF issuance.


&&

.FIRE WEATHER...
Issued at 514 AM MDT Wed Jul 17 2019

A few afternoon and early evening thunderstorms possible today
across the northern Nebraska Panhandle and Converse/Niobrara 
Counties in southeast Wyoming. All other areas expected to be dry 
today. Areas west of the Laramie Range today expected to see gusty
west winds and very low humidity. These dry/windy conditions
expected to spread east of the Laramie Range Thursday. Critical
fire weather conditions looking likely across FWZ 310...where
fuels have been reported as receptive to rapid fire growth on
Thursday. Thus...a Fire Weather Watch has been issued for FWZ 310.
Increased humidity levels east of the Laramie Range expected 
Friday afternoon as subtropical moisture moves back into the area.
It will still be very dry and breezy west through
Saturday...before subtropical moisture moves into the area from
the south. Unsettled weather next week across much of southeast
Wyoming and Nebraska Panhandle with daily chances for
thunderstorms and wetting rains.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Fire Weather Watch from Thursday morning through Thursday 
     evening for WYZ310.

NE...None.
&&

$$

UPDATE...CW
SHORT TERM...GCC
LONG TERM...RE
AVIATION...CW
FIRE WEATHER...GCC