Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Denver/Boulder Colorado
906 PM MDT Tuesday Sep 30 2014
issued at 858 PM MDT Tuesday Sep 30 2014
Weak upper trough moving across northern Colorado at this time. Some
lightning over the mountains with some light showers over the northestern
plains. This all consistent with the ongoing forecast so only
minor adjustments planned for the grids this evening. Should see
conditions improve after midnight...with just some lingering
orographic snow showers in the mountains overnight.
Short term...(this evening through wednesday)
issued at 309 PM MDT Tuesday Sep 30 2014
Latest satellite loop shows a rather distinct short wave moving
into central Colorado at this time. While the airmass is only
marginally unstable...it will produce more rain/snow showers in
the high country as well bring a low threat of showers on the
plains tonight. Highest mountains may see another 1-2 inches of
snow but most of that should be confined above 10500 feet. Not a
whole lot of orographic support with only 15-20 kts middle level
flow...but enough for numerous showers.
For Wednesday...next upper level disturbance and increasing q-g
vertical motion will reach the forecast area. Q-g increases
through the day and airmass eventually saturates in moist
adiabatic lapse rates. As a result...any lift should be rather
efficient and producing precipitation...although plains will have
to saturate the lower layers before precipitation. Cold front
expected to arrive in the afternoon will help that process with
weak upslope component. Increased probability of precipitation a bit more for the late
afternoon hours. Temperatures will be several degrees cooler with
thickening clouds and afternoon frontal passage. High country snow
mainly above 10500 feet during the day will increase in intensity
with 1-3 inches possible before dark.
Long term...(wednesday night through tuesday)
issued at 238 PM MDT Tuesday Sep 30 2014
Upper level trough of low pressure is centered over the Rocky
Mountain region Wednesday night with some weak upslope flow east
of the mountains. Models show qg lift Wednesday evening...being
replaced by qg decent by Thursday morning. Showers should continue
across north central and northeastern Colorado Wednesday
evening...with a few thunderstorms possible. There may be a mix of
rain and snow over the foothills and Palmer Divide above 6500
kft...with another two to four inches of snow possible above 9500
feet. The showers should diminish across the Front Range
foothills...adjacent plains and Palmer Divide by late
evening....with a good chance of showers continuing over the
mountains and far northeast corner of Colorado through midnight.
Skies should begin clearing by Thursday morning...with lingering
showers over the far northeastern plains and higher mountains.
The upper trough will move into the Central Plains states on
Thursday...with a dry northwest flow aloft setting up over Colorado.
This pattern will bring dry conditions to the region with breezy
conditions over the high country. Temperatures on Thursday will
remain at below normal values as cool air aloft associated with the
upper trough remains over the area.
An upper level ridge of high pressure over the western states will
nudge toward Colorado beginning on Friday...with the northwest flow
over Colorado weakening. This trend will continue through the
weekend and into early next week. This pattern will result in a
gradual warming trend with lighter winds over the mountains.
Aviation...(for the tafs through 06z Wednesday evening)
issued at 858 PM MDT Tuesday Sep 30 20w14
West to northwest surface winds will back around to drainage
overnight. High based showers shifting to the east with front to
the south and east of Denver.