657
FXUS65 KBOU 112019
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
219 PM MDT Sun May 11 2025

.KEY MESSAGES...

- Warm weather continues through early next week. A few afternoon
  high-based showers and storms expected over the higher terrain
  and adjacent plains today.

- Well above normal temperatures likely Monday and Tuesday, with
  the potential for some areas to reach 90 degrees.

- Increasing chances for elevated/critical fire weather conditions
  through mid-week.

&&

.DISCUSSION /Through Sunday/...
Issued at 206 PM MDT Sun May 11 2025

This afternoon`s satellite imagery shows cumulus clouds stretching
across the higher elevations. Like yesterday, the Day Cloud Phase
channel shows a few of the cumulus starting to show signs of
glaciation wanting to take hold over the central mountains and
foothills, with some weak storms already forming over the Palmer
Divide. With forecast soundings showing a near inverted-v profile,
and SBCAPE values increasing to around 800 J/kg over the higher
elevations, we anticipate some of the aforementioned cumulus
growing enough to produce some scattered hi-based showers and
weak storms this afternoon. The main impacts would be gusty
outflows as the dry low-levels support sufficient downward motion
from evaporative cooling represented in DCAPE values of around
900 J/kg in forecast soundings. A few of these may push of the
mountains and onto the plains, but with MLCAPE values remaining
below 300 J/kg, storms will weaken as they enter a less conducive
environment. Gusty outflows around 35-45 mph will be the most
likely impact as these pass.

Warm and dry conditions are still on track to persist into the start
of the week as a lingering vertically stacked low over the Gulf
states keeps Colorado under upper-level ridging for another day,
despite an upper-level trough pushing ashore the Pacific Northwest
on Monday.

700 mb temperatures will warm a few degrees on Monday, ranging from
11C - 15C across the forecast area. This will result in afternoon
high temperatures at the surface also warming a few degrees from
Sunday, bringing widespread upper 80s to the lower elevations, with
portions of the South Platte River valley expected to hit the 90
degree mark. The foothills and mountain valleys will remain mild,
with high temperatures in the 70s. With moisture lacking under the
subsidence aloft, we should see some increased snowmelt over the
mountains and our current moist fuels will have ample time to
begin drying. With the persistent warmth and dryness, developing
fire weather conditions will be our main concern for the week, and
fuel conditions will need to be monitored. Over the weekend,
there has been a noticeable drying trend in the 10-hr fuels,
especially across the northeastern portion of the state, and into
the mountain valleys. Tuesday and Wednesday look to be the days
with the highest fire weather concerns at this time, and will
continue to be monitored, but with the majority of our fuels
remaining below critical status, critical fire weather concerns
look to be patchy, and dependent on how drying trends continue
over the next few days.

The synoptic pattern will shift as the aforementioned low over the
Gulf states will begin to eject to the northeast on Tuesday,
allowing for the Pacific Northwest trough to push eastward.
Height falls will begin across Colorado on Wednesday as the
approaching trough axis to the west passes through the Great
Basin, and we will see increasing southwesterly flow throughout
the day. The main impacts still look to remain to the north, but
we should see moisture increase along the northern tier of the
forecast area, and between a cold front passage around Wednesday
and increasing PVA, we should see some increasing chances for
thunderstorms across the northern portion of the forecast area,
and even some snow return to the northern mountains.

Temperatures will moderate towards normal behind the cold front,
remaining near normal through the end of the week, but there is
still plenty of time for things to change between now and then.

&&

.AVIATION /18Z TAFS through 18Z Monday/...
Issued at 1141 AM MDT Sun May 11 2025

The main concern for this afternoon will be with passing hi-based
showers/weak thunderstorms that produce variable wind gusts
across the TAF sites, with little precipitation. Hi-res guidance
continues to show showers passing over the TAF sites late this
afternoon, and with developing cumulus clouds already in place
over the central mountains, and mesoanalysis showing increasing
instability over the past few hours, confidence has increased
enough to move the PROB30 up to a TEMPO for the 23-3Z hours.
Depending on how the showers progress, there may be a few hours on
the back end that a few outflow boundaries may pass over the
airfields (~20% chance), but there is higher confidence in a
return to southerly winds once showers pass by.

Drainage winds are expected for the overnight hours, with VFR
conditions expected after the showers move out (~3-4Z) through
tomorrow.

&&

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

&&

$$

DISCUSSION...Bonner
AVIATION...Bonner

NWS BOU Office Area Forecast Discussion