Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 210310

Area Forecast Discussion
National Weather Service Denver/Boulder CO
910 PM MDT Mon Mar 20 2017

Issued at 910 PM MDT Mon Mar 20 2017

No need to make any changes to the forecast at this time. High
pressure building in from the northeast has spread easterly winds
across the plains and back into the Denver area. A short wave
aloft moving over from the west has produced high based shower
activity over the northeast plains, but surface dew points are so
low that precipitation has failed to reach the ground up to this
point. Should continue seeing east-northeast winds overnight
across the plains as shower activity gradually wanes.


.SHORT TERM...(This evening through Tuesday)
Issued at 213 PM MDT Mon Mar 20 2017

Water vapor satellite imagery showing a plume of moisture
stretching from Colorado southwest into Arizona. This is expected
to keep mostly cloudy skies over the area tonight. Mid level lapse
rates of 7-9 C/KM will result in a few showers. Low levels to
remain dry through the evening. Expect most of the rainfall will
evaporate before reaching the surface. Over the northeast plains,
a cold front will back southwest across the area tonight. This
will bring northeast winds and cooler overnight lows.

For Tuesday, cooler air will settle over the area behind the cold
front. Due to easterly upslope winds and cloud cover, will keep
temperatures a few degrees cooler than what most of the models
show. Mid level moisture will continue to stream across Colorado.
This combined with the steep lapse rates should produce more
afternoon showers. Low levels will remain dry and limit the amount
of precipitation reaching the ground.

.LONG TERM...(Tuesday night through Monday)
Issued at 213 PM MDT Mon Mar 20 2017

Storm off the coast of CA will bring moisture to the region later
this week.

For Tuesday night into Wednesday the upper ridge pattern continues
with increasing SW flow. Moisture embedded in the flow will help
to bring a slight chance of precipitation to the mountains on
Wednesday. Precip will most likely be in the form of rain and
rain/snow mix given 700 mb temperatures and accumulation will be
little to none. During the day Wednesday upper SW flow will
strengthen with a deepening surface low over the front range
foothills. Increasing pressure towards the eastern plains will
help to increase the pressure gradient and bring strong southerly
winds for Wednesday afternoon on the plains. Temperatures will
continue to be above normal with highs in the 70s.

For Wednesday night into Thursday the upper level trough will move
just west of the Great Basin with strong SSW flow aloft. QG fields
increase which will help to provide a better chance for some snow
development in the mountains into thursday. On the surface the low
pressure will deepen over the Lincoln county area and possibly
west that will help to bring strong winds from the south that will
combine with a frontal push from the north aiding in the potential
for afternoon convection. Model sounding show a dry lower level
further south that would result mainly in gusty winds and virga
but with increasing moisture from the north could have some
precipitation and thunder for Thursday afternoon. Temperatures
will be slightly cooler with highs in the 60s. Initial warming
with winds from the south will give way to the cooler air from the
north and a quick drop in temperatures by Thursday evening will
be possible ahead of the trough.

By Friday morning both the EC and GFS show the upper closed low
over the southern border of CO. By 18z the low center will track
to the NE according to the EC with less of a northerly shift for
the GFS. Both solutions at this time will result in a very strong
push from the North that will bring abundant moisture to the
plains and mountains. For the higher terrain the synoptic set-up
isn`t ideal for a major snow maker but possibly 5 to 10 inches
over the course of the event with blowing snow. Over the plains
the current set-up could result in a high impact event during the
day Friday. The combination of moisture with QG ascent values up
to -50 will help to increase the chance of rain changing over to
snow. The area that would see the greatest impact and snow
accumulation would be further south over the Palmer Divide and
south of I-70. Further north will be a battle with rain and a
rain/snow mix. With the QG and cooling I do expect conditions to
changeover during the day Friday...albeit slushy and wet snow. The
snow mixed with strong winds will cause hazardous conditions on
the plains by Friday afternoon and evening. A highlight may be
needed but will have to see how the system progresses over the
next few days.

The system will quickly exit by Friday night into Saturday.
Behind it an upper ridge will build in across CO as the next
system moves onshore over the Great Basin. Temperatures Friday
will be in the 40s and 50s with a gradual warm-up on Saturday.
The active pattern continues for Sun and Mon with another system
moving into the region.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 910 PM MDT Mon Mar 20 2017

Easterly and northeasterly winds should continue much of the night
as high pressure builds into Colorado from the northern plains.
Elevated showers over the plains will continue a few more hours
and then dissipate. Very little measurable precipitation is
expected to the dry air present at the lower levels. Tomorrow will
see southeasterly winds across the plains, and a possibility of
showers developing in the afternoon. Ceilings should remain above
6000 feet AGL.


Issued at 508 PM MDT Mon Mar 20 2017

Red Flag warning has been cancelled early this evening since
humidities were beginning to improve in the foothills, and wind
had also decreased. Conditions will continue to improve through
the course of the evening.

It will be cooler with higher humidities on Tuesday. Gusty
southeast winds are expected on the eastern plains. However,
relative humidity values will be much higher, 30 to 40 percent, so
a Red Flag Warning will not be needed.

Fire danger will increase in advance of the cold front on
Thursday. Dry, warm, and strong southwesterly flow ahead of the
front may lead to critical conditions from Park county and the
southern Front Range Foothills eastward across the Palmer Divide
area and adjacent plains.




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