Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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617
FXUS65 KBOU 191609
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1009 AM MDT Tue Sep 19 2017

.UPDATE...
Issued at 949 AM MDT Tue Sep 19 2017

Overall, current trends still on track so any adjustments to the
grids will be minor. Weak mid level qg ascent this afternoon and
evening with the passage of the trough to the north. Its
associated cool front will push through the area this evening.
Stronger mid level subsidence and drying kicking in overnight.
Best chance of any showers, albeit slight, will be along the
northern border. This is already reflected in the forecast.

&&

.SHORT TERM...(Today and tonight)
Issued at 209 AM MDT Tue Sep 19 2017

An upper level trough will move across the nrn Rockies this aftn and
evening with brisk WSW flow aloft over nrn CO.  There will be some
mid lvl ascent, which will combine with just enough moisture to
produce a chc of showers in the mtns mainly nr the WY border late
this aftn and evening. Otherwise the rest of the area will be dry
with gusty winds thru the aftn hours. As for temps, with downslope
WSW low lvl flow, this should allow for aftn highs to reach the
mid 80s to lower 90s over nern CO.

For tonight the shower threat in the nrn mtns should end by
midnight.  Meanwhile a pacific fnt will move across the plains
during the early evening hours with a brief period of gusty NWLY
winds behind it which will bring cooler temperatures.

.LONG TERM...(Wednesday through Monday)
Issued at 335 AM MDT Tue Sep 19 2017

West-southwesterly flow aloft is progged on Wednesday.  The flow
aloft becomes southwesterly Wednesday night trough Thursday night.
As an upper trough/closed low gets into the Great Basin by 12Z
Friday morning, the southwesterly flow aloft over Colorado
increases in speed. The synoptic scale energy is benign Wednesday
trough Thursday, but weak upward motion gets over the CWA Thursday
night on the QG Omega fields. For the boundary layer winds, there
is southeasterlies progged on Wednesday, normal drainage patterns
Wednesday night, downsloping southwesterlies on Thursday and more
drainage Thursday night. There is little moisture around through
the periods. Precipitable water values are in the 0.25 to 0.50
inch range for the CWA Wednesday through Thursday night. There is
no measurable rainfall on the QPF fields Wednesday through
Thursday night. No pops. For temperatures, Wednesday`s highs are
1-4 C cooler than Tuesday. Thursday`s readings are 1-5 C warmer
than Wednesday`s. Concerning the days Friday through Monday,
increasing southwesterly aloft is progged on Friday. A fairly
strong cold front moves in Friday night. There is a jet maximum
over the CWA on Saturday with southwesterly flow aloft. South-
southwesterly flow aloft is progged Sunday. On Monday the ECMWF
starts getting the trough into the forecast area. The GFS still
has southwesterly flow aloft with the trough axis still to our
west. Moisture increases significantly later Friday through next
Monday. There is some QPF as well. Temperatures cool off to below
seasonal normals Saturday through Monday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 949 AM MDT Tue Sep 19 2017

VFR conditions thru the period. Winds will be SSW this morning and
is progged to pick up from the west/southwest this afternoon.
Surface trough appears to be to the east of the metro area at this
time, so expect wind should transition in this manner. Should see
stronger gusts to 25 kts developing by 21z as mixing occurs.
Gusts should continue until around 01z. By 03z-05z a cool front
will move across with winds becoming northerly for a few hours.
Overnight expect winds will gradually shift to drainage by 09z.

&&

.FIRE WEATHER...
Issued at 949 AM MDT Tue Sep 19 2017

Critical to Extreme Fire Danger will exist this afternoon into
the early evening hours across most of the area due to low
humidity and gusty winds. Fire danger will decrease after 8 pm as
winds gradually decrease and humidity levels recover behind a cool
front. Wednesday is expected to be a cooler and a little less
windy but there will still be elevated fire danger. Temperatures
increase again Thursday, but the winds are not very strong. As a
result, the fire danger will remain elevated.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM MDT this evening for COZ212>216-
238>251.

&&

$$

UPDATE...Cooper
SHORT TERM...RPK
LONG TERM...RJK
AVIATION...Cooper
FIRE WEATHER...Cooper



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