Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 120301

Area Forecast Discussion
National Weather Service Denver/Boulder CO
901 PM MDT Fri Aug 11 2017

Issued at 858 PM MDT Fri Aug 11 2017

With only one main thunderstorm left in the forecast area, and
drier air filtering in behind, have decreased pops over the
forecast area. May still see a few showers over the mountains
through the rest of the evening, but very isolated.

Recent models have come in with less fog expected over the plains,
and due to less convective action over the plains compared to
yesterday, agree with their solutions. Will only have patchy fog
over the South Platte River valley and down over Lincoln County.


.SHORT TERM...(This afternoon through Saturday)
Issued at 333 PM MDT Fri Aug 11 2017

Areas of clouds across the plains earlier today and the presence
of a fair amount of low level moisture helped keep temperatures
cooler on the plains. A few showers have moved over the foothills,
especially in Jefferson County, but have not seen any showers on
the plains yet. LAPS analysis of CAPE and CIN shows 1200+ j/kg
over Weld County, but also 40-60 j/kg of CIN holding showers in
check. The CIN may still erode, allowing strong convection to
develop over the next couple hours. Also keeping an eye on
thunderstorms over southeast Wyoming which might produce outflow
boundaries that move across the border and begin initiating
convection. Will hold on to isolated thunderstorms over the
northern plains through this evening. Any showers that develop
should weaken and dissipate through the evening as it looks like a
weak upper level disturbance tracks across the state in the next
few hours.

Amounts of possible fog and stratus tomorrow morning will depend a
lot on how much rain falls this evening. The surface wind pattern
will be in place to help pool low level moisture in the South
Platte River valley overnight. If rain falls this evening, then
tomorrow could be a repeat of this morning. If it stays dry, the
chances for low clouds and fog will be reduced.

Saturday looks like a repeat of today as sub-tropical moisture
will continue moving over the state from the southwest and
moderate westerly flow aloft will continue. Daytime heating will
be sufficient to de-stabilize the airmass in the afternoon with
isolated-scattered thunderstorms developing.

.LONG TERM...(Saturday night through Thursday)
Issued at 333 PM MDT Fri Aug 11 2017

Upper level ridging will slowly build in over Central CONUS
through the extended with a deepening trough over the western
states. Subtropical moisture will get trapped under the ridge and
continue to bring an influx of moist air into Colorado aiding in
the formation of afternoon convection through the middle of next

For Saturday night into Sunday...remnants of a shortwave Saturday
afternoon will keep thunderstorms moving over the plains into the
late evening hours. Fast moving flow aloft under the upper jet
will help to keep storms moving so flooding is not
expected...however, storms could still produce strong gusty winds,
hail and brief moderate to heavy rain. By Sunday morning models
show moisture moving south out of Wyoming behind a weak front.
This could bring some lowered ceilings onto the plains for the
morning hours. Expect areas further west to be more scattered
with the deepening surface low helping to keep some westerly
downslope winds over the area. By the afternoon, a shortwave
will move West to East kicking off another round of afternoon
convection. Conditions appear slightly better with strong and
moist southerly flow over the plains with a building surface high
over western Kansas. This extra moisture source and strong
southerly flow will allow for higher instability and better shear.
Stronger storms with large hail, damaging winds and brief rain
will be possible. Temperatures will be very similar to Saturday
with highs in the lower 80s.

By Monday...the upper ridge builds in over the state with increase
Gulf moisture moving north into Colorado. The upper level flow
will turn more southwesterly ushering in warmer and moist flow.
This will help to build storms over the mountains with a slight
chance on the plains depending on direction of the surface flow.
Tuesday appears to be a good day for decent precipitation coverage
over the NE with an upper shortwave embedded in the SW flow and a
moist 700 mb profile. Heavy rainfall will be possible along with
hail and gusty winds. Models show increased drying by mid week as
flow turns more zonal and the moisture from the south is cut off.
Temperatures will gradually warm through the week with a chance of
90s by the weekend.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 858 PM MDT Fri Aug 11 2017

No more showers or thunderstorms are expected for the Denver area
airports, and skies will be clearing overall. Overnight, skies
will remain mostly clear, although some stratus and possible fog
may form in the South Platte River valley. A weak low is expected
to form, however moisture levels are less than last night, and at
this point the stratus and fog isn`t expected to move into the
area airports with enough southerly flow off the Palmer Divide. If
it does end up forming, it will likely wait until 4 AM,
dissipating by 9 AM. Saturday afternoon could see a round of
showers or thunderstorms roll across the airports between about 2
PM and 5 PM, more likely at BJC and APA.




SHORT TERM...Dankers
AVIATION...Kriederman is the U.S. government's official web portal to all federal, state and local government web resources and services.