Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Grand Junction Colorado
444 PM MST Thursday Jan 29 2015

Short term...(tonight through Friday night)
issued at 340 PM MST Thursday Jan 29 2015

Current infrared satellite and surface observation indicate clouds beginning to
thicken from south to north due to the oncoming weather system.
Subtropical moisture is being fed into the forecast area from the
southwest thanks to an upper low off of the coast of Baja California
California. As the center of the upper level low reaches socal
Friday morning...pieces of energy and plenty of moisture will
result in widespread rain and snow developing over The Four
Corners and pushing into NE Utah and northwest Colorado throughout the
day Friday. In looking at 500 mb vorticity maxima and 500 mb qc vertical
velocity...instability will be greatest during the day on Friday
over The Four Corners and progressing east throughout the event.
Cross sections across the forecast area indicate complete
atmospheric saturation across The Four Corners by Friday morning
and the southern San Juans by middle morning. Cross sections and
model skew ts are not indicating a warm tongue of air above the am not expecting any freezing rain with this event. With
700 mb temperatures around -3 c to -4 c during this event...expecting the
rain/snow line to be right around or minus 500ft
depending on what time of day the precipitation is falling.
The heaviest 5+ inch amounts will accumulate above 8000ft with
lesser amounts down to 6500 feet. This forecasted rain/snow line
flirts with the possibility of accumulating snow in the southern
valleys including Pagosa Springs at ~7100ft and Durango at
~6500ft. Do expect snow at these locations but anticipating a
slushy mix less than 3 inches...but these should be highly
monitored if cooler air changes things. Elsewhere...feeling
confident for the advisories in the San Juans and abajos/la sals
above 8000ft with slightly lesser but still confidence over the
Uncompahgre Plateau. See long term discussion for more details on
the latter part of this system.

Long term...(saturday through thursday)
issued at 340 PM MST Thursday Jan 29 2015

Precipitation will remain widespread across the forecast area from
about the Tavaputs and Flat Tops southward Saturday morning with
the upper low positioned over the western Arizona border. Snow will
continue in the mountains...but snow levels remain a bit tricky
due to neutral or weak warm advection still into the 4 corners
Saturday morning. May see snow in the central and southwestern Colorado valleys
early Saturday morning with rain or rain/snow mix expected by
midday. The upper low drops into the northwest corner of Mexico during
the day Saturday. Drier northerly flow will spread into NE Utah/northwest
Colorado Saturday afternoon then spread to The Four Corners Saturday
night...but no strong influx of cold air is expected. Mostly sunny
skies are expected Sunday with seasonable temperatures.

The upper ridge re-forms along the West Coast Monday. Pacific
moisture topping the ridge with embedded pieces of energy will bring
a chance of snow to the northern Colorado mountains and adjacent valleys Monday
through Wednesday. Temperatures to remain near or above normal for early


Aviation...(for the 00z tafs through 00z Friday evening)
issued at 438 PM MST Thursday Jan 29 2015

Clouds continue to stream up from the south this evening though
little in the way of the precipitation so conditions will remain VFR.
After midnight...07z...chances will start increasing for vcsh many
taf sites as clouds continue to lower. This trend continues
through 18z or so with shower coverage increasing with vcsh
possible for just about all taf sites with more predominant
rain/snow starting around 21z or so. Flight conditions from there
on out will vary from MVFR/IFR from time to time under low ceilings
and visible.


Gjt watches/warnings/advisories...
Colorado...Winter Weather Advisory from 8 am Friday to 8 PM MST Saturday
for coz017>019.

Utah...Winter Weather Advisory from 8 am Friday to 8 PM MST Saturday
for utz028.



Short term...jam
long term...jad

National Weather Service Glossary of Abbreviations