Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Cheyenne Wyoming
1158 PM MDT Tuesday Sep 30 2014

Short term...(this evening through Thursday night)
issued at 331 PM MDT Tuesday Sep 30 2014

Main story through the day has been the windy conditions across
the region. The strongest winds this afternoon have generally been
across the northern Nebraska Panhandle and Arlington with gusts
to 40-45 miles per hour. Will keep the Wind Advisory going for the northern
Panhandle through 4pm. Starting to see gusts coming down in the past
hour up in Dawes and Box Butte counties. Would expect this trend
to continue through the remainder of the afternoon as the surface pressure
gradient weakens in response to the surface low shifting quickly off
to the northeast. Otherwise...highs have been a bit cooler than
fcsted to the west of the Laramie range with widespread cloud
cover out there. With weak instability (li values around -1c)
combined with westerly middle level winds and some orographic
enhancement...scattered showers will be possible especially in the
mountains through the evening. Winds will decrease areawide after
sunset with the loss of daytime mixing.

Attention on Wednesday will turn to the upper level disturbance that is
prognosticated to amplify just to the west of the County Warning Area by midday. With the
upper jet across Colorado by 18z and large scale qg ascent
increasing will see an increase in precipitation chances from middle morning
through the evening especially along the Colorado border. The models
continue to indicate that large scale ascent will be maximized
over the northern half of Colorado. Thus...will keep high end
chance to likely probability of precipitation for areas along the Colorado border during
the afternoon. The system is quite progressive so only expecting a 3-6
hour period of precipitation. With 700mb temperatures of -2c to 0c will definitely
see a few inches of snow in the Sierra Madre and snowy ranges at
elevations above 9000 feet or so. If the system were slower moving
and the best lift was located to the north of the border would be
more concerned about a Winter Weather Advisory.

It will be a cool Wednesday night with most locations to the west of the
Laramie range below freezing. Much drier weather is expected on
Thursday but it will still be rather cool and breezy. The main
disagreement on Thursday night between the GFS and European model (ecmwf) involves how
far west the shortwave moves as it dives southeastward into the
northern plains. Will side with the less amplified and drier GFS
solution for now and keep slight chance probability of precipitation out...however this will
have to be monitored by future shifts.

Long term...(friday through tuesday)
issued at 331 PM MDT Tuesday Sep 30 2014

Dry northwest flow will dominate the period with the main northern stream
jet stream held to the northeast extending from Alberta into the
middle-Mississippi River valley. The trickiest part of the forecast in
trying to time any backdoor front that brushes the area cooling
temperatures mainly over north and east zones. Friday will be a transition
day as the cool Canadian air mass is finally replaced by a warmer
Pacific air mass. It will still be cool but dry as 700 mb temperatures climb
back to around 5c producing high temperatures in the 60s. A developing Lee
side pressure trough Friday night will slide east on Saturday
producing breezy west/northwest conditions with gusts of 20 to 30
miles per hour common. It will be warmer though with 700 mb temperatures of around 7c
producing highs back to near or into the lower 70s. A weak boundary
may sneak into north and east zones Saturday night...but should only
cool highs back into the 60s for Sunday. Flow will turn more
west/northwest for Monday and Tuesday which will eliminate the
possibility of an intruding boundary north and east. It still looks
dry early next week...with highs climbing back into the 70s for most


Aviation...(for the 06z tafs through 06z Wednesday evening)
issued at 1158 PM MDT Tuesday Sep 30 2014

A few showers linger over the County Warning Area at taf issuance...but should not
impact the terminals tonight. Winds will shift to the north-
northwest through the morning behind a weak front dropping south
across the area. Showers and T-storms will redevelop in the
afternoon and evening as another upper level disturbance moves
over The Rockies...especially for areas near the Colorado border
with the strongest upslope flow in place. Looking at mainly MVFR
conditions with this activity.


Fire weather...
issued at 331 PM MDT Tuesday Sep 30 2014

Minimal fire weather concerns through Thursday. Windy conditions
will continue through the afternoon with gusts to 40 miles per hour
possible...however relative humidity values are elevated and
generally above 40 percent. Temperatures will be cooler than
normal through Friday with minimum afternoon humidity values above
30 percent. An upper level disturbance will move across Colorado
on Wednesday and provide a good chance of wetting precipitation
in areas near the Colorado border during the afternoon and evening.


Cys watches/warnings/advisories...


Short term...Finch
long term...Hahn
fire weather...Finch

National Weather Service Glossary of Abbreviations