Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 270232

Area Forecast Discussion
National Weather Service Denver/Boulder CO
832 PM MDT FRI AUG 26 2016

Issued at 832 PM MDT Fri Aug 26 2016

The last of the evening showers are rolling across Weld County at
the present time, diminishing in strength as they move into cooler
and more stable air. Another batch of shower activity is moving
over northwest Colorado which will keep the chance of showers or
thunderstorms going in the north-central mountains for a few more
hours. Adjusting the sky cover during the overnight hours and
removing the showers after midnight were the only changes to the
forecast at this time. More low level moisture is present along
the eastern border, and these areas may see fog and stratus
develop before sunrise. This part of the forecast was left as is.


.SHORT TERM...(This evening through Saturday)
Issued at 133 PM MDT Fri Aug 26 2016

Challenging forecast today with the main branch of the upper level
trough still hanging out over Nevada bringing increasing westerly
flow over the state. A more diffuse trough is currently pushing
through the eastern plains with mid level forcing seen on water
vapor. This is helping to created scattered convection on the
plains. It appears the mountain and plains convection are driven
by two pieces of energy from the separate troughs with subsidence
between over the lower foothills and urban corridor. This will
help to keep storms at bay at least over the next few hours. Some
storms may come off the foothills and with dewpoints currently
hovering in the 40s to lower 50s cannot rule out a storm or two
over the Denver metro area. Main threats will be moderate
rain...lightning and gusty winds with the stronger storms. Some
graupal will be possible at higher elevations with a rain and snow
mix later this evening above 12000ft.

Overnight some showers may persist over the mountains as the
trough to the west will help to keep forcing over the area.
Elsewhere conditions will scatter out...especially over the
eastern plains as subsidence moves in. This will help to lower
overnight temperatures and create some areas of fog in the early
morning hours.

Tomorrow models have the upper trough firmly entrenched into
southern CA with weak SW flow aloft. Moisture is lingering around
and will be enough for a slight chance of storms in the mountains
by saturday afternoon. Temperatures will be slightly warmer with
highs reaching back into the 80s.

.LONG TERM...(Saturday night through Friday)
Issued at 133 PM MDT Fri Aug 26 2016

Saturday night into Sunday: Long range models are in agreement
that a mid and upper level short wave trough will be over the
lower Colorado River Valley (NV/AZ) on Sunday, placing Colorado
in a southwest flow pattern. The best synoptic scale vertical
lift associated with the trough remains across Arizona, New Mexico and
the extreme southern parts of Colorado on Sunday. Expect a few
thunderstorms to form in the mountains with the heating of the
day. Instability is limited east of the mountains so any storms
that form Sunday afternoon will have a hard time surviving as they
move over the Plains. Temperatures will warm into the mid 80s
across the Plains under mostly sunny skies, with afternoon clouds
via mountain convection spreading over the Plains through the late
evening hours. Mountains will warm into the 60s before isolated
thunderstorms form early afternoon.

Monday: The short wave trough remains disconnected from the
strong westerly flow across the northern U.S. and as a result does
not progress much. On Monday the trough should weaken and slide into
southern Arizona, reducing the synoptic scale lift across the
state. A robust mid and upper level ridge develops Monday and
continues to dominate Colorado weather through the week. Low
levels are dry on Monday with dewpoints in the mid 40s throughout
the Plains. PWATs remain below 0.75" for all but the far NE part
of the CWA.

Tuesday through Thursday: The mid and upper level ridge remains
in place and in fact build strength during the week because of
what is occurring upstream off the West Coast. An anomalously
strong long wave trough remains just off the West Coast, 3
standard deviations below normal for this time of year in that
region. The net result is a downstream ridge parked right over
Colorado with above normal temperatures and very low chances of
rain across the CWA. Can`t rule out isolated diurnal convection in
the mountains but the Plains should remain dry throughout the
remainder of the week. Temperatures across the Plains of Colorado
will be in the upper 80s to near 90, mountains will be in the mid
to upper 60s through Thursday. Will be watching the progression
(or not) of the anomalously deep/strong long wave trough along the
West Coast as it could become a player in Colorado`s weather late
next week.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 832 PM MDT Fri Aug 26 2016

Outflow easterly winds from the evening convection over the
northeast plains have moved across the Denver area. These winds
should transition to drainage southerlies by around 06z. No other
aviation impacts are expected through most of the night. Late
tonight, areas of fog or stratus may develop in the South Platte
River valley and move into KDEN from the north. Have mentioned the
possibility of IFR conditions at KDEN for a few hours around


.BOU Watches/Warnings/Advisories...


LONG TERM...Schlatter
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