Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 100224
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
824 PM MDT Wed Aug 9 2017

.UPDATE...
Issued at 804 PM MDT Wed Aug 9 2017

One defined disturbance in satellite is moving across
nern CO early this with a band of showers.  Meanwhile
hi res data shows another round of activity affecting the mtns
around midnight and then moving across the plains overnight.
Appears this may be related to another feature which is moving
into nern Utah. Thus will leave in chc pops across nrn CO after
midnight.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 130 PM MDT Wed Aug 9 2017

West to NW flow aloft continues over the region with high pressure
to the south and a deep trough over the Great Lakes. PW values
started low with the main branch of moisture and accompanying jet
to the North. As the jet drops south per varies models the
moisture levels will slightly increase. Specific humidity values
for this afternoon and evening will increase over the higher
terrain and along the south of the Palmer Divide. Surface winds
will predominately be from the NNE with increasing NW mid and
upper level flow. This will help increase deep shear values and
sustain stronger storms for the late afternoon and evening hours.
Current instability levels over the plains are not high with weak
mid level forcing. However...further south over the Palmer divide
and east into eastern Elbert and Lincoln county instability values
increase enough to create stronger storms. The main hazards
expected are brief moderate to heavy rainfall, gusty winds up to
45 mph and nickel sized hail. Elsewhere some pea size hail, brief
heavy rain and winds to 35 mph will be possible into the evening
hours. Models also indicate a small shortwave in the NW flow
aloft around 03z Thursday. This will bring enough forcing for some
showers to linger into the overnight hours. Expect some formation
of lower ceilings and mist for the early morning hours Thursday.

For Thursday another disturbance in the NW flow will move over
northern and eastern CO by peak heating time. this will interact
with a stalled cold front over the eastern CO border with
moderately moist ESE flow. This will help to increase storm
chances for Thursday afternoon and evening. Moderate instability
combined with deep shear values in the 45 to 55 kt range suggest a
good environment for the development of supercells with large
hail, damaging wind gusts being the main threats. Temperatures
will be similar to today with mid to upper 70s along the urban
corridor and low 80s over the plains.

.LONG TERM...(Thursday night through Wednesday)
Issued at 130 PM MDT Wed Aug 9 2017

West-northwesterly flow aloft will continue through the weekend
as upper troughing remains over the upper Midwest and high
pressure remains over Texas. This pattern will maintain below
normal temperatures and ample moisture with several weak
disturbances aloft for continued daily thunderstorms.

Thursday evening...the main area of convergence and potential
stronger thunderstorms across the east central plains of Colorado
will push southeast, and should be out of the area by midnight.
There still may be a strong storm or two in the early evening,
however they will have likely morphed into an MCS with heavy rain
being the main threat. Clearing skies and a weak surface low will
again provide an opportunity for fog across the plains.

Another disturbance will cross over the area Friday. No real surface
focus on the plains like Thursday, however with warmer temperatures
and more southeasterly surface flow advecting in moisture, expect
storms to fire off over the high terrain, moving east-southeast
across the plains. CAPE values of 1600-2000 J/kg, especially along
the northern border and east of the I25 corridor, will allow for a
chance of severe strength storms, with hail and strong outflow winds
being the main impacts.

Over the weekend, an upper trough over the Dakotas will push a front
down to provide perhaps some upslope flow, or at least more of a
focus for stronger storms over the eastern plains. Little change to
temperatures is expected however.

On Monday, the upper pattern will finally change as the upper ridge
will pass over the state, likely bringing warmer and drier weather
to the eastern half for the first half of the week. However models
get muddy with the upper pattern, with major differences by
Wednesday even. There are even run-to-run difference within each
model as well, therefore confidence in the forecast for next week is
low.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 804 PM MDT Wed Aug 9 2017

One band of higher based showers has moved across early this
evening with nly winds at the airport.  Overnight hi res data
indicates another round of showers and isold storms may affect the
area between 09z and 12z with a breif period of gusty winds. Until
this second round of activity moves in winds should eventually go
to light drainage before midnight. By 12z a cool fnt will affect
the area with winds becoming nly. At this point stratus/fog
potential look low overnight based on current trends in hi res
data.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...RPK
SHORT TERM...Bowen
LONG TERM...Kriederman
AVIATION...RPK



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