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Area Forecast Discussion (AFD)

Issued by Denver/Boulder, CO (BOU)

FXUS65 KBOU 212156 CCA

Area Forecast Discussion
National Weather Service Denver/Boulder CO
338 PM MDT Sat Sep 21 2019

.SHORT TERM...(This evening through Sunday)
Issued at 226 PM MDT Sat Sep 21 2019

Jet related forcing is progressing east into Colorado while the
winds in Wyoming have been slow to turn northerly. Hence the
cooler, moister air looks like it will be late to arrive this
evening. The interaction between these two will likely be over
northeastern Colorado and areas a bit north and east from there,
in the evening hours and most likely mid to late evening. There's
still a chance of something in Denver that would most likely have
to back in here from the northeast. The HRRR is still trying to do
this but doesn't quite bring the rain into Denver, and the larger
scale models are similar. The current forecast is focused in the
right place so we're just making some timing adjustments with an
emphasis on mid to late evening. The forcing is mostly aloft and
low levels aren't very moist, so any rain amounts should be light.

For Sunday, drier and warmer air aloft with subsidence will move
in early. Can't rule out a few cumulus over the mountains, but it
should be nearly clear. Warming at the surface will lag the air
aloft, but it should recover to be at least as warm as it is 
today, with warmer highs likely over the mountains. It will be 
breezy in the mountains in the afternoon with low humidities, but 
not quite meeting Red Flag criteria.

.LONG TERM...(Sunday night through Saturday)
Issued at 336 PM MDT Sat Sep 21 2019

Corrected typos. 

Models have upper ridging over the CWA Sunday night, then strong 
southwesterly flow aloft is progged Monday and Monday evening. A 
weak upper trough is progged to move in and across the CWA early 
Tuesday morning. By midday Tuesday, through the afternoon, 
northwesterly flow aloft moves in and continues overnight. The QG 
Omega fields have weak downward synoptic scale energy over the area 
Sunday night. Weak upward energy is in place Monday and Monday 
evening. Back to weak downward energy is in place Tuesday and 
Tuesday evening. The low level winds look to be normal drainage 
patterns Sunday night, east and southeasterlies Monday, downsloping 
northwesterlies Monday night, variable and weak flow Tuesday, then a 
cold front and upslope Tuesday night late. For moisture, it is 
pretty dry Sunday night through Tuesday night. Through those five 
periods, precipitable water proggs show values in the 0.25 to 0.50 
inch range. There is nothing in the way of any measurable 
precipitation on the QPF fields through Tuesday night. Will leave 
pops out through Tuesday night. For temperatures, Monday's highs are 
1.5-4.0 C higher than Sunday's. Tuesday's highs are 0-2 C warmer 
than Monday's. For the later days, Wednesday through Saturday, 
models have west and southwesterly flow aloft through Thursday 
evening. Then a weak upper trough moves across into Friday morning. 
Then southwesterly flow aloft returns through Saturday. Moisture 
increases a bit from Thursday onward.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 226 PM MDT Sat Sep 21 2019

VFR conditions are expected through Sunday. Scattered showers and
a few thunderstorms will develop mainly east of Denver after 00z.
There's a slight chance of a thunderstorm with wind gusts to 30
knots in the Denver area through about 06z, and instrument
approaches to KDEN may be needed overnight. Ceilings will
dissipate by 12z Sunday.




SHORT TERM...Gimmestad