Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 171723
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1123 AM MDT Thu Aug 17 2017

.UPDATE...
Issued at 1041 AM MDT Thu Aug 17 2017

Convective cloudiness is slow to start this morning according the
satellite and radar pictures. As mentioned below, precipitable
water amounts are down again from both 24 and 48 hours previous.
There is not much in the way of any convergence boundaries on the
area radars currently. CAPE values are not very impressive.
Surface dew points are about 10 degrees F higher over the far
eastern plains compared to the western half of the plains right
now. Will leave "chance"s in the mountains and 10-20%s out on the
plains. Big hail is possible over the far eastern plains. Will
make some cosmetic alterations.

&&

.SHORT TERM...(Today and tonight)
Issued at 340 AM MDT Thu Aug 17 2017

Colorado will be under a moderate northwest flow aloft through
tonight. Water vapor imagery showing a disturbance in the flow
along with 60kt jet streak now over Idaho which will clip the far
northeast plains later today with some weak upward ascent.
Meanwhile there is another jet streak across southeast colorado
which is creating scattered showers and a few thunderstorms over
southern Lincoln county early this morning.

Overall moisture values are less today as integrated precipitable
water values from GPS are running .10-25 inches less than this
time yesterday. Best chance of storms today will be over
mountains, higher terrain areas and over far Eastern Colorado
where moisture and instability will be greatest. Surface trof over
the plains will create some convergence this afternoon over the
far plains with surface based CAPES of 1000-1500j/kg. Marginal
severe weather threat give instability and marginal shear profile.
Further west towards the Front range, much of the low level
moisture will mix out with CAPE values generally under 500j/kg
and the main threat will be gusty winds but only brief light rain.
Storms will diminish rapidly this evening with weak subsidence
and drying behind the trof.

.LONG TERM...(Friday through Wednesday)
Issued at 241 AM MDT Thu Aug 17 2017

On Fri the flow aloft will become more wly with a drier airmass
across the area.  However there will still be enough moisture for
isold-wdly sct aftn tstms over the higher terrain generally south of
I-70.  Elsewhere no tstms are expected.  Highs on Fri will be near
seasonal normals.

For the weekend the flow aloft will become more wsw on sat and then
swly on Sun.  Both the GFS and ECMWF shows a gradual increase in
subtropical moisture through the weekend. Thus will see a better chc
of sct storms over the higher terrain.  Outflow boundaries fm these
storms will probably trigger isold-wdly sct storms along the urban
corridor and over portions of the plains in the late aftn/early
evening hours.  As for highs readings across the plains will be
mostly in the upper 80s to lower 90s both days.

By early next week little change is expected as there will still be
an influx of subtropical moisture in weak flow aloft.  Thus will
continue to see a chc of aftn tstms over the higher terrain with a
slight chc of storms elsewhere.  Highs will continue in the upper
80s to lower 90s over nern CO on Mon.  On Tue there could be a wk
fnt affecting portions of the plains which may keep readings in the
80s.  For Wed current data still shows some subtropical moisture
affecting the area so expect sct storms over the higher terrain with
wdly sct activity over the plains.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1041 AM MDT Thu Aug 17 2017

Low level winds are trying to go all westerly at DIA late this
morning. Speeds are not significant. Most of the models keep some
sort of westerly component to the wind fields all day and even
some westerly influence on the normal drainage patterns tonight.
There will be no ceiling issues. Will keep the mention of thunder
out of the TAF at this time.

&&

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

$$

UPDATE...RJK
SHORT TERM...Entrekin
LONG TERM...RPK
AVIATION...RJK



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