Scientific Forecaster Discussion

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Area forecast discussion...corrected 
National Weather Service Denver/Boulder Colorado
410 am MDT Sat Apr 19 2014

Short term...(today through tonight )
issued at 410 am MDT Sat Apr 19 2014

Middle- and high-level moisture continues to flow in from the Desert
Southwest in advance of a closed low over Southern California and
upper level open wave trough slowly progressing eastward across
the region. Infrared Sat imagery has shown a dramatic increase in
middle/high cloud cover over eastern Colorado in the past hour in
response to this influx of moisture and warm sector isentropic
lift. Not seeing any precipitation reaching the ground as of yet...
except perhaps on the High Mountain peaks. Meanwhile a surface trough in
eastern Colorado intersects with a relatively weak surface cold front
advancing sewrd across northern Wyoming and northwest Nebraska at this
time. Temperature...thickness and wind fields show this nebulous
frontal boundary reaching the northeast corner of Colorado just
before 1200z and moving into the Denver metropolitan area around 1500z.
Air only slightly cooler and more humid behind this boundary. Pockets
of gusty northeasterly winds can be seen just behind this front. With the
main rise/fall pressure couplet remaining well east of the
County Warning Area...models show Post-frontal winds weakening as they make their
way to the Front Range. However may still see a short period of
15-20kt northeasterly winds with frontal passage. With Post frontal upslope
flow in place should see a steady lowering of cloud bases along
and east of the Front Range as the boundary layer continues to
moisten. In addition...the passage of a weak vorticity lobe now
crossing southwestern Colorado will provide additional lift and moisture
for fairly rapid shower formation in the central mountains around South
Park later this morning. Models indicate this happening after
1500z.

Should see synoptic scale lift and instability increase through the
day over the County Warning Area with the upper trough inching closer. WRF...NAM
and hrrr show scattered convection over the Front Range drifting
over the I-25 urban corridor after 2000z today. Model
reflectivities are generally of low intensity. Although the WRF
and NAM show a band of 20-35dbz cells swinging sewrd across the
Denver metropolitan area just prior to 20/0000z and then over Douglas and
western Elbert counties between 0000z and 0300z. Models show a
fairly deep easterly low-level flow setting up along The Spine of
the Palmer Divide this afternoon which drives a Theta-E ridge up
against the southern foothills. This is where the potential for
brief heavy rainfall will exist late this afternoon and evening.
Could see upwards of a half inch of rain in a short period with
isolated storm cells along this axis. Gusty outflow winds also
possible. Not as confident we/ll see any hail from these low-top
T-storms as convective available potential energy and lapse rates not as impressive as models
indicated yesterday. Elsewhere...low probability of precipitation warranted under mostly
cloudy to overcast skies. Temperatures today as much as 15 degree f
cooler than yesterday.

Shower activity appears to quickly drop off from north to south this
evening. Although...a smattering of weak showers may linger over the
high terrain southwest of Denver and across South Park through the
wee hours of the morning. Overnight...temperatures will low enough
for a rain/snow mix in this area. It is possible the southern
foothills could see an inch or two of wet snow before midnight.

Long term...(sunday through friday)
issued at 410 am MDT Sat Apr 19 2014

On Sunday...the upper level trough will slowly shift eastward into
the Central Plains with most of the moisture and energy across
southeast portion of County Warning Area. This already reflected in forecast with
little change needed. Drier further north but enough moisture and
instablity for scattered shower coverage in the mountains.

High pressure ridge builds in aloft over Colorado as flow aloft
shifts more northwest on Monday. A cold front pushes across
northeast Colorado Sunday night with slightly cooler temperatures
on Monday. Dry and more stable on the plains behind the front but
there will be some showers and storms over mountains and east
slopes as light southeast flow pools moisture over east slopes.

For Tuesday and early Wednesday next trough deepens over the
northern Great Basin with increasing southwest flow aloft. This
will result in big warmup over lower elevations as strong
southerly flow develops over the plains. Could be a dry line setup
over the eastern border with Kansas with higher dewpoints in the
40s. Best chances for storms will be over the far plains with
better low level moisture. Further west towards the Front
Range...generally dry southwest flow. The upper trough lifts
northeast into the northern Rocky Mountain region and High Plains
late Wednesday and Thursday. This will result in dry...cooler and
windy conditions on the northeast plains.

High pressure aloft will build again into Colorado on Friday for
generally dry conditions and warmer temperatures again.

&&

Aviation...(for the tafs through 18z Sunday afternoon)
issued at 410 am MDT Sat Apr 19 2014

Cold front is expected to move trough the Denver area from the
northeast around 1500z this morning. Winds will shift from west-
northwest to a northeast component with its passage. Could see a
1-2 hour period of 15-20 kts gusts with frontal passage. Cloud bases will
lower through the day with bases as low as 5000-6000 feet above ground level with
scattered showers and isolated T-storms this afternoon. Best
chance for these showers in the Denver area between 19/2100z and
20/0100z. Overnight...should see a gradual rise in cloud bases
with partial clearing after midnight. Expect east-northeast surface
winds of 8-15kts in the afternoon...southeast winds of 7-12kts in
the evening...then light drainage flow after midnight.

&&

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

$$

Short term...Baker
long term...entrekin
aviation...Baker