Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 282103
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
303 PM MDT Tue Mar 28 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 221 PM MDT Tue Mar 28 2017

Mixture of rain and snow will continue over the region through the
overnight hours and into the early afternoon on Wednesday. The
upper level low over Central AZ will continue to move east into NM
then into the TX panhandle through Wednesday morning. This will
bring southerly flow aloft through 00z Wednesday before turning
more northerly by 09z. At the surface thermal ridging over the
urban corridor will slowly degrade with the onset of cooling aloft
as a colder airmass moves into the region. With the surface winds
turning more NE after 03z snow fall rates and intensity will
increase along the foothills and Palmer divide region. The
orographic influence will help to bring enough lift to create 1 to
2 inch per hour rates through the overnight hours with continued
accumulations expected between 6 and 12 inches with the higher
amounts over southern Douglas county. The warnings will remain in
place and go into effect at 6 pm this evening. Winds will increase
from the north that will reduce visibilities down to less than a
mile at times over portions of the southern foothills and I-25
south of Denver. At this time the snow level looks to possibly
drop between 5500 and 6000ft by the early morning hours on
WEdnesday. This will bring a chance of light snow to south Denver
and a rain/snow mix north into Downtown and possibly DIA.
Accumulations will be a trace up to possibly 3 inches over
southern denver by Wednesday afternoon. Much of this is expected
to melt on warm roads and will be very wet and slushy. Conditions
will slowly improve by the late afternoon as upper level ridging
and subsidence increases. Temperatures overnight will get into the
lower 30s with 50s expected for Wednesday.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 221 PM MDT Tue Mar 28 2017

In the wake of the storm system that generated precipitation on
Wednesday, a weak ridge develops over the eastern half of
Colorado, resulting in a brief warm-up and a dry day area-wide.
Attention then turns to a potent storm system digging southeast from
Northern California into Southern Utah by early morning Friday.
This storm will advect Pacific moisture along southwest flow into
the state. Precipitation chances go up across the mountains
first, with the best chances occurring across the northern
mountains and Front Range. Snow levels look to be around 8500 feet
until the trough gets closer to Colorado. By Friday evening the
500mb trough is centered over the Four Corners. In the lower
troposphere, a deep fetch of southeast flow will draw moisture
northwest into the Plains of Colorado. A surface low develops
across NE New Mexico, and deepens overnight into Saturday. During
the day Saturday, with the trough over northern New Mexico proving
synoptic scale lift over the eastern half of Colorado, and a
strong fetch of upslope moisture, a good precipitation event
should occur all across the Front Range and into the Foothills,
especially along and west of I-25, though all of the Plains should
see beneficial precipitation by Saturday evening. Snow levels
will be declining throughout the day Saturday as cooler air is
advected from the north and northeast with the 700 mb low across
the CO/NM border. For now, the snow level looks to be around 6000
feet elevation during the day on Saturday, which means for Denver
metro areas and along I-25 a rain snow mix or at times mostly snow
is possible, though with wet bulb temperatures in the mid 30s,
accumulating snow may be difficult to achieve. Above 6000 feet,
especially in the Front Range foothills, temperatures will be cold
enough for a fair amount of snow. If things continue along these
trends, highlights in the foothills and mountains will likely be
needed. As opposed to the recent storms we`ve had, this does not
look like as significant an event for the Palmer Divide given
easterly low-level flow. Given how close the snow level is
projected to be, confidence in precipitation type and
accumulations for Saturday below 6000 feet are generally low.

Saturday night the models diverge on where the storm goes. The EC
and Canadian models are a bit more progressive, moving the storm
into the OK/TX panhandles by sunrise Sunday. The GFS is slower and
elongates a long wave trough with an axis right over eastern
Colorado. Suffice to say the GFS solution would favor a longer
precipitation event across the southern 2/3 of Colorado through
Sunday morning while the other 2 models would indicate a drying
trend. Given the model performance prior to the recent series of
Pacific storms that have taken a track across N. New Mexico over
the past week, will side with the quicker/drier solutions and re-
evaluate as we get closer.

Monday a weak short wave trough approaches from the Northern U.S.
(as opposed to the last 4-5 storms that moved across California)
crosses the northern half of the state, so light PoPs are
included for the northern mountains and northern Plains. This one
does not look to be a significant precipitation event at this time
but it is a signal that there is a good chance for cold air to
impact the state at the end of the extended period. In the wake of
this storm a good fetch of northwest flow aloft will draw air
south from near the Canadian border. There is decent model
agreement that sometime on Monday or into early Tuesday a
significant cold front will move across the Plains of Colorado,
ushering in below normal temperatures and providing early
indications of a hard freeze Tuesday night across a good portion
of the Plains, including the Denver and Fort Collins metro areas.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 221 PM MDT Tue Mar 28 2017

IFR/MVFR conditions will persist through Wednesday afternoon with
ceilings between 005 and 020. Winds will be hovering between 350
and 030 with speeds between 08 and 15kts. Some gusting from the
NE between 01 and 05z will be possible with speeds up to 22 kts.
Light rain and some reduced visibility due to mist will continue
through 18z Wednesday as the storm continues to bring rain/snow to
the region. APA will have a slight chance of snow after 08z with
cooler and and orographic influence from the south.

&&

.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.

&&

$$

SHORT TERM...Bowen
LONG TERM...Schlatter
AVIATION...Bowen


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