371
FXUS65 KBOU 181140
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
540 AM MDT Sat May 18 2024

.KEY MESSAGES...

- Warm through Sunday. Isolated to scattered high based showers
  and storms this afternoon and evening with strong wind gusts
  possible.

- Breezier Sunday into Monday.

- Cooler, wetter pattern late Monday into Tuesday as a couple weak
  systems track across the region.

- Warming/drying trend for the second half of next week.

&&

.SHORT TERM /Through tonight/...
Issued at 413 AM MDT Sat May 18 2024

Surface observations and radar indicate a cold front is moving
southward through Wyoming and Nebraska and will move through eastern
Colorado around sunrise. The cold front is rather weak and it`s only
impacts will be a wind shift to the northeast and high temperatures
being about 5 F cooler today.

Water vapor imagery shows a shortwave trough over Montana that will
miss our area to the north. There is zonal flow over Colorado and an
area of mid level moisture is seen over western Colorado and Utah
currently that will move directly over our forecast area this
afternoon. Weak instability will form this afternoon due to decent
lapse rates. The moisture and weak instability will combine with
light upslope flow to create enough lift for showers and weak storms
to form across a decent portion of our CWA. These showers and
storms will not have very heavy rain associated with them and
likely minimal hail. However, they may create strong wind gusts up
to 45 mph. The primary time for these showers and storms will be
between 20-02Z. However, the area of mid level moisture will
continue to be over Colorado through tonight so showers may
continue past midnight.

&&

.LONG TERM /Sunday through Friday/...
Issued at 413 AM MDT Sat May 18 2024

Warmer and relatively quiet conditions are forecast for Sunday as
westerly flow aloft gradually strengthens. Temperatures should
warm back into the 80s across most of the plains. Scattered
showers/storms are possible across the high country, mainly north
of I-70. Generally dry conditions are forecast of the I-25
corridor. Further east, a dryline is expected to setup near the
CO/KS border into SW Nebraska during the morning hours and remain
nearly stationary through the afternoon. A few storms should
develop along the dryline in the afternoon as a weak shortwave
traverses the area. Still quite a bit of uncertainty as to where
that dryline does stall out and how much capping exists in our far
eastern CWA. Overnight CAMs paint a mixed picture, with a few of
the HREF members implying a severe risk here while the NCAR FV3
ensemble keeps any severe risk well east of our forecast area.

By Monday, a broad upper trough axis is expected to dive into the
intermountain West, with a series of shortwaves ejecting into the
Plains. Guidance has generally come into better agreement, with a
strong lead shortwave tracking across the region Monday evening
into Tuesday, with a secondary wave Tuesday into Tuesday night. As
a result, the initial surface low is much stronger as it develops
and shifts east into the plains... with a fairly strong cold
front tracking across the forecast area late Monday evening.
Guidance develops a broad swath of precipitation across our
northern border into Nebraska Monday night, with the ECME/GEFS
suggesting the potential for >1" of precipitation in the far
northeast corner of the state.

Tuesday will be much cooler behind the front, with highs likely
remaining in the upper 50s to mid 60s across the lower elevations.
Modest moisture/instability lingers across the plains during the
day... and combined with shallow upslope flow and larger scale
ascent from the trailing shortwave, should promote widespread
showers and a few storms across the Front Range and adjacent
plains. This likely wouldn`t be a washout day but enough for a
nice wetting rainfall for a large chunk of the forecast area.

The second half of the week should be quieter under a weak zonal
flow pattern. A few shortwaves tracking to our north could provide
brief glancing blows - slightly cooler temperatures/higher PoPs -
but there are significant differences in the the timing/location
of these features beyond Wednesday. In general, a gradual warming
trend is expected through Friday with isolated/scattered PoPs,
mainly across the higher elevations.

&&

.AVIATION /12Z TAFS through 12Z Sunday/...
Issued at 534 AM MDT Sat May 18 2024

A cold front will move through the terminals between 12-13Z.
Winds will turn to the northeast after the front with potential
for brief gusts to 20 knots. Winds will likely become east to
southeast by 18z and then more south to southeast later in the day
at 10 to 20 knots. The concern for the terminals is in the
afternoon when elevated showers and weak storms may produce gusty
winds. The dry airmass will lead to the potential for gusts up to
35 knots if a storm were to go directly overhead. Visibilities
and ceilings should stay in the VFR category. There will be
drainage winds tonight with increasing southwest winds tomorrow
morning.

&&

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

&&

$$

SHORT TERM...Danielson
LONG TERM...Hiris
AVIATION...Danielson