Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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759
FXUS65 KBOU 200316
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
816 PM MST Mon Feb 19 2018

.UPDATE...
Issued at 813 PM MST Mon Feb 19 2018

Areas of banded snow continues along the urban corridor and
appears to be consolidating into one general area with snowfall
rates up to 2 inches per hour in some areas. Thus have decided to
issue a short fuse advisory thru midnight in the Denver and
Boulder areas to Greeley.  This activity is supposed to gradually
move east by 10 pm so we shall see if that happens or not.


UPDATE Issued at 705 PM MST Mon Feb 19 2018

Will continue to see areas of banded snow for the next 2 to 3
hours. The heaviest snow has been generally along and northwest of
a Boulder to Greeley line. Meanwhile additional snow has begin to
develop over srn Lincoln county and will spread northeast the
rest of this evening. Snowfall in the heavier bands has been from
1 to 2 inches per hour. So far most of the heaviest snow has been
in the advisory areas except areas of ern Boulder county where up
to 6 inches may fall before it ends. Hi res data continues to show
most of the snow ending by 10 pm along the front range and around
1 am or so over the far ern plains.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 310 PM MST Mon Feb 19 2018

Southwesterly flow aloft continues ahead of the strong upper
trough over the Great Basin. The system was a little slower than
expected today, so it took awhile to see the heavier snow over the
mountains, but we are headed into the heaviest snowfall period now
through the early evening. Instability ahead of the system has
allowed for a few thunderstorms to form over western and southern
Colorado, and won`t discount any forming over the northern and
central mountains this afternoon as CAPE values of around 200 J/kg
have been modeled. As the 120 kt jet max approaches central
Colorado by early this evening, QG upward motion will be maxing
out as well as CSI banding potential. Models have kept this area
of best ingredients pretty consistent, over the central mountains
stretched northeast to over the northern urban corridor. Some
slight trend south may allow for slightly higher amounts this
afternoon and evening over the plains. Still thinking the Advisory
area for zone 38 will do just fine as amounts should decrease
further south. Still looking for total amounts of 4 to 8 inches
over the mountains and northern foothills, with pockets of closer
to a foot over the high mountains mainly north of I70, and 3 to 6
inches over the northern urban corridor. Elsewhere on the plains
and southern foothills, amounts of less than 3 inches will likely
occur. Did have to bump up the far eastern plains as some
instability and lingering moisture out there will likely cause a
few hours this evening of slightly heavier snowfall.

Downward QG pushes in after midnight to start to shut down the
snowfall over most areas, however some light shallow upslope may
keep some light snow near the base of the foothills. Light snow
will continue over the mountains with orographic flow. After
today`s cold temperatures, additional cold advection from the
north will bring single digit or lower minimum temperatures
overnight.

Northeastern Colorado will be under the left entrance region of
the jet Tuesday, however surface high pressure will be sliding
down from the northern Great Plains as well to create light
upslope. Will continue to see cold temperatures, light upslope
flow and possible light snow showers and light orographic snow in
the mountains.

.LONG TERM...(Tuesday night through Monday)
Issued at 310 PM MST Mon Feb 19 2018

Our winter of persistent weather patterns continues. This week`s
pattern features strong upper ridge off the southeastern United
States, a broad upper trough over the western half of the
country, and a high amplitude ridge over the northeastern
Pacific. This basic pattern stays in place through Thursday
evening and then undergoes some changes through the weekend. By
the start of next week most of the country will be under a zonal
flow pattern. For Colorado, the upper trough will be anchored
over Nevada with persistent southwesterly flow aloft across the
state. Quasi-geostrophic diagnosis and QPF fields from the medium
range models show a mostly dry day on Wednesday and then another
round of rising motion and precipitation on Thursday. Mountain
areas will receive the most precipitation from this Thursday
event. At lower levels, high pressure over the northern plains
will continue pouring cool air into northeast Colorado.
Temperatures will remain much below normal through Wednesday with
only slight moderation Thursday and Friday. It will be Sunday or
Monday before temperatures make it back to normal values.

Over the weekend, the ECMWF and GFS show the main trough beginning
to move eastward as another trough develops over the Alaska
panhandle and begins it trek southward toward what is still the
longwave trough position over the southwestern United States. The
departing trough should produce another round of mountain
precipitation during the Saturday/Sunday time frame.

The prevailing southwesterly flow pattern is not particularly
favorable for producing heavy snowfall in the northern mountains,
so only light to moderate amounts are expected at this time. No
need for any highlights. Plains weather should be dry and cool
through the end of the week, as the southwesterly flow aloft will
tend to have a downslope component downstream from the mountains.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 738 PM MST Mon Feb 19 2018

Banded snowfall expect to impact terminals until 04-05z, then it
is expected to shift east of the Denver area, with decreasing
snowfall overnight. IFR cig/vsby restrictions under the heavier
bands of snowfall with 1-2 inch/hr snowfall rates under the 30 dbz
bands. MVFR cigs expected to prevail after 05z with localized IFR
restrictions possible with any lingering snow showers. Ceiling
will improve by late Tuesday morning but still ILS restrictions
with bkn-ovc cigs 040-050 kft agl through Tuesday afternoon. East
to northeast surface winds may still shift to a north-
northwesterly component after 05z, then decrease and become
easterly Tuesday morning after 10-11Z.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 AM MST Tuesday for COZ030>035-
038.

Winter Weather Advisory until midnight MST tonight for COZ039-
040-043.

&&

$$

UPDATE...RPK
SHORT TERM...Kriederman
LONG TERM...Dankers
AVIATION...Cooper



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