National Weather Service Forecast Discussion

000
FXUS65 KBOU 010644
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1244 AM MDT Thu Jun 1 2023

.UPDATE...
Issued at 735 PM MDT Wed May 31 2023

Satellite and radar both indicate that most of our storms have
weakened over the past couple of hours. The one notable exception
was the storm north of New Raymer in northeast Weld county, that
likely dropped greater than golf ball sized hail across rural
portions of the county... but that storm has exited the CWA and
now only weak convection remains.

Across the metro, we should see a brief increase in showers/weak
storms this evening as one last wave of convection enters the
area, but these storms aren`t likely to produce any severe risk
given a largely unfavorable environment. A few isolated storms
will continue across the plains this evening as well. Most places
should see rain come to an end around midnight, with just an
isolated shower or storm possible after.

Have made some changes to the PoP grids to match up with current
radar and the latest forecasts from the RAP/HRRR through the
overnight, but otherwise the grids were in good shape.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 243 PM MDT Wed May 31 2023

Scattered thunderstorms initiated over the foothills and southern
Front Range mountains early this afternoon, and will slowly drift
into the urban corridor and plains over the next couple of hours.
Dew points over much of the plains are hovering in the 50`s under
moist southeasterly low-level flow, except for the Denver metro
which is staying drier owing to the downslope flow from the Palmer
Divide and warmer urban temperatures. As previously stated, shear
is very marginal today and not particularly supportive of long-
lived severe thunderstorms, however some stronger to locally
marginally severe storms will certainly still be possible in the
plains later this afternoon. Greatest threat for small hail and
heavier rain should be east of the I-25 corridor, particularly in
the northern plains, where MLCAPE values near or slightly above
1,000 J/Kg this afternoon will be more supportive. Storms that
drift east off the higher terrain may initially carry a threat of
strong gusty outflow winds with drier near-surface conditions and
healthy DCAPE progged to be exceeding 1,000 J/Kg over the next few
hours.

Forecast soundings suggest mid-level moisture will be slow to
clear overnight, and we could very well see lower cloud cover
persist into the morning on Thursday. This will help sustain lower
temperatures with highs that will likely struggle to climb into
the mid 70`s across the lower elevations tomorrow. With that,
instability will also be more marginal, and suspect convective
activity over the urban corridor and plains may be late to develop
and somewhat subdued. The mountains will be better positioned to
be the focus of activity Thursday, with increased moisture and
potentially less morning cloud cover. Southerly to southeasterly
winds also look fairly robust tomorrow as the closed low ejects
northeast into western Colorado, and may help promote convergence
over the foothills to enhance rainfall as well as sustain
convection over the higher terrain for longer. Considering this,
anticipate a slightly higher threat of heavy rain for recent burn
scars, but overall threat of severe weather will be on the low
end.

.LONG TERM...(Thursday night through Wednesday)
Issued at 243 PM MDT Wed May 31 2023

A shortwave trough will move across our CWA Friday morning and
will end up near Cheyenne, WY during the afternoon. This will push
the best lift and instability away from our CWA but there will
still be upward motion over the far northeast plains of Colorado.
With good moisture in place and morning sunshine, weak
instability will develop and showers and storms will form in the
afternoon and evening. The lack of deep layer and low level shear
will keep the majority, if not all, of the storms below severe
limits. There is a small concern about flash flooding over the
burn areas but not a particularly high threat.

A shortwave over northeast New Mexico will develop an MCS on
Friday night which models are predicting to develop an MCV. This
MCV moves northwestward into northeast Colorado on Saturday
morning. This could have moderate to heavy rainfall associated
with it if it does develop as models say. Saturday looks like a
cool day with a good chance of rain showers across much of our
CWA. Highs will likely stay in the 60s across the plains. The
precipitable water values will be near the max moving average on
the SPC sounding climatology page. With so much moisture in place,
there is a possibility that warm rain processes develop and some
areas may see some minor flooding although the risk seems low at
this time.

A ridge aloft will strengthen over the Northern Plains on Sunday
and the shortwave trough over Colorado will slowly weaken and move
off to the west. The ridge will help develop deep upslope flow
across eastern Colorado although the strength of the winds will be
low. Ample moisture will stay in place so Sunday will be another
day of widespread showers and storms.

The ridge aloft becomes more dominant on Monday through mid next
week. This will likely allow for more sunshine than clouds each
morning which would result in better instability. Since good
moisture will linger in Colorado, scattered to widespread showers
and storms will remain likely. A flash flooding threat exists
during this period but details are low. Otherwise, temperatures
will be below normal with light winds.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1237 AM MDT Thu Jun 1 2023

VFR conditions are expected through Thursday morning, though there
is a chance of some localized IFR/MVFR ceilings for a few hours
around 12z. Scattered thunderstorms are expected between 21z and
02z with localized MVFR visibilities and variable winds gusting to
35 knots.

&&

.HYDROLOGY...
Issued at 243 PM MDT Wed May 31 2023

Another round of afternoon showers and thunderstorms can be
expected over the high country Thursday. These may produce heavier
precipitation relative to previous days with increased moisture in
place. Some may be slow moving, with general progression being
south to north, and will thus result in a slightly higher burn
scar flash flood threat.

The latest data suggests storms on Friday will not be very strong
and they may avoid the burn areas for the most part. However, they
will be moving slowly so a limited flash flood threat over the
recent burn areas will still exist.

On Saturday and Sunday, precipitable water values will be near
record levels. The limiting factor will be the amount of sunshine,
or lack thereof, throughout the day. At the moment, each day
appears very cloudy which would keep the flash flood threat at
limited. However, if more instability is expected to develop in
future forecasts, these days could have an elevated risk of flash
flooding.

During next work week, instability will increase with similar
moisture values and storm motion. Therefore, an elevated risk of
flash flooding may exist over the burn areas.

&&

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

$$

UPDATE...Hiris
SHORT TERM...Rodriguez
LONG TERM...Danielson
AVIATION...Gimmestad
HYDROLOGY...Rodriguez/Danielson

NWS BOU Office Area Forecast Discussion