Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Grand Junction Colorado
1058 am MDT sun Apr 26 2015
Short term...(today through monday)
issued at 327 am MDT sun Apr 26 2015
The storm continues to develop mostly as forecast with good
confidence for the large-scale details. The elongated negatively
tilted trough form a closed low south of The Four Corners this
morning as jet energy starts to work into the base of the trough.
This low slowly shifts east of the Texas Panhandle by Monday
Strong cyclonic flow with deep moisture continues over the region
today. The cold front was in eastern Utah this early morning and
will work through all of western Colorado by early afternoon. Best
dynamical forcing continues over the San Juans and west elks
through the day today. The closed low creates a strong area of
upper divergence across SW Colorado as it curves back into the
main trough wall. Instability will still drive snow levels down to
7500ft or so in the stronger convective showers but overall the
9000ft snow level still looks good. Isolated lightning strikes are
expected mainly during the afternoon hours.
The north has some instability and decent moisture but lacks upper
support. Cyclonic north flow overnight will continue to produce
widespread showers across the south and scattered more orographic
showers across the north. Freezing temperatures still a concern
for the southern valleys Sunday night.
The exiting low on Monday will limit showers mainly to the western
Colorado mountains...most numerous near the Continental Divide.
Eastern Utah and far western Colorado see drier air and warm
advection aloft through the afternoon.
Long term...(monday night through saturday)
issued at 327 am MDT sun Apr 26 2015
By sunset Monday evening the main low should be well east of the
forecast area over Oklahoma...but models have consistently showed
another brief increase in precipitation as a trough along the Canadian
border pushes another "backdoor" cold front into the area from the
north and northeast. This disturbance pushes a band of precipitation west
and south Monday night and Tuesday morning. The precipitation
projected to accompany it diminishes as the band moves west of a
line from kcag to kril to kmtj during the day on Tuesday.
A Sharp Ridge will spread drier and warmer conditions over the
area Tuesday night and Wednesday. Models show this ridge collapsing to the
southeast Thursday as a trough and its cold front move through the
northern rockies. The front will stretch across the area Thursday night
through Sat...while gradually sagging to the south. This should
provide a bit of lift for diurnal convection...mainly over the
Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 1058 am MDT sun Apr 26 2015
Low clouds and showers often obscuring mountains are expected for
much of the forecast area through Monday morning. Valley fog
An upper low continued to consolidate over northestern Arizona late this morning
with an elongated upper trough extending north-northwest across Utah. A favored
band of low clouds and precipitation extended from extreme northwest Colorado to
SW Colorado affecting kgjt...kmtj...ktex...kdro. This should show
little movement today as the upper low moves into western nm this
afternoon...but precipitation will transition to more convective
showers. VFR conditions across much of eastern and Utah northwest Colorado will
deteriorate as the convective showers expand across the forecast
area this afternoon. Isolated thunderstorms possible. Low clouds
trapped in the kase valley should mix out by 19z but expect flight
conditions to then be impacted by an increase in -shra this
afternoon and -shra/-shsn tonight. Clearing expected for eastern Utah by
Colorado...Winter Weather Advisory until 9 am MDT Monday for coz010-013.
Winter Storm Warning until 9 am MDT Monday for coz009-012-018-
Utah...Winter Storm Warning until 9 PM MDT this evening for utz028.