139
FXUS65 KBOU 181641
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1041 AM MDT Sat May 18 2024

.KEY MESSAGES...

- Isolated to scattered high based showers and storms this
  afternoon and evening with strong, gusty outflow winds

- 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

&&

.UPDATE...
Issued at 1041 AM MDT Sat May 18 2024

Forecast is on track for this afternoon and evening with
scattered but generally high based showers and storms with gusty
outflow winds. Visible and water vapor satellite imagery shows
increasing moisture from west to east across the state this
morning, and 12Z Grand Junction sounding concurs with precipitable
water value increasing over a tenth of an inch from 12 and 24
hours ago, and was up to 0.50 inch. That`s a respectable number,
but thermal profiles still show a pretty deep subcloud layer. That
sets the stage for about 1000 J/kg of DCAPE, enough to support
wind gusts to around 45 mph from most showers and storms today. It
was interesting to note the CAMs showing potentially stronger and
low end severe gusts, so that is something to monitor with any of
the showers and storms that develop this afternoon with a small
potential of a couple severe outflows (>58 mph).

Overall, just minor changes for the latest trends and
temperatures.

&&

.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 /18Z TAFS through 18Z Sunday/...
Issued at 1041 AM MDT Sat May 18 2024

A cold front moved through earlier this morning, with post-frontal
easterly flow dominating across the TAF sites. Those winds should
trend a bit more southeasterly through 21Z, and increase with
gusts 20-25 knots possible. After 21Z, it appears surface winds
will likely be interrupted by high based shower/storm outflows,
making it difficult to pin down any particular direction. That
said, the higher coverage of showers/storms just to the south
would favor more southerly outflows prevailing than any other
direction. The dry airmass will lead to the potential for gusts
up to 35-40 knots. At this point, will lean toward TEMPO VRB gusty
winds between 21Z-01Z. Still can`t rule out VRB winds thereafter
with a few lingering showers, but overall winds should settle
back toward enhanced southerlies after 01Z.

Winds tomorrow afternoon could get variable again, or at least
will be hard to pinpoint any changes. Odds would favor a push from
the north/northwest late in the day given more convection to our
north. VFR conditions will persist with the generally dry low
levels holding firm.

&&

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

&&

$$

UPDATE...Barjenbruch
SHORT TERM...Danielson
LONG TERM...Hiris
AVIATION...Barjenbruch