654
FXUS65 KBOU 220121
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
721 PM MDT Tue May 21 2024

.KEY MESSAGES...

- Scattered showers and isolated thunderstorms continue through
  this evening. Small hail and gusty winds are possible from the
  storms.

- Ongoing light snow showers may lead to slick travel along
  mountain passes through Wednesday morning.

- Warming/drying trend for the second half of next week with
  elevated fire weather conditions likely Thursday.

&&

.UPDATE...
Issued at 721 PM MDT Tue May 21 2024

Updated to increase PoPs over the plains where there is a good
amount of rain showers now, and one more scattered batch to come,
which is crossing the Urban Corridor. Though skies are mostly
cloudy to overcast now, the airmass stabilizes and drier air moves
in overnight resulting in mostly clear skies after midnight.
Lowered temperatures a couple degrees, which puts overnight lows
in the 30s. The typical low lying areas may fall into the lower
30s and may see frost. Therefore issued a Frost Advisory for
tonight and early Wednesday morning with temperatures falling to
32-37 degrees.

&&

.SHORT TERM /Through Wednesday/...
Issued at 241 PM MDT Tue May 21 2024

Radar reflectivity has increased across the foothills and plains
displaying scattered to numerous showers. A few webcams along
mountain passes present flurries for areas above 8,500 feet. This
pattern will continue as the shortwave trough passes through
northeastern Colorado. Snowfall totals for areas above 9 thousand
feet range between 1-4 through Wednesday morning. Showers should
become isolated by midnight tonight. With model soundings along the
plains showing an inversion and low level moisture lingering
through early morning Wednesday, it is possible patchy fog could
occur along I-25 corridor near the Wyoming Colorado border and
along I-76 near Morgan county.

Cross sections indicate drier air throughout the 500-700mb layer
thus limiting any storm development Wednesday afternoon. An isolated
shower or two could occur for the southern foothills and Palmer
Divide but chances are low (10-15%). Wednesday afternoon 700mb
ing.temperatures range between 3-6C along the foothills and
plains which should lead to a slight warm up compared to
yesterday. Foothills and plains range from 60-72F Wednesday
afternoon; Additionally, the mountains and valleys increase near
45-60F. Partly cloud skies will begin to clear by late Wednesday
afternoon.

&&

.LONG TERM /Wednesday night through Tuesday/...
Issued at 241 PM MDT Tue May 21 2024

Colorado will be under the influence of a quasi-zonal flow Wednesday
night through Monday with occasional upper level shortwaves and
cold fronts moving across the Northern and Central Rockies. This
pattern should result in near normal temperatures along with
isolated to scattered afternoon and evening showers and storms
across the forecast area most days. Warm temperatures combined with
breezy conditions and low relative humidity may lead to fire weather
concerns across South Park, the Palmer Divide and much of the
plains Thursday afternoon and evening. A cold front expected to
move across Northeastern Colorado Friday evening may produce wind
gusts up to 35 mph across the northern sections of the plains.
Friday should be the coolest day of the week in the wake of the
front with temperatures only climbing into the upper 60s on the
plains. Most of the showers and storms during this period should
be high based with gusty winds and brief light to moderate rain.
However, there is the potential for some stronger storms across
the plains, mainly east of the Front Range Urban Corridor, both
Thursday and Saturday afternoon/evening due to better available
surface moisture along with increased convergence and lift
associated with the passing shortwaves and cold fronts.

Warmer and drier weather is expected on Tuesday as upper level high
pressure builds over the Rocky Mountain Region.

&&

.AVIATION /00Z TAFS through 00Z Wednesday/...
Issued at 543 PM MDT Tue May 21 2024

Threat for showers continues through 03Z with ceilings down to
4000 feet. Chances for a thunderstorm continue to decrease as the
showers stabilize the airmass. However, can`t totally rule out a
brief weak thunderstorm affecting the terminals. Drier moves in
overnight with mostly clear skies expected by 06Z. Southerly winds
should prevent fog from forming. Best chance for fog will be in
the low lying areas north of Denver, in the GXY area. For
Wednesday, southerly winds to continue through the morning.
Eventually expect a Denver Cyclone to form. As the cyclone
progresses eastward, a wind shift from the south to the north to
northwest is expected sometime after 20Z.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from midnight tonight to 8 AM MDT Wednesday for
COZ038-041>047-049.

&&

$$

UPDATE...Meier
SHORT TERM...AD
LONG TERM...JK
AVIATION...Meier