932
FXUS65 KBOU 170543
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1143 PM MDT Wed Apr 16 2025

.KEY MESSAGES...

- Transition day Thursday with gusty winds and arrival of a
  significant cold front.

- Critical fire weather conditions expected late Thursday morning
  through the afternoon from South Park & southern foothills
  through east central Colorado. Denver still on the edge.

- Moderate to locally heavy snow for mountains, foothills Thursday
  night through Saturday; A few inches for the lower elevations,
  with minor travel impacts.

- Much colder Friday and Saturday, with warming temperatures
  Sunday through Tuesday.

&&

.UPDATE...
Issued at 808 PM MDT Wed Apr 16 2025

High based showers along with an isold tstm have been producing
gusty winds early this evening. Expect most of the activity to end
over the far nern plains in the next hour or so.  The nrn mtns
will continue to see periods of showers overnight as that area
will be in the favored left exit region of an upper level jet.

&&

.SHORT TERM /Through Thursday/...
Issued at 245 PM MDT Wed Apr 16 2025

Satellite initially showed trapped waves indicating mid level
stability, but now some shallow cumuliform growth on those waves.
The waves are also slowly diminishing per recent trends as the
airmass stability decreases. Thus, a few showers have popped up on
radar.  That said, they are high based with only light
precipitation/sprinkles.  Given the well mixed sub-cloud layer and
DCAPE near 800 j/kg, we`ll likely see a few gusts to 30-40 mph out
of those into the evening hours.  The northern mountains will be
getting into the left exit region of an upper jet, so that should be
enough to keep showers going there through the overnight. We made a
slight increase in mountain PoPs and QPF, with snow amounts on a
couple ridgelines expected to be near 3". Travel impacts should be
minimal in all but the high passes like Rabbit Ears and Cameron.
Eisenhower Tunnel area will likely see less coverage.

On Thursday, a cold front is likely to sneak into northeast Colorado
in the morning. It`s quite uncertain how far south it makes it, but
typically a little farther than most models suggest.  At this point,
the front is already through southeast Montana so we`d expect it to
have at least enough push to make it to about Denver by mid to late
morning before stalling or washing out, and then retrograding a tad.
That makes for a trick temperature forecast with a relatively high
bust potential anywhere from Denver northward.  That frontal
location/retrograde will also affect fire weather concerns - see
discussion below.  South of the front, west/southwest winds will be
howling with gusts to 35-45 mph expected most of the day. By late
afternoon, we do expect a more significant push of the front and
that will bring strong, gusty north winds across all of the
plains. With gusts to 45 mph or more, there may also be some
blowing dust in spots. We`ll also see a plunge in temperatures
with the frontal passage - likely a quick 20 degree F drop late in
the afternoon.

With regard to precipitation, there is some drying aloft noted
during the afternoon. Thus, a break in northern mountain
precipitation is expected for a few hours, before convective showers
fill in again with daytime heating and destabilization. More
widespread precipitation will develop in the evening - more on that
in the long term section below.

&&

.LONG TERM /Thursday night through Wednesday/...
Issued at 245 PM MDT Wed Apr 16 2025

Rain and snow will spread south across our area Thursday evening
into Friday morning as moisture deepens behind Thursday`s front,
with the lower elevations seeing the dominant precipitation type
transition to snow mid to late evening on Thursday. Warm
temperatures preceding this system should cause road temperatures
to lag noticeably behind their ambient counterparts, so
accumulations outside of colder surfaces are expected to be
limited for the lower elevations until reinforcing cold air
arrives later on Friday.

Synoptically, we`ll have weak QG ascent in place, with a departing
jet to our southeast along the eastern periphery of a shearing
trough over Utah. At the surface, winds will maintain a prevailing
northeast direction in the morning, keeping temperatures cool and in
the 30`s for the urban corridor, with gradual veering towards
increasingly easterly flow later in the afternoon. Combined with
steeper lapse rates during the second half of the day, snowfall
intensity should pick up across all areas (i.e. mountains ,
foothills and plains) Friday afternoon as the colder trough axis
passes overhead. The lower elevations will have better potential for
accumulations on all surfaces early Friday morning and later in the
day, but unless temperatures trend a few degrees colder, travel impacts
should remain minor for most of the I-25 corridor. However, will
need to keep an eye on areas closer to the foothills and the
Palmer Divide, which may creep into Winter Weather Advisory
territory.

By daybreak Saturday, mid-level dry air will rapidly intrude and put
an end to most of the snow by midday. Storm-total snowfall of 6 to
12" is expected to be quite widespread for our central foothills
and the mountains, with locally higher amounts possible.
Highlights have been posted for these areas through early
Saturday afternoon. Several inches can be expected for the urban
corridor, but with melting, compaction, and marginal temperatures,
travel impacts will be reduced (although impacts to vegetation
will likely be more notable). Lastly, robust south/southeast flow
Friday and Friday night across Park County will present a
favorable upslope environment for moderate snowfall, so have
extended winter weather headlines into South Park as well.

Only modest warming is expected Saturday as we hold on to some cloud
cover and cool easterly flow over the plains, so temperatures
shouldn`t climb out of the low/mid 40`s outside of the northeast
plains.

As flow aloft turns more zonal Sunday through Tuesday, temperatures
will warm back to near-normal values, with breezy conditions across
much of the region. The flow pattern would sustain some chances (20-
50%) of showers mainly in the high country most days, with dry
conditions prevailing across the lower elevations.

&&

.AVIATION /06Z TAFS through 06Z Friday/...
Issued at 1143 PM MDT Wed Apr 16 2025

VFR will prevail through Thursday morning and most/all of Thursday
afternoon. Southwest winds to prevail into Thursday morning 15Z,
then the wind forecast becomes very uncertain. A weak front pushes
into northeast Colorado Thursday morning, possibly as far south
as DEN. Some models show this front stalling out with variable
winds into Thursday afternoon. Other models show southwest winds
prevail through the day until the main cold front arrives. The
main cold front plows south through the Denver area bring
northeast winds to 40 knots. Northeast winds continue through
Thursday and slowly decreases behind the front.

Showers a possibly a thunderstorms (10% chance) will be possible,
mainly after 00Z Friday. It becomes cold enough for all snow
after 06Z Friday. However, cross sections only show the airmass
saturated up to 700mb until 12Z Friday. If this happens to be the
case, we could see a brief period of freezing drizzle. Air
temperatures will be in the upper 20s during this time. This would
limit impacts to elevated surfaces.

&&

.FIRE WEATHER...
Issued at 245 PM MDT Wed Apr 16 2025

While fuel status is somewhat mixed with patchy greenup over the
Palmer Divide and east central plains, we`ve upgraded to a Red
Flag Warning for those locations due to still dry fuel loads from
last season and the magnitude of winds and low humidity. We`ve
also included South Park and the Southern Front Range Foothills.
Gusts of 35-45 mph are expected, with humidity dropping to 9-14%,
lowest in southern Lincoln County. Farther north, there is much
more uncertainty with how winds evolve due to a cold front. That
front is likely to stall near I-70 on the plains in the mid to
late morning, and then retreat northward a bit before plunging
south late in the afternoon. Thus, there`s still uncertainty with
regard to the wind forecast. At this time, we still think a narrow
corridor (south of I-70) will blow quite strong for a little while
with RH down to criteria, but that`s only about half of the zone
and still plenty of uncertainty with regard to how long that would
occur (need 3 hours for Red Flag issuance). Thus, we kept zones
240 and 245 (Denver and rural Adams and Arapahoe Counties) in a
Fire Weather Watch until more certainty can be achieved.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Thursday evening through late Friday
night for COZ031-033-034.

Winter Weather Advisory from 4 AM Friday to 6 AM MDT Saturday
for COZ035-036.

Red Flag Warning from 10 AM to 7 PM MDT Thursday for COZ214-216-
241-246-247.

Winter Weather Advisory from 9 AM Friday to 6 AM MDT Saturday
for COZ037.

Fire Weather Watch from 10 AM MDT Thursday through Thursday
evening for COZ240-245.

&&

$$

UPDATE...RPK
SHORT TERM...Barjenbruch
LONG TERM...Rodriguez
AVIATION...Meier
FIRE WEATHER...Barjenbruch

NWS BOU Office Area Forecast Discussion