Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 272207
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
407 PM MDT Mon Mar 27 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 407 PM MDT Mon Mar 27 2017

Southwest flow aloft will be over the area through tomorrow
morning with the incoming trough continuing to progress SE over
the Great Basin. By 12z tomorrow both the GFS and EC have the low
center progressively further south along with the the Canadian and
NAM solutions. Ahead of the main trough the moisture will continue
to increase over the Western portions of the state and into the
higher terrain bringing rain and snow starting this evening.
Cooler air will move into the mountains along with decent QG lift
that will allow for the snow level to drop down to 8500 ft by
Tuesday morning and continue to lower through Wednesday morning.
Current forecast accumulations have possible 6 to 12 inches for
the higher terrain with the most above 7000 ft and over the
Central mountains south of I-70. By Tuesday morning the models
show the upper low moving eastward across New Mexico increasing
SSE flow on the plains turning more easterly by Tuesday afternoon
and evening. This initial SE flow and increasing lee trough will
dry slot closer to the foothills delaying the onset of
precipitation until later in the afternoon/evening Tuesday for
areas west of I-25. By late Tuesday models have surface winds
switching to a more NE direction as the low moves south.
Temperatures will cool tomorrow with highs in the upper 40s to
lower 50s with some areas dropping into the 30s as precipitation
develops.

.LONG TERM...(Tuesday night through Monday)
Issued at 407 PM MDT Mon Mar 27 2017

Deep moisture and lift will move over Tuesday night into
Wednesday. Models have consolidated on a track that keeps the
best lift will be across southern Colorado, with moderate lift as
far north as Interstate 76, and less further north. Blended model
QPF looks reasonable with amounts of one- half to one inch plus a
bit more for modest upslope enhancement in the southern foothills.
Big question remains the temperatures. Trend here is also
relatively warm, suggesting a sharp gradient in snowfall at around
6000 feet. It may be cold enough for some snow in Denver Wednesday
morning, but at elevations between 5 and 6 thousand feet there
should be a mix of rain and snow and air and ground temperatures
staying above freezing will limit the impact. Would not be
surprised to see some of these areas get a couple inches of snow
on the grass and maybe a little slush on the roads at rush hour,
but probably not enough for big problems. Higher elevations should
see a period of heavier snow during the late night until about
rush hour. Putting together the precipitation and temperature
patterns leaves us with needing a Winter Storm Watch for areas
west and south of Denver, while other areas are expecting much
less or no snowfall. We may need to look at an advisory for other
mountain areas, but the upslope enhancement should limit the heavy
snow to the watch areas.

This storm will be moving out slowly on Wednesday, with
temperatures recovering fairly well as there is no cold air mass
coming in its wake. There will be a break Thursday with warming
southerly low level flow on the plains, then a little moisture and
instability arrives ahead of the next system that could bring some
light showers to the mountains late Thursday.

There is reasonable agreement on the next system for Friday and
Saturday. Again the details of placement and temperature will be
important, but it does look like a pretty good chance of
significant precipitation again, and with temperatures similar to
the Tuesday night/Wednesday storm. There are some model runs that
are a few degrees cooler, which could make a difference for
Denver, but there isn`t anything to point at a more widespread
significant snow. Consensus now seems to be about the same with
temperatures dropping into the lower 30s in Denver and significant
snow starting somewhere between 5,000 and 6,500 feet.

Once again, there is no cold air behind the Friday/Saturday system
so we should warm right back up again. There is some divergence in
the models after this. Most keep a string of strong systems moving
through every two or three days. Again, mostly warm, though a few
dew tap some slightly colder air and could pose a threat of snow
in the middle of next week. The latest operational ECMWF is an
outlier building a broader ridge for mild and dry weather in the
early part of next week. In any event, that next system does not
appear to come before next Monday night, so mild and drier in the
meantime.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 407 PM MDT Mon Mar 27 2017

VFR conditions are expected through 11z tomorrow as the next
weather disturbance moves into the area. Mid level moisture will
increase by this evening dropping the ceiling to 060 with light
rain possible between 01 and 05z. The progress of the low will
allow for a dry slot to set up helping to decrease precipitation
chances between 11 and 20z...however low level moisture will move
in as winds transition to westerly then north bringing in IFR
ceilings by 11z. Rain will pick up shortly after the onset of the
northerly winds by 21z with some gusting up to 20 mph. Have high
confidence that the precipitation will remain liquid at the Denver
terminal through Tuesday evening with temperatures being too high
for snow.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Tuesday evening through Wednesday
morning for COZ036.

Winter Storm Watch from late Tuesday night through Wednesday
morning for COZ041.

&&

$$

SHORT TERM...Bowen
LONG TERM...Gimmestad
AVIATION...Bowen


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