Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Cheyenne Wyoming
1151 am MDT Wednesday Jul 30 2014

issued at 937 am MDT Wednesday Jul 30 2014

Light to moderate rain continues to fall mainly along the i80
corridor from Rawlins eastward to Pine Bluffs across southeast
Wyoming. Additional rainfall amounts through the middle of this
afternoon should remain between one tenth to one half inch near
the Colorado border...with locally higher amounts possible. Added
a slight chance of thunder near the Colorado border late this
afternoon since a few lightning strikes can not be ruled out as
the slow moving upper level disturbance will likely still be over
central Wyoming this afternoon. Precipitation will gradually come
to an end this evening.


Short term...(today through Friday night)
issued at 234 am MDT Wednesday Jul 30 2014

A large area of stratiform rain persists across much of the County Warning Area
this am with good low level upslope flow along and east of the Laramie
range. Latest water vapor loop shows an upper low moving toward
the Central Plains from northeast Colorado...with abundant middle and high
level moisture in place from southeast Wyoming into portions of the
southern Panhandle. This should keep light to moderate rain going
for several more hours. Rainfall rates through the overnight have
been between one and two tenths of an inch per have not
been seeing anything particularly heavy. Modeled soundings for cys
have shown a gradual decrease in heavy rain parameters with precipitable water
values closer to 1 inch and the k-index under 30 as of 08z. Most
importantly...air mass is now much more stable than it was on Tuesday
afternoon and evening. The threat for flash flooding has
will drop the Flash Flood Watch prior to its scheduled expiration
at 12z this am. Upslope will weaken through early afternoon and upper
level support will be lost as favorable jet dynamics shift across
the Midwest states and midlvl positive vorticity advection spreads into Colorado. Should see the
main area of precipitation gradually shift south and diminish in coverage
through the day. Removed mention of thunder from the grids as both
the GFS and NAM show virtually no cape through the period. It will
be quite cool today...particularly along and just east of the Laramie
range with persistent upslope keeping it cloudy and wet through at
least peak heating. Highs around 60 for cys would put US close to
a record low maximum of 59 f for this date.

Upper-level ridging will shift eastward across the central rockies
through the remainder of the period. 700 mb temperatures increase another 5
to 8 degree c through Friday afternoon per both the GFS and NAM...and modest
moisture above 700 millibars should yield plenty of sunshine on
Thursday and Friday with upper 80s returning to the Panhandle. No further
significant precipitation expected as the overall pattern would favor any
activity to be over the mountains. Most of the models show a bit
of midlvl moisture spreading along the northern edge of the ridge
on Friday cannot rule out a few showers or thunderstorms associated
with that. Believe it will remain isolated though given the lack
of any substantial forcing went ahead and brought
probability of precipitation down slightly from the previous forecast.

Long term...(saturday through wednesday)
issued at 234 am MDT Wednesday Jul 30 2014

Upper-level ridge axis located across the intermountain west will
amplify through the upcoming weekend before being flattened as the
pattern turns more active early next week. Latest medium range
models have trended drier with the available monsoonal moisture over
the weekend. As such...have removed mention of showers/thunderstorm
from lower elevations...instead confining any precipitation chances
to the afternoon/evening above 7000 feet over the snowy/Sierra
Madre/southern Laramie ranges. Temperatures will return to
summertime norms over the weekend as the ridge axis and reflected
thermal ridge builds over the County Warning Area. 700 mb temperature forecasts climb to
around 12c on Saturday...and to around 14c for Sunday. Higher values
will be found over the western County Warning Area...with slightly cooler values east.
The result will be for high temperatures to reach the 70s and 80s Saturday
and 80s and 90s for Sunday.

The ridge axis shifts to near the Front Range early next week as
shortwave energy rotates northeast towards the County warning forecast area from The Four
Corners. Models differ somewhat on the timing and strength of this
ftr with the European model (ecmwf) quicker and stronger compared to the GFS. Have
boosted shower/thunderstorm chances as a result Monday afternoon
through Tuesday night. Precipitable water values return to values similar those seen
yesterday. If this pattern materializes...the combination of the
abundance of moisture and slow steering flow will again heighten at
least the possibility of flooding late Monday through Tuesday.
Temperatures will cool somewhat as the unsettled conditions return.
Should see conditions dry towards the middle of next week behind the
departing shortwave.


Aviation...(for the 18z tafs through 18z Thursday morning)
issued at 1151 am MDT Wednesday Jul 30 2014

MVFR ceilings/visibilities will persist through this afternoon in rain
showers mainly over extreme southeast Wyoming and into southern
Nebraska as well. This includes krwl...klar...kcys...and ksny.
Conditions will slowly improve for these locations late this
afternoon...with a return to VFR anticipated by this evening. The
mountains of southeast Wyoming will remain obscured through
Thursday morning. Elsewhere...dry air moving in from the north
will keep VFR ceilings in place. Winds overall will remain
light...with the exception being much of Carbon County where gusts
of 20 to 25 kts will occur through the afternoon.


Fire weather...
issued at 234 am MDT Wednesday Jul 30 2014

Minimal fire weather concerns. Rain will gradually decrease in
coverage and intensity today across southeast Wyoming and the western
NE Panhandle. Another half to one inch of rain will be possible
along and on either side of the Laramie range through Wednesday
afternoon. Very cool today with highs struggling to reach the
lower to middle 60s at Cheyenne and Rawlins. Cooler conditions
combined with new moisture will mitigate any notable fire weather
hazards. A gradual warming trend is expected through the end of
the week...but afternoon relative humidity values are expected
to remain above 20 percent through the period.


Cys watches/warnings/advisories...


short term...hammer
long term...Hahn
fire weather...hammer

National Weather Service Glossary of Abbreviations