Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 170949

Area Forecast Discussion
National Weather Service Denver/Boulder CO
349 AM MDT Mon Apr 17 2017

.SHORT TERM...(Today and tonight)
Issued at 319 AM MDT Mon Apr 17 2017

The upper level ridge axis will shift to the east this morning
with a southwesterly flow aloft over the region today and tonight.
An upper level trough axis is progged to pass well to the north of
Colorado this afternoon. In the mountains, some high level
moisture will move over the area, but too dry in the lower levels
to support thunderstorms. Temperatures will continue to climb in
the afternoon. Mid level warm air advection through the afternoon,
with some areas climbing above 50 over 10 thousand feet. Over the
urban corridor and northeast plains, plenty of low clouds and
patchy fog through the mid morning hours especially to north and
east of Denver. A dry line will develop this afternoon, which at
this time looks like it will be somewhere along a line from around
Sterling to Akron by midday. Forecast soundings show the potential
for strong psbl severe storms, with CAPES around 1500 j/kg east of
this dry line. Overall coverage in the 10-20 percent range, with
SPC including the area in a marginal risk for severe thunderstorms
this aftn. It all depends on how fast the boundary layer mixes
out but could see a storm there produce wind gusts to 50 mph and
hail up to nickel size. Along the Urban Corridor the fire danger
will be elevated with relative humidities possibly dropping into
the teens from Denver southward, but winds generally in the
10-20 mph range. For tonight, some lingering convection over the
far eastern plains this evening, but dry elsewhere with partial
clearing overnight.

.LONG TERM...(Tuesday through Sunday)
Issued at 319 AM MDT Mon Apr 17 2017

An upper level ridge over the central part of the country and a
trough off the west coast will produce a southwest flow aloft over
Colorado. Tuesday is expected to be dry and mild ahead of a short
wave trough embedded in the southwest flow. Models show a surface
low forming over the Denver area or near by plains. Gusty west winds
may form behind it and increase the fire danger along the Front
Range. As the short wave approaches the region, moisture will
increase. The main wave and best lift is expected to move across
Wyoming Tuesday night. There will be a chance for rain and snow in
the mountains and rain showers over the far northern areas Tuesday
night. Pacific moisture and orographic lift is expected to keep snow
going over the mountains into Wednesday afternoon. For the Front
Range and eastern plains, a cold front will drop south early
Wednesday bringing cooler temperatures and gusty northerly winds. By
Wednesday evening, subsidence and drier air will end precipitation

An elongated trough along the Pacific coast Thursday morning will
move over the Great Basin by Thursday evening. Models still trying
to resolve the details with this system as it moves into the Central
Rockies. The latest trends have been to shift the storm track north
and not close off the low until it reaches eastern Colorado or
Kansas. Still should be enough moist and lift with this system for
precipitation for most locations. Showers and a few storms will be
possible Thursday afternoon. Precipitation is expected to increase
Thursday night with widespread precipitation possible for Friday.
Will continue with the high chance and likely pops for Thursday
night and Friday. Given that every run is still changing a fair
amount, there is still uncertainty on how much and when
precipitation will fall. Still appears snow levels start off high
Thursday night and lower to around 6000 feet by Friday evening. At
this time, if significant snow falls it would occur over the
mountains and higher foothills. The Urban Corridor and eastern
plains still look to warm for snow with a chance at a change over
late in the storm.

Models in decent agreement showing that this system will be east of
the area by Saturday morning with a cool north/northwest flow aloft
over the area. Still little precipitation in the models and will
have a slight chance for Saturday. Upper level ridging should bring
all precipitation to an end late Saturday. This ridging is then
expected to bring dry and mild conditions for Sunday.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 319 AM MDT Mon Apr 17 2017

Latest LAPS observations show the circulation centered over
southeastern Weld County early this morning. The HRRR has it a
little further north of this location through 15z. If this pans
out, then the stratus/fog progged to wrap around this center
should stay to the north of KDEN this morning. At this point do
not planning on introducing the IFR/MVFR restrictions at KDEN but
may mention vcfg 12-15z there. If this feature shifts south then
the tables will turn and the low cigs/vsbys would have to be
addressed. Overall confidence in the moderate category that the
stratus/fog stays to the north of KDEN. Otherwise, VFR conditions
expected at the terminals over the next 24 hrs. Northwest winds
should transition to south/southwesterly after 15z and continue
that way through this evening, then going to drainage overnight.




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