Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 170249

Area Forecast Discussion
National Weather Service Denver/Boulder CO
849 PM MDT Sat Sep 16 2017

Issued at 831 PM MDT Sat Sep 16 2017

Departing upper trof over the northern high plains but are seeing
some weak ascent noted with associated jet streak with the trof.
This is creating a redevelopment of high stratus deck and some
banded showers and a few thunderstorms over the plains. Have
expanded the coverage of the showers this evening and have added
more cloud cover as well for tonight.


.SHORT TERM...(This evening through Sunday)
Issued at 239 PM MDT Sat Sep 16 2017

Shallow convective clouds gradually decreasing as expected this
afternoon. Main feature for tonight is an area of weak lift in the
warm advection behind the through. This area is now from northern
Arizona into southern California and is only showing high clouds,
but lift should increase as it moves into the temperature gradient
over eastern Colorado. Redeveloping a cloud deck makes sense, but
I`m not convinced the air being lifted over our area will be
unstable enough for a lot of shower activity or thunderstorms.
Enough of a threat to keep low PoPs on the plains east of Denver
through the night, but I resisted the northward extent that some
of the models are showing and hold the threat roughly east and
southeast of Denver.

This lift should be east of our area by the morning with clouds
diminishing again. Expecting some weak diurnal convection Sunday
afternoon. However the plains will still be relatively cool, so
the mode will likely be scattered showers/storms over the
mountains that drift east in the late afternoon and over the
plains in the evening. Forecast/guidance temps about 5 degrees
warmer than today look good.

.LONG TERM...(Sunday night through Saturday)
Issued at 239 PM MDT Sat Sep 16 2017

West-southwesterly flow aloft is expected over the forecast area
Sunday night into Tuesday morning. An upper trough axis moves in
on later on Tuesday and Tuesday evening. There is weak to no
synoptic scale energy for the CWA Sunday night through Monday
night. Upward QG energy is progged on Tuesday and Tuesday evening.
Downward motion is in place overnight Tuesday into Wednesday
morning. The low level winds will be drainage Sunday night,
southeasterly Monday, normal drainage again Monday night, and
downsloping southwesterly on Tuesday. There may be a weak cold
front come into Tuesday night with a brief shot of northerly flow.
There is plenty of moisture around Sunday evening, then is dries
out significantly by 12Z Monday morning. There is a bit of mid
level moisture Monday late, but it pretty dry through Tuesday.
Some moisture increases in the mountains Tuesday night, but
nothing great. Precipitable water values range from 0.50 inch
over western CWA to 1.10 inches over the plains Sunday evening.
The atmosphere dries out after midnight. It dries out more for
Tuesday with values in the 0.25 to 0.50 inch range. There is
limited CAPE progged Sunday evening, the highest values over the
southeastern CWA. There is very little to no CAPE Monday and
Tuesday. For pops, will go with 10-30%s Sunday evening for much of
the CWA. After that it will be dry through Tuesday morning. Will
go with "chance"s Tuesday afternoon and evening in the mountains.
For temperatures, Monday`s highs climb some 4-9 C above Sunday`s
reading`s. Tuesday`s highs are right near Monday`s highs. For the
later days, Wednesday through Saturday, Models show zonal flow on
Wednesday, then increasing southwesterly flow aloft Thursday
through Saturday. A pretty decent upper trough/closed low is
progged into the CWA Saturday afternoon into Sunday on the ECMWF.
The GFS is slower with the feature. Moisture increases from
Thursday onward with the approaching trough.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 831 PM MDT Sat Sep 16 2017

High stratus deck has redeveloped over local terminals as shallow
upslope flow continues and some weak ascent from departing trof.
Looks like this will remain through much of the night. Easterly
surface winds will gradually shift southeast after midnight.


Issued at 239 PM MDT Sat Sep 16 2017

Fire Danger will increase from Monday into Tuesday across the
higher terrain and plains due to above normal temperatures, low
humidities and increasing wind.




SHORT TERM...Gimmestad
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