Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 200201

Area Forecast Discussion
National Weather Service Denver/Boulder CO
801 PM MDT Sat Aug 19 2017

Issued at 801 PM MDT Sat Aug 19 2017

High based showers and thunderstorms will continue to progress
east across the eastern plains over the next couple hours. These
will produce more wind than rain. Wind gusts to 40 mph will be
possible. Will adjust the forecast to mention slight chance for
storms through mid to late evening over parts of the plains.


.SHORT TERM...(This evening through Sunday)
Issued at 250 PM MDT Sat Aug 19 2017

A weak westerly flow aloft will be over the region tonight.
Through this evening, sfc observations show the dry line boundary
east of a Sterling to Akron line with 100 mb mix layer CAPES
around 1000 j/kg along the eastern border. Marginal risk there.
Elsewhere it is drier in the lower levels with sufficient mid
level moisture around along and south of I-70 to support weaker
thunderstorms until 02z. Late tngt a weak upper trough will pass
to the north of the state with an associated cold front slipping
into the cwa Sunday morning. Best chc of thunderstorms through
early aftn will be over the higher terrain, with just isolated
thunderstorms developing along the Palmer Divide south and
southeast of Denver late in the day. The mdls all show mid level
moisture in the 700/300 mb layer advecting northward fm New Mexico
late in the day towards 00z. Highs on Sunday will be hot, but 2-4
degrees less than today. CAPES Sunday afternoon progged to be in
the 300-800 j/kg range for Denver and Limon with higher CAPES
around 2000 j/kg along the eastern border. This may be overdone,
but there could be a marginal risk of severe storms late in the
day along the far eastern border.

.LONG TERM...(Sunday night through Saturday)
Issued at 250 PM MDT Sat Aug 19 2017

Flat upper ridging Sunday night give way to weak upper troughing
On monday. Upper ridging builds back into the CWA Monday night
through Tuesday night. An upper ridge axis is over the western CWA
Wednesday morning at 12Z. There is no synoptic scale energy in
place for the forecast area Sunday night through Tuesday night.
The boundary layer winds are progged to be easterly Sunday
evening, with normal diurnal trends overnight and Monday. A cold
front is progged into the CWA Monday overnight with decent upslope
Tuesday morning and much of the day. Pretty strong southeasterly
winds are progged Tuesday evening with normal drainage after 06Z
Tuesday night. Precipitable water values are in the 0.50 to 1.00
range Sunday night into Monday. By Monday afternoon into the
evening they are in the 0.70 to 1.50 range. Late Monday night
through Tuesday night, values are in the 0.50 to 0.80 inch range
in the mountains and foothills, with 0.80 to 1.25 inches over the
plains. There is pretty high CAPE over the northeast corner Sunday
evening; 2000-3000 J/Kg. CAPE is pretty high again over the
northeastern plains late day Monday. The best CAPE on Tuesday is
over the mountains, with little over the stable plains behind the
cold front. The QPF fields have a slight amounts of measurable
rainfall mostly over the mountains south of I-70 and Park County
Sunday night. Rainfall is a bit more widespread for late day
Monday. For Tuesday and Tuesday night, measurable rainfall is
relegated to the mountains and foothills, the plains are dry. Will
go with 10%-30% pops for the mountains, foothills and Palmer
ridge Sunday evening. Will go with 10%-40% pops fore all the CWA
late day Monday. For late day Tuesday, will go with 30%-60% pops
for the mountains and foothills only. Temperatures-wise, Monday`s
highs are 1-4 C cooler than Sunday`s. Tuesday`s highs are down
another 1-4 C from Monday`s readings. For the later days,
Wednesday through Saturday, the upper ridge over the CWA on
Wednesday flattens on Thursday with some weak upper troughing
Thursday night into Friday. Upper ridging builds back in on
Saturday, by the CWA stays in weak northwesterly flow aloft.
Moisture is pretty good Wednesday night through Friday.
Temperatures look to be below seasonal normals.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 801 PM MDT Sat Aug 19 2017

High based showers and storms brought variable outflow winds to
40 knots at KDEN. This activity is shifting off to the east. Winds
are expected to be east-southeast and then turn clockwise through
the late evening hours and settle at a south-southwest direction
by 06Z. A weak front will bring northeast winds around 16-17Z
Sunday. Chances for thunderstorms will be low Sunday, but outflow
winds from nearby storms could cause problems after 23Z Sunday.




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