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Area forecast discussion 
National Weather Service Denver/Boulder Colorado
841 PM MDT Friday Apr 18 2014

Update...issued 0845 PM Friday Apr 10 2014
the forecast looks on track...but it appears northerly flow on
plains will develop a bit earlier than earlier forecast. Rap has
well established low near Kansas border.


Aviation...cold front will push through a bit earlier than
previous forecast. Will bring northerly winds in around sunrise.
Will keep scattered showers and thunderstorms can be
expected in area Saturday afternoon.


Previous discussion... /issued 336 PM MDT Friday Apr 18 2014/

Short term...(this evening through saturday)
issued at 335 PM MDT Friday Apr 18 2014

Some middle and high level moisture spreading into the region from
the southwest. Airmass slightly unstable with high based cumulus
developing along and near foothills and across South Park into the
southern foothills. Laps surface analysis indicating convective available potential energy of
around 100 j/kg across Park County into the southern foothills and
along the Palmer Divide. At this convection indicated on
radar. Latest models continue to show some showers developing
across the high country and southern foothills as well as the
Palmer Divide by this evening. Will maintain a slight chance of
thunder in this area through the evening. Gusty winds in and near
the storms that develop...with only light rainfall. Dry conditions
to prevail elsewhere. After midnight...middle level moisture to
gradually increase with flow aloft becoming southwest. Enough
moisture for some showers overnight across the mountains and South
Park...mainly south of Interstate 70. On Saturday...upper trough
moves into the Great Basin during the morning edging into western
Colorado during the afternoon. Model consensus shows trough axis
roughly across central Utah into central Arizona. Fairly moderate
southwest flow aloft across northeast and north central Colorado.
Moisture will continue to stream over Colorado from the southwest.
There is some increase in middle level ascent across the mountains
during the morning and across the plains in the afternoon. Should
see a good chance chance for showers over the mountains by middle
morning and continuing through the day. Cape limited
initially...but increases during the day with values around 250
j/kg by the evening. So some thunderstorms also possible. Airmass
to be fairly mild so snow levels to be rather high...around 10000
feet above ground level. Any accumulation to be light mainly across the higher
mountain passes. Across plains...models continue to show weak
surface front pushing south across the plains during the
morning...reaching Denver area around 15z. Front appears to
briefly stall along the Palmer Divide early afternoon before
pushing into southeast Colorado. Upslope develops by the afternoon
in and near the foothills and along the Palmer Divide. Airmass
initially fairly stable as cooler air moves in behind front...but
becomes slightly unstable during the afternoon. Latest models
showing only limited cape...with values around 250 j/kg along the
Palmer Divide into Lincoln and Washington counties. Values less
north of Denver. So best chance for showers and thunderstorms to
be along the Palmer Divide and souther section of Washington
County. Probability of precipitation to be lower elsewhere on the plains. There may be
some weak convergence across eastern Douglas into Elbert County
early in the afternoon and may help a few of the storms produce
brief moderate rainfall and perhaps some small hail.
Otherwise...rainfall to be fairly light across the northeast
plains. Airmass to be cooler with temperatures roughly 10 degrees
cooler that friday's readings.

Long term...(saturday night through friday)
issued at 315 PM MDT Friday Apr 18 2014

Enough moisture and instability will keep a few showers and
thunderstorms in the area Saturday evening. These should gradually
dissipate as they move eastward with the upper trough through the
course of the evening and night. The GFS does seem to suffer from
too much convective feedback and thus slower trough movement...but
will continue to monitor potential for more persistent rainfall
over the Palmer Divide area. Will keep the higher probability of precipitation there with
best low/middle level focus still advertised in that part of the
forecast area.

By Sunday...upper level trough continues to move east with
generally a more stable atmosphere pushing in behind this feature.
There is still enough moisture...daytime heating...and
instability to allow a few afternoon showers/storms to redevelop
especially in/near the higher terrain of the Front Range and Park

On upper level ridge will build over the central
rockies with warming temperatures aloft. This will act to cap off any
convection but still cant rule out a few afternoon storms along
the higher terrain of the Front Range.

By Tuesday...temperatures will warm further and boundary layer is
expected to dry as a stronger southwesterly flow begins to develop.
The latest models have slowed the development of these
southwesterlies...but winds should still increase over the
eastern plains by afternoon ahead of Lee trough. This will lead to
higher fire danger. Will also keep a low chance of thunder over
the far eastern plains given a potential for dryline development
and local convergence...but capping may be too strong to allow any
convection to develop. Convective available potential energy are limited to just a few hundred
j/kg too.

Wednesday may feature higher fire danger as stronger westerly flow
occurs and winds increase in all areas. However...there is some
Greenup of fuels occurring from now through that time which will
help offset the windy conditions and lower humidities.
Meanwhile...shower coverage is expected to increase in the
mountains with trough passage to our north later Wednesday into
Wednesday night. Cold advection and westerly flow aloft will aid
orographic precipitation generation with potential for generally
light snow accumulation.

By Thursday and Friday...cooler conditions will prevail in the
wake of wednesdays system. Airmass looks rather dry and stable for
this time period as well.

Aviation...(for the tafs through 00z Saturday afternoon)
issued at 335 PM MDT Friday Apr 18 2014

Southeasterly winds prevail across the area airports...a bit more
northeast at kbjc. Winds expecting to become southerly this
evening before drainage prevails by 04z. Some high based showers
still possible across the southern foothills and Palmer Divide
this evening. Should not affect area airports. VFR conditions to
continue with ceilings above 12000 feet above ground level. Front to move into
the area around 15z with winds shifting to the north. Winds to
then become northeast after 18z as upslope develops. Ceilings to
lower to around 8000 feet above ground level during the afternoon. Chance for
thunderstorms...mainly at kapa and kbjc with possible ceilings
around 6000 feet above ground level.


Bou watches/warnings/advisories...


Short term...rtg
long term....99