Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 211547

Area Forecast Discussion
National Weather Service Denver/Boulder CO
947 AM MDT Mon Sep 21 2020

Issued at 947 AM MDT Mon Sep 21 2020

Lift on the tail end of a short wave trough over Nebraska and
weak low level converge is producing some showers over eastern
Colorado. This activity will continue to progress eastward through
the morning hours and be east of the area by noon. The past
several runs Hi-Res models have been showing a little more showers
moving off the foothills late this afternoon and evening. Added
isolated showers to the forecast for this. May have a few storms
as well south of Denver near the Palmer Divide.


.SHORT TERM...(Today and tonight)
Issued at 317 AM MDT Mon Sep 21 2020

Weaker WSW flow will be over the area today with limited moisture.
Overall instability is weak, however, may still see some high based
showers and isold storms, mainly over the higher terrain, along
and south of I-70 this aftn. May also see a slight chance of
showers or storms over the Palmer Divide as well. Otherwise the
rest of the area looks dry. Highs over nern CO will remain above
normal with readings in the mid to upper 80s.

For tonight, any lingering shower and tstm activity should end
during the early evening hours.  As for smoke activity, really hard
to say how bad it will be. Appears the worst conditions would be
over northern portions of the I-25 Corridor and higher terrain of
Larimer county.

.LONG TERM...(Tuesday through Sunday)
Issued at 411 AM MDT Mon Sep 21 2020

Models continue to have upper ridging over the forecast area
Tuesday through Wednesday night. The flow aloft is very weak and
mainly zonal Tuesday and Tuesday evening. The flow increases a bit
and is north-northwesterly Wednesday and Wednesday night. The QG
Omega fields show mostly weak downward vertical velocity in the
synoptic scale for the CWA through Wednesday night. The low level
pressure and wind fields, again, have normal diurnal wind patterns
for the CWA all four periods. For moisture, models keep Tuesday
fairly moist with precipitable water values in the 0.45 - 0.70
inch range. It dries out somewhat Tuesday overnight through late
this week. The best instability is progged during the afternoon
and early evening of Tuesday, especially in the mountains,
according to the CAPE and lapse rate fields. Wednesday is stable.
The QPF fields show some measurable rainfall mainly over the
mountains late day Tuesday, with nothing for Wednesday. For pops
will go with 30-60%s in the mountains late day wednesday and
0-20%s over the plains. The only pops on Wednesday will be for the
southwestern quarter of the CWA where there will be 10-20% pops
for late day. Temperature-wise, both Tuesday & Wednesday`s highs
will remain above seasonal normals and be similar to today`s
highs. For the later days, Thursday through Sunday, the upper
ridge continues in control well into Friday, then an upper trough
pushes across the state late Friday into mid day Saturday. This
feature looks weaker than it did yesterday. On Sunday, some models
have northwesterly flow aloft, others show upper ridging returning
from the northwestern U.S.  The airmass still looks dry with no
pops expected the last four days. The upper trough will usher in a
cooler airmass for next weekend.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 947 AM MDT Mon Sep 21 2020

VFR conditions are expected to prevail through tonight and into
Tuesday. Southwest winds this morning will become a northerly
component around 17Z. Winds then slowly turn clockwise this
afternoon and return to a southerly component this evening.
Isolated showers are expected after 21Z. Outflow from this
activity may produce a wind shift or two through mid evening.

As far as smoke goes, it will be a tough forecast. Satellite
imagery shows a little smoke across the region and it is expected
to persist through Tuesday. Smoke from near by fires to the
northwest of Denver will produce a good amount of smoke, but
southwest flow aloft should keep most of it to the north of the
Denver area. Some low level northerly winds could bring some smoke
into the area tonight and Tuesday morning, however future smoke
conditions remain highly uncertain.




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