National Weather Service Forecast Discussion

000
FXUS65 KBOU 181427
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
827 AM MDT Wed May 18 2022

.UPDATE...
Issued at 816 AM MDT Wed May 18 2022

Taking a look at current temperature observations across the
region, the high country remains on the cooler side this morning.
GOES-16 indicates mid-high level cloud cover over the mountains
and valleys; NBM has a persistent cloud decks staying over this
region through the afternoon thus this update includes lower
afternoon high temperatures for areas west of I-25. Relative
humidity remains on the higher side (35-50 percent) this morning
which should lower to 20-30 percent this afternoon. This will lead
to pockets of near critical fire weather conditions in northern
Weld/Lamar counties through late afternoon.

&&

.SHORT TERM...(Today and tonight)
Issued at 437 AM MDT Wed May 18 2022

Today, temperatures will be a few degrees cooler, with highs in
the low 80s on the plains and 50s and 60s in the high country. A
weak disturbance in the flow aloft will force scattered afternoon
convection concentrated in the southern part of the forecast area,
generally Park County, the Palmer Divide and adjacent plains,
where there should be a little more heating, moisture, and
instability. There is a marginal risk of severe storms bringing
lightning, gusty winds, hail, and light rainfall. Inverted-v
forecast soundings suggest the primary threat will be the gusty
outflow winds. By evening, most storms should have exited east.
Tonight, there will be increasing northwesterly to westerly flow
aloft a strong jet moves over the Pacific Northwest.

.LONG TERM...(Thursday through Tuesday)
Issued at 437 AM MDT Wed May 18 2022

On Thursday a broad upper trough will stretch from the Pacific
Northwest eastward into the Northern Great Plains States. Colorado
will lie on the southern side of this system under the influence of
a moderate westerly flow aloft. This pattern will lead to dry, very
warm and breezy conditions across North Central and Northeastern
Colorado. Downsloping flow east of the mountains will result in much
above normal temperatures on the plains with max temperatures
ranging between the mid 80s and lower 90s.

Drastically colder and wetter weather is expected Thursday night
through Saturday as the upper trough deepens over the Southern
Rockies. Snow should develop in the Northern Mountains around
midnight as mid level moisture and QG lift increases. A Canadian
Front associated with the trough is expected to move across
Northeastern Colorado Thursday evening bringing a sharp drop in
temperatures along with gusty north to northeasterly winds.

There could be some timing issues in when the precipitation develops
across the area. The consensus of the models is that initially the
moisture behind the front may be too shallow to produce
precipitation overnight across the Front Range Urban Corridor. The
exception may be areas further north such as the Fort Collins area
where there will be better QG lift associated with the upper jet.
The showers should gradually shift southward into Metro Denver
sometime during the morning hours as the upslope deepens and QG lift
increases. Model cross sections are suggesting a ramping up of the
precipitation Friday afternoon as the upslope deepens behind a
secondary surge. Many of deterministic and ensemble members are
showing the deep upslope flow continuing across the Northern/
Central Front Range mountains and foothills and adjacent
Plains/Palmer Divide through noon Saturday. In addition, there
looks to be plenty of QG ascent from a 100KT upper jet over
Central Colorado. The combination of these factors should produce
a good amount of much needed precipitation across most of the
forecast area.

Confidence is growing that heavy snow will fall across the Front
Range Mountains and foothills above 7000 feet with 6 to 18 inches of
accumulation possible, Therefore, have decided to issue a Winter
Storm Watch from midnight Friday through Noon Saturday for these
areas. The heaviest snow should be focused over the eastern slopes
with lighter amounts expected west of the divide. Snowfall
amounts for the lower elevations are a little more tricky. At this
time, it appears that the rain over the Front Range Urban
Corridor may mix and change over to snow Friday night and continue
into Saturday morning. The current thinking is that most of the
snow should melt as it falls due to warm ground temperatures with
mainly light accumulations expected. The Palmer Divide could see a
few inches of accumulation due to colder temperatures. In
addition, many plains locations could see a freeze both Saturday
and Sunday morning as temperatures are forecasted to dip below 32
degrees. For Sunday into early next week, we should see a warming
trend. However, the cool and unsettled weather may continue as
another upper level shortwave is progged to move across the
region.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 437 AM MDT Wed May 18 2022

Expect VFR conditions through the TAF period. Moderate drainage
wind should persist this morning until a weak northerly surge
around noon. Tomorrow afternoon, storms will probably stay mostly
south and east of the terminals. Outflow from those storms should
turn winds southeasterly in the evening, then drainage winds are
likely for the night.


&&

.FIRE WEATHER...
Issued at 437 AM MDT Wed May 18 2022

Today, much of our northern plains will have minimum humidity in
the 15 to 20 percent range and a few areas may briefly fall below
15 percent. These areas may also see a few marginal gusts of 25 to
30 mph, but any critical fire weather conditions should be limited
in coverage and duration and in areas that have recently received
precipitation, so we have decided not to issue any fire
highlights.

Very warm, dry and breezy weather will result in near-critical to
critical fire weather conditions across South Park, the Southern
Foothills, Plains and Palmer Divide on Thursday.

&&

.HYDROLOGY...
Issued at 437 AM MDT Wed May 18 2022

Today, scattered showers and storms will be concentrated in the
southern part of the forecast area, generally Park County, the
Palmer Divide and adjacent plains. Few storms are expected near
the burn areas, and storms should move quickly and bring light
precipitation.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Thursday morning through Thursday
evening for COZ214-216-238>251.

Winter Storm Watch from late Thursday night through Saturday
morning for COZ031-033-035.

Winter Storm Watch from Friday afternoon through Saturday
morning for COZ034-036.

&&

$$

UPDATE...AD
SHORT TERM...EJD
LONG TERM...jk
AVIATION...EJD
FIRE WEATHER...EJD/jk
HYDROLOGY...EJD

NWS BOU Office Area Forecast Discussion