255
FXUS65 KBOU 091558
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
958 AM MDT Sun Jun 9 2024

.KEY MESSAGES...

- More thunderstorms today and Monday with a lower severe threat
  but a risk of heavy rain and localized flooding.

- Minor snowmelt impacts from rising streams, mainly in Grand
  County. Thunderstorms this weekend could further increase stream
  flow.

- Hot and mainly dry weather towards the middle to end of next
  week. There is potential for a day or two to need a Heat
  Advisory, most likely Thursday.

&&

.UPDATE...
Issued at 958 AM MDT Sun Jun 9 2024

Going forecast on track. Did make a few changes to match up with
the current trends. Stratus looks to hold on into the early
afternoon over eastern Larimer and Weld Counties and
east/southeastward over the eastern plains. Lowered highs a few
degrees in these area. Also lowered PoPs, especially over the
eastern plains where it should stay too stable for storms today.
Kept lower PoPs in the for Fort Collins and Greeley areas, but
delayed the chances by a few hours. If this far northern Front
Range see storms it would be this evening. Increased temperatures
1-3 degrees over the Denver area where mostly sunny skies are
expected to prevail until convection fires mid afternoon. Speaking
of convection, along the Front Range where it will stay mostly
sunny, MLCAPE will reach 1000-2000 J/kg. Shear will be on the weak
side, but a few brief severe storms with one inch diameter hail
or slightly larger will be possible. Precipitable water values
climb to an inch or slightly higher. Heavy, locally very heavy,
rain will be possible with the thunderstorms today due to the
moist unstable airmass with slow storm motions.

&&

.SHORT TERM /Through tonight/...
Issued at 400 AM MDT Sun Jun 9 2024

While showers have diminished across northeast Colorado,
lingering low level moisture and easterly flow have supported fog
and low stratus development across the plains. Nighttime
Microphysics RGB satellite imagery shows the fog/low stratus in
the far northeast corner/far east gradually filling in and
extending westward early this morning. Can`t rule out some light
drizzle in some of the widespread thicker layers. If widespread
dense fog becomes more evident, a short-fused Dense Fog Advisory
may be in order for the plains this morning. The question will be
how far this will extend toward the urban corridor. It may be
more favorable to extend north into Weld County, potentially even
nudging south to parts of Boulder, Broomfield. Confidence is low
in it getting that far south and west. Denver is tricky as they
are observing sufficient SW flow which could hold the advancing
fog/stratus further east. Any stratus/fog should start to
scatter/erode mid-morning.

Today an upper level ridge builds in from the west with the axis
over the Four Corners region. This will bring weak NW flow aloft
over CO. There will still be plentiful moisture under the ridge
aloft and easterly surface flow will keep it in place across the
plains and Front Range today. Although more stable than yesterday,
there will still be instability building in the afternoon as long
as there is an ample period of heating. This will depend on how
extensive the stratus is this AM and how quickly it erodes.
Ensemble guidance shows mean CAPE values in the 500-1200 J/kg
range with the higher end of the range centered around the urban
corridor where there will be more ample heating. Moisture and
instability will be sufficient to support some strong to severe
storms this afternoon; however, weaker 0-6km bulk shear will keep
storms less organized. Wind and hail 1"/just above are possible.
With weaker winds aloft, storm motions are expected to be slower
which will add a heavy rain threat as well. More in the Hydro
Discussion. Scattered thunderstorms develop closer to mid-
afternoon, continuing through the early evening with the higher
chances west of I-25.

&&

.LONG TERM /Monday through Saturday/...
Issued at 400 AM MDT Sun Jun 9 2024

Not a lot of change to the extended forecast this morning. Main
trends are less warming on Tuesday and better confidence in
increased thunderstorm activity on Friday.

On Monday, the plains look mostly capped, but there should be enough
instability over the mountains to generate scattered afternoon
thunderstorms that should drift east onto the adjacent plains in the
late afternoon and early evening. There`s still enough moisture for
some strong storms with locally heavy rain, though storm motions
should be a bit faster.

There`s a little more emphasis to a weak shortwave that passes early
Tuesday. This ushers in drier air aloft, but also a bit of cooling
in the lower atmosphere. The result is that this day may not have
much warming and could even be less capped. There should be less
moisture and instability though, and faster storm motions, so
perhaps it`s just a low grade convective day with fairly benign
storms.

An upper level ridge does build west and south of us for Wednesday
and Thursday, with pretty good agreement on temperatures reaching
into the 90s. Thursday has been looking like the hottest day, and it
still could be, but there are quite a few model runs that are
showing a little cold front associated with a weak wave passing over
the northern plains that could drop our temperatures a few degrees
and even bring some clouds and isolated showers/storms to the
northern border areas. There are still some runs that have the
temperature close to 100 degrees in Denver, but sticking with the
NBM keeping us in the mid 90s looks reasonable given the increasing
chance of some clouds or a puff of less hot air from the north.

Another change associated with that shortwave in combination with a
trough approaching from the southwest is that there`s an influx of
low level moisture onto the plains for Friday. There may be some
high level moisture too, with dry air in between. Convective
activity will be determined by how much cooling there is with the
incoming air. Latest guidance mostly shows just a little cooling
which would make this a fairly ripe convective day.

&&

.AVIATION /12Z TAFS through 12Z Monday/...
Issued at 538 AM MDT Sun Jun 9 2024

Still continuing to monitor the fog/low stratus potential early
this morning. Fog/low stratus has developed to the north and east. It
would take 1 or two hours for it to reach the edge of DEN (around
14Z) and with solar heating, shouldn`t last too long if it did
get there or it could sit at the edges of the field. Similar
story for BJC. Confidence low on if it gets to DEN/BJC before it
erodes/scatters, but worth mentioning with recent trends on
satellite.

Any fog/stratus should start eroding mid morning. There is
potential for showers and a few thunderstorms this afternoon,
mainly after 21Z. Chances are a little higher at BJC/APA compared
to DEN. Nearby or passing storms may bring brief gusty winds up
to 35 kts and outflow boundaries bringing vrb wind direction
changes. Early evening, any remaining showers/storms weaken and
move eastward. Enhanced southerly flow persists for most of the
overnight period at APA/DEN and lighter at BJC.

&&

.HYDROLOGY...
Issued at 400 AM MDT Sun Jun 9 2024

Elevated flows continue across the upper Colorado River basin and
additional rainfall this weekend could lead to further increase in
the flows. Remain cognizant of the dangers of these cold flows,
and be aware of any Flood Advisories.

Storms will be moving much slower today and Monday. However, they
will likely be weaker than Saturday. The primary threat during
the forecast period will be in Cameron Peak today as a moderate
threat for flash flooding will exist. The threat will be minor
again on Monday. Periods of heavy rain are possible in storms
today, mainly west of I-25 with a marginal risk for localized
flood impacts.

&&

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

&&

$$

UPDATE...Meier
SHORT TERM...Mensch
LONG TERM...Gimmestad
AVIATION...Mensch
HYDROLOGY...Gimmestad/Mensch