456
FXUS65 KBOU 230830
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
230 AM MDT Fri May 23 2025

.KEY MESSAGES...

- Warmest day of the week today. A couple severe storms possible
  northeast plains in the afternoon/early evening.

- Severe storm threat increases Saturday, but hinges on stratus
  and amount of warming.

- Higher shower and storm coverage through the Memorial Day
  Weekend, along with cool temperatures.

- Gradual warming next week with more typical shower/storm
  coverage each afternoon and evening.

&&

.UPDATE...
Issued at 230 AM MDT Fri May 23 2025

Upper level ridging to bring the warmest day that we will see for
a while. Highs are still on track for the lower to mid 80s across
much of the urban corridor and eastern plains. However, lowered
highs by about 5 degrees over the northeast corner where more
cloud cover will reside and southeast winds will keep the airmass
moist making it harder to warm up. This moisture will help fuel
strong/severe thunderstorms over the far northeast plains this
afternoon/evening. Other change for today was to limit the west
winds to the higher terrain. Appears the hi-res models are over
mixing the airmass because the lowest surface pressure stays over
the mountains/foothills.

For tonight and Saturday, outflow from the strong/severe
thunderstorms over the northeast plains pushes westward bringing
gusty northeast to east winds this evening. The east winds
continue through tonight and into Saturday. Low clouds will form
overnight and Saturday morning across the Front Range and eastern
plains. Cross sections show the moist layer being deep enough for
areas of drizzle towards 12Z Saturday until 18Z. That`s about the
only precipitation chances during the 06Z to 18Z Saturday period,
so lowered PoPs during this time frame. Any rainfall will be
light.

As we look to Saturday afternoon and evening. Still a severe
threat across the urban corridor, that`s if we can clear the low
clouds long enough to heat up into the lower to mid 70s. Otherwise
we are looking at a capped airmass.

&&

.DISCUSSION /Through Thursday/...
Issued at 257 PM MDT Thu May 22 2025

Main forecast concern will surround thunderstorm chances and
intensity as we head into this Memorial Day Weekend.

We still have a chance of a few showers and storms this evening,
as we are now getting closer to convective temps (upper 70s).
We`re starting to see a little cumulus along a north-south
oriented Denver Convergence Vorticity Zone (DCVZ) from around
Johnstown to the west side of DIA to near Centennial. Low level
moisture has been a little more than earlier advertised, with
lower to mid 40s dewpoints on most of the plains. Thus, MLCAPE
has been able to increase to over 500 j/kg while CIN is eroding as
we continue to warm. Latest ACARS soundings also show us getting
close to breaking the cap. Thus, it`s not entirely impossible we
don`t pop a couple strong thunderstorms late this afternoon into
early evening. Marginal severe hail and/or a landspout can`t be
ruled out. Also, a couple storms will be possible near the
Wyoming/Nebraska border overnight as a weak shortwave moves across
Wyoming - we think the main chance of storms would stay farther
north.

On Friday, flat upper level ridging occurs and the thermal ridge
shifts east across the state. This will be the warmest day with
highs pushing into the lower to mid 80s across the plains.
Southerly low level flow will continue to advection moisture
northward across the eastern plains, while a dryline forms along
the downslope moving off the Front Range and shifts east. MLCAPE
will rise into the 1000-1500 J/kg range where the best combination
of heat and moisture exists. Right now, the most likely location
for that would be along/east of a Sterling to Akron line, but some
chance moisture could hold as far west as Fort Morgan. Anywhere
east of that a couple severe storms/supercells are probable (>50%
chance) with large hail, damaging winds, and even a tornado
threat.

The weather pattern becomes more active this weekend, as an upper
level trough, increasing low level moisture, and some upslope all
join together. For Saturday, low level moisture is expected to
increase further as east/southeast winds develop and advect higher
dewpoints across the High Plains. This occurs as surface pressure
falls are expected ahead of an upper level trough pushing east
across the Great Basin and Northern Rockies. There will be another
risk of severe storms, but this time pushing back to the Front
Range and I-25 Corridor. That severe threat, however, hinges on
the depth of the stratus deck and how much surface heating occurs.
The models have trended cooler which seems reasonable in this
pattern, but that doesn`t necessarily mean we won`t break the cap.
The low levels may be only warming slightly to moist adiabatic,
but there`s still sufficient MLCAPE and rather strong shear to
warrant a risk of severe storms with all hazards possible. SPC
outlook is Marginal Risk at this time but considering the time of
year, low LCLs, and potential this could get upgraded especially
if we can still get MLCAPE of ~1000 J/kg.

Sunday is still shaping up to be the wettest day, as there may be
morning showers or light drizzle, replaced by more convective
shower and storm coverage in the afternoon. That would occur given
a more neutral but moist stability profile (still some weak
MLCAPE <600 J/kg). We could even see some locally heavy rain
(30-40% chance) if we get a little heating. High temperatures,
however, will be quite cool with highs only expected in the lower
to mid 60s, and that could be generous if we fill in with a low
level stratus deck.

While the trough is still near us for Memorial Day, it is forecast
to move east of the forecast area during the day. Thus, as long as
it doesn`t slow any further we shouldn`t see a washout. However,
that does bear watching since timing of just a few hours could
make a big difference. For now, we`ll have a lower chance of
showers and storms in line with ensemble guidance. Temperatures
will still be below normal, with highs in the 60s expected.

There`s not much to change in the expectations for the eventual
weather pattern early next week - we`ll still be caught somewhere
in between a trough to the east and a building ridge/weak zonal
flow over the Great Basin or Northern Rockies. This would keep
scattered showers and storms in the forecast each day due to
lingering moisture in light flow aloft. Temperatures should begin
a slow warming trend.

&&

.AVIATION /06Z TAFS through 06Z Saturday/...
Issued at 1130 PM MDT Thu May 22 2025

Gusty southerly winds will continue at APA and DEN through about 10Z
and then slowly decrease. Wind direction will turn clockwise through
12-18Z hours with a southwest direction through roughly 15Z then
west to northwest 15-18Z and then northerly after 18Z. Some of the
hi-res models show gustier west winds, but believe this
over mixing the flow aloft down to the surface. Then around or
shortly after 00Z Saturday, outflow from thunderstorms over far
northeast will bring stronger northeast winds. Winds then settle
some sort of easterly direction by 06Z.

&&

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

&&

$$

UPDATE...Meier
DISCUSSION...Barjenbruch
AVIATION...Meier