753 
FXUS65 KBOU 292035
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
235 PM MDT Wed Jul 29 2020

..SHORT TERM...(This evening through Thursday)
Issued at 235 PM MDT Wed Jul 29 2020

Upper level trough over eastern Wyoming will track southeast over
the next 24 hours. This puts Colorado under a northwest flow 
aloft. Most of Colorado is under a dry subsident airmass this 
afternoon. A couple strong/severe storms will be possible over the
far northeast corner of Colorado where better moisture will 
linger. Elsewhere, a few weak showers/storms could pop where this 
is some convergence. A cold front/outflow from thunderstorms 
pushes through early this evening with northeast upslope flow 
behind it. This will increase low level moisture across the area 
tonight. A slight chance this triggers a few weak showers and 
storms this evening along the Front Range. Best chance for 
convection this evening will be over far northern/northeast 
Colorado where there is a SVR watch out right now.

Thursday is expected begin cloudy over northeast Colorado due to 
the increase in moisture. Lift from the upper level trough is 
expected to bring showers and thunderstorms to the northeast 
corner. With CAPE less than 1000 J/kg and very little shear, no 
severe storms are expected. Moist northeast upslope flow and a 
slightly unstable airmass is expected to trigger 
isolated/scattered convection along the Front Range during the 
afternoon. Northeast winds, cloud cover, and cooler airmass will 
result in a cool day across northeast Colorado with highs in the 
upper 70s and lower 80s. If clouds/precipitation persist through 
the day over the northeast corner, highs may struggle to reach the
mid 70s.

.LONG TERM...(Thursday night through Wednesday)
Issued at 235 PM MDT Wed Jul 29 2020

By early Friday the convection should be southeast of our area. 
The mid- and upper-level ridge remains centered over Arizona, 
preventing monsoonal moisture from getting into Colorado. That's a
recurring theme through next week as well. More on that later. 
For Friday, flow aloft becomes almost due northerly, and PW values
drop to under 1.0" across northeast colorado, and to around 0.5" 
across the high country. At the surface the flow will become north
and northeast during the afternoon, advecting much drier near- 
surface air east of the Divide. Dewpoints should remain in the 40s
and cool advection should limit convection as well. The plains 
should remain dry throughout the day, maybe a trace of rain. 
Across the West Slope there is scant mid-level moisture, and even 
then only across the central mountains, so convective chances in 
the mountains will be limited Friday afternoon as well, mainly 
confined to along and south of I-70. Highs across the plains will 
be below normal, with low to mid 80s expected. The West Slope 
valleys should be in the 70s.

On Saturday, more of the same with some mid-level moisture coming in 
from the north, resulting in scattered afternoon convection forming 
across the northern mountains and Cheyenne Ridge, moving south-
southeast across the western half of the plains.  Surface moisture 
remains weak with dewpoints again less than 50 degF.  Just light 
rain, lightning, and gusty winds should be the main impacts.

On Sunday, a heat-induced surface low pressure centered over Utah
paired with a 1022 mb surface high over Saskatchewan will result 
in decent east to southeast flow across the plains of Colorado 
during the day. This will allow much better moisture east of the 
Divide, with dewpoints ranging from 60-63 degF across the 
northeast plains to mid 50s into the foothills. PW values reach an
inch across the plains westward into the foothills, and increase 
to around 0.7" in the mountains as some Pacific moisture works 
south, advected by northwest flow aloft. Precipitation chances 
should be pretty good for most areas given the moisture 
availability and upslope flow. There will be good cooling aloft as
well, especially across the northeast quarter of Colorado where 
700 mb temps will be +6-7 degC. High temps thus will be cool for 
July standards even with sunshine. Highs may not reach 80 across 
far NE Colorado, but should reach the mid 80s across the I-25 
corridor, with 70s in the mountain valleys.

Next week the global models and ensemble solutions are in fair 
agreement on the position of the mid- and upper-level ridge.  From 
Monday through the later part of the week, it slowly migrates east 
from Arizona into New Mexico, with the ridge axis extending into 
western Colorado. The Monsoon will still be shut off into later 
next week at least, especially for Colorado. As the trough 
migrates east and with a ridge axis over Colorado, we should begin
hitting 90 again across I-25 corridor and the rest of the plains,
by Tuesday and perhaps beyond. The northwest flow aloft with some
embedded moisture will continue to bring isolated afternoon 
showers and thunderstorms for our area. PW values don't look to 
exceed 1" other than the far eastern Plains, so for now not 
looking like a heavy rain set up but interestingly on Tuesday with
an increase in low-level moisture (SBCAPE >2,000 J/kg northeast 
plains) and 500 mb flow out of the northwest at 40-50 kts 
(depending on model), severe potential will need to be monitored 
as we get closer.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 235 PM MDT Wed Jul 29 2020

Northwest to north winds will become northeast after 00Z when a 
weak cold front/thunderstorm outflow push through the Denver area.
Gusts to 20-30 knots will remain possible through 03Z. Winds then
quickly decrease. The best chance for thunderstorms will be over 
far northeast and eastern Colorado after 20Z. There is a slight 
chance for thunderstorms in the Denver area, mainly after 00Z 
behind the wind shift. After light winds late tonight and early 
Thursday, northeast winds will prevail for Thursday. Moisture 
increases tonight and by Thursday morning low clouds are expected 
over northeast Colorado. There is a chance these clouds make it to
the Denver after 12Z. The increase in moisture will lead to a 
chance for showers and thunderstorms Thursday afternoon.

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Meier
LONG TERM...Schlatter
AVIATION...Meier