Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 151600

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1000 AM MDT Thu Mar 15 2018

Issued at 1000 AM MDT Thu Mar 15 2018

Strong early spring storm to race across the region later today and
tonight. Rain and snow has moved into the western Colorado already
this morning. Precipitation will increase and spread eastward
through the day as the negatively tilt upper level trough moves into
the Central Rockies. By 12Z Friday, an upper level and surface low
is expected to be centered over northwest Kansas. Going forecast of
5-10 inches of snowfall for the mountains appears on track. Will
increase pops for most of the area, especially northern parts
where precipitation appears more certain.

Biggest uncertainty with this storm is over the northeast plains. An
area of precipitation is expected to form on the backside of the
low. The strong northwest winds will help to pull in cooler air.
Most models indicate it should get cold enough for this
precipitation to change to snow after midnight. If there is a
quick change over to snow up to 6 inches will be possible. This
combined with northwest winds gusting to 50 mph may produce
localized blizzard conditions. Leaning towards issuing a Winter
Weather Advisory for the northeast plains. Will take a look at the
least 12Z GFS and GEM and then make the decision in the next hour
or two.


.SHORT TERM...(Today and tonight)
Issued at 258 AM MDT Thu Mar 15 2018

Active and complicated weather day coming up across Northern
Colorado with the anticipation of an intensifying storm system
across far east central Colorado tonight and into northwest Kansas
by Friday morning. Main threats will initially be critical fire
weather concerns over Lincoln county this afternoon (see fire
weather discussion below), Snow and winds developing over the
mountains, and potential for high winds over Front Range foothills
later tonight and early Friday.

As the upper trof approaches Colorado, showers and deepening
moisture expected over the mountains during the day time with a
noticeable uptick in areal coverage of showers this afternoon. QG
fields showing increasing ascent with modest numbers of -20 to
-40mb/hr over a good swath of northern Colorado this afternoon and through
 tonight. Surface low expected to intensify somewhere over
 Northern Lincoln and Washington counties by this evening with the
 brunt of the showers to the North of the low and developing
 downslope flow over the Front Range. Despite the downslope flow,
 the NAM continues to generate high numbers of QPF north of Denver
 and over Larimer and Weld counties. Seems that this is overdone
 considering the fight with the downslope flow and prefer the more
 realistic GFS solution. Will still have likely pops over the
 plains this evening, but then transition with best chance of
 showers over the far northeast plains. Temperatures will remain
 warm enough for rain and then a possible mix to snow later

As for the mountains have opted to go with a winter weather
advisory for this afternoon and continue through early Friday
morning. Could certainly see a burst of heavier snow this
afternoon/evening with a convective element and evening an
isolated thunderstorm. Snow will transition to a more orographic
enhanced snowfall as strong northwest flow develops behind the
low along with cold advection and increasing flow of 20-30kt at
700mb. Overall, looks to be a 5-10 inch snowfall for the higher
mountains. Certainly some variation in snowfall amounts given
locations of the heavier convective elements.

The other issue is the potential for high winds later tonight and
through Friday morning. Cross sections showing 40-50kt cross
barrier flow, developing inversion at 750 mb and critical level
may result in potential for high winds in the foothills. Will
issue a high wind watch for this potential.

.LONG TERM...(Friday through Wednesday)
Issued at 258 AM MDT Thu Mar 15 2018

An upper level low will intensify over nwrn KS by 12z Fri and then
move into ern NE by late Fri aftn.  With favorable QG ascent still
over nern CO at 12z will see rain continue over the far nern plains
in the morning with wet snow possible on the back edge of the pcpn
band.  Further west stg downslope flow will be in place so pcpn
chances will be basically zero along the front range urban
corridor. In the mtns, cross-sections show a gradual decrease in
moisture during the morning hours so snow potential should
diminish by mid to late morning.

Meanwhile cross-sections show some potential for high winds in the
foothills Friday morning as a mtn wave develops and component along
winds increase to 50-55 kts. Thus will continue a high wind watch
until 18z. In addition will see gusty winds across the rest of
nern Co as well, however, gusts should stay blo high wind
criteria. As for highs readings across the plains will range from
the 40`s over the far nern corner with upper 50s to lower 60s
around the Denver area.

For Fri night into Sat an upper level ridge will build into the area
bringing dry conditions along with warmer temperatures.  By Sat
night into Sun an upper level trough over the wrn US will begin to
move eastward into the region.  Both the ECMWF and GFS show this
trough splitting as one piece of energy moves across the nrn Rockies
while a 2nd piece moves across CO with a closed low eventually
forming over sern CO.  In addition a cold front will move across
nern CO by aftn.  QG fields show favorable mid lvl ascent on Sun
with decent lapse rates.  Thus should see another good chc of snow
in the mtns.  Across nern CO there should be a chc of pcpn with the
greatest threat over the Palmer Divide if the low lvl flow becomes
northerly as shown by latest data.

By Mon the weather system will be east of the area with WNW flow
aloft.  There is some moisture embedded in the flow so will keep in
a chc of -shsn in the mtns with dry conditions elsewhere.  Highs on
Mon will be a few degrees blo normal across nern CO.   For Tue the
ECMWF has a weak upper level trough moving across the area while the
GFS does not show this feature.  At this point not sure what to
believe so will just mention a slight chc of snow in the mtns.  On
Wed a flat upper level ridge will build into the region with dry
conditions and warmer temperatures.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1000 AM MDT Thu Mar 15 2018

MVFR conditions with showers at times from 21Z to 06Z.

As surface low develops south and east of the terminals expect
winds to shift northwest and then northeast this afternoon.
Airmass to become marginally unstable along with increasing
moisture from developing storm system. Best chance of showers will
be from late afternoon through the early evening before strong
downslope flow begins to dry out low levels of the atmosphere.


Issued at 258 AM MDT Thu Mar 15 2018

Lowering humidities and gusty southerly winds will develop over
Lincoln county this afternoon and continue through early evening
ahead of the developing storm system. will be continuing the Red
flag warning for fire weather zones 246 and 247.

Fire danger will remain elevated both Friday and Saturday across the
plains especially from Denver to Limon southward. Gusty winds and
low humidity levels are expected both afternoons.  Fire danger will
decrease on Sunday due to cooler temperatures and higher humidity.


Red Flag Warning until 7 PM MDT this evening for COZ246-247.

High Wind Watch from late tonight through Friday morning for

Winter Weather Advisory until 9 AM MDT Friday for COZ031-033-034.



SHORT TERM...Entrekin
FIRE WEATHER...Entrekin/RPK is the U.S. government's official web portal to all federal, state and local government web resources and services.