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Area forecast discussion 
National Weather Service Cheyenne Wyoming
1150 PM MDT sun may 3 2015

Update...
issued at 949 PM MDT sun may 3 2015

Thunderstorms have dissipated across the area with several
remnannt bands of rain showers remaining across the southeast
Wyoming plains and extending into far western Nebraska. The main
forecast concerns tonight and into early Monday morning will be
the potential for fog along and east of the Laramie range...and a
slow moving shortwave...which will eject northeastward tonight and
into Monday. Upper level shortwave appears to be over south
central Colorado at this hour...but is not very well defined. 00z
NAM shows this shortwave lifting northward with a band of locally
heavy rain showers developing over the Palmer Divide and lifting
northward into southeast Wyoming and western Nebraska by early
Monday morning. In addition...at least half of the 21z sref
members show between one half inch to one inch of rain along and
east of the i25 corridor. Kept pop as is...but lowered them a bit
around midnight with a lull in the activity expected. Not totally
confident about the precipitation associated with this shortwave...but
kept pop between 50 to 60 percent through Monday morning since
there appears to be a decent chance of a rainy Monday morning
along the i80 corridor east of Laramie.

&&

Short term...(this evening through Tuesday night)
issued at 358 PM MDT sun may 3 2015

A weak surface cold frontal boundary remains stalled this afternoon
along the i80 corridor in southeast Wyoming. Low-level convergence along
this feature...combined with moist upslope flow east of the Laramie
range has contributed to numerous showers/thunderstorms across southeast Wyoming
as of 21z. Very modest instability across the area today with less
than 500 j/kg sbcapes indicated by Storm Prediction Center mesoscale analysis. Thermal
profiles have been cooling throughout the day...with NAM/GFS both
showing 700 mb temperatures falling to 3-4 degree c by 00z Monday. We are definitely
getting enough support for hail production with the steepening lapse
rates aloft and 25-30 kts of effective bulk shear. Had a few reports
of nickel size hail northwest of Cheyenne earlier. Current forcing
mechanisms will remain in place through the night...so see no reason
to cut back on probability of precipitation. Will keep categorical wording through late afternoon
and maintain likelies through Monday am. Water vapor satellite shows a
new disturbance over eastern nm this afternoon. NAM led The Race with middle
level vorticity energy lifting into the cys-sny corridor after 06z. Quantitative precipitation forecast
signals are good from both models...with several tenths of an inch
suggested by the NAM. BUFKIT soundings show an abundance of moisture
in the low-levels. Fog is a concern with upslope remaining in place
overnight...but could be mitigated if precipitation becomes persistent. Went
ahead and added patchy fog despite those questions as boundary layer
will undoubtedly be very moist.

The overall pattern will remain unsettled through middle week. A strong
shortwave will move into the Pacific northwest on Monday...serving as a
kicker system for a separate wave over southern CA/AZ. An excellent
moisture feed will continue with southeast low level flow expected across
much of southeast Wyoming and the western NE Panhandle. Afternoon/evening showers
and thunderstorms will be likely each day. A hail threat will exist as high
pressure over the northern plains will keep 700-500 millibar temperatures
on the cooler side...though latest instability forecasts from the GFS
are less than impressive. Widespread...upslope-driven clouds/precipitation
will promote cooler highs and warmer lows through the period.

Long term...(wednesday through sunday)
issued at 358 PM MDT sun may 3 2015

The unsettled period will continue through the latter half of the
week and into next weekend as active southwest flow gives way to
the eventual passage of an opening upstream closed low. Activity
will be most numerous during the afternoon and evening
hours...though cant rule out convection even lingering into the
overnight. Several leading shortwaves embedded within persistent
southwest flow will be passing overhead for Wednesday.
Shower/thunderstorm activity will be most widespread during the
afternoon and over the southeast Wyoming and western NE plains. Surface
front remains stalled in the vicinity of the Laramie range for
Thursday which will provide the focus for convection despite the
departing upper energy. Flow amplifies on Friday with the
stationary surface boundary again providing the focus for convective
activity. The upstream upper low will open as it passes near the
area on Saturday. The upper low will be slow to open likely
lingering through Sunday before departing next week. At this
point...instability parameters look pretty meek through the
period...so dont expect widespread severe potential. High
temperatures will only rise into the 50s and 60s through the period.

&&

Aviation...(for the 06z tafs through 06z Monday night)
issued at 1141 PM MDT sun may 3 2015

Mostly VFR across the area tonight although some low stratus and
fog is expected along the eastern slopes of the Laramie range. Low
stratus and fog will likely persist in this area through much of
Monday. A few rain showers are expected in far southeast Wyoming
and into the Nebraska Panhandle late tonight into Monday morning
with some MVFR possible. Easterly winds will be in place across
the plains Monday and into Tuesday. Widespread low clouds will
develop Monday night with some fog expected...especially along the
eastern slopes of the Laramie range.

&&

Fire weather...
issued at 358 PM MDT sun may 3 2015

A cool and wet weather pattern will give way to minimal fire weather
concerns over the next several days. Afternoon and evening showers
and thunderstorms can be expected each day...with good chances for
measurable precipitation. Minimum relative humidity values should be
well above critical thresholds.

&&

Cys watches/warnings/advisories...
Wyoming...none.
NE...none.
&&

$$

Update...tjt
short term...clh
long term...cah
aviation...small
fire weather...clh

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