Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 181724
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1024 AM MST Sun Feb 18 2018

.UPDATE...
Issued at 1024 AM MST Sun Feb 18 2018

Gusty winds are occurring in the foothills, but only above warning
criteria at one or tow locations. Elsewhere, gusts are only in the
35 to 50 MPH range. Models continue showing a gradual decrease in
winds through the rest of the day, so the threat of damaging winds
appears to be over. Will cancel the High Wind Warning, which was
set to expire here in another half hour. Otherwise the forecast
for today remains as is. Temperatures should continue rising as
humidity levels drop across the plains. Red Flag Warning will
remain in place for the elevated fire danger over the Palmer
Divide.

&&

.SHORT TERM...(Today and tonight)
Issued at 445 AM MST Sun Feb 18 2018

A hodge podge of weather to deal during the with next 24 hour
starting with the high wind potential for the Front Range mtns and
foothills. High winds have not yet materialized on a large scale
yet, although the usual spots up around timberline such as
Berthoud Pass have recorded gusts in excess of 70 mph. Overall
sustain speeds and gusts have remained under 50 mph. Strongest
sustained winds have been observed over southwest sections of the
CWA such as across South Park and the Teryall Mtns in Park County
and southern Front Range foothills in Jefferson and Douglas
counties where gusts have been in the 30-50 mph range past
several hours. These gusty winds have kept temperatures up and
produced large temp-dewpt spreads down there. A similar situation
existed for much of the night in Middle Park around Kremmling
where gusty southwest winds of 15-30 mph have kept temps near
freezing - quite unusual for nighttime this time of year.

Indicators such as falling lee slope pressure, increasing west-
southwest mtn top flow and a strengthening mid-level inversion
still point to the development of strong and gusty Chinook winds
in the ridge tops and east slopes of the Front Range before
sunrise. Still believe winds many locales within the current high
wind warning will reach criteria. Since we`re dealing with a
Chinook wind set-up, wind speeds will be highly erratic. Warning
goes to 8 AM this morning, but HiRes models and the approach of
jet speed max from the north requires that I extend the warning to
late morning (18z). Update to the warning out shortly. Next, strong
gusty swly winds of 20-35 mph, very low RH and unseasonably warm
temperatures expected today will also require adding eastern
Douglas and western Elbert Counties (zone 41) to the Red Flag
Warning already issued for eastern Elbert and Lincoln Counties
(zones 46/47). It may be necessary to begin the warning earlier
should thresholds be reached earlier than expected. Min RH values
already getting close.

Lastly, the Winter Storm Watch for the Park and Gore Ranges (zone
31) is slated to begin at 9 PM MST this evening. Latest model
guidance would suggest a later start to accumulating snowfall with
a high snow level because of the warm swly flow. After midnight
decent jet forcing (CSI), cooling aloft and increasing moisture
should have little problem generating bands of moderate to
heavy snowfall over these ranges. Snowfall in nearby valley
locations should hold off until after midnight because of warm
temps.

If that weren`t enough, a strong cold is still progged to slip
south across northeast Colorado late tonight. Latest model
guidance points to an ETA in the Denver area between 3 and 4 AM
MST. With its passage should see a fairly abrupt shift to a cold
and moist north-northwest winds of 15-25 mph. This initial surge
appears shallow, and as a result could only see areas of light
snow and light freezing drizzle forming before morning. Best
chances for this mix along the I-25 corridor where the saturated
layer will be thickest banked up against the fthls. Any snow and
ice accumulation before 6 AM MST will be minor, but surfaces could
acquire a thin glaze of ice.


.LONG TERM...(Monday through Saturday)
Issued at 445 AM MST Sun Feb 18 2018

A chance in the weather on Monday and Monday night as next upper
level disturbance effects Colorado with colder temperatures and
some accumulating snowfall. Surface cold front will have pushed
through much of northeast Colorado by Monday morning with stratus
deck developing and the potential for flurries and/or freezing
drizzle with shallow moisture depth. The best chance of
accumulating snowfall will be Monday night as the 120kt jet streak
traverses across Northern Colorado with potential with banded
snowfall and enhanced northeast surface winds. Still looks like a
light snowfall event on the plains with anywhere from 1 to 4
inches of snow, highest amounts under the banded snowfall. The
mountain regions look to be more in advisory range. Will maintain
the winter storm watch for now. Looks like a lull in the moisture
Monday morning and does not get going again until midday and afternoon.

Improving conditions on Tuesday as main energy with the trof moves
into the northern high plains with a drier and more subsident
airmass moving into Colorado. This will set the stage with warmer
temperatures for Wednesday and Thursday. The next weather maker
will bring the next chance of snow into Colorado late Thursday and
Friday time frame.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1024 AM MST Sun Feb 18 2018

Winds are expected to become more west to southwesterly through
this afternoon. Gusts up to 30 MPH will be possible. Winds will
diminish in the evening and then become northeasterly later
tonight with the arrival of the shallow cold front. No ceiling or
visibility problems are expected until late tonight when IFR
conditions in fog and possibly some freezing drizzle will develop.

&&

.FIRE WEATHER...
Issued at 445 AM MST Sun Feb 18 2018

Critical high fire danger conditions likely today from late this
morning through late this afternoon for areas along the Palmer
Divide in east central Colorado. Fire weather zones 246 and 247
are now under a Red Flag Warning which starts at 1100 MST today.
Because of warm, gusty southwest winds and very low relative
humidities, fireweather zone 241 (eastern Douglas-western Elbert
counties) will be added to this warning. Warning ends at 5 pm MST
this afternoon.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 5 PM MST this afternoon for COZ241-246-
247.

Winter Storm Watch from 9 PM MST this evening through late
Monday night for COZ031.

&&

$$

UPDATE...Dankers
SHORT TERM...Baker
LONG TERM...Entrekin
AVIATION...Dankers
FIRE WEATHER...Baker


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