Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 281630
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1030 AM MDT Tue Mar 28 2017

.UPDATE...
Issued at 1019 AM MDT Tue Mar 28 2017

Rain showers continue to fall over areas in the foothills below
700ft with rain snow mix from 7 to 8500 ft with snow in the higher
elevations. A surface low circulation has kept snow and rain/snow
mix forming along the northern foothills throughout the morning so
have pushed up the advisory to start now and go through tomorrow
morning. With the intense upslope provided by the circulation and
increased moisture fetch 1 to 2 inches of snowfall per hour will
be possible over the next few hours before the drying moves in
from the south. Still expect 4 to 10 inches of snow with the
possibly of up to 12 over the higher elevations of east-facing
slopes. With the drying over portions of southern Douglas and
Elbert counties before the wind shift change and onset of
precipitation later this evening some convection will be possible.
Model upper air soundings show some CAPE and with even a bit of
warming could see a couple storms pop up that could produce some
lightning.

&&

.SHORT TERM...(Today and tonight)
Issued at 425 AM MDT Tue Mar 28 2017

Loosely wound up upper low presently over northeast Arizona is
still projected to track south-southeast across central New
Mexico today and then curve slightly northeastward over nern New
Mexico/nw Texas panhandle by 12z/Wednesday. Height tendency and
QG Omega plots indicate the best large scale ascent ahead of the
upper low in the warm air conveyor will pass to the south of the
forecast area, and not until tonight. Temperature fields reveal a
sfc to 500 mb thermal ridge over ern Colorado this morning, which
would account for the high snow level in the high country at this
time. Through the day, models show this tongue of warm air
shifting area of the state which will signal the start of cooling
aloft. Models also show strengthening southerly low-level flow on
the plains spinning up a sfc-700 mb low southeast of the Denver
metro area this afternoon. Circulation around this low will
enhance upslope flow along the Front Range which should then
quickly expand shower coverage from the Continental Divide to east
of the I-25 corridor. In the vicinity of this sfc low, mesoscale
models indicate a band of low sfc based CAPE which may be
sufficient to generate a few t-storms mid to late afternoon--should
the sun peak out long enough. Otherwise...precipitation is likely
to start out in the high country and up along the Wyoming/Nebraska
border this morning, and as the upper low moves east, become more
widespread this afternoon. Precip intensity should generally be
light today due to weak forcing aloft.

It`s overnight when QG ascent peaks and orographic forcing maxes
out over and east of the Front Range with deep east-northeast
flow that precip rates peak out. Should see the rain/snow line
drop through the evening to around 6000 feet by midnight, and with
further cooling down to around 5200 feet by dawn. Front Range
areas above this rain-snow line are expected to see significant
snow accumulation with the greatest totals in the foothills
southwest of Denver and higher elevations of the Palmer Divide in
Douglas County. Could see anywhere from 6 to 12 inches here. For
that reason the winter storm watch for forecast zones 36 and 41
will be upgraded to a warning. Furthermore, a winter weather
advisory will be hoisted for the northern foothills and the Front
Range mtns, zones 33-35, where 4 to 9 inches of snow is predicted
by morning. Along the base of the Front Range, could see anywhere
from 0.40 to 1.1 inch of beneficial rainfall next 24 hours. In areas
near the base of the foothills, could see up to 2-3 inches of
slushy snow by morning. Farther east, rain totals will generally
be under a half inch.

.LONG TERM...(Wednesday through Monday)
Issued at 425 AM MDT Tue Mar 28 2017

By Wednesday morning the upper low will be centered over east
central New Mexico with the best qg ascent across southeast
Colorado and Kansas. The low during the day will weaken and shift
east and northeast by late Wednesday. Model consensus begins to
diverge as the low becomes more elongated from kansas through the
Texas panhandle. As the low pulls away further from Colorado
expect the precipitation to diminish in most areas during the
afternoon. Still some question on rain and snow line with the
denver area still may see a mix of rain and snow but mainly all
rain over the plains. Main impact area will be over the Palmer
Divide with still mainly snow above 6000 feet and some northerly
winds of 15 to 25 mph. Overall additional snowfall in the morning
only looks to be another 1-3 inches but still some impact for
morning commuters, especially south of i-25 from Castle Rock to
Monument. Will continue with the warning over zone 41 through the
morning but suspect it may be able to be cancelled earlier.

There will be ridging aloft which will move into Colorado
Wednesday night and continue on Thursday with dry conditions and
warming temperatures. The dryness will be short lived as the next
in a series of storm systems takes aim on Colorado in Friday and
Saturday time frame. This next system looks to take a similar
track into New Mexico but still enough moisture and upslope flow
for another decent shot of precip across much of the cwa with rain
mainly on the plains and snow in the mountains and mix rain/snow
in the foothills.

Long range models really diverge by early next week with nearly
zero consensus with the GFS/Canadian runs have a ridge while
European solution indicates a trof over Colorado. For now will
only have low pops for those further out periods.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1019 AM MDT Tue Mar 28 2017

IFR condtions will persist through the period with LIFR possible
from 04 to 08z tomorrow with the onset of increased rain
intensity. Storm will continue to bring rain and light mist
through the period with visibility going down to less than a mile
by 04z. Prior to expect some VCSH and lowered ceilings below
1000ft with increased low level moisture. Winds will be from
310-330 before moving more northerly by 18z. NE flow will increase
later this evening and continue through the period.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 6 PM this evening to noon MDT
Wednesday for COZ041.

Winter Storm Warning from 6 PM this evening to 6 AM MDT
Wednesday for COZ036.

Winter Weather Advisory until 6 AM MDT Wednesday for COZ033>035.

&&

$$

UPDATE...Bowen
SHORT TERM...Baker
LONG TERM...Entrekin
AVIATION...Bowen



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