Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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029
FXUS65 KBOU 270218
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
818 PM MDT Mon Jun 26 2017

.UPDATE...
Issued at 812 PM MDT Mon Jun 26 2017

Widely sct storms will continue over Park county and across srn
Lincoln county the next few hours. Outflow bndry has moved into
the Denver area fm the east however visbile imagery shows very
little cumulus developing along it. Thus doesn`t look like this
feature will produce any tstms.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 305 PM MDT Mon Jun 26 2017

Low level moisture is mixing out about as expected this afternoon.
Dew points are down into the 30s near the Front Range, with 40s
from Sterling to Akron. There is still more moisture further east,
though temperatures are also a little cooler. Still a slight
chance of getting some storms in southern Lincoln county and
possibly from Holyoke to the southeast corner of Washington
county. Also a possibility of some mountain storms but in a much
drier environment this should be quite weak/isolated if there is
any.

Low level moisture returns on southeasterly flow overnight. A
chance of some low clouds or fog south of Limon, but probably too
well mixed for any substantial fog. Warmer and drier air aloft
will move over this low level moisture on Tuesday. This will
provide a capping inversion, and more dry air to mix out the
moisture over the western two-thirds of our area. Once again there
will be less mixing over the eastern border areas, and there
could be enough moisture for strong to severe storms, though the
odds get better further east.

Forecast temperatures look reasonable. There may be enough high
cloud cover to hold back highs on Tuesday a little bit, in which
case our mid 90s highs across most of the plains may be a couple
degrees too warm.

.LONG TERM...(Tuesday night through Monday)
Issued at 305 PM MDT Mon Jun 26 2017

On Wednesday zonal flow will be over Colorado. A ~996mb surface
low pressure area moving east across the Central Plains will pull
a weak cold front south across our area early morning Wednesday.
Temperatures will be a little cooler behind the front, with high
temperatures 7-10 degrees cooler across the Plains. The mountains
will also get a slight break from the heat with 700 mb temps
cooling 2-3 degC compared to Tuesday, resulting in high temps
generally 4-7 degrees cooler. Despite FROPA the winds return west
at all levels during the daylight hours and rapidly scour out
available moisture. PWATs will be in the 0.25 to 0.40" range, and
our area should remain dry. With the dry conditions and gusty
winds in the 20 mph range and above, despite cooler temps, fire
weather will still be a concern across the valleys of Summit and
Grand counties, much like Tuesday. Given a red flag warning for
Tuesday will hold off on highlights for Wednesday but conditions
for fire growth will continue to be favorable.

On Thursday a broad trough over MT/ND shifts east, putting
Colorado in northwest flow which will continue into Saturday. The
low levels remain very dry on Thursday and rain chances are very
low mountains and Plains. The exception could be the far eastern
Plains where surface dewpoints after mixing should be in the mid
40s, supporting marginal instability. Thunderstorm chances are
similarly low but non-zero for the Plains and High Country on
Friday afternoon as low-level moisture starts to increase behind
another weak cold frontal passage, with easterly low-level flow
and PWATs increasing to near 0.5" across the I-25 urban corridor.
Temperatures will be right at seasonal normals Thursday with
highs mid 80s across the Plains and upper 60s to upper 70s in the
mountains, but 3-5 degrees cooler on Friday with the frontal
passage and a glancing blow of cooler 700 mb temps across far
northern Colorado.

This weekend the models differ on thunderstorm chances based on
the mid and upper level flow patterns. The GFS indicates a weak
short wave trough moving within the mean northwest flow Saturday
afternoon, which initiates robust convection over the high country
and moves it over the Plains. The ECMWF builds a ridge over
Colorado with scattered convection confined to the southern half.
Either solution favors a warming trend with seasonal high
temperatures in the mid 80s both days across the Plains, Sunday
warmer than Saturday. In terms of thunderstorm chances, given
model differences, low PoPs are prudent from the Continental
Divide east to Kansas Saturday afternoon. If the GFS is right
CAPE/Shear combinations Saturday and Sunday afternoons are
favorable for organized and strong convection. Low-level moisture
return with the GFS looks too optimistic so have not bought into
the GFS solution for this weekend...yet.

On Monday models generally agree a weak ridge approached Colorado
from the west with dry conditions and near normal temperatures.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 812 PM MDT Mon Jun 26 2017

Ely flow has developed behind an outflow bndry but winds
should become more sely by 10 pm and then sly by 06z.  Winds
will become more ssw by 09z.

&&

.FIRE WEATHER...
Issued at 305 PM MDT Mon Jun 26 2017

Warm temperatures, low humidities, and winds gusting to 30 mph
will create Red Flag conditions in the mountain valleys on Tuesday
afternoon. There may also be some isolated dry lightning over the
mountains. It will also be breezy with low humidities in and near
the east slopes of the mountains, where the fuels are not as dry.

On Wednesday conditions will be similar to Tuesday across the
valleys of Grand and Summit Counties. Slightly cooler temps and
less wind relative to Tuesday, but the combination of low RH and
wind around 20 mph with higher gusts will keep the risk of rapid
fire growth elevated. Given the Red Flag warning Tuesday
afternoon and slight better conditions expected Wednesday
afternoon, will hold off on a watch or warning.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 9 PM MDT Tuesday for COZ211-213-
214.

&&

$$

UPDATE...RPK
SHORT TERM...Gimmestad
LONG TERM...Schlatter
AVIATION...RPK
FIRE WEATHER...Gimmestad/Schlatter



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