Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 180327
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
927 PM MDT Mon Apr 17 2017

.UPDATE...
Issued at 925 PM MDT Mon Apr 17 2017

There was a bit of weak convection over Washington County early
this evening, but it died out. There has been no convection for
last two hours anywhere in the CWA. The new satellite mid level water
vapor pictures marginally show a weak upper trough pushing
eastward out the CWA right now. The flow aloft right now is due
northwesterly. The easterly 3/5ths of the plains are holding on to
lower 50s F dew points right now, but to the west the dew points
are in the 20s F. There is nothing upstream as far as convection
goes. Will get ride of any pops this update.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 131 PM MDT Mon Apr 17 2017

Upper low over northern rockies with tail end of upper trof will
move across Colorado tonight. There is some weak qg ascent with
this system but still a batch of high clouds which are moving
across the plains this afternoon and may be cutting down the
heating a bit. Main concern still centers on thunderstorms
developing over the plains later this afternoon and evening with
the potential for an isolated severe storm. Surface dewpoints
maintaining in the mid 40s to lower 50s over the far plains ahead
of the dry line. With temperatures in the low/mid 70s expect
surface based CAPES in the 1000-2000j/kg. Sufficient shear for a
few severe storms with mainly large hail and damaging winds.
Despite lingering low level inversions feel large scale lift and
additional heating will allow a few storms to develop. Latest HRRR
showing strongest storm mov ing across Washington county later
this afternoon/evening.

For later tonight and Tuesday, some drier air will move in behind
tonight`s trof but still could be some patchy fog and low clouds
over far eastern Colorado. Drier on Tuesday but could see a few
showers developing in the mountains late in the day in advance of
next trof.

.LONG TERM...(Tuesday night through Monday)
Issued at 131 PM MDT Mon Apr 17 2017

Flow aloft will be southwesterly Tuesday evening with the jet
moving from the SW to NE over portions of western CO. At the
surface, a low centered east of I-25 will help to bring increased
SW winds over the southern plains. This will help to increase fire
danger into the evening hours for areas on the plains south of
I-70. By midnight on Tuesday the surface low will move east over
the plains with a cold front dropping south bringing flow on the
plains more northerly by early Wednesday morning. A trough
embedded in the SW flow will increase moisture in the high
country and bring a chance of rain and snow to the mountains
through Wednesday. Colder air will move in by the late morning
dropping the freezing level to 8500 ft. A lee side surface low
will build on the plains increasing downsloping off the
foothills. The upper jet will set itself up over Central CO
increasing westerly winds into the mountains with gusts to 55 mph
possible at mountain top by the afternoon. This will help to
increasing downsloping and keep conditions over the lower
foothills out to Denver Metro dry. Further east wrap around
moisture will bring a slight chance of rain to the far eastern
plains by the afternoon. Winds will also increase on the plains
behind the frontal push with sustained winds of 15 to 20 mph with
gusts to 30 mph. By Wednesday evening increased subsidence from
the west and high pressure building on the plains will help to end
any showers over the east. Temperatures for Wednesday will be in
the lower 70s.

By Thursday upper ridging between systems will build in clearing
out any precipitation. The cold push from the North will have
settled in bringing temperatures down into the mid 60s. The next
system to affect CO will be over the West Coast Thursday afternoon
with models bringing it into CO by Thursday night. At this time
both the EC and GFS keep the system as an open wave as it makes
its way over the state. Upon exiting into KS is when the GFS cuts
it off. At the surface, a building surface low to the SW will help
to keep SE flow over the plains and into the base of the
foothills Thursday evening. This will help to create orographic
convection over the foothills Thursday afternoon. Precipitation
will become widespread through Friday as the trough pushes
through the state. Continue with likely pops for both Thursday
and Friday with some changes still possible as models refine the
path of the system. Temperatures for Thursday and Friday will
continue to decrease with 60s on Thursday and 50s by Friday. Do
not believe that freezing levels on the plains will get low enough
for snow, however decent rain will be possible with snow still
expected for the higher foothills and mountains.

Precipitation will slowly come to an end Saturday with cooler NNW
flow aloft. Upper ridging will increase by Saturday night with
mild conditions expected for Sunday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 925 PM MDT Mon Apr 17 2017

The DIA LLWAS winds on the IDS4 are showing weak drainage winds in
place at many of the sensors. Some have weak westerly winds.
The numerous models show weak wind speeds all night at DIA but
few of them show south-southwesterlies. There is not much of a low
level pressure gradient in place overnight so it seems normal
drainage pattern winds should be the rule. I will go that route.


&&

.FIRE WEATHER...
Issued at 131 PM MDT Mon Apr 17 2017

Some elevated fire weather concerns for Tuesday afternoon with
some southwest wind gusts in the 10-20 mph for a brief time
Tuesday afternoon over the Palmer Divide region. Humidities will
drop to around 15 percent. Overall conditions for red flag are
marginal and there is some green up underway so will not issue any
fire hilites.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...RJK
SHORT TERM...Entrekin
LONG TERM...Bowen
AVIATION...RJK
FIRE WEATHER...Entrekin



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