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Area forecast discussion 
National Weather Service Cheyenne Wyoming
1028 PM MDT Sat Jul 23 2016

issued at 911 PM MDT Sat Jul 23 2016

We continue to monitor a few weak showers and thunderstorms across
far southern Wyoming and the southern NE Panhandle this evening, mainly
along a frontal boundary draped from west-east across the area. We
have seen a few strong wind gusts around 40-50 miles per hour due to the high
based nature of this convection; however, believe that threat will
diminish after sunset with higher T/TD spreads.

One major change to the inherited forecast for the rest of tonight
with respect to pops. The GFS/NAM both suggest very good low-level
warm air advection over the plains after 06z, likely associated W/
the next shortwave currently upstream over northwest Colorado. Models do
show upwards of 1000-1500 j/kg of elevated cape overnight, and all
available guidance shows at least light quantitative precipitation forecast. The hrrr continues to
show robust convection well after midnight, which definitely makes
sense with an h25 speed Max over our northern zones, and resulting
divergence aloft. Added mention of scattered showers/thunderstorms
through the night. Organized severe weather is unlikely with shear
being quite weak, but a few stronger storms are possible.

Update issued at 550 PM MDT Sat Jul 23 2016

Numerous showers and thunderstorms are occurring along i80 between
Pine Bluffs and Sidney late this afternoon. Based on recent trends
in radar/satellite imagery and hrrr guidance, added likely pops in
these areas through 03z this evening. Updates have been sent.


Short term...(this evening through Monday night)
issued at 310 PM MDT Sat Jul 23 2016

Afternoon water vapor loop showed the County Warning Area between a upper trough
moving across the northern rockies and another lifting northeast
across the northern Great Plains/upper Midwest. Mesoanalysis/radar
analysis placed a weak front just east of I-25 with north-northeast
winds across the Nebraska Panhandle and far eastern Wyoming plains.
As predicted by the short-range models, isolated convection formed
along and just north of the Colorado border. Much of this activity
is high-based with inverted-v soundings indicating potential for
gusty outflow winds to 50 mph along with occasional lightning.
The convection should remain confined to far southeast Wyoming,
but a few could sneak into far southwest corner of Nebraska late
this afternoon. Convection should dissipate later this evening.

The short term model consensus shows the west-southwest flow aloft
veering to west-northwest and amplifying somewhat Sunday through
Monday as the southern Continental U.S. Upper high retrogrades westward across
The Four Corners region. Diurnal convection under this flow regime
will be limited to the higher terrain and nearby plains of southeast
Wyoming. Models prog a upper level disturbance to move southeast
across the Dakotas late Monday which may trigger isolated thunderstorms
over northwest Nebraska. Sunday will be about 10 degrees cooler than
today across the plains with highs in the 80s. Temperatures warm
into the upper 80s-mid 90s Monday with the amplifying ridge.

Long term...(sunday night through saturday)
issued at 310 PM MDT Sat Jul 23 2016

West-northwest flow will be overhead at the start of the long
term period, veering more northwest by Friday as the upper high
retrogrades westward. A fairly steady stream of Pacific moisture
with embedded shortwave disturbances will remain overhead through
midweek, meaning there will be chances for showers and
thunderstorms each day across the region. Still looks like
Wednesday and Thursday could be the best chance for strong/severe
storms with increased llvl moisture, shear, and upslope flow
behind a cold front dropping south across the region late
Tuesday/early Wednesday. Temperatures will trend cooler, back to
more seasonable readings for this time of year. A reinforcing
front on Friday will maintain chances for T-storms over the
forecast area.


Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1026 PM MDT Sat Jul 23 2016

Latest guidance showing the possibility of convection becoming
more widespread tonight. Hrrr showing this as well. Did include
thunderstorms in the vicinity wording in all the Nebraska Panhandle aerodromes as well as
kcys for the overnight hours. A return of thunderstorms for Sunday
afternoon for kcys and possibly ksny.


Fire weather...
issued at 310 PM MDT Sat Jul 23 2016

Warm, breezy and dry conditions will continue for much of east
and south central Wyoming through Monday with a ridge of high
pressure along the Continental Divide. Fire weather danger will
remain high in these areas. Across portions of southeast Wyoming
and western Nebraska, there wil be slight chances for afternoon
and evening showers and thunderstorms. As the ridge shifts further
west next week, a northwest flow aloft and a couple of upper level
disturbances will increase chances for late day showers and
thunderstorms east of the Laramie range.


Cys watches/warnings/advisories...


short term...maj
long term...rjm
fire weather...maj

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