Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 301634
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1034 AM MDT TUE AUG 30 2016

.UPDATE...
Issued at 1034 AM MDT Tue Aug 30 2016

No changes to the forecast package necessary at this time.
Precipitable water values are about 0.20 inches higher than this
time yesterday, around 0.95 inches this past hour. Skies are
mostly sunny now, allowing for strong heating of the airmass. Wind
fields at the surface and aloft are weak, which will result in
poorly organized convection developing during the afternoon.
Showers are expected to develop during the afternoon, most
numerous over the Front Tange foothills, Palmer Divide and plains
to the south of I-76. With the weak steering winds, storms will
likely be slow-moving and capable of producing heavy rainfall.
Model soundings only show 600-1200 j/kg of CAPE so hail should not
be a problem. Some locations picked up an inch of rainfall from
yesterday afternoon and evening`s showers, so that is certainly in
the realm of possibility again today.

&&

.SHORT TERM...(Today and tonight)
Issued at 339 AM MDT Tue Aug 30 2016

Water vapor/ir satellite imagery showing good mid level
circulation to the West of Colorado Springs early this morning.
Quite a bit of mid level clouds around this circulation around the
Front Range and a few showers still closer to the circulation
over the Palmer Divide. The upper trof progged to move very slowly
to the East today across Eastern Colorado with weak to moderate
ascent over the Palmer Divide and Eastern Plains. So expect
highest chances of showers will be along and ahead of the trof
axis as we go into the afternoon and evening hours. Temperatures
will be a bit cooler today with the abundant cloud cover this
morning and readings around 80 over the plains. Surface based CAPE
values under 1000j/kg while Precipitable water values just under
an inch over the Front Range and a bit higher on the Eastern
plains. With very slow storm motions expect heavy rain and small
hail with the stronger storms. Severe storms are not expected with
the marginal instability and weak flow aloft. Lower chances for
storms will be North of Denver and stretching back up to Wyoming
border.

With subsidence moving in tonight behind the trof expect better
clearing and pronounced ending of showers by late evening.
Models showing some increasing low level moisture under Southeast
flow and potential Denver cyclone so some amount of clouds an
patchy fog over the plains and inching back towards the urban
corridor by late in the night.

.LONG TERM...(Wednesday through Monday)
Issued at 339 AM MDT Tue Aug 30 2016

A large upper level ridge over the Rocky Mountain region on
Wednesday will slowly migrate eastward Wednesday night into
Thursday as a deep upper trough moves over the the Pacific Coast.
Beneath the ridge models show anticyclonic upslope flow pushing
low-level moisture up the South Platte River valley during the
morning hours potentially leading to areas of stratus and fog on
the plains to start the day. It`s possible some of this fog and
low cloud could cyclone in over northern portions of the Denver
metro area during the early morning hours. This relatively shallow
upslope flow will also result in slight cooling during the
morning for the plains, but with a shift to southeasterly winds in
the afternoon should see max temps similar to those anticipated
today. Meanwhile weak subsidence and a mid-level cap with warming
aloft should concentrate any late day convection to the mtns and
higher sections of the Palmer Divide. Should see the higher pops
/in the 30-40 pct range/ over the mtn ridges surrounding South
Park as a consequence of the southeasterly boundary layer flow in
place. However due to a lack of upper air support should see a
quick cessation in this shower/t-storm activity by mid-evening.

On Thursday...with the upper ridge axis over the western Great
Plains the prevailing flow aloft goes from light westerly component
to a somewhat stronger southwest component. The shift in wind will
elevate temperatures Thursday and Friday. Models also show this same
flow structure gradually advecting a fair amount of subtropical
moisture northeastward across the state leading to a day-to-day
increase in precip probability. On Thursday...the bulk of this
precipitation should be confined to the mtns and high valleys where
PWAT and humidity levels will be greater to start out. On Friday...a
weak mid-level shortwave disturbance in this southwest flow is
forecast to pass over the forecast area during the afternoon and
evening hours. This feature is expected to provide the additional
lift...moisture and instability to generate scattered t-storms in
the mtns and on the plains. With sfc based CAPES approaching 1500
j/kg on the plains could see a few of these late day storms
producing small hail and gusty winds. Spotty heavy rainfall also
possible across the nern corner of the CWA during the evening hrs
where low-level moisture will be more plentiful. Should see near
to slightly above average temperatures both days with Friday being
the warmer day.

For the upcoming Labor Day weekend...medium range models indicate
gradual drying as the mean layer flow assumes a more westerly
component with the large west coast upper trough moving inland.
Saturday should the warmest of the three days with sunshine for much
of the day before isolated/widely scattered storms move off the high
terrain. With the upper trough nearing the region...cooling aloft
should produce a 3-6 deg f cool down on Sunday and another deg or
two drop on Monday. May see max temps on Labor Day ranging from the
upper 70s/lower 80s at lower elevations and mainly 60s in the high
country.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1034 AM MDT Tue Aug 30 2016

VFR conditions should prevail until scattered afternoon showers
develop which will contain lower ceilings and visibilities due to
the falling rain. Winds will be light and from variable directions
until showers begin producing outflow boundaries containing wind
gusts up to 25 or 30 mph. Showers should begin by around 3 PM and
continue through 7 or 8 PM. No other aviation impacts are
anticipated through tonight and tomorrow morning.

&&

.BOU Watches/Warnings/Advisories...
None.
&&

$$

UPDATE...Dankers
SHORT TERM...Entrekin
LONG TERM...Baker
AVIATION...Dankers



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