National Weather Service Forecast Discussion

000
FXUS65 KBOU 181635
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1035 AM MDT Sat Sep 18 2021

.UPDATE...
Issued at 1000 AM MDT Sat Sep 18 2021

The forecast remains mostly on track this morning as high
temperatures will return to the 90s across much of the plains. The
only change that was made was to delay the time of the best PoPs
this evening. Latest guidance shows the best forcing ahead of a
shortwave will come between 9pm to midnight so the highest PoPs
are at that time. The mountains will be favored for precipitation
with the downslope flow keeping the plains mostly dry.

&&

.SHORT TERM...(Today and tonight)
Issued at 416 AM MDT Sat Sep 18 2021

Upper ridge of high pressure over Colorado this morning but will
be shifting east this afternoon and tonight in advance of weak
trof and increasing southwest flow. Water vapor imagery showing
this weak trof over the desert southwest with some hints of
moisture streaming north and northeast over Utah and Arizona.
Satellite imagery also showing low clouds across closer to our
eastern border, mainly east of a Limon to Sedgwick line. Clouds
expected to shift east of our area by mid morning hours.

Good low level warming expected today as 700mb temperatures climb
to around +16c at Denver and this will support high temperatures
around 90 over the plain. Forecast soundings hinting at some mid
level moisture moving in later this afternoon/evening with
inverted-v profile towards evening. Could see some very weak
showers and gusty winds over mountains and adjacent plains with
better chance this evening for scattered showers and a few
thunderstorms.

.LONG TERM...(Sunday through Friday)
Issued at 416 AM MDT Sat Sep 18 2021

Sunday, temperatures will be slightly cooler but still well above
normal. Northeast Colorado should remain mostly clear and dry
through the afternoon with just isolated showers and storms over
the high terrain, bringing very little to no precipitation.

Precipitation will increase through the evening as a trough
starts to move over the central and northern Rockies. Expect
breezy conditions in the high terrain late Sunday and early Monday
as the trough passes, with gusts up to around 40 mph. QG fields
show generally weak subsidence turning to moderate ascent late
Sunday night through early Monday morning, then a return to weak
to moderate subsidence by Monday evening. The trough will also
push a cold front across northeast Colorado early Monday, which
will bring gusty northerly winds and high temperatures Monday
down to the upper 60s and lower 70s across the plains and 40s and
50s in the high country. This cold air will bring the snow level
down quickly, to minimums around 8000 to 8500 ft MSL across the
area on Monday. Light snowfall is possible for the peaks of the
Front Range mountains, and there may even be some flurries in the
northern mountain valleys. The trough is expected to progress
quickly, with Northeast Colorado behind the axis already by Monday
evening. This means any impacts will likely be brief and limited.
Continue to expected scattered showers and light precipitation
across the much of the area Monday. The trough will be exiting
east by Tuesday morning and skies will clear, though highs will
remain well below normal Tuesday.

There is still much less certainty in the synoptic situation
behind the trough. Continue to expect mild ridging with warmer and
drier conditions Wednesday and Thursday. The GFS and Canadian are
coming to some agreement about another shortwave trough
approaching from the Pacific Northwest while ECM continues to show
a cutoff low over or just off the west coast, which imply very
different outcomes for Northeast Colorado in the latter part of
the week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1000 AM MDT Sat Sep 18 2021

VFR through the TAF period. Some increase in mid level moisture
by late in the day and through the evening with possibly some
virga towards evening. Latest guidance shows a weak DCVZ will keep
winds more easterly than originally expected. Drainage tonight.

&&

.FIRE WEATHER...
Issued at 416 AM MDT Sat Sep 18 2021

Expect elevated fire danger again over the mountain high valleys
this afternoon but conditions are marginal again for red flag
warning. Could see a few hours of gusts 20 to 30 mph with humidity
levels 15-20 percent. Another area of elevated fire danger over
the eastern plains with increasing southerly winds this
afternoon and dropping dewpoints.

Fire danger will be mitigated by higher humidity Sunday through
Tuesday. Dry conditions set back in mid-week but the fire danger
should be mitigated by generally lighter winds. However, there
may be elevated fire danger in the northern mountain valleys and
on the northern plains Wednesday and Thursday, as wind gusts
approach 25 mph in the afternoon coincident with minimum humidity
near or below 15 percent.

&&

.HYDROLOGY...
Issued at 416 AM MDT Sat Sep 18 2021

Isolated to scattered coverage of showers developing this evening
but any rainfall will be light with very low threat of flash
flooding.

The flash flood threat will remain very low through Sunday
afternoon as more isolated showers bring little, if any
precipitation. Precipitation will remain light as coverage
increases Sunday evening through Monday, and the threat will
remain low. Dry conditions will then set back in Tuesday.

&&

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

$$

UPDATE...Danielson
SHORT TERM...Entrekin
LONG TERM...EJD
AVIATION...Danielson
FIRE WEATHER...Entrekin/EJD
HYDROLOGY...Entrekin/EJD

NWS BOU Office Area Forecast Discussion