National Weather Service Forecast Discussion

000
FXUS65 KBOU 060327
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
927 PM MDT Thu Aug 5 2021

.UPDATE...
Issued at 852 PM MDT Thu Aug 5 2021

There are a few showers and storms over the northeast corner of
Colorado this evening. PoPs were added to the forecast through
midnight to account for these showers and storms. They should end
around midnight as stability increases. There were a couple storms
in Grand County as well so PoPs were added there too but these
will have even less instability to work with and should end soon.
Some of the high resolution models are starting to show a good
signal for strong outflow winds across the northeast corner
tomorrow afternoon. There was not high enough confidence at the
moment to change the forecast but a severe wind gust is possible
across the northeast corner tomorrow.

&&

.SHORT TERM...(This evening through Friday)
Issued at 211 PM MDT Thu Aug 5 2021

The upper level ridge has pushed in over the Great Basin and is
pulling northwest flow into the region. This is also bringing
increased levels of smoke down from fires across California and the
northwest. Some CU has developed across the higher elevations but
mid-level drying will help to keep convection at bay and conditions
dry for the late afternoon and evening. Current HRRR smoke
projections have elevated smoke sticking around through the evening
ahead of the incoming shortwave. This and the aforementioned upper
flow will keep overnight lows more mild in the mid-60s across the
plains.

Looking to Friday, a shortwave embedded in the upper flow aloft that
is currently pushing into western WY will move into CO during the
morning hours. There is some weak forcing associated with it that
will help to fire off some afternoon convection across the higher
terrain that will move onto the plains by the late afternoon. Model
upper air soundings indicate more high-based storms with DCAPE
values from 1400-1500 J/kg that will equate to more gusty wind
impacts then intense rainfall. Some storms could produce winds up to
50 mph with outflows into the evening hours. Outside of the storms
winds will stay elevated with subsidence increasing behind the
disturbance with gusting from 35 to 45 mph across the higher
elevations with mixing by the afternoon. In return, this will help to
scour out the low lying smoke and provide some relief over the next
few days. Highs will continue their upward climb with temperatures
in the mid to upper 90s across the lower elevations and 70s to low
80s in the mountains and high mountain valleys.

.LONG TERM...(Friday night through Thursday)
Issued at 211 PM MDT Thu Aug 5 2021

FRIDAY NIGHT INTO SATURDAY, AN UPPER LEVEL TROUGH OF LOW PRESSURE
WILL MOVE ACROSS THE NORTHERN AND CENTRAL ROCKIES WITH A DRY WEST TO
NORTHWESTERLY FLOW ALOFT OVER COLORADO. THIS PATTERN WILL BRING
MOSTLY DRY, COOLER AND BREEZY CONDITONS TO NORTH CENTRAL AND
NORTHEASTERN COLORADO WITH ONLY A FEW HIGH BASED SHOWERS POSSIBLE
MAINLY OVER THE MOUNTAINS and far northeastern plains. With low
relative humidity, gusty winds and dry fuels, fire danger will be
elevated across the far northeastern corner of Colorado.

FOR SUNDAY AND MONDAY, DRY WEATHER AND ABOVE NORMAL TEMPERATURES are
expected AS UPPER LEVEL HIGH PRESSURE DOMINATES THE SOUTHERN TIER OF
THE U.S and ANOTHER UPPER LEVEL TROUGH OF LOW PRESSURE MOVING ACROSS
THE NORTHERN ROCKIES.

For Tuesday through Thursday, upper level high pressure begins to
build over the Western U.S. with a northwesterly flow aloft over
Colorado. There is some differences between the models in how they
handle an upper level low pressure system over the Central Plains
States. The ECMWF shows an upper level low centered over the Black
Hills by 00Z Friday with the GEM solution having a deeper low
centered over Eastern South Dakota. The GFS solution shows no such
low and has an open trough covering much of the Central and Eastern
U.S. Both the ECMWF and GEM solutions show some increase in
subtropical moisture and QPF during this period, while the GFS keeps
things dry. For now will go with the forecast model blend and make
some tweaks to lower the pops somewhat.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 852 PM MDT Thu Aug 5 2021

Smoke will continue to impact visibility through this evening but
it will improve during the early morning hours as clearer air will
move in. It`s possible some smoke may linger into the daylight
hours tomorrow but it should be low enough to avoid ILS. Drainage
winds will be a bit stronger than normal tonight. A weak boundary
will move through midday tomorrow which may shift winds towards a
northerly component. There is a good chance that some showers will
produce strong outflow winds and impact the terminals.

&&

.FIRE WEATHER...
Issued at 211 PM MDT Thu Aug 5 2021

Elevated fire weather conditions will be possible Friday afternoon
across the northeast plains with RH values dropping below 15% with
some wind gusts from 20 to 25 mph. Fuel status across the
northeastern plains counties are cured enough to promote fire
spread so caution is advised.

Dry fuels combined with gusty winds to 30 mph and low relative
humidity will lead to elevated fire danger across Sedgwick and
Phillips Counties on Saturday. Despite marginal relative humidity
values, have decided to go with a Fire Weather Watch for those
areas after coordinating with adjacent offices. The fire danger
will remain elevated through early next week.

&&

.HYDROLOGY...
Issued at 211 PM MDT Thu Aug 5 2021

The threat of burn area flash flooding will be quite low on Friday.
Only scattered but high based showers/storms can be expected.
Limited moisture, a dry and deep sub-cloud layer, and relatively
fast storm movement will support only light rainfall amounts (less
than 0.25 inch).

Mostly dry weather is expected through Monday with a slight
increase in shower and thunderstorm activity beginning on Tuesday.
With limited moisture available, the flash flood threat at this
time looks to limited.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Saturday afternoon through Saturday
evening for COZ250-251.

&&

$$

UPDATE...Danielson
SHORT TERM...Bowen
LONG TERM...Kalina
AVIATION...Danielson
FIRE WEATHER...Bowen/Kalina
HYDROLOGY...Bowen/Kalina

NWS BOU Office Area Forecast Discussion