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Area forecast discussion 
National Weather Service Denver/Boulder Colorado
1151 am MDT Monday Aug 31 2015

Update...
issued at 1141 am MDT Monday Aug 31 2015

Todays front has partially washed out with the best pressure rises
moving east into the Dakotas. Still some north winds advancing
across the northeast plains...but not strong enough to push their
way firmly back to the mountains...so we have a weak anticyclone
close to the Front Range from the slight blocking of the low level
flow. Still think we will eventually go to more of an east-NE flow
later this afternoon...but it will not be much...and certainly not
much of a source of convergence. Meanwhile the cloud band
associated with the upper trough continues to move slowly over US.
Some very weak convection in this elevated layer...and this should
increase with the diurnal heating. We should still get a good crop
of convection over the mountains...but there will not be much
energy to work with on the plains with the cooler and drier air in
place at low levels. Most likely to see some showers driven by the
forcing aloft move off the mountains...probably with some decrease
in number and intensity. I lowered probability of precipitation a little bit for the
afternoon and evening since it is clear that surface based
instability will be minimal.

There has been a noticeable increase in the smoke behind the
front but between the weaker air movement and the continued
diffusion of the smoke we are not getting a high
concentration...visibilities will probably just drop into the
10-15 mile range.

&&

Short term...(today through tonight )
issued at 358 am MDT Monday Aug 31 2015

Early morning satellite imagery shows a well defined plume of
moisture stretching north/northeast from the Desert Southwest
across much of western and central Colorado into the northern High
Plains. Scattered showers and isolated thunderstorms were
occurring throughout this moisture plume. At the surface...a
cold front was pushing southward across eastern Wyoming. A few
showers were already beginning to spill across the Front Range as
anticipated...and this trend should continue this morning with the
plume shifting slowly eastward. Weak q-g ascent along with the
frontal passage by middle morning should also help generate a few
showers. However...this lift arrives during the typically diurnal
minimum of shower activity around middle/late morning. Still feel
enough factors are there to mention scattered showers with a band
working slowly east/southeast across the mountains...I-25 urban
corridor and adjacent plains throughout the morning.

By afternoon...the airmass will destabilize with daytime heating
and scattered to numerous showers and storms are expected to
redevelop over the higher terrain. On the plains...the airmass
will be more stable due to the morning clouds...showers...and
frontal passage...so will have to rely on passing upper level
speed maximum to our north to help precipitation chances on the
plains. With the right rear entrance region of the upper level jet
nearby...think there would be enough support to keep a chance of
storms in the forecast even in the lower elevations. Elevated
terrain of the Palmer Divide may also help so will have highest
afternoon/evening probability of precipitation there with decreasing probability of precipitation farther north.

Expect a gradual decrease of showers and storms by middle to late
evening as upper level speed maximum exits the region and drier air
works in from the west.

Temperatures will be cooler today with the clouds and scattered
showers...but still near normal levels. Finally...the front may
bring in a little more smoke but so far visibilities are not being
obscured to anything less than 10 miles behind the front...so if
we do see smoke should not be as significant as the last couple
fronts.

Long term...(tuesday through sunday)
issued at 358 am MDT Monday Aug 31 2015

Southwesterly flow aloft will remain over the area both Tuesday and Wednesday. Some
subtropical moisture will linger as well on Tuesday so will keep a
chance of thunderstorms in the mountains with isolated to widely scattered thunderstorms elsewhere.
On Wednesday the European model (ecmwf) shows some drying occurring while the GFS shows
another surge of subtropical moisture affecting the area. At this
time will lean towards the European model (ecmwf) and only mention a slight chance of
storms over the mountains as for highs readings will continue above
normal both days with readings rising back into the lower to middle
90s over northestern Colorado by Wednesday.

For Thursday and Friday little change is expected as the area will remain
under SW flow aloft. Some subtropical moisture will be over the
area on Thursday so will mention a slight chance of storms across portions
of the plains and in the mountains by Friday there may be an increase in
subtropical moisture which could lead to a better chance of storms.
Highs on Thursday will remain in the lower to middle 90s over northestern Colorado but
may drop back into the upper 80s to lower 90s by Friday.

By Sat the GFS shows an upper level trough moving across the northern
rockies while the European model (ecmwf) keeps this trough over the Pacific northwest.
Either way the flow aloft will continue southwesterly with some potential for
additional subtropical moisture embedded in the flow. This will
keep in a slight chance of storms across the area. 850-700 mb temperatures
drop a few degrees on Sat so will keep highs in the 80s over northestern
Colorado.

For sun the GFS has mainly westerly flow aloft across the area while the
European model (ecmwf) slowly moves the upper level trough from the Pacific northwest into
the northern rockies with southwesterly flow aloft. Meanwhile there are large
differences in the surface pattern as the GFS has a decent cold fnt
moving across northestern Colorado with highs only in the 70s while at the
same time the European model (ecmwf) keeps this fnt to the north as readings stay
in in the 80s. At this point hard to say which solution is the
best but will go with consensus forecast and have highs in the 75 to
80 degree range. As for precipitation if the fnt does blast through like
the GFS shows then a rather stable airmass will be in place east
of the mountains which would keep most thunderstorm activity combined to the
higher terrain.

&&

Aviation...(for the tafs through 18z Tuesday morning)
issued at 1141 am MDT Monday Aug 31 2015

VFR through tonight. Weaker than expected cold front is
struggling to get into Denver despite north winds on the plains.
Still think that the current pattern will shift to a northerly
component at kden/kapa this afternoon for at least a few
hours...then back to southeast or S this evening. Now only isolated
showers/storms are expected through this evening with a higher
threat at kbjc. There is still a chance of getting gusty winds to
25 knots for an hour or two. If they do occur the direction will
most likely be from the SW.

&&

Bou watches/warnings/advisories...
none.
&&

$$

Update...gimmestad
short term...barjenbruch
long term...rpk
aviation...gimmestad

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