Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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230
FXUS65 KBOU 202057
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
257 PM MDT TUE SEP 20 2016

.SHORT TERM...(This evening through Wednesday)
Issued at 257 PM MDT Tue Sep 20 2016

For the remainder of today it will unseasonably warm and will
remain dry area-wide other than an isolated storm or two for the
Central Colorado Rockies. This evening and tonight the remnants
of Tropical Storm Paine off the coast of Mexico will phase with a
cut off low off the coast of southern California. Zonal flow at
500 mb exists across the northern Rockies, while the 500 mb ridge
is centered over Oklahoma. The result for Colorado is SW mid and
upper level flow across Colorado with considerable upper level
moisture continuing through the short term. The moisture from the
is advected for the next 36 hours and should keep us mostly
cloudy. A subtle short wave trough crosses Colorado before sunrise
Wednesday and both the NAM and the HRRR initiate light
precipitation in the mountains and sustains the showers across
the Denver metro area. It`s still quite dry in the low levels so
have low confidence in rain reaching the ground, but have seen
enough in the high res model signal to raise PoPs after 3 AM local
time to slight chance for the metro area. Minimum temperatures
tonight will stay in the low 60s across the Denver metro area and
eastern Plains, and in the 40s in the mountains given the warm
temperatures this afternoon and expected cloud cover tonight.

Throughout the day on Wednesday, a deep/strong trough will dig
south along the Pacific Northwest coast. This will continue to
advect upper level moisture across Colorado keeping the area
mostly cloudy. The low-levels will continue to be dry with surface
dewpoints will be in the lower and mid 40s across the Plains, 30s
in the mountains. Once again the best chance for afternoon
thunderstorms will be over the central Colorado Rockies. In terms
of temperatures, the warm overnight lows coupled with the dry low-
level air means temperatures should still have little trouble
getting into the mid 80s east of the mountains despite the mid and
high cloud cover. However, the cloud deck should be thicker than
today as so temperatures will be a few degrees cooler than
Tuesday, but still well above average for this time of year.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 257 PM MDT Tue Sep 20 2016

For Wednesday evening, could see just a couple showers and an
isolated storm drift northeast across the mountains, but overall
the airmass will be too stable and subsident to support much
precipitation. Lower elevations should remain dry. Temperatures
will stay quite mild but a cold front is expected to push into
the northeast plains toward Thursday morning.

This front may usher in some stratus across the northeast plains
and lead to some cooling especially on the northeastern plains for
Thursday. The airmass will destabilize in the afternoon but
mainly over the mountains as the boundary layer cools slightly on
the plains. Could still see a couple storms drift off the higher
terrain or develop on the plains toward late in the day if slight
cooling aloft occurs ahead of the deep upper level low dropping
into the Great Basin.

It appears the best chance of precipitation may occur Friday as
the upper level low approaches from the west. Right now, all
medium range models are pointing to a piece of energy rotating out
of this low and across the forecast area. This along with cooling
aloft should effectively destabilize the atmosphere so will have
the best PoPs then. Winds are also expected to increase from the
mountains eastward across the Palmer Divide and most of the plains
with strong southerly flow and pressure gradient in place.
Temperatures expected to get cold enough in the mountains for some
snow potential but appears we`ll be getting into the dry slot so
threat for much accumulation appears quite limited into Friday
night.

By Saturday, the upper level trough will begin to fill and
gradually shear. We will still be under the cold pool aloft so
will continue to keep a chance of showers and a few storms in the
forecast. Temperatures will turn considerably cooler with highs
mostly in the 60s on the plains and 40s/lower 50s in the
mountains.

The cooler weather will remain in place through Sunday, Monday,
and Tuesday as the trough weakens and/or shears southward into the
Desert Southwest. The chance of precipitation will likely decrease
through this period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 257 PM MDT Tue Sep 20 2016

VFR conditions with mid/high level clouds this afternoon,
overnight, and through tomorrow morning. Winds should remain light
and follow diurnal patterns through 18Z. No significant weather
impacts expected.

&&

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

$$

SHORT TERM...Schlatter
LONG TERM...Barjenbruch
AVIATION...Schlatter



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