Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 201628
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1028 AM MDT TUE SEP 20 2016

.UPDATE...
Issued at 1028 AM MDT Tue Sep 20 2016

Forecast for today looks on track. Despite the thicker cloud cover
temperatures a few areas are actually a few degrees warmer than
yesterday. The exception is along the foothills/areas west of
I-25 and the South Platte valley in NE CO where it is
significantly cooler than at the same time on Monday. Overall,
highs of 90 should occur far eastern Plains, with mid 80s west of
I-25 into the foothills,a nd upper 60s to mid 70s in the
mountains. Best chance of thunderstorms (still low ~20% range) appears
to occur late evening/after midnight over the central Colorado
mountains associated with a weak short wave trough crossing the
state late today. Rest of the area will remain dry.

&&

.SHORT TERM...(Today and tonight)
Issued at 300 AM MDT Tue Sep 20 2016

Southwest flow aloft will prevail today around a ridge over Texas
and a trough over the Pacific Northwest. This is transporting
moisture from tropical storm Paine in the eastern Pacific across
the Desert Southwest and into Colorado. The moisture being
advected into the area is at the upper levels of the atmosphere
and the lower levels will remain dry. Surface dew points will
generally be in the 20s and 30s through tonight. High clouds will
increase and thicken through the day. Expected warm temperatures
again today, but a couple degrees cooler because of the increased
cloud cover.

Isolated showers and thunderstorms will be possible over the higher
terrain tonight with the best chance being south. Any precipitation
that occurs is expected to be light. Overnight lows will be mild
due to the warm airmass and cloud cover.

.LONG TERM...(Wednesday through Monday)
Issued at 300 AM MDT Tue Sep 20 2016

Southwesterly flow aloft dominates the CWA Wednesday through
Thursday. By Thursday night, the flow aloft increase and becomes
more southerly as an upper trough moves into the Great Basin. The
QG Omega fields bring in some upward vertical motion Thursday and
Thursday night. The low level winds are dominated by normal diurnal
patterns Wednesday and Wednesday evening. Models have a cold
front and upslope flow moving into the plains Thursday
morning. Normal drainage wind patterns are progged Thursday
night. There is some moisture around Wednesday through Thursday
but mostly in the mid and upper levels. Thursday night is fairly
dry. Precipitable water values are in the 0.50 to 1.00 inch range
from west to east all four periods. There is a tad of measurable
precipitation on the QPF fields most of the four periods, with
even less coverage over the plains during the two late day
periods. There is a bit of CAPE over the foothills late day
Wednesday, but better CAPE late day Thursday, with values over
1000 J/KG over the far northeast corner. For pops, will go with
0-30%s in the mountains through Thursday, with almost nothing on
the plains. For temperatures, Wednesday`s highs will be 0-2 C
cooler than today`s, with Thursday`s highs close to Wednesday`s.
For the later days, Friday through Monday, models have an upper
trough/closed low over Utah on Friday, then the trough pushes
into Colorado on Saturday with a circulation center moving
northeast into eastern Montana. By Sunday late, the upper
trough axis is just east of Colorado with a weak circulation
center over New Mexico. On Monday, the GFS still has a weak
closed low over New Mexico and the ECMWF has northerly flow aloft
over the CWA with an upper trough axis east of the state. The
models are pretty good agreement through sunday, but on Monday
they differ. They pretty much have some moisture for the
mountains, but little for the plains with the upper trough.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1028 AM MDT Tue Sep 20 2016

Should be a very low impact day and night. VFR conditions with a
broken mid/high level cloud deck today and tonight. Diurnal wind
shifts should occur this evening typical for this time of year
with wind speeds staying in the 10 kt range or less throughout the
period.

&&

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

$$

UPDATE...Schlatter
SHORT TERM...Meier
LONG TERM...RJK
AVIATION...Schlatter


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