Scientific Forecaster Discussion

Return to Local Conditions & Forecast
Area forecast discussion 
National Weather Service Denver/Boulder Colorado
744 am MDT Thursday Apr 24 2014

Short term...(today through tonight )
issued at 351 am MDT Thursday Apr 24 2014

Northwest flow aloft will prevail behind the exiting trough and the
approaching ridge today. This will bring dry conditions and mostly
sunny skies. Some high clouds will pass over the top of the ridge
later in the day. Airmass will be slightly cooler today which will
put most locations in the 60s for highs. Surface high pressure over
the Great Basin and lower pressure over the Central Plains will
produce mainly west to northwest winds. However an anti-cyclone may
form and cause winds to turn southerly along the Front Range and
parts of the plains this afternoon.

The upper level ridge will move across the state tonight. This will
continue to keep the area precipitation free. There will be some
moisture at the middle and upper level of the atmosphere which will
lead to middle and high clouds at times. Overnight lows will again be
mild with readings mainly in the upper 30s to middle 40s over northeast

Long term...(friday through wednesday)
issued at 351 am MDT Thursday Apr 24 2014

Attention over the next few days certainly surrounds deep upper
level trough which is expected to drop into the southwestern
United States and then deepen significantly somewhere over the
Central High plains. Model consensus is coming around to a more
consistent path...although differences on timing and trends still
abound. At this time...per water vapor loop seems like the European model (ecmwf)
has a handle on the significant pieces of energy in the Pacific
between 140w and 170e. This should allow ample buckling of the
flow with a rather sharp trough reaching the West Coast Friday. If
the sharper trough solution is correct...then would prefer the
slower and ever so slightly deeper solution offered by the European model (ecmwf).

For Friday....deep warm advection will occur with Lee troughing
and warm/ridging southwest flow aloft. This should allow
temperatures to warm 10-15 degrees above normal. Increasing
southerly winds especially over the Palmer Divide area will lead
to increasing fire danger but most of that area saw light/moderate
precipitation last night and green-up continues. Only marginal
area would be southern Lincoln County again.

By Saturday...the digging trough to our west and continued warm
advection will bring another very warm day to the forecast area.
Have boosted highs several degrees for Saturday considering the
warm advection...strong Lee troughing and mixing...and only slight
increase in clouds during the day. Fire danger will increase again
over the plains with strong and dry south/southwest winds.

With regard to severe weather threat late Saturday afternoon/
Saturday night...the amount of dry air ahead of system appears to
be quite substantial. Almost all models suggest a dryline pushing
well east into the Central Plains...but models usually overdo
this eastward push of the dryline when deep pressure falls occur
in eastern Colorado. At this time...while we dont think the
dryline will push as far east as models would be hard
to get the deeper moisture to hold even over the northeast corner.
Will still mention some threat in the hazardous weather outlook
and a couple of the sref plumes are showing near 1000 j/kg cape
over the northeast corner.

Q-g lift increases significantly and is deep and strong with the
upper level trough...again depending on its exact movement. This
would result in higher shower and storm coverage Saturday night
into Sunday morning although timing is still somewhat in question.
Will trend pop forecast toward European model (ecmwf) solution for now given
preference mentioned above. If system continues to pull to the
northeast...then stronger downslope would be developing by Sunday
with drier air especially along the Front Range where downslope is
maximized. the mountains strong orographic flow
developing on backside of upper trough combined with middle level
instability and lift could produce a significant snowfall for the
high country. Still too early to issue any watches but potential
is certainly there. With regard to foothill quantitative precipitation forecast and potential
runoff...if persistence due to any slower storm motion or upslope
would occur then precipitation would likely change to snow at most
elevations above 7000-7500 feet. That would effectively limit any
runoff even if storm is slower/deeper than most model runs

For Monday-Wednesday...a deep and closed upper trough seems
content to spin over the Midwest. This would keep temperatures
about 10 degrees below normal along with a low chance of showers.


Aviation...(for the tafs through 18z Friday morning)
issued at 744 am MDT Thursday Apr 24 2014

Have updated tafs with wind directions this morning. Seems as
though northwest winds are decreasing and there will be a brief
period of weak diurnal drainage flow this morning. Then
forecasting a Lee surface low developing around or south of the
Palmer Divide which will likely combine with northwest flow over
the eastern plains to anticyclone the winds around to a southeast
direction around noon time. Some high res models are picking up on
some westerly winds moving out of the foothills later this
afternoon from the leeside low....have added a hint of these winds
to the bjc and den tafs...not too sure it will reach apa if they
do develop.

Otherwise an upper level ridge and surface high pressure over
the Great Basin will keep the area dry with some high clouds today
and tonight. Forecasting wind direction will continue to be
tricky through this evening. South to southwest winds will
prevail tonight...through 12z.


Bou watches/warnings/advisories...


Short term...meier
long term...barjenbruch