630
FXUS65 KBOU 051944
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
144 PM MDT Tue May 5 2026

.KEY MESSAGES...

- Heavy, wet snow will likely damage tree limbs and powerlines,
  resulting in scattered power outages along the Front Range and
  I-25 Corridor.

- Significant travel impacts for the northern mountains and
  foothills, with locally greater than 2 feet of snow. Slick and
  slushy roads possible overnight into Wednesday morning for the
  I-25 Corridor.

- Snow tapers off north to south late Wednesday morning into the
  afternoon.

- Return to a warmer weather for the latter half of the week into
  early next week, with just a couple chances of showers and
  storms due to passing disturbances.

&&

.DISCUSSION /Through Tuesday/...
Issued at 144 PM MDT Tue May 5 2026

A lot to talk about in the short term, with potential high impact
late season winter storm shaping up for the Front Range.

Current analysis shows a plume of mid level moisture in a region
of moderate frontogenesis stretching across northern Colorado.
Precipitation was enhanced in the northern tier of Colorado
counties, with persistent periods of moderate rain/heavy mountain
and foothill snow. The snow level had dipped down as low as ~4600
feet early this morning in that band, but has since risen to
around 5500-6000 feet with May solar insolation and lack of
further cold advection. This main band will start to sink
southward through this evening as the kicker shortwave drops
across the northern Rockies. This is where it gets interesting...

With an expected uptick in precipitation rates late this afternoon
and early evening, we should see snow levels start to drop again
with increased diabatic cooling. However, we`ll still be fighting
wet bulb issues as we don`t see much in the way of cold advection
in the low levels. At the same time, there was already one surge
across the Wyoming border, and these types of systems can be
difficult to time/place the next surges so some opportunity for
low level cooling still exists - especially with the loss of
daytime heating. Thus, we still expect a changeover to all snow
above 4,500-5,000 feet through the course of this evening. How
much accumulates is yet another question though, as the ground is
still quite warm. We could/should even see a brief lull late this
evening, before the next push occurs overnight.

That next push will be driven by the upper level trough dropping
across the Rockies. This will bring in a more organized push of
upslope and cold advection, which would be more typical of a Front
Range winter storm. Thus, snowfall ratios and rates are expected
to have an uptick from midnight/shortly thereafter through about 9
am Wednesday morning. Forecast soundings show near moist adiabatic
lapse rates redeveloping as we cool aloft as the upper level
trough approaches. With upward forcing and upslope, we`d expect
snowfall rates to increase to 1" per hour (locally 2"/hr in the
foothills). That`s when more significant impacts from this late
season winter storm can be expected as heavy, wet snow
accumulating on trees will likely result in broken tree limbs and
scattered power outages. Road conditions will deteriorate
significantly across the foothills as deep snow accumulations, and
slush expected to develop in the I-25 Corridor as road
temperatures cool in the overnight and early morning commuting
hours of Wednesday. The snow will taper off north to south late
Wednesday morning into early afternoon. All this is forecast
relatively well by the previous shifts, so we`ll maintain all
Winter Storm Warnings and Advisories as is.

With regard to specific impacts, it is difficult to pinpoint the
total snow accumulations and thus load on fully leafed out trees
and potential damage. The latest guidance (nudged for decreasing
snow levels this evening) supports 5-8" over most of the I-25
Corridor, with local heavier amounts >9" at the base of the
foothills. However, there is uncertainty in the accumulations as
near surface temperatures are relatively warm and we`re unsure of
the changeover time to all accumulating snow as discussed above.
Also, there is a fair amount of variation in the latest guidance,
with some hitting the northern tier of counties more than Denver,
while others still favor locations from Boulder southward with the
heavier totals in the 24 hours from 6 pm this evening - 6 pm
tomorrow. Average QPF pointed to near 1" of precipitation in this
time frame, most of which should be snow. Totals in the northern
Front Range Mountains and Foothills will be much greater (close to
2 feet and locally higher), given the already impressive snow
totals approaching a foot in Estes Park and surrounding areas.
Mountain areas farther south should see amounts closer to 6-14",
while mountain valleys and plains east of the I-25 will be closer
to 2-6".

Snow accumulation numbers like those mentioned above for the I-25
Corridor can cause considerable damage. Just 3-5" of wet snow
typically causes small limbs to break, while amounts closer to 8"
can produce significant damage to large trees and limbs, and up
to 12" could result in widespread/nearly catastrophic tree
damage. If we did see those heavier totals (20-30% probabilities)
they should be confined to right near the base of the foothills.
Trees or limbs falling on powerlines will likely cause scattered
power outages, and provide a hazard to pedestrians.

After this storm exits by late afternoon/early Wednesday evening,
drier weather arrives for most of Thursday. Cold temperatures
Wednesday night under clearing skies will warrant another Freeze
Warning with lows in the 22 to 28 degree range for most locals,
coldest in the low lying areas of the plains. A couple spots
in/near Denver could only drop to ~30F with return of downslope.

The next chance of showers will arrive late Thursday afternoon or
evening with a fast moving disturbance in northwest flow, while
another arrives toward Saturday and Saturday night.

Outside of that, look for relatively mild and pleasant
springlike weather.

&&

.AVIATION /18Z TAFS through 18Z Wednesday/...
Issued at 1224 PM MDT Tue May 5 2026

Cross sections and soundings point to keeping ceilings in the
BKN-OVC010-025 range through the afternoon. Will go with visibilities
in the 3-5SM range due to BR and sometimes -RA or -SHRA. Latest
timing for all snow at DIA should be about 01Z. From then on,
will keep ceilings below OVC006 and visibilities of 1/2SM with SN
FG or FZFG. Light east and northeasterly winds are expected at DIA
through around mid evening. More northerly directions are
expected from mid evening continuing overnight into Wednesday.
Speeds look to be under 10 knots through much of tonight with a
slight increase around 12Z Wednesday morning. There doesn`t look
to be any improvement until late Wednesday morning.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 8 PM this evening to 3 PM MDT
Wednesday for COZ030-032-037-042>046-049.

Winter Weather Advisory until noon MDT Wednesday for COZ031.

Winter Storm Warning until 3 PM MDT Wednesday for COZ033>036.

Winter Storm Warning from 8 PM this evening to 3 PM MDT
Wednesday for COZ038>041.

Freeze Warning from 8 PM Wednesday to 8 AM MDT Thursday for
COZ038>051.

&&

$$

DISCUSSION...20
AVIATION...66

NWS BOU Office Area Forecast Discussion