National Weather Service Forecast Discussion

000
FXUS65 KBOU 031826
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1226 PM MDT Sat Jun 3 2023

.UPDATE...
Issued at 916 AM MDT Sat Jun 3 2023

An impressive plume of moisture can be seen on water vapor imagery
extending from the Gulf of Mexico northwest through Colorado and
into the northern Rockies. On the ground, widespread and mostly
light to moderate rain can be found over a good portion of the
plains, the Palmer Divide, and northern I-25 corridor. A few
localized heavier cells have been forming throughout the morning
south and southeast of Denver, coinciding with a water vapor
maxima and likely some subtle surface boundaries. The heaviest
cells have produced 0.25-0.50" of rainfall, and have certainly
been slow moving. ACARS soundings depict very week winds through
at least 500mb with some directional shear. The forecast for
today looks on track. Did increase PoPs for tonight and Sunday
morning, when a stronger surge of easterly flow looks to push into
the northeastern quadrant of the state and reinvigorate
precipitation.

&&

.SHORT TERM...(Today and tonight)
Issued at 331 AM MDT Sat Jun 3 2023

The 00Z synoptic analysis showed the large, negatively tilted
trough over the western states and the ridge building to our
northeast. There is moderate, southeasterly flow aloft over
Colorado and an MCS coming in, and there should be widespread,
persistent showers through today and tonight. Localized heavy
rainfall is possible. Models continue to be very reliable and
consistent, and I made no particularly significant changes to the
forecast in this package.

Expect persistently cloudy to overcast skies, with quite cool
temperatures today followed by slightly warm nights, the range
narrowed by the sky cover. High temperatures should be in the the
60s across the plains and mostly 40s and 50s across the high
country, then lows in the 50s across the plains and mostly 30s
across the high country.

There is great moisture in place. Surface dewpoints will stay in
the 40s and 50s across the plains and mostly 30s across the high
country. The closest upstream sounding at AMA showed deep
saturation and precipitable water of almost an inch, and that
should be higher come 12Z. Models have precipitable water
generally 150 to 200 percent of normal over our through tonight.
All the associated cloudiness should also limit instability,
however, and lapse rates look modest at best most places most of
the time. Forecast soundings show long, skinny CAPE profiles and
warm rain processes will dominate. Due to the unusual flow aloft,
shower and thunderstorm motions will be southeasterly, upslope
into the foothills which should mean increased coverage and
intensity over the eastern slopes and the adjacent urban corridor
compared to our usual routine. There is just a marginal risk of
excessive rainfall across much of the area and widespread impacts
are not currently expected, though locally heavy rainfall will
probably result in localized impacts around burn, urban, and poor
drainage areas. There is an elevated threat of flash flooding to
the Cameron Peak burn area. Along with the lack of instability
there is a lack of shear, enough to support multi-cell storms but
not many (or probably any) supercells, and so there is very little
threat of severe storms. There will probably be small hail and
breezy, maybe a few incidents of marginally severe hail or gusts,
but the primary hazard is heavy rainfall.

.LONG TERM...(Sunday through Friday)
Issued at 331 AM MDT Sat Jun 3 2023

Blocking pattern will persist for the upcoming week keeping a
cool and unsettled pattern in place through next week. Each day
will feature scattered to numerous showers and thunderstorms.

Strong upper level high will remain centered over the Northern
Plains and Prairie Providences Sunday and through next week. This
high only drifts westward a few hundred miles all of next week.
Over Colorado, a weak low trapped under the ridge will continue to
slowly dissipate Sunday and Monday. Southeast flow around the
dying low will keep the airmass moist with showers and
thunderstorms tracking west to northwest. For Tuesday and the rest
of next week, a closed low will be parked over southern
California. Colorado will see weak flow aloft between the low and
high with no well defined features to move across the region.
Moisture will remain in place, and produce showers and storms each
day. There will be more sunshine early next week, which will lead
to slightly warmer temperatures. This will help the airmass to
become more unstable and lead to an increase in thunderstorms. Not
enough instability or shear for severe storms. However, heavy
rainfall and localized flooding could become an issue with
continued daily rainfall.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1222 PM MDT Sat Jun 3 2023

We`ll start with the easier aspect...the winds. Should see
prevailing NE winds through early evening, followed by a period of
variable and light winds in the evening before light northwesterly
flow takes hold overnight.

Widespread moderate rain is overspreading NE Colorado and will
continue throughout the day, with CIGS primarily in the 030-060
range but with occasional lowering to 010-020 possible during
heavier showers. With limited instability, believe TS potential
will remain low today. Cannot completely rule out some VFR
conditions at times later this evening or tonight, but even then
expect periods of showers and lower CIGS. Visibility may lower to
3SM during the heaviest showers. Tomorrow, expect another active
day with renewed showers and likely a higher chance of a
thunderstorm in the afternoon.

&&

.HYDROLOGY...
Issued at 331 AM MDT Sat Jun 3 2023

Today and tonight are the most likely periods for heavy rainfall
and flooding impacts. An MCS is coming in from the southeast and
with near record values of precipitable water. There will probably
be a lack of instability and shear, but widespread and persistent
showers will still likely lead to impacts. Upstream and forecast
soundings show deep moisture and warm rain processes are likely.
Shower and thunderstorm motions will generally be southeasterly,
upslope into the foothills which should mean increased coverage
and intensity over the eastern slopes and the adjacent urban
corridor compared to our usual routine. There is just a marginal
risk of excessive rainfall across much of the area and widespread
impacts are not currently expected, though locally heavy rainfall
will probably result in localized impacts around burn, urban, and
poor drainage areas in particular. There is at least a limited
threat of flash flooding to all burn areas, and an elevated threat
to the Cameron Peak. If cloud cover breaks enough to build some
instability today then those would rise to elevated and
significant threats, respectively, but I don`t think that`s very
likely at this time.

For Sunday and next week, there will be a limited to elevated
flash flood threat for the burn areas each day. A moist easterly
flow into the foothills Sunday and Monday will lead to an elevated
threat for flooding in the Cameron Peak Burn Area. Meanwhile the
fires west of the divide will be somewhat rain shadowed, which
will keep the threat limited. For Tuesday and the rest of next
week, there will be warmer temperatures, which will increase the
instability and result in better chances for thunderstorms. The
airmass will remain moist and heavy rain will accompany the
thunderstorms each day.

&&

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

$$

UPDATE...Rodriguez
SHORT TERM...EJD
LONG TERM...Meier
AVIATION...Rodriguez
HYDROLOGY...EJD/Meier

NWS BOU Office Area Forecast Discussion