Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 201534
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
934 AM MDT FRI MAY 20 2016

.UPDATE...
Issued at 926 AM MDT Fri May 20 2016

Low lying fog and stratus over the eastern portions of the
state...especially central Lincoln into eastern Washington are
continuing to diminish and will lift and clear by 10 am. Light
showers over the mountains have ended with CAPE values and strong
lapse rates still indicating potential for afternoon thunderstorm
development by late afternoon. Overall conditions are drier as
upper level ridging continues to build. The surface trough over
the lee side of the mountains will continue to usher in light SE
flow with warmer and drier SSW flow aloft. Like previous days this
will kill much of the convection possibility on the plains with
just a slight chance of storms closer to the foothills.
Temperatures will be well above normal today with highs close to
80s for the urban corridor.

&&

.SHORT TERM...(Today and tonight)
Issued at 300 AM MDT Fri May 20 2016

An upper level ridge will be over eastern Colorado today then
will gradually shift into western Kansas by late tonight. At the
surface...a lee side trough is oriented along the Interstate 25
corridor. South-southeast winds ahead of this trough is advecting
low level moisture north/northwest towards Weld County at this
time. The latest satellite shows an area of stratus over
Washington...Lincoln and eastern Elbert Counties early this
morning. The latest HRRR shows this moisture making its way into
Weld County through 12z this morning. Still expecting this
moisture to remain north of Denver so wl not include fog in the
grids for Denver at this time...but will need to watch the winds
closely this morning. If there is a wind shift to the
west/northwest then may need to add this to the grids. some
showers over northwestern Colorado as well and this is shifting
eastward into the our mtn zones. Wl keep isold pops in the high
country this morning. The mdls show showers and tstms increasing
in coverage over the high country on or after 18z today. nam12
forecast soundings show decent cape for denver by 21z...but not
sure where the dryline will be. it will likely be further north
and east this aftn which should lessen those values. this coupled
with mid level warming associated with the ridge may limit the
tstm potential over the northeast plains. slgt chc in the grids
this aftn/evening and this looks reasonable. Should see tstms die
off this evening...but mdls show a Denver cyclone and more
fog/stratus advecting back into the urban corridor late tonight.
Should see this moisture spread further west so will add
patchy/areas of fog for the urban corridor as well. extent of fog
will be greatest north of Interstate 70.

.LONG TERM...(Saturday through Thursday)
Issued at 300 AM MDT Fri May 20 2016

Saturday should start the day with widespread stratus and areas of
fog over the eastern plains of Colorado with moist south/southeast
flow and a Denver cyclone in place. Fog could wrap back as far as
Denver with a relatively well organized cyclone expected, so will
continue to monitor that. The stratus will delay the warming but
with daytime heating, mixing, and warm advection highs should
still be able to reach 80F or more across most of the plains.
Airmass will likely remain capped off on the plains due to the
morning stratus and slight warming aloft. However, if a storm was
able to pop through then it would likely become severe with CAPE
values of 2000-3000 j/kg. There is rather significant drying aloft
late in the day so even in the mountains where cap erodes
convective coverage should be limited.

By Sunday, a stronger short wave will rotate northeast out of the
base of the trough with a significant speed max lifting across
northwest Colorado and Wyoming. The synoptic scale lift and
cooling expected by late in the day will allow for more numerous
thunderstorm development. Potential for severe weather will depend
on exactly how far east low level moisture scours. Most models
push the moisture just to our east, but there is typically a
slight eastward bias so will mention some threat of severe storms
over the far eastern plains Sunday afternoon and early Sunday
evening.

For Monday into Tuesday, it appears we will be transitioning into
west/southwest flow aloft. There is potential for a couple short
waves to help spark convection, but overall there is some drying
noted so only a slight chance of afternoon/evening showers and
storms. Temperatures will settle to closer to normal levels.

By Wednesday and Thursday, the storm chances may increase again as
deep trough moves into the southwest U.S. This should allow low
level moisture and instability to gradually build across the
forecast area so will have a little better chance of showers
and storms for this period. Temperatures should remain near
normal.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 926 AM MDT Fri May 20 2016

VFR conditions are expected for the next 24 hours. Ceilings from
this morning will scatter out before convection this afternoon.
Mid level drying will help to prevent thunder at local airports
but a stray shower will be possible later this afternoon. Winds
will be light from the south before turning SE by the afternoon.
Current models are indicating increased boundary layer moisture by
early tomorrow that will help usher in fog in low lying areas
around KDEN.

&&

.BOU Watches/Warnings/Advisories...
None.
&&

$$

UPDATE...Bowen
SHORT TERM...Cooper
LONG TERM...Barjenbruch
AVIATION...Bowen



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