Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 191847
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1147 AM MST Sun Feb 19 2017

.UPDATE...
Issued at 1130 AM MST Sun Feb 19 2017

There still is very little of no precipitation falling anywhere
in the CWA at this time. Satellite picture show the upper low
circulation near the four corners presently. I made some changes
to temperatures and winds based on actually conditions. I  will
leave the pops alone for now as the upper feature, although
weakening a bit, should still supply some synoptic scale vertical
motion.

&&

.SHORT TERM...(Today and tonight)
Issued at 343 AM MST Sun Feb 19 2017

Satellite shows upper low just west of Phoenix this morning, and
moving slowly northeast. Forward speed is expected to increase as
the low opens up slightly and tracks northeast into Colorado. Best
lift associated with the low weakens, but appears there should be
a decent deformation zone developing on the back side of this
feature somewhere across the northern/central Colorado mountains
by late afternoon and evening. That in combination with increasing
lapses rates, deep moisture, and cold advection, should bring a
period of moderate to heavy snow in the mountains. Initially, road
temps are warm and heaviest precipitation is expected to hold off
until dark and just after the big traffic rush out of ski
country. However, still potential for enough impact to warrant an
advisory. Will continue to monitor through the course of the day
as these events can be fickle. In any case, we did increase the
PoPs and snow amounts for the evening hours per factors mentioned
above and short range model guidance.

On the plains, gusty southerly winds will develop by late this
morning and afternoon as deep mixing and strong southerly pressure
gradient strengthen. This occurs as surface low pressure deepens in
northeast Colorado and moves northeast. Should see gusts reach
35-45 mph per max wind in the mixed layer, with the strongest
gusts from the Palmer Divide east/northeast across the plains.
Those winds will then switch northwesterly but remain gusty behind
the passage of a cold front this evening. Enough lift to warrant
a few showers, too. Probably quite a bit of virga initially with
a little better chance of rain reaching the ground in the evening
as column cools and moistens with frontal passage. Slight chance
of a thunderstorm but odds look rather small with limited CAPE
under 200 j/kg.

Finally, there is a period of reverse shear and possibly a mean
state critical layer 03Z-06Z tonight. That would likely bring a
period of stronger downslope winds associated with deflected
mountain wave energy down the Front Range. Have increased winds
for this period with gusts in excess of 50 mph likely in/near the
Front Range Foothills.

.LONG TERM...(Monday through Saturday)
Issued at 343 AM MST Sun Feb 19 2017

Drier air in wnw flow aloft will spread across the area on Mon with
only a slight chc of -shsn in the morning in the mtns.  Winds will
be gusty at times over the higher terrain and across the plains nr
the WY-NE border area.  850-700 mb temps don`t change much on Mon so
aftn highs will be in the lower to mid 60s across nern CO.

For Mon night into Tue the flow aloft becomes more wly.  There is
some moisture embedded in the flow which could bring a a chc of
-shsn in the mtns mainly nr the WY border. East of the mtns a sfc
lee trough will become better defined with downslope flow. As a
result will see warmer temps with aftn highs in the lower to mid
70s across nern CO.

On Wed the flow aloft will become more wsw.  The GFS shows some
increase in moisture by aftn while the ECMWF is drier.  For now will
trend towards the drier ECMWF and keep pops mostly in the slight chc
category in the mtns.  At lower elevations sfc low pres will
intensify over ern CO.  The ECMWF has this low over sern CO which
allows for a wk fnt to move across nern CO during the day.  The GFS
does not have this fnt affecting nern CO until late in the aftn as
it has downslope wly flow across most of the plains.  At this point
will keep hghs in the 65 to 70 degree range across the plains but it
could be cooler if the ECMWF verifies.

By Thu an upper level trough will move across the area as sfc low
pres intensifies fm sern CO into swrn KS. QG fields show
favorable ascent across the area during the day with decent
moisture in the mtns which will bring a good chc of snow. At lower
elevations there will be a surge of colder air moving across nern
CO late in the aftn or by early evening. The GFS shows decent
upslope flow while the ECMWF has a more nly component. At this
point will trend pops higher across nern CO for Thu aftn into Thu
evening. Highs on Thu will be colder across the plains with
readings ranging fm the mid to upper 30`s nr the Wy border with
lower to mid 50s across far srn area. Readings will likely peak in
the morning and then drop thru the aftn hours.

On Fri the upper level trough moves east of the area with zonal flow
aloft.  Cross-sections show some moisture embedded in the flow which
may bring some orographic snow to the mtns.  At lower elevations
there could be a chc of light snow early in the morning across the
far nern plains otherwise it will be dry.  Aftn highs across nern CO
will only be in the 30s.

For Fri night the ECMWF and GFS have another surge of cooler air
moving across the plains as a disturbance moves across in wly flow
aloft. This feature will bring another chc of snow to the mtns and
could allow for a chc of light snow across portions of nern CO.

On Sat the flow aloft will remain wly with some moisture embedded in
the flow so will keep in some low pops in the mtns.  Across nern CO
it will be dry with highs in the upper 30s to lower 40s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1130 AM MST Sun Feb 19 2017

Models keep showing decent southerly winds to kick in at DIA early
this afternoon. I took out any mention of precipitation in the
take. There should be no ceiling issues at DIA.

&&

.FIRE WEATHER...
Issued at 343 AM MST Sun Feb 19 2017

Brisk southerly winds on the plains and Palmer Divide will bring
elevated fire danger today. Humidities do not reach critical
levels and should stay above 20%, but the risk of fire spread in
grasslands and fine fuels will still exist. Open burning should be
avoided given the strong winds.

Fire Danger will be elevated Mon through Wed across northeast CO,
Palmer Divide and Foothills below 8000 feet due to much above
normal temperatures and low humidity levels. The strongest winds
on Monday will be in the nrn Foothills and across the plains nr
the Wyoming...Nebraska border. Gusty winds may become more
widespread across the entire for Tue and Wed.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...RJK
SHORT TERM...Barjenbruch
LONG TERM...RPK
AVIATION...RJK
FIRE WEATHER...RJK/RPK


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