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383
FXUS65 KBOU 061819
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1219 PM MDT Mon May 6 2024

.KEY MESSAGES...

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- Very active weather pattern through the next couple days, with
  Winter Weather, Fire Weather, and High Wind highlights in effect

- Periods of snow and blowing snow through Tuesday. Travel
  impacts likely, especially across the Park Range/Rabbit Ears
  Pass.

- Widespread gusty winds continue through at least Tuesday, with
  the strongest winds expected across the higher Foothills.

- Cool and unsettled weather along with much lighter winds
  Thursday through Saturday.
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&&

.UPDATE...
Issued at 1025 AM MDT Mon May 6 2024

High winds continue across the Front Range mountains/foothills and
plains this morning. The push of high winds across the southern
Denver metro and Palmer Divide has filtered out as the pressure
rises weaken across the area. This reflects well with the
shorter-fused High Wind Warning for the Palmer Divide expiring at
noon today. Minor changes to the grids for this update. Made some
small tweaks to the winds. With gusty winds and dry conditions in
southern Lincoln County, added in areas of blowing dust now
through the afternoon.

&&

.SHORT TERM /Through tonight/...
Issued at 407 AM MDT Mon May 6 2024

Snow, wind, fire, and slightly cooler air. These four elements will
lead to hazardous weather conditions across northeastern Colorado
today. GOES-18 water vapor displays a decent plume of moisture
across our mountains this morning. As this trough enters portions
of western Colorado, winds aloft shift west increasing between
70-90kts throughout the 500-700mb layer. In fact, vort max pivots
along the foothills and areas west of I-25. This will allow for
orographic snowfall for elevations above 8 thousand feet to
persist which will lead to totals between 3-8 inches through
Tuesday. The Winter Weather Advisory will continue through 6 PM
this evening; it is likely snow will continue after this time
period but intensity should decrease as the trough axis begins to
exit.

Wind. Similar to yesterday, deep mixing will occur which will
maximize surface winds especially along the urban corridor.
BUFKIT soundings momentum xfer presents 35-45kts mixing down to
the surface well before noon for urban corridor areas west of
I-25. Given the strong signals of this bora event, decided it was
possible for gusts up to 60 mph to occur for these areas which
lead to additional High Wind Warnings through midnight tonight. It
is possible these conditions may become spotty reach 60 mph
across these zones but given the threat along I-25 on a Monday
morning/afternoon commute, it was evident to issue. Additionally,
parts of the mountains and foothills will gusts up to 75 mph.
Wouldn`t be surprise as the trough passes through, gusts peaking up
to 80-85 mph occurring on mountain passes. Tonight, expect
westerly winds to continue gusting but decreasing in intensity
along the urban corridor and plains. Across the foothills and
mountain passes late this evening, wind gusts up to 40-50 mph and
low visibilities due to blowing snow proceeds through Tuesday.

Fire. Minimum relative humidities this afternoon range between 35-55
percent for areas west of I-25 and slight lower between 20-25
percent for areas east of I-25 outside of southern Lincoln county.
Although these areas are not included in a Red Flag Warning, if a
fire were to occur, expect rapid spread as westerly winds will
produce wind gusts up to 50 mph. Critical conditions are possible
for southern Lincoln county this morning through this evening.. see
fire weather sections for more.

Slightly cooler air. As the trough approaches, 700mb temperatures
this morning range between -4C to -2C through late afternoon. With
cold air advection passes with the trough, expect afternoon
temperatures to sit almost 10 degrees cooler than yesterday.
Mountains and valleys range between low 30s to low 40s. Parts of
the foothills, urban corridor and plains will reach the mid 40s to
upper 50s with a few spots in the northeast corner slightly above
60. Lows remain slightly cooler than normal as well.

&&

.LONG TERM /Tuesday through Sunday/...
Issued at 407 AM MDT Mon May 6 2024

An intense storm system will be over the nrn High Plains on Tue
with stg WNW flow aloft remaining over the area. Cross-sections
show favorable moisture and orographics in the mtns along with
lapse rates around 8 c/km. Thus will see another round of snow
with advisory amounts likely along with areas of poor visibility
due to blowing snow. As far as winds, cross-sections show cross
barrier flow won`t be as stg and there is a lack of a mtn wave.
So, although it will be windy the threat of winds meeting high
wind criteria look low at this time. Across the plains it will be
manly dry with another day of gusty winds but speeds should also
stay below high wind criteria. Highs on Tue will be in the 60s
over nern CO.

For Tue night into Wed, the upper level storm system will begin to
weaken and move southeast into the central plains.  Cross-sections
show decreasing moisture in the mtns so snow shower activity will be
less in coverage. Across the plains, it will remain mainly dry
with lighter winds. Highs will be in the upper 50s to mid 60s
over nern CO. Meanwhile, one thing to watch overnight into Wed
morning will be the possibility of freezing temperatures over
portions of nern CO.

By Wed night into Thu, the storm system is fcst to elongate as one
piece of energy moves eastward out of the Central Plains while
another piece of energy redevelops further west from the central
Rockies into the Great Basin. As this occurs, another cool front
will move across the area. The combination of these two features
may bring a chc of light precip to the area on Thu along with
cooler temperatures. Highs across the plains may stay mostly in
the 50s.

Looking ahead to Fri, there is still alot of uncertainty as to how
far west a weak upper low will be located and how much moisture will
be across the area. The GFS has a considerable amount of moisture
affecting the higher terrain with widespread precip. Meanwhile,
the ECMWF keeps this moisture further west with much lower precip
chances across the higher terrain. For now, will continue with the
blended solutions until it becomes more clear how things will
evolve.

For next weekend, there are major differences between the ECMWF and
GFS in the overall pattern.  The ECMWF has a weak closed low moving
into the area late Sat into Sun while the GFS has a disturbance in
NNW flow aloft moving across on Sat.  Overall, the ECMWF solution
would bring a good chance of precip to the area on Sun while the
GFS generates a good chc of precip on Sat. Once again, confidence
in either of these solutions is very low at this time.

&&

.AVIATION /18Z TAFS through 18Z Tuesday/...
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Issued at 1219 PM MDT Mon May 6 2024

Expect VFR conditions through the TAF period. Strong westerly,
gusty winds continue this afternoon through the early evening.
Gusts in the 30-40 kt range are likely this afternoon with higher
gusts at BJC (~40-55 kts). Winds decrease gradually early
evening 23-03z at APA and DEN out of the W/WSW. Winds may stay
more elevated at BJC for for the early evening, decreasing toward
midnight. 09-12z winds turn more westerly at the terminals. Winds
mix out in the 14-17z timeframe Tuesday morning, bringing back
gusty WNW winds although not as high as Monday. Gusts up to 35 kts
possible in the afternoon.
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&&

.FIRE WEATHER...
Issued at 407 AM MDT Mon May 6 2024

A Red Warning is in effect for southern Lincoln county for critical
fire weather conditions this morning through this evening as very
windy conditions exist across the plains. Relative humidity will
drop between 11-15 percent and wind gusts up to 50 mph could
occur.

Gusty winds and low humidity will continue on Tuesday across the
plains with critical fire conditions over southern Lincoln county.
Elsewhere across the rest of the plains elevated fire conditions
will be in place.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM MDT this evening for COZ031-
033-034.

High Wind Warning until 6 AM MDT Tuesday for COZ035-036.

High Wind Warning until midnight MDT tonight for COZ038-039.

High Wind Warning until noon MDT today for COZ041.

Red Flag Warning until 9 PM MDT this evening for COZ247.

Red Flag Warning from 11 AM to 7 PM MDT Tuesday for COZ247.

&&

$$

UPDATE...Mensch
SHORT TERM...AD
LONG TERM...RPK
AVIATION...Mensch
FIRE WEATHER...AD/RPK