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Area forecast discussion 
National Weather Service Cheyenne Wyoming
507 am MDT Monday may 4 2015

issued at 459 am MDT Monday may 4 2015

Webcams along Interstate 80 have shown visible really coming down from
The Summit to just east of Buford. Moist southeast winds will
continue through the morning and hrrr shows LIFR conditions
continuing in the southern Laramie range and to the east of the
Albany-Laramie County line through 16z. Thus...with the
expectation that the fog will be quite persistent through middle
morning...decided to issue a dense fog advisory for the southern
Laramie range and adjacent foothills through 16z.


Short term...(today through wednesday)
issued at 230 am MDT Monday may 4 2015

The GFS and NAM both forecast a weak midlvl vorticity maximum moving into
northeast Colorado and the southern Nebraska Panhandle through middle
morning. Radar imagery shows some weak echoes across portions of
northern Colorado (generally moving northward)...but no lightning
or stronger convective cells. While these showers could move into
areas along Interstate 80 through middle morning...any accumulations
will be light. With surface high pressure across the Dakotas...low level
winds over the plains are turning to the east and southeast. The
hrrr has LIFR conditions developing after 10-11z along the
Cheyenne Ridge from the Interstate 80 Summit to Cheyenne. With
good low level upslope...these lower ceilings and visible persist through 18z.
Thus...kept the mention of fog going through the entire morning.
Temperatures will be around 15 degrees cooler today for areas along and
east of the Laramie range in the Post frontal airmass. The airmass
is rather stable with Li values generally above 0c...thus afternoon
convection will be quite limited. A better chance of thunderstorms will
exist to the west of the Laramie range. While an isolated higher
rainfall amount is possible through midday Tuesday...the models
really do not show much quantitative precipitation forecast with the increase stability.

On Tuesday low clouds will be much more widespread and persistent
across the plains through the morning or even early afternoon with the
potential for fog once again mainly along the Cheyenne Ridge.
Subtropical midlvl low over Arizona today will progress
northeastward into Colorado on Tuesday. Cooling aloft ahead of this
feature along with increasing precipitable water values (up to 1.0 inches across
the Panhandle by Tuesday aftn)...will promote a more widespread
coverage of showers and thunderstorms. Have the highest probability of precipitation on Tuesday afternoon
and evening over the Panhandle where the models have been
consistently showing the best forcing. Storm Prediction Center does have the southern
Panhandle in a marginal risk for severe storms on Tuesday...however with
rather weak instability and shear...only small hail would be a
concern. The upper level wave will move into western South Dakota
by Wednesday with surface winds becoming north to northwest over much of the
County Warning Area by the afternoon. Kept the 40-50 percent probability of precipitation going during the afternoon
as rather high precipitable water values (0.75-1.0 inches) are shown across the
plains along with weak instability.

Long term...(wednesday night through sunday)
issued at 230 am MDT Monday may 4 2015

Active weather in the long term continues with daily rain/thunder
chances also the possibility of a winter weather event for next

For Wednesday night...first low looks to track off to the
northeast into central South Dakota and we should be seeing
showers and thunderstorms coming to an end by late evening.

Another cold front looks to move into the area Thursday morning
with another round of rain showers developing across the area
Thursday afternoon...persisting into Friday.

Remarkably strong agreement between the GFS and European model (ecmwf) on the
movement of the second low through The Rockies through the
weekend. Both bring the low through southern Nevada Friday...with
it ejecting northeast into northern Colorado Saturday night. Both
show -4 to possibly -6c temperatures at 700mb Saturday night into
Sunday...which would turn rain over to snow for many locations
above 6000 feet. Need to be watching for winter headlines for
possible heavy snow this weekend. We will certainly be monitoring
this low as it draws closer.


Aviation...(for the 12z tafs through 12z Tuesday morning)
issued at 459 am MDT Monday may 4 2015

Impacts today will be low conditions around kcys this morning in
upslope fog/stratus...then showers and thunderstorms mainly west
of the Laramie range today. Hrrr used for kcys and shows IFR/LIFR
fog/stratus developing shortly after 12z. Already seeing dense fog
just west of kcys. Looks to stay IFR/LIFR through 18z before
lifting. More widespread low conditions expected tonight.


Fire weather...
issued at 230 am MDT Monday may 4 2015

A cool and wet weather pattern will mean minimal fire weather
concerns through the week. Afternoon and evening showers and
thunderstorms can be expected each day...with good chances for
measurable precipitation and wetting rains. Minimum relative
humidity values should be well above critical thresholds.


Cys watches/warnings/advisories...
Wyoming...dense fog advisory until 10 am MDT this morning for wyz116-117.



short term...zf
long term...gcc
fire weather...zf

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