Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 201028
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
428 AM MDT Mon Mar 20 2017

.SHORT TERM...(Today and tonight)
Issued at 428 AM MDT Mon Mar 20 2017

Warm dry air remains over the area this morning with slightly
cooler and more humid air lurking behind a weak cold front over
Nebraska and the Dakotas. This front will gradually ease across
northeastern Colorado today as pressure rises will continue over
the northern Plains, but mixing of westerly flow aloft should keep
west winds in and near the foothills through the afternoon.
Frontal boundary may become more diffuse due to the mixing. Main
change to the forecast at this time was to show a little more wind
in the foothills, as the models typically underdo the mixing in
these situations. Also dropped high temperatures a couple of
degrees due to more cloud cover.

For tonight, a weak shortwave trough will move north of us. This
could bring a few showers to the northern mountains and northern
border areas overnight. This should also help the cooler air to
become more widespread on the plains.

.LONG TERM...(Tuesday through Sunday)
Issued at 428 AM MDT Mon Mar 20 2017

SWLY flow aloft will be across the area on Tue with increasing mid
lvl moisture thru the day.  At the sfc a fnt will be stalled out
nr the foothills with sely low lvl flow across the plains. The
ECMWF shows a weak disturbance moving across late in th aftn or
Tue evening. Thus will mention a chc of showers in the mtns. Over
the plains as waa ptrn develops Tue evening may see a chc of
showers as well as the wk disturbance moves across. As for highs
readings will be cooler across nern CO with temps ranging from the
50s across the far nern plains while closer to the foothills
highs reach the mid 60s.

On Wed swly flow aloft will strengthen with still some mid and
higher level moisture embedded in the flow.  At the sfc low pres
will intensify along the front range as high pres is over the
central plains.  This will lead to increasing sly flow across the
plains.  Overall the threat of showers in the mtns looks lower on
Wed so will only mention low pops.  Over nern CO it looks dry and
windy with warmer temperatures except possibly over the far nern
corner.

For Wed night into Thu an upper level trough will move into the
Great Basin with stg ssw flow aloft over the area.  QG fields show
increasing mid ascent by aftn which should bring a better chc of
showers to the mtns.  Across nern CO sfc low pres will intensify
over the plains with the ECMWF having the low near Limon by late
aftn while the GFS has it over the far nern corner.  My guess would
be neither position will be correct as main low will probably end up
closer to Denver.  At any rate if the sfc low ends up further west
this would allow for a potential triple point to dvlp somewhere over
the nern plains by aftn with the possibility of strong storms along
and east of a Sterling to Akron line.  As for highs will keep
readings in the mid 60s to lower 70s across the plains.

By Thu night into Friday there is better agreement tonight that a
storm system will affect the area.  The ECMWF has been consistent so
far in showing a deepening upper level low nr the four corners
Thu evening which then moves into far sern CO by 12z Fri. The GFS
shows a somewhat similar solution as well. Naturally if the upper
level low takes this track then a widespread pcpn event would
occur over much of nrn CO with the potential for heavy snow in the
mtns and foothills. At lower elevations current fcst temps are
borderline for snow across the plains so will mention a rain/snow
mix for now.

Meanwhile one thing that bothers me is that the current trend of
fcst height falls and 250 mb waa suggest a more srn track across
central NM into wrn TX.  If that occurs then the more significant
pcpn could end up being further south across srn CO so that will be
something to watch in the days ahead.

By Fri night the storm system no matter where it tracks will
gradually move east of the area with pcpn ending by early evening.
On Sat an upper level ridge builds across CO as another system moves
into the Great basin by Sat night.  Thus will allow for a dry day
with seasonal temperatures.

For Sun both the ECMWF and GFS show another upper level trough
affecting the area which would bring a good chance of snow to the
mtns.  At lower elevations the ECMWF is more closed off with this
feature which could also bring a chc of pcpn to nern CO as well.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 428 AM MDT Mon Mar 20 2017

VFR through tonight. Westerly winds will mix down at KDEN/KBJC by
18z with gusts in the 15 to 25 knot range. The stronger values are
more likely at KBJC. Winds at KAPA may be more erratic and will
generally be weaker.

&&

.FIRE WEATHER...
Issued at 428 AM MDT Mon Mar 20 2017

Warm dry air remains in place. West winds are expected to mix to
the surface over the Front Range foothills this afternoon,
spilling onto the adjacent plains in some places. This is most
likely in Boulder and Jefferson counties and areas bordering those
counties. Wind speeds may be marginal, but the air is very dry, so
a Red Flag Warning has been issued for the foothills as well as
the lower elevations of Boulder and Jefferson counties. Both the
wind and humidity should improve quickly this evening.

Fire Danger will decrease in most areas on on Tue as cooler air
behind a cold front affects northeast Colorado.  The only exception
would be across Park county and the southern Foothills.  On Wed fire
danger will increase over the front range urban corridor, foothills
and Park county due to increasing wind and lower humidity values.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon until 7 PM MDT for the Front Range
foothills and lower elevations of Boulder and Jefferson
counties...Fire weather zones 215...216...and 239.
&&

$$

SHORT TERM...Gimmestad
LONG TERM...RPK
AVIATION...Gimmestad
FIRE WEATHER...Gimmestad/RPK



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