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Area Forecast Discussion (AFD)

Issued by Denver/Boulder, CO (BOU)

                            
000
FXUS65 KBOU 241513
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
913 AM MDT Sat Aug 24 2019

.UPDATE...
Issued at 902 AM MDT Sat Aug 24 2019

Water vapor imagery showing upper trof center across east central
Wyoming and tail end of trof extending into northeast Colorado and
supported by 60kt jet streak. QG fields still showing weak to 
moderate ascent over the far northeast Corner this morning. 
Result of this feature has been showers that have developed and 
has expanded in the past hour. Given still a moist, southeast low
level flow, expect a few thunderstorms as well this morning. Have
already adjusted forecast to add some showers this morning over 
the northeast corner but will need to expand this area a bit more 
west into Washington and Logan county as well. 

Further west, a drier airmass will continue to filter in from the
west and northwest as a moderate northwest flow aloft develops.
Already seeing some gusty winds in the mountains with Berthoud
Pass gusty winds to 50 mph. No thunderstorms expected anywhere
today except the far northeast corner of Colorado. 

&&

.SHORT TERM...(Today and tonight)
Issued at 406 AM MDT Sat Aug 24 2019

There are still a few tiny showers over the plains, a little
surprise apparently reflecting a little pocket of weaker capping
behind last night's shortwave trough. These should dissipate
quickly as the expected warming aloft and drying moves in from the
west. There are a few patches of stratus over the plains but so
far higher than the last couple of mornings. This should increase
through sunrise, especially over the eastern part of the plains
and it should be slower to dissipate in that area as well. This
will keep temperatures cooler through the day, which should also
keep convection from forming on the west edge of the moisture.
There will likely be some late afternoon storms further east where
the moisture is richer, but this will likely be along or east of
the state line. 

Further west, it should be too dry for much more than cumulus
clouds this afternoon, and if the warming aloft comes fast enough
that may even be difficult. There will be some wind mixing down
this afternoon, mainly over the mountains, which will cause fire
weather concerns. East of the mountains the low level flow will be
dominated by the shedding of a Denver cyclone vortex that should
develop in the next few hours and move east, leaving north winds
into Denver. This could transition to a better mixed northwest
flow near the end of the day, but even then it would likely be
northwest near Wyoming and curl around into Denver from the north
or northeast. Forecast temperatures for today remain a bit above
guidance and still look good given the amount of sun and drying we
expect today. It will be a mild night in most areas with enough
wind to keep some mixing, though calm spots could drop more under
clear skies.

.LONG TERM...(Sunday through Friday)
Issued at 406 AM MDT Sat Aug 24 2019

High to extreme fire danger expected on Sunday, reference the 
fire weather discussion below. For Sunday and Sunday night, a 
strong northwesterly flow will be over the region with the passage
of a 110 kt upper level jet max moving across Wyoming. Forecast 
models keep northern Colorado on the warm and subsident part of 
the right exit region of the jet. 250 mb winds over northern CO in
the 60-70kt range for Sunday. In addition, high temperatures will
be just shy of record highs. The record high in Denver for the 
25th is 99 set in 2011. A lee trough over eastern CO should help 
to enhance the downslope warming over the foothills with min rh 
below 15 percent. Expect very gusty winds in the Front Range 
mountains and foothills, anywhere from 35 to 55 mph. There will be
a slow recovery Sunday evening with gusty winds persisting 
especially along the Front Range ahead of an approaching cool 
front. This feature should push into the region from the 
north/northeast after 06z Sunday night. Monday through Tuesday, 
temperatures across the urban corridor and northeast plains will 
drop back into the low to mid 80s. The flow aloft will continue 
to be northwesterly across the forecast area with a secondary cool
front pushing through the northeast plains around 12z Tuesday. 
The fire danger will not be as extreme but will remain elevated in
the mountains west of the Continental Divide where these fronts 
will have no significant impact. From the Front Range Foothills 
eastward however, the models show at least enough moisture over 
the plains for a slight chance of showers/thunderstorms Tuesday 
into Wednesday. Temperatures are expected to start climbing back 
up on Wednesday, with a few solutions forecasting highs back around
90. Consensus however keeps the highs just shy of that. Thursday 
through Saturday, the upper ridge is forecast to be over the 
Desert Southwest with a zonal flow aloft over Colorado. The models
indicate another front bringing cooler temperatures and better 
moisture into the northeast plains from the Great Plains. It may 
be overdone but overall there should be a better chance of 
thunderstorms each day, mainly from the Front Range Foothills 
eastward with a drier zonal flow over the mountains. 

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 902 AM MDT Sat Aug 24 2019

VFR with drier airmass today and no thunderstorms expected.
Surface winds shifting northwest this morning before shifting
east and southeast later this afternoon and evening. Speeds
generally 15kt or less through the period.  

&&

.FIRE WEATHER...
Issued at 406 AM MDT Sat Aug 24 2019

Warmer and drier air will move in today along with a little
stronger winds aloft. This will create conditions near Red Flag
criteria over the northern Colorado mountains and near the
foothills north of Denver this afternoon. Both the weather and 
fuel conditions look marginal in most areas, so no warning will be
issued for today, but heightened caution is still advised.

Critical fire weather conditions are forecast for Sunday 
afternoon. The combination of hot temperatures, low relative 
humidities and gusty northwest winds will likely impact favored 
elevated locations. The wind will be strongest in the mountains
north of I-70 and along the Wyoming border.  The main areas set 
for high to extreme fire conditions will be the Medicine Bow and 
Front Range mountain ranges below 10 thousand feet, the high 
mountain valleys as well as areas in and near the northern Front 
Range foothills and Cheyenne Ridge. Some question as to whether 
zone 242 in northeast Weld County should be included in the 
watch. Observed rainfall in the last 7 days is in the 2-4 inch 
range. Will leave the watch as is for now and let the day shift 
have the final call on that zone.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Sunday morning through Sunday evening 
for COZ211-213>215-238-242.

&&

$$

UPDATE...Entrekin
SHORT TERM...Gimmestad
LONG TERM...Cooper
AVIATION...Entrekin
FIRE WEATHER...Gimmestad/Cooper