Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Denver/Boulder Colorado
1041 am MDT Tuesday Oct 6 2015

issued at 1041 am MDT Tuesday Oct 6 2015

Fog is slowly lifting but conditions have improved enough to allow
expiration of dense fog advisory on the eastern plains. Next
concern surrounds convection.

There are already a few showers developing above the stable
boundary layer and these will continue through the noon hour. By
early afternoon...surface based convection will become widespread
over the mountains and foothills where due to stronger daytime
heating where more sunshine has occurred this morning. These
showers and storms are expected to push northeast across the
plains later in the afternoon and evening as upper level
divergence increases in left exit region of the jet rounding the
base of the Desert Southwest cutoff low. The idea of high probability of precipitation for
this period looks good. Any severe threat is limited by the lack
of sufficient heating and destabilization on the plains.
However...stronger storms will still produce brief heavy rain and
small hail. Main forecast changes were to delay clearing of the
stratus on the plains and slightly cooler temperatures.

Update issued at 707 am MDT Tuesday Oct 6 2015

Widespread fog had developed on the plains and web cams/metars
show sufficient coverage of 1/4 mile visibility for a dense fog
advisory. There is not much cloud cover above the stratus deck and
its fairly thin so visibilities will improve between 9 and 10 am.


Short term...(today through tonight )
issued at 400 am MDT Tuesday Oct 6 2015

A moist southwesterly flow aloft will stream over the region
through tonight...ahead of an upper level low pressure system
currently over Southern California. This system is expected to
track slowly eastward...moving into west central Arizona by 00z Wednesday
then into east central Arizona by 12z Wednesday morning. Over Colorado a moist
diffluent flow aloft will be impacting the region... especially
this afternoon and evening. The forecast soundings from the nam12/GFS buffer
data indicate 300-500 j/kg of cape this afternoon. In addition...there
is an 80 knots jet rounding the trough today and it expected to nose
its way into southern Colorado. As a result the combination of some jet
dynamics aloft coupled with the instability should produce a good
support of widespread showers along with some embedded thunderstorms.
It should be too warm for snow showers in the high country
today...but cool enough tonight for some light snowfall above 12k will keep the mention of 1 to 3 inches in the grids. The
hrrr/RUC start to develop some showers from Denver east and south
this will mention rainfall early. A surface low is
prognosticated to form over southeastern Colorado this morning with the surface
winds shifting from northeasterly to north-northwesterly later today. Light winds and
lingering low level moisture early this morning has resulted in
more fog from Denver east and will add patchy coverage
through 15z. It could be dense in spots with visibility less than one
half mile. Plenty of cloud cover today as well will limit heating
so have trimmed the probability of precipitation back by a couple of degrees.

Long term...(wednesday through monday)
issued at 400 am MDT Tuesday Oct 6 2015

The closed upper low over Southern California at the moment the will
continue its lumbering southeasterly trek across Arizona during the day
Wednesday. Then models show it making a sharp right turn into
northern Mexico by early on Thursday. Due to the slow progression of
this system...Wednesday will remain relatively cool and unsettled.
Particularly during the morning hours due in part to the passage of
a weak pertabation at mid-levels. For that reason will keep a chance
of showers mainly in the mountains Wednesday morning and as drier air
moves down from Wyoming during the afternoon...decrease precipitation
chances from north to south. Cannot rule out a stray T-storm but
limit instability due to lingering cloud cover should pretty much
confine any thunder to marginally warmer southeastern sections of the County Warning Area.
Clearing will continue overnight as the upper low continues to move
away and with subsident side of the speed maxima passing over the
area. Near average temperatures expected Wednesday and Wednesday

On Thursday...strong upper level ridging over the West Coast causes
flow aloft to veer more northwesterly over the Rocky Mountain region.
This flow drives a weak cold front south out of Wyoming and across
northeast Colorado during the day bringing with it another batch of
clouds and cooler air. Mostly cloudy skies are expected on Thursday
along with a slight chance of showers both mountains and plains. Post
frontal northeasterly flow may concentrate most of this shower activity to
the east slopes of the Front Range west and southwest of Denver.
However precipitation amounts will be minimal. Temperatures on Thursday are
forecast to be 4-6 degree f lower than the day before. See no reason to
argue with that.

Looking ahead to the period Friday-Sunday...the big upper ridge
building out west is prognosticated to migrate east during the period...
with its apex reaching Colorado this weekend. This will result dry
conditions and above average temperatures areawide. On the
plains...high temperatures are expected to Hoover around the 80 degree
mark both days.


Aviation...(for the tafs through 18z Wednesday morning)
issued at 1041 am MDT Tuesday Oct 6 2015

Visibility slowly improving and will continue to do so through
18z-19z. Stratus breakout program showed a very slow erosion
today...but with convective clouds developing quickly to our south
and spreading north expect enough mixing for lower clouds to break
up through the early afternoon hours. Showers and storms will form
shortly thereafter and become more widespread through late
afternoon and evening. Feel enough instability to our southwest to
warrant tempo thunder for a few hours...highest probability 22z-
04z. There is some fog threat again overnight as boundary layer
moisture may now scour eastward.


Bou watches/warnings/advisories...


short term...Cooper
long term...Baker

National Weather Service Glossary of Abbreviations