Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 211609

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1009 AM MDT Wed Sep 21 2016

Issued at 1004 AM MDT Wed Sep 21 2016

Overcast skies over the region with some lingering showers over
the Northern mountains. The column is dryer over the eastern
plains that will keep conditions dry through the morning hours.
Cloud cover will keep temperatures mild with highs into the lower
to mid 80s further east. Moist SW flow will continue through the
day and bring a chance of showers to the mountains. There will be
enough lift for afternoon thunder over the higher terrain with a
slight chance of showers south of I-70 on the plains.


.SHORT TERM...(Today and tonight)
Issued at 319 AM MDT Wed Sep 21 2016

A moist southwest flow aloft will persist over the region through
tonight. This is expected to keep skies mostly cloudy to overcast
today. Because of the cloud cover and slightly cooler airmass,
highs will be lower today but still mild with readings in the 80s
across northeast Colorado. Precipitation chances will remain low
due to the dry lower levels and limited lift. Best chance for
showers will be over the higher terrain where the dry layer will
not be as thick. Models showing airmass becomes slightly unstable
this afternoon, mainly along and south of Interstate 70. Will go
with 10-30 pops over the higher terrain south of I-70. For the
lower elevations where it will be drier, will go with mainly 10
pops. Precipitation amounts are expected to be light where
convection moves off the higher terrain.

Drier air aloft starts to move into the region tonight and cloud
cover will decrease. Lows will be cooler tonight but still above
normal. A cold front is expected to enter the northeast corner
late tonight and could bring low clouds Thursday morning.

.LONG TERM...(Thursday through Tuesday)
Issued at 319 AM MDT Wed Sep 21 2016

Southwesterly flow aloft will increase in speed as an upper
trough/closed low moves east-southeastward on Thursday and
Thursday night. On Friday morning, a nearly due southerly jet
maximum is over the western CWA with speeds at about 100 knots. At
00Z late Friday afternoon, the closed low is over northern
Utah/western Wyoming with the trough axis along the western
Colorado border. The trough axis is over the western CWA at 12Z
Saturday morning. The QG Omega fields show a pretty decent batch
of upward vertical motion for the CWA Friday afternoon and and
some of the evening. By 12z Saturday morning, most models have
downward synoptic scale energy for us. There are easterly upslope
low level winds progged on Thursday, but only a slightly cooler
airmass gets into the far northeast corner. A real cold front
moves into the plains late Friday evening and overnight. Pretty
normal drainage wind pattens are expected Thursday night with
southerly winds on Friday. There is some moisture around Thursday
through Friday, more so on the NAM compared to the rest. Moisture
increases a bit Friday night for the eastern two-thirds of the
CWA. Precipitable water values are still progged in the 0.50 inch
to 1.00 inch range from west to east Thursday through Friday.
There is some drying Friday night as the upper trough axis moves
across. There is limited CAPE over the CWA Thursday afternoon,
with the highest values over the northeast corner. There is a bit
more CAPE on Friday and it is mostly over the northern plains.
There is a bit of measurable rain over the western half of the CWA
late day Thursday on through mid day Friday. There is some over
all the CWA Friday afternoon through Friday evening, then it
decreases overnight. The upper trough`s supposed weather is not
very exciting, however models do have a bit more QPF for the
plains than yesterday`s 00Z model runs. For mountain pops, 30-50%s
are good for Thursday through Friday night. Will go with 10-30%s
for the plains Friday afternoon and Friday night. For
temperatures, Thursday highs are close to today`s, but a little
colder over the far northeast corner. Friday`s highs are 1-3 C
cooler than Thursday`s. For the later days, Saturday through
Tuesday, the models have the upper trough pushing slowly eastward
across the CWA Saturday and Sunday, with the ECMWF a bit slower.
North and northwesterly flow aloft dominates on Monday and
Tuesday. There is moisture around into Sunday, more so on the
ECMWF, then it dries out the last two days. Temperatures will be
below seasonal normals Saturday, Sunday and Monday.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1004 AM MDT Wed Sep 21 2016

Cloud deck will remain through the day with winds switching to a
more northerly direction by 16z. This will help to keep showers
out of KDEN with most to the south over APA. Any precipitation
will be light and short-lived. Drainage will move in by 00z with
scattering out due to the drier airmass for the overnight hours.




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