582 
FXUS65 KBOU 181758
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1158 AM MDT Sat Apr 18 2020

.UPDATE...
Issued at 1156 AM MDT Sat Apr 18 2020

Adjusted max temperatures down across eastern Larimer and Weld
counties due to the prevailing cloud cover not allowing the
airmass to mix. Temps are about 10 degrees cooler than surrounding
areas, adjusted max accordingly.

UPDATE Issued at 850 AM MDT Sat Apr 18 2020

Updated shower coverage this morning and into early this 
afternoon across the mountains due to current activity, as well as
increasing chances across the southern foothills and metro areas
due to the expected shortwave and northeasterly winds. Believe the
HRRR is warming the surface temps up way too fast, and hence the
higher chances for thunder across the southern/western metro
areas. With the surface flow turning northeasterly in response to
the deepening surface low over southeastern CO, expect some higher
dewpoints to move in, but also some cloud cover to reduce the
amount of warming. So increased PoPs slightly, but not the chances
of thunder. Will monitor temperature trends however and the
advancement of the convective activity over SW Colorado currently,
and may need to bump TS chances later. 

&&

.SHORT TERM...(Today and tonight)
Issued at 300 AM MDT Sat Apr 18 2020

Water vapor satellite imagery showing a well defined low tracking
across northwest Arizona early this morning. This system will 
weaken as it tracks east-northeast today across southern Colorado.
This will increase mid and upper level moisture and by noon 
result in mostly cloudy skies. Should be enough lift and 
instability to produce scattered showers. Best chance for showers 
will be to the south. Can't rule a storm or two, mainly over the 
mountains. Precipitation is expected to be light with less than a 
quarter inch under the stronger showers. This system quickly 
shifts east of the area and brings the chance for showers to an 
end by early evening. A few light snow showers may linger longer 
in the mountains. Cloud cover may limit the amount of warming 
today. Expect 50s for most areas, though over the far eastern 
plains where clouds arrive last, lower 60s will be possible. For 
tonight, temperatures fall into the upper 20s to lower 30s across 
northeast Colorado. A cold front enters the state after midnight 
and may bring low clouds to far northeast Colorado by sunrise 
Sunday morning.

.LONG TERM...(Sunday through Friday)
Issued at 300 AM MDT Sat Apr 18 2020

Northwest flow will be over Colorado on Sunday as a trough
drifting southeastward over the Intermountain West weakens 
throughout the day. Steep lapse rates of 8-9 degrees C per km 
will develop during the afternoon and may be enough to generate 
scattered showers and perhaps a couple thunderstorms mainly 
across the northeast corner of the state. However, northwesterly, 
downslope flow at the surface along with QG descent should hinder 
the coverage and intensity of showers. Therefore, the forecast has
a majority of our CWA under slight chance PoPs. 

Weak ridging will develop over Colorado on Monday resulting in
subsident flow. Most areas will be dry but steep lapse rates of
around 9 degrees C per km will allow showers and thunderstorms to
develop over the mountains and foothills mainly south and west of
Denver. Some of these showers may linger into the overnight hours
Monday night over South Park and the Palmer Divide. 

During the day on Tuesday, a trough will move from California 
towards the Four Corners region. There is still a decent amount of
disagreement in the global models on the location of this trough.
The GFS, ECMWF, and Canadian have the center of the 500 mb trough
in northern New Mexico, northern Arizona, and southern Nevada 
respectively around midday Tuesday. While the GFS has the most 
widespread precipitation and the Canadian has the least 
precipitation for our CWA, I trended the forecast toward the ECMWF
as it is a reasonable middle ground of solutions. The forecast 
has a mention of showers and storms across the majority of the CWA
but the best PoPs remain over the I-70 corridor mountains and the
Palmer Divide. 

A brief period of ridging will move over Colorado late Wednesday
into Thursday morning which will result in a dry period. A quick- 
moving, broad trough will then dig across the high plains by 
Thursday evening. This trough is poised to bring a good chance of 
precipitation to the entire CWA from Thursday afternoon and into 
the weekend with the mountains seeing the most precipitation. 

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 850 AM MDT Sat Apr 18 2020

VFR conditions will prevail through tonight across the Denver 
area. Variable winds across the airfields are expected to become
northerly to northeasterly around 18Z and prevail through the 
afternoon. Clouds will increase this morning and afternoon as an 
upper level systems tracks across the region. Isolated to 
scattered showers will form this afternoon, mainly over central 
and southern Colorado. At this time, scattered thunderstorms over 
the higher terrain are not expected to make it in the more stable 
airmass over the plains at this time, so not including any chance 
of TS in the terminals. Could see a wind shift or two from the 
showers. By early evening the showers will dissipate and winds 
will return to a southerly direction. A cold front is expected to 
push through the Denver area around 12Z Sunday morning. Low clouds
will be possible to the northeast of Denver, but are not expected
to reach KDEN at this time.


&&

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

$$

UPDATE...Kriederman
SHORT TERM...Meier
LONG TERM...Danielson
AVIATION...Meier/Kriederman