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Area forecast discussion 
National Weather Service Cheyenne Wyoming
412 am MDT Wednesday may 27 2015

Short term...(today and tonight)
issued at 412 am MDT Wednesday may 27 2015

Maintained scattered showers with isolated T-storms through the
morning as a piece of energy evident on water vapor imagery
continues to move up from the southwest. In outflow
boundary has moved up from Colorado into the plains of southeast
Wyoming and the southern Nebraska Panhandle. Expect some
development off this boundary as the wave moves overhead.

The shortwave will move off to the northeast today...with models in
agreement that some subsidence will overspread the forecast area in
its wake through the afternoon. Brought down probability of precipitation a tad with
subsidence in place...however do think that mountain convection will
develop in the afternoon with some sunshine producing marginal
instability. The leeside trough should deepen in the afternoon as
well with moist southerly flow ahead of the trough. Anywhere from
500 to 1500 j/kg of SBCAPE is analyzed for this area after 18z
which could result in a few stronger storms developing off the Lee
trough across the Cheyenne Ridge and the Nebraska Panhandle. Brief
heavy rain remains a possibility with any storms as well...but
expect the flash flooding threat to remain localized.

The Lee trough looks to weaken Wednesday night while another vorticity
maximum rounds the base of the trough situated over the northern
rockies and moves over the forecast area. Maintained some low
chances for showers through the overnight period to account for
this wave. The main upper trough will move into Wyoming on
Thursday with a weak Pacific front dropping south across the area
in the afternoon. The combination of upper and low level forcing will
promote more widespread coverage of showers with scattered storms
through the day...although modest instability in place will keep
coverage of strong storms quite isolated. Again...looks to be
mostly moderate to brief heavy rain producers with perhaps some
small hail. The upper trough will steadily move overhead Thursday
night with shower activity likely continuing at times.

A secondary cold front is prognosticated to slide south through the region
on Friday with surface winds shifting to the northeast behind the front.
Cold air aloft will remain overhead as the upper trough begins to
exit the region to the southeast. Combination of surface and residual
upper forcing along with some marginal instability will maintain
widespread showers with isolated thunderstorms through the day.

Long term...(friday night through tuesday)
issued at 412 am MDT Wednesday may 27 2015

Extended models do show some improvement to the overall pattern
this weekend and early next week an upper level ridge strengthens
over the southern and central Rocky Mountains...resulting in
warmer/near normal temperatures and somewhat drier conditions. In
fact...models are trending drier on Saturday as they trend more
progressive with the Pacific upper level trough pushing across the
area on Friday. So this whole weekend may be pleasant across the
forecast area with seasonable temperatures. Conditions will begin
to improve late Friday night as the upper level trough quickly
slides southeast of the forecast area. Continued to trend pop
below 10 percent by Saturday morning. There may be some isolated
thunderstorms along and just east of the Laramie range Saturday
afternoon due to low level moisture and unstable conditions...but
coverage will be limited across the High Plains with only light to
moderate rainfall expected. Maintained the low to middle 60s for
highs on Saturday...but these might need to be nudged a few
degrees higher since guidance is suggesting highs closer to 70
across the lower elevations.

All models indicate the upper level ridge building into southeast
Wyoming and western Nebraska on Sunday and Monday. High
temperatures are expected to increase...with readings in the 70s
to low 80s possible by Monday afternoon. Can not rule out a few
thunderstorms however across the mountains and High Plains near
the Wyoming/Nebraska border...but activity should be relatively
weak and quick to dissipate. Models show the ridge axis moving
eastward into the plains by late Monday...and then east of the
forecast area by Tuesday while the next Pacific upper level trough
moves onshore and towards the central Rocky Mountains. Both the
European model (ecmwf) and GFS are in good agreement for day 7 and 8...showing this
system taking its time moving into Wyoming. For some reason...the
GFS pushes too much dry air into southeast Wyoming for middle next
week with dewpoints below 30. This is a typical bias with the GFS
in the long range...and do not think this will happen since most
of the area is pretty saturated and winds will be relatively
light. Can not rule out some tstorm activity...and believe thunderstorms
will increase in coverage by Wednesday as the upper level trough
moves eastward. will remain warmer than average
with highs in the 70s to low 80s Wednesday afternoon before the
next cool front pushes into the High Plains.


Aviation...(for the 12z tafs through Wednesday night)
issued at 412 am MDT Wednesday may 27 2015

VFR conditions expected for all southeast Wyoming and Nebraska
Panhandle terminals this morning. Showers and isolated thunder
will continue early this morning across the High Plains...but no
major impact besides some isolated lightning is expected. After a
brief break between 11z and 17z...convection will return
Wednesday afternoon. Added thunderstorms in the vicinity wording for all tafs. Will narrow
in on timing as the event gets closer with brief MVFR visible
possible in the heavier showers and thunderstorms.


Fire weather...
issued at 412 am MDT Wednesday may 27 2015

Daily chances for showers and thunderstorms will continue across
the area through the end of the week. No fire weather concerns as
a result.


issued at 919 PM MDT Tuesday may 26 2015

Latest river forecast has been issued. Forecasts at the river
forecast points along the North Platte river and Laramie river
have generally been lowered as most thunderstorm activity missed
the runoff basin today. Actual river crests could certainly be
adjusted depending on exact location of convection the next few
days but given the random nature of convective activity...any new
precipitation will need to be closely monitored.


Cys watches/warnings/advisories...


Short term...rjm
long term...tjt
fire weather...rjm

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