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FXUS65 KBOU 202105

Area Forecast Discussion
National Weather Service Denver/Boulder CO
305 PM MDT Wed Sep 20 2017

.SHORT TERM...(This evening through Thursday)
Issued at 305 PM MDT Wed Sep 20 2017

Southwest flow aloft around an upper level trough over the 
western part of the country will continue over Colorado tonight 
and Thursday. Airmass will continue to be dry with only a few 
clouds over the higher terrain. The dry airmass will allow 
temperatures to fall tonight where winds become light. Expect lows
in the 40s to lower 50s over northeast Colorado. 

On Thursday, it will be a very warm day with gusty southwest 
winds over parts of the area. The windy conditions combined with 
low relative humidity will increase the fire danger. Upgraded the 
Fire Weather Watch to a Red Flag Warning because of the windy and 
dry conditions over the Palmer Divide and near by plains. Record 
high for Denver tomorrow is 89 degrees and could be reached. 

.LONG TERM...(Thursday night through Wednesday)
Issued at 305 PM MDT Wed Sep 20 2017

A deep upper level trough of low pressure covers the western half
of the United States Thursday night with an area of low pressure 
centered over southwestern Idaho. Colorado is on the leading edge 
of the trough...under the influence of a moderate southwesterly 
flow aloft. The atmosphere looks to be somewhat dry...therefore 
precipitation is not expected across the CWA. Gusty south to 
southwest winds and low relative humidities will result in 
increased fire danger across the Palmer Divide and portions of the
northeastern plains through the evening hours. 

On Friday...models show a 90KT+ jet oriented from southwest to 
northeast across the western two thirds of Colorado. QG forcing 
associated with the jet combined with increased mid level 
moisture will result in a better chance for showers and 
thunderstorms...mainly across the high country. Temperatures on 
Friday should also be a few degrees cooler than Thursdays readings
due to increased cloud cover and some cold air advection. 

Much cooler temperatures are expected across all of north central
and northeastern Colorado over the weekend into early next week 
as the upper trough moves across the Rocky Mountain Region and a 
series of cold fronts move across the northeastern plains of 
Colorado. The combination of upslope flow...increased low and mid 
level moisture and QG lift from a 90kt+ upper level jet should 
result in better precipitation chances as well. Snow levels should
remain above 10,000 feet.

There is quite a bit of difference when comparing the NAM with 
the GFS and ECMWF in Saturday's weather. The NAM sounding and 
cross section suggest drizzle and light rain in Denver much of the
day with high temperatures only in the 40s...while the GFS and 
ECMWF runs have temperatures in the upper 50s to lower 60s along 
with scattered showers possible. Think the NAM is too cool and 
wet...while the NAM and ECMWF may be a little too warm and dry. 
Therefore...have decided to do a compromise of the models and have
lowered Saturday's max temperatures a few degrees while raising 
pops slightly. 

Sunday should be a cool and cloudy day across northeastern 
Colorado with scattered to numerous rain showers possible. Max 
temperatures will only be in the 50s across most plains locations.
Precipitation chances should taper off on Monday as the main 
upper trough weakens and lifts northeast out of the area. 
However...temperatures should remain on the cool side. A gradual 
warming and drying trend is expected by the middle of next week. 
However...temperatures should still remain below normal values.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 305 PM MDT Wed Sep 20 2017

VFR conditions will prevail through Thursday under mostly clear 
skies. Southerly winds with gusts to 25 knots will prevail through
mid evening before decreasing at KAPA and KDEN. Southerly wind 
are expected overnight and will increase to 25 knots again 
Thursday. A Denver Cyclone will result in weaker winds at KBJC, 
and may bring a wind shift to KDEN after 18Z Thursday.


Issued at 305 PM MDT Wed Sep 20 2017

Still on track for windy and dry conditions over the Palmer 
Divide and across parts of the eastern plains Thursday afternoon. 
Upgraded the Fire Weather Watch to a Red Flag Warning. Windy 
conditions are expected for the mountains and foothills, however 
relative humidities are expected to remain above 15 percent. 

Dry and windy conditions are expected Friday over most of the area 
ahead of a cold front. 


Red Flag Warning from noon to 7 PM MDT Thursday for COZ241-



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