858
FXUS65 KBOU 180021
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
621 PM MDT Tue Jun 17 2025

.KEY MESSAGES...

- Severe storm threat with high winds and large hail will continue
  through 6 PM.

- Warm and dry conditions are expected Wednesday through the
  weekend.

- Strong signal for record breaking heat from Friday into the
  weekend, along with potential for critical fire weather
  conditions.

&&

.DISCUSSION /Through Tuesday/...
Issued at 302 PM MDT Tue Jun 17 2025

After quite an active night and morning, we have the last round
of strong/severe storms moving through the region for the next few
hours. So far, these thunderstorms have been producing hail up to
1.5", but only sub-severe wind gusts (up to 50 mph). We expect the
hail and wind threat to continue as storms travel east, but mainly
be confined to the northern/northeastern counties. SPC
mesoanalysis has a widespread SBCAPE of up to 2,000 J/Kg across
the northern plains, but the Palmer Divide and southeastern plains
are more stable due to early morning storms and overall lack of
sunshine. Model Skew-T from most recent CAMs indicate the
potential for 60 mph winds and large hail before the storms leave
our area a little after 6 PM.

This evening, there will be scattered lingering showers due to
residual moisture across the Front Range and adjacent plains.
With clearing skies overnight, relatively light winds and dew
point depressions close to zero, there could be fog across the
plains Wednesday morning. If this happens, the morning commute
would be impacted with low visibility.

A warming and drying trend will begin Wednesday afternoon as an
upper level ridge amplifies and travels east towards central
CONUS. With southwest flow aloft, warm and dry air will be
advected into the region. Temperatures should get up to the mid
80s across the plains on Wednesday. However, the main concern is
towards the end of the week, where guidance has consistently
trended towards 97+ degree max temperatures Thursday through
Saturday, with Friday being the warmest day. ECMWF and GEFS have
multiple members reaching over 100 degrees. But, there is still
some uncertainty if we will reach triple digits or not as the
ECMWF has trended down a little from yesterday. The record high
temperatures for the 20th and 21st are 99 degrees (set in 2017 and
2007 respectively), so there is a chance we could break the
record.

Another concern with the prolonged heat, is the fire weather
threat. With the drier air being advected into the region,
relative humidity values are expected to dip into the single
digits, especially on Friday and Saturday. With breezy wind gusts
possible towards the weekend, there could be elevated to critical
fire weather conditions. However, fuels still being green will
keep fire danger low. We will continue to monitor.

Guidance has continued to indicate an upper level trough
traversing the region at the beginning of the week. This will
bring more precipitation to the mountains and plains as well as a
brief cooldown.

&&

.AVIATION /00Z TAFS through 00Z Thursday/...
Issued at 553 PM MDT Tue Jun 17 2025

The threat of severe storms has subsided this evening, but some
showers still remain surrounding all the TAF sites early this
evening. We expect showers to be the main concern this evening
considering the area has been worked over pretty well through the
afternoon, and the airmass has begun to stabilize. Winds should
keep a northerly component as some heavier showers pass to the
north for the next few hours. Once showers subside (between 1-2Z),
we do not expect any CIG issues through the TAF period. The only
caveat would be if FG develops (~20% chance) in the early morning
hours as some hi-res guidance show a signal between 8-13Z.
However, with winds expected to turn to the south by this time,
the more likely scenario would be that it stays out of the TAF
sites with some aid from light downsloping off the Palmer Divide.

Light winds are expected through the day tomorrow with a normal
diurnal shift "around the horn" through the morning, becoming
easterly by the afternoon.


&&

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

&&

$$

DISCUSSION...Ideker
AVIATION...Bonner