474
FXUS65 KBOU 171757
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1157 AM MDT Fri May 17 2024

.KEY MESSAGES...

- Much warmer and drier today. Only isolated high based
  shower/storm possible mainly in the mountains.

- Breezier Sunday into Monday.

- Cooler, unsettled pattern with increasing precipitation chances
  across the region early next week.

&&

.UPDATE...
Issued at 1020 AM MDT Fri May 17 2024

Satellite shows mostly sunny skies across the forecast area.
Temperatures were responding quickly to the sunshine, weak
downslope flow, and shallow inversions. We`ve already warmed into
the mid 70s as of 10 am across the plains, and well on our way to
the mid 80s and summerlike warmth today.

There is some mid level moisture noted in the water vapor and IR
satellite imagery skirting through northern Utah and into
northwest Colorado this morning. As a result, we will be adding
some low PoPs for most of the northern mountains this afternoon
and early evening. Most of these would be only isolated very light
showers/sprinkles, but can`t totally rule out an isolated rumble
or two of thunder. Plains should see scattered virga and gusty
outflow winds to around 35 mph possible.

Finally, we`ve received fuel status updates from our fire weather
partners. Not surprisingly, the greenup appears sufficient now to
reduce any significant wildfire threat due to the breezier
conditions Sunday into Monday.

&&

.SHORT TERM /Through tonight/...
Issued at 223 AM MDT Fri May 17 2024

Water vapor imagery shows a very dry airmass entering Colorado as
well as upper level ridging. Colorado will be under the right exit
region of a jet that moves over Wyoming today. This will lead to
strong subsidence and the vast majority of our forecast area will be
dry as a result. Some high resolution models indicate that very weak
instability in the late afternoon could lead to a few virga
showers. Some of these could create brief wind gusts and perhaps a
few rain showers could make it to the surface.

The strong subsidence aloft and downslope, westerly winds at the
surface will lead to very warm conditions across the urban corridor
and plains. Highs will reach well into the 80s and it is even
possible a location or two could reach 90 in the usual warm spots in
the South Platte River Valley. The record high for Denver is 91 and
that is out of reach.

The only minor weather concern today is elevated fire weather
conditions across northern Larimer and Weld Counties. Minimum
relative humidity will drop to as low as 12 percent there and wind
gusts could reach 25 mph. Across the rest of the plains, winds will
be too light to increase fire weather conditions.

&&

.LONG TERM /Saturday through Thursday/...
Issued at 333 AM MDT Fri May 17 2024

Cooler weather is expected Saturday behind a weak cold front. This
should keep highs in the 70s across most of the plains, though a
few of our warmer spots still could reach 80F. Main question for
Saturday is how much moisture lingers across the region behind the
front, and what that looks like for a PoP forecast. Pretty good
confidence that the high country (especially along/south of I-70)
sees typical afternoon showers and storms, with lower confidence
along/east of I-25. High resolution guidance supports at least
widely scattered convection across the plains by the late
afternoon hours which is reflected in the current grids.

Sunday should be warmer and drier as westerly flow aloft begins to
gradually strengthen ahead of a trough axis. The added downslope
component to the flow should usher out any lingering moisture with
the best chance of any showers/storms confined towards the Wyoming
border. Highs again should rebound into the upper 70s to low 80s
across the lower elevations.

Southwesterly flow aloft will increase Monday as the trough axis
approaches, with a lead shortwave expected to eject into the
Central Plains from Monday into Tuesday. A surface low is
generally expected to form across southern Colorado on Monday
afternoon and quickly shift east... with a strong cold front
expected behind it. There are still a few questions about the
timing and evolution of the primary shortwave (and the overall
synoptic pattern) which will ultimately influence the mesoscale
environment as well. While it`s a fairly low confidence forecast
period, the overall pattern does look quite favorable for
cooler/wetter weather across the forecast area.

Model guidance gradually diverges by mid/late next week. The mean
pattern would favor zonal flow with enough moisture embedded to
support isolated/scattered showers and storms, mainly across the
higher elevations. Temperatures in this period look to be near
normal.

&&

.AVIATION /18Z TAFS through 18Z Saturday/...
Issued at 1153 AM MDT Fri May 17 2024

VFR through the TAF period. Winds will be the biggest challenge as
usual. We`re already seeing signs of channeling of west winds,
which means some places will see northerly or even light easterly
winds, while others in the channels will see gusts to 20-25 knots
through the afternoon. We`ll mention some of this variability in
the TAFs for now, but then shoot for more dominating WNW winds
after 21Z with further mixing. Some virga is also possible which
could bring a few VRB gusts to 30-35 knots (20-30% chance) given
the deep and well mixed sub-cloud layer.

Winds are expected to weaken again by about 02Z, and then return
to fairly normal south/southwest flow. A weak cold front will try
to push towards the terminals overnight with a shift to the north
or northeast possible after 10Z, but there are equal odds of just
variable winds until a stronger anticyclone develops 12Z-18Z with
an increase in southeast winds to 10-15 knots. Southeast winds
will likely strengthen further on Saturday afternoon with gusts
upward of 25 knots possible. Isolated to scattered high based
showers/storms will develop late in the afternoon and evening,
warranting a PROB30 of VRB gusty winds and -TSRA after ~22Z.

&&

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

&&

$$

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