Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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582
FXUS65 KBOU 230921
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
321 AM MDT Tue Oct 23 2018

.SHORT TERM...(Today and tonight)
Issued at 320 AM MDT Tue Oct 23 2018

GOES-16 shows a short wave trough across northern Utah which
continues to push northward. The weak forcing associated with the
trough was mainly across the western half of Colorado, though
radar is confirming a few light showers are ongoing across the
higher terrain, with very little precipitation reaching the
ground. These showers are possible for a few more hours before the
trough moves further north. High res models have a good handle on
the evoluation of this short wave trough.

As the Utah short wave trough moves north into the northern
Rockies, it will finally allow a second trough that had been
meandering across the desert southwest to impact Colorado later
this evening. This trough should be more effective at generating
precipitation across our area starting this afternoon and
continuing into Wednesday morning. For the high country, moisture
and orographics look pretty good for the west slopes after sunset.
The trough is not particularly cold, and the snow level is
expected to only drop to around 10,000 feet later this evening,
then drop a bit more to maybe 9,500 feet by early Wednesday
morning. The trough contains a little dynamic lifting to aid the
west upslope, and so 1-4 inches are possible along the I-70 high
mountains and passes and across the Mosquito range in Park County.
Lift and moisture is less across the Park and Medicine Bow
ranges, as well as the Front Range north of Rocky Mountain
National Park. Thus not much snow is expected across the northern
ranges. With 700 mb temps well above freezing this afternoon, high
temperatures will be in the 50s in the elevations up to 9,000
feet, and mostly in the 40s above that. Temperatures will drop
some after sunset with diurnal cooling and some cold advection,
but not much colder than the mid 20s for the coldest spots,
especially given the ample cloud cover.

Across the plains, southerly low-level flow will result in
another warm day with highs expected in the mid to upper 60s.
Cloud cover will be much greater than yesterday, thus keeping
temps below 70 for a change. The dynamic lift from the short wave
trough, combined with weak instability (100-300 J/kg) should be
enough to generate rain showers after sunset. Only an isolated
chance of thunder.  QPF looks to be pretty light across the
Plains, and the best chances of measurable precip seem to be along
and south of I-76 given the best forcing should be in those
areas, especially south of I-70. Weld and Larimer Counties may not
see much precipitation from this event given the track of the
short wave trough. Cloud cover tonight will keep lows in the 40s
across the Plains.

.LONG TERM...(Wednesday through Monday)
Issued at 320 AM MDT Tue Oct 23 2018

For Wednesday, the upper trough will be over the western portions of
the state moving east through the day. Mid level ascent along with
decent moisture will bring scattered precipitation mainly to the
plains through the early evening hours. Some light, lingering snow
showers will still be possible over the higher terrain but drying
behind the trough will move in and clear out precipitation by late
Wednesday evening. Conditions will be cloudy for much of the day
with highs in the lower 60s for the plains and 30s to 40s in the
high country. On Thursday, the ridge over the West coast will
strengthen bringing CO under increase NW flow aloft. In this pattern
mid and high level moisture will increase. Models are hinting at a
disturbance embedded in the flow that could bring light rain and
snow to the mountains late Thursday into early Friday. Moisture is
weaker with this feature so do not expect much in the way of
accumulation at higher elevations with isolated showers most likely
for the mountains. Temperatures will increase slightly on Thursday
with highs in the upper 60s on the plains and 40s to low 50s in the
high country.

For Friday and into the weekend, the ridge that was over the West
coast deepens and starts to move over the SW portion of the CONUS.
Friday will remain dry with highs continuing to be above normal in
the upper 60s to possibly lower 70s on the plains. Model cross
sections showing some increased pressure gradients over the
mountains that could bring some gusts in the he 35 to 40 mph range
for Friday. For Saturday and Sunday NW flow over the state continues
as the upper ridge moves eastward into the Great Basin region and
into the TX panhandle. Flow will be dry so do not expect any
precipitation for the region. Highs will continue above average with
highs in the 70s Saturday. For Sunday, although the models stay dry,
the EC and GFS show a weak cold front moving down from the North
bringing a slight cool down for the region. Highs are currently
looking to be in the upper 50s to lower 60s range on the plains and
40s in the mountains.

Monday will see continued dry weather as the upper flow starts to
transition to a more zonal pattern. This is due to the deepening of
the next disturbance over the Pacific that could bring weather later
in the week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 320 AM MDT Tue Oct 23 2018

VFR conditions expected throughout the TAF period though clouds
will be increasing today into tonight. By late evening/overnight
expect an overcast deck around 060. Winds will remain generally
out of the south the remainder of this morning before going
variable around 5 kts after 12Z. By midday winds should pick up
out of the south- southeast at DEN. A Denver Cyclone is once again
possible if not likely by early afternoon. It shouldn`t be
particularly strong given the flow around the Palmer Divide is
only around 10-16 kts. Around 00Z winds could shift to the
southwest at DEN as the cyclone moves north of the airport, but
confidence in the wind direction is low. Confidence is reasonably
high that winds with any shift will be less than about 10 kts,
hopefully minimizing impacts to aviation. BJC will have north
winds and less than 10 kts throughout this afternoon until
shifting to southwest if the cyclone moves across Weld County
around 00Z. APA should remain generally out of the south
throughout the day and into the evening.

Light rain showers are possible after about 02 or 03Z this evening
at all metro area terminals. The overall chance is less than 30
percent so left them out of the TAFs for now, especially at DEN.
Slight chance of rain continues through about 12Z, and winds
should be weak Wednesday morning, generally out of the south 10
kts or less.

&&

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

$$

SHORT TERM...Schlatter
LONG TERM...Bowen
AVIATION...Schlatter



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