Area Forecast Discussion
Issued by NWS Cheyenne, WY

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540
FXUS65 KCYS 231751
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1151 AM MDT SAT JUL 23 2016

.UPDATE...
Issued at 1039 AM MDT Sat Jul 23 2016

A weak cool front and accompanying light showers exited the CWA
by mid morning. Temperatures have been warming a bit faster than
forecast across the plains, and have nudged afternoon high
temperatures upward a few degrees. Short range model guidance
including the CAM, HRRR and SREF are indicating only isolated
convective coverage over the southeast Wyoming mountains and
adjacent plains including Cheyenne. Therefore, lowered PoPs
to around 20 percent for this afternoon and evening.

&&

.SHORT TERM...Today through Monday.
Issued at 247 AM MDT Sat Jul 23 2016

Front is progged to move across the plains later this morning
associated with upper level shortwave moving across Montana. The
airmass will be drier and more stable this aftn behind the fropa.
The GFS/NAM along with convective allowing models have trended
toward at least isolated to scattered convection developing during
the aftn along the southern Laramie Range. This occurs as winds
become easterly and convergence improves. Thus, raised pops into
the 20-30 percent range for areas along the Colorado Border in
Albany/Laramie counties. Not expecting the storms to be severe,
however cannot rule out an isolated stronger storm with CAPE
values rising to around 500 J/kg. Temps will be 5-10 degrees
cooler across the plains.

Midlvl subtropical ridge will build northward into Colorado through
Monday. Temps will be even cooler on Sunday as southeasterly winds
develop to the east of the Laramie Range. Convective chances look
rather limited Sunday with much of the plains capped. Warming
occurs by Monday as 700 mb temps rise to 18-20C and heights aloft
increase. Dryline will set up along the WY-NE border with decent
instability across the Nebraska Panhandle (CAPE values of
1500-2000 J/kg). While warm temps aloft and convective inhibition
will keep tstm chances low, any storm that initiates along the
dryline could be strong to svr into the evening. SPC has much of
the plains in a marginal risk on Monday.

.LONG TERM...(Monday night through Friday night)
Issued at 247 AM MDT Sat Jul 23 2016

Medium to long range models continue to show the center of the
upper level high pressure...currently across the southern Great
Plains this weekend...retrograding westward into the Great Basin
region next week. Northwest flow aloft will develop across Wyoming
and Nebraska by Wednesday with temperatures lowering towards near
normal for this time of the year. Although the high will block
subtropical moisture from advecting northward into the forecast
area...upslope easterly flow will be common by the middle of next
week with model sounding showing a good supply of low to midlevel
moisture. In addition...several shortwave disturbances embedded in
the northwest flow will move southeast out of Canada and will
likely result in some cooler air aloft and added instability and
jet dynamics. Will need to monitor the potential for strong to
severe thunderstorms on Wednesday and even more-so on Thursday due
to increased instability and 0-6 bulk shear. Temperatures will
remain in the 80`s to 90`s during the day Tuesday and Wednesday...
and then likely trend lower by late in the week with highs in the
mid 70`s to mid 80`s expected by Friday as a pretty strong cold
front moves south across the plains.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1151 AM MDT Sat Jul 23 2016

A cold front dropping south across the plains today will shift
west-northwest winds to the north-northeast by this evening.
Isolated thunderstorms are possible along and east of the Laramie
Range late this afternoon and into the evening as winds become
more upslope. May see storms continue overnight across the plains,
but confidence is low that this scenario will pan out so will keep
t-storm mention out of the tafs for now.

&&

.FIRE WEATHER...
Issued at 247 AM MDT Sat Jul 23 2016

Minimal fire weather concerns through early next week. Minimum
humidity values will fall to 10 to 20 percent each afternoon
through Monday for areas to the west of the Laramie Range. However,
wind gusts will stay mostly below 20 mph and thus no fire weather
threat is anticipated across zones where fuels are ready.

&&

.CYS Watches/Warnings/Advisories...
WY...None.
NE...None.
&&

$$

UPDATE...MAJ
SHORT TERM...ZF
LONG TERM...TJT
AVIATION...RJM
FIRE WEATHER...ZF



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