Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
000
FXUS65 KBOU 211747
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1147 AM MDT Fri Apr 21 2017

.UPDATE...
Issued at 1147 AM MDT Fri Apr 21 2017

Temperatures continue to fall up north and now have cold enough
air for a few snowflakes even down into the Greeley area. Have
updated for stronger winds behind the surface cyclone, with gusts
around 35 mph. Even a few thunderstorms down south across the
Palmer Divide into Lincoln county. Showers should spread back
against the Front Range as long as we have some shallow upslope
component later today. Had earlier made adjustments to PoPs and
this trend looks reasonable for now. Bumped up additional snow
amounts a bit in the foothills based on potential convection and
heavier snow bursts with showers this afternoon into the evening.

UPDATE Issued at 813 AM MDT Fri Apr 21 2017

Temperatures had turned just cold enough for accumulating snow
right near the Wyoming border extending as far east as I-25 with
slush on roads. Main band of precipitation extends east across the
plains in the form of rain and will continue there for the rest of
the morning. Have updated forecast for drier conditions south of
Fort Collins to Denver and the Palmer Divide this morning, but
will increase PoPs this afternoon with convective showers likely
to develop. Conditions should improve overall in the mountains
with decreasing snow rates this morning, so will let advisory
expire there. Will have to watch the northern foothills especially
for more widespread heavier showers into the afternoon.

&&

.SHORT TERM...(Today and tonight)
Issued at 330 AM MDT Fri Apr 21 2017

Elongated upper trof extending from western Colorado through
western Wyoming and Montana. Water vapor imagery showing
circulation over North central Colorado with most intense precip
now occurring just ahead of the surface low/circulation and
moving over the urban corridor. Automated rain gauges showing .1
to .2 tenths of rain has it moves across the area. There is some
drying again behind this wave but there is still more scattered
showers still over Western Colorado. Latest RAP/HRRR seem to have
the precip bands handled fairly well with the most intense
rainfall this morning staying north and east of denver as the
surface low tracks east near the Denver area.

Despite a lack of ongoing snowfall in the mountains, the
orographic flow will improve as mountain top flow shifts more
northwest behind the trof. Looking at mountain cams, appears 2-4
inches of snow have already fallen with some snow/icy and slush on
roadways. Overall qpf amounts were way overdone with this storm
especially the GFS, as most places in Denver will only around a
quarter to a half of an inch but more East and north of Denver.
Southern sections of Denver and south over the Palmer Divide even
less rainfall due to unfavorable flow from the southeast for much
of the night.

Precip will become more scattered coverage in the showers by
afternoon as the low moves into kansas and diminishing QG ascent.
There is a secondary wave which will slide into Colorado tonight
which will keep the threat of showers for much of the night.

.LONG TERM...(Saturday through Thursday)
Issued at 330 AM MDT Fri Apr 21 2017

A 2nd piece on energy associated with an elongated upper level
trough will move east of the area by midday Sat.  Lingering moisture
combined with wk mid lvl ascent will allow for some showers in the
morning hours across the plains and higher terrain. Soundings
show there could be a mix of rain and snow down to 5500 ft. By
aftn will begin to see subsidence across the area with some drying
occurring. However with aftn heating and favorable lapse rates
still may see a chc of showers over the higher terrain with a
slight chc at lower elevations. As for highs, readings will be
from 55 to 60 across nern CO.

By Sun drier air will spread across the area in wsw flow aloft as a
sfc lee trough intensifies over nern CO.  This will lead to a dry
day with much warmer temps.  Aftn highs across the plains will rise
into the low to mid 70s.

For Sun night into Mon the flow aloft will become more wnw as a wk
mid lvl trough moves across WY.  There will be enough moisture in
the mtns for a slight chc of showers mainly north of I-70.  Across
nern CO it will be dry with gusty wnw winds on Mon.  Highs will
remain abv normal with readings in the upper 60s to lower 70s.

By Mon night into Tue wnw flow aloft will remain over the area.
Meanwhile placement of upper lvl jet would put nrn CO in favorable
left fnt quadrant for increasing vertical motion. In addition
with cross-sections showing increasing moisture and favorable
lapse rates this would lead to a good chc of pcpn in the mtns.
Over nern CO there may be a chc of showers as well as a wk cool
fnt moves across Mon night. Highs on Tue will drop into the lower
to mid 60s across the plains.

Looking ahead from Tue night into Wed the ECMWF and GFS have a broad
upper level trough developing over the nrn and cntrl Rockies with
quite a bit of moisture embedded in wly flow aloft.  Orographics and
lapse would be favorable for pcpn in the mtns which could be
enhanced by banding due to position of upper level jet.  Across nern
CO sely low lvl flow would allow for increasing moisture leading
to a chc of showers and a few tstms.

For Wed night into Thu the ECMWF and GFS show vastly different
solutions.  The ECMWF develops an upper level low over srn CO Wed
night which then moves into cntrl KS by late Thu.  Meanwhile the GFS
develops an upper level low over the Great Basin on Thu with stg ssw
flow aloft over the area.  Tonight`s solutions are quite a bit
different than what I saw last night. Thus confidence in any
solution by the middle part of next week is very low. At this
point will keep in a chc of pcpn across the entire area with temps
nr seasonal levels.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1147 AM MDT Fri Apr 21 2017

Main change was to lower the ceilings through the night with
expected shallow upslope component. MVFR and local IFR a high
probability. Still expect rain showers to redevelop this
afternoon, and could mix with a few flakes from time to time this
evening into the overnight hours. North winds gusting to around
30 knots will gradually decrease through late afternoon and then
turn more easterly around 10 knots 00Z-04Z.

&&

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

$$

UPDATE...Barjenbruch
SHORT TERM...Entrekin
LONG TERM...RPK
AVIATION...Barjenbruch



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.