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Area forecast discussion 
National Weather Service Cheyenne Wyoming
338 am MDT Tuesday may 26 2015

Short term...(today through thursday)
issued at 337 am MDT Tuesday may 26 2015

Patchy areas of fog developed overnight over northeastern portions
of the County Warning Area with light winds in place and increasing boundary layer
moisture behind a subtle surface boundary that moved southwest across
this area earlier in the evening. Otherwise...the overnight period
has been generally calm under partly to mostly cloudy skies. The low
amplitude shortwave ridge will move overhead today with temperatures
looking to be about 5 to 10f warmer today within warm air advection. Surface winds are
expected to veer to the southeast across the plains today in advance
of a weak vorticity maximum moving into western Wyoming this afternoon.
Sbcapes of 500 to 1000 j/kg are prognosticated for this afternoon...and
along with strengthening upslope flow through the day...looking at
isolated-scattered thunderstorms developing by early afternoon and continuing
through the evening. The focus for highest coverage will be over the
high country towards the Wyoming/NE border...and expect this activity to
remain on the weaker side due to relatively weak winds aloft.

For Wednesday...the ridge will slide to the east while a weak upper
low slowly treks southeast from the Pacific northwest toward Wyoming. Models
develop a weak surface low and leeside pressure trough in the afternoon
stretching from northeast Wyoming southward...with the main
convergence line along the Wyoming/NE border in the afternoon. Continued
warm temperatures and dew points forecast to be in the middle 40s should
produce modest instability once again...with the focus for higher
values east of the leeside trough. Winds through the column will be
slightly stronger compared to Tuesday...although still relatively
weak overall so not expecting any organized convection. Looks to be
pulse-like in nature with perhaps a few stronger storms within the
higher axis of instability over the Panhandle. Models allude to a
few storms persisting into the early overnight hours as weak energy
moves across the County Warning Area in advance of the upper low so maintained a
slight chance for showers/storms overnight.

The surface trough will shift east/southeast on Thursday as the upper
low moves into western Wyoming. Convection will likely be more
widespread in nature with increasing upper level forcing. Could
perhaps see a few more strong storms overall as deep layer shear
increase to around 30 kts across the County Warning Area.

Long term...(thursday night through monday)
issued at 337 am MDT Tuesday may 26 2015

The moist unsettled weather pattern will linger into late this
week and early next weekend as another Pacific trough moves across
the region. Extended models do show some improvement by 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.

All models indicate the upper level trough axis sliding through
the area on Friday as a weak cold front moves southward across the
region. 700mb temperatures will lower between -1c to 4c by early
Saturday...so expect below normal temperatures in the 50s and low
60s both Friday and Saturday. The trough axis will take its time
moving across the area...so expect showers and thunderstorms to continue
through Friday and Friday night. Expect a widespread coverage of
showers Friday and Friday night...so increased pop between 50 to
70 percent across most of the forecast area east of Carbon
County. Moderate to locally heavy rainfall amounts are possible
with this system...with the Laramie range and higher mountains
receiving more precipitation this time around. Rivers and streams
are already high at this time and forecast to be near record
levels by Thursday and Friday. Any additional rainfall upstream
will just exacerbate flooding concerns along and east of the
Laramie valley. In addition...flash flooding may also be a concern
with this system due to the very saturated ground. Severe thunderstorms
are not expected at this time...although some stronger thunderstorms are
possible along the i80 corridor on Friday. Low level frontal boundary
will stall just west of the Laramie range on Saturday resulting in
much cooler than normal temperatures across the High Plains.

Some changes to the overall pattern are expected late this weekend
as an upper level ridge builds into southeast Wyoming and western
Nebraska. High temperatures are expected to increase into the
upper 60s to middle 70s with only a slight chance of thunderstorms
across the mountains. Models show the ridge axis moving eastward
into the plains by Monday...and then east of the forecast area by
Tuesday. Although it will be slightly warmer than normal early
next week...expect a daily threat of showers and thunderstorms to
continue due to low level moisture and some instability.

&&

Aviation...(for the 12z tafs through Tuesday night)
issued at 245 am MDT Tuesday may 26 2015

MVFR conditions will prevail through 15z this morning across most
Nebraska terminals due to low stratus clouds and patchy fog...with
IFR visibilities expected to continue near kbff. Further
west...expect VFR conditions across southeast Wyoming terminals
through this morning. Another round of showers and thunderstorms will
develop over the mountains and move eastward across the High
Plains this afternoon. Brief MVFR ceilings and visible are possible with
these thunderstorms through this evening.

&&

Fire weather...
issued at 337 am MDT Tuesday may 26 2015

Chances for showers and thunderstorms with wetting rains will
continue through the week. Therefore...not expecting any fire
weather concerns in the near term.

&&

Hydrology...
issued at 337 am MDT Tuesday may 26 2015

Flood warnings continue for the North Platte river in the western
Nebraska Panhandle...and the Laramie river at Fort Laramie due to
expected flooding from increasing releases from upstream reservoirs
in addition to continued runoff from shower and a thunderstorm
activity through the week. Precipitation should be more scattered in
nature but it will take a while to move all the excess water
downstream.

&&

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

$$

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

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