616 
FXUS65 KBOU 290259
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
859 PM MDT Sat May 28 2022

.UPDATE...
Issued at 858 PM MDT Sat May 28 2022

Critical fire weather conditions on the plains east and south of 
the Palmer Divide lasted a few hours longer than expected, so I 
extended our Red Flag Warning for fire zone 247 (southern Lincoln 
and southeastern Elbert Counties) through about sunset. Conditions
have improved and I allowed the warning to expire. We maintain 
our Fire Weather Watch for the same area tomorrow afternoon. 
Mostly cloudy skies should persist overnight but the lower 
elevations remain mostly dry and only light precipitation should 
be confined to the high terrain. The forecast is performing well 
with only minor updates this evening.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 224 PM MDT Sat May 28 2022

Tonight, the ridge axis aloft will shift to the east with an 
increasing southwesterly flow developing. Instability still 
appears to be limited, with weak high based convection developing 
with the cloud deck around 500 mb. Still looks like just some 
virga will develop along the urban corridor, but chances for 
thunderstorms will improve over the mountains and maybe NE corner 
of the state by 00z. Most of the HiRes models develop the 
strongest thunderstorm potential east of CO this evening, so pops 
in the northeast corner will still be low, 10 percent at best. 
More a mix of scattered showers and thunderstorms developing over 
the mountains this evening. The HRRR shows better shower and 
thunderstorm coverage there. A cold front does push across the 
plains late tonight/early Sunday morning, but more of a 
weak/subtle wind shift expected. 

On Sunday, the upper level trough will be over southern ID with a 
moderate to strong southwesterly flow over CO.  The forecast area 
will be on the north side of a 90kt upper level jet over southeast 
CO. Moderate mid/upper large scale QG ascent developing (around 
minus 20 mb/hr) over northern and eastern CO by late afternoon. 
Increasing PWAT values to around 0.6 inches at Denver, with a 
lowering LCL to around 700 mb Sunday afternoon.  It will be cooler 
with high temperatures closer to seasonal normals in the mid 70s. 
The models show better shear and instability profiles for 
thunderstorms Sunday afternoon. NAM12 forecast sounding near 
Sterling indicates surface based CAPES 1000-1200 j/kg Sunday 
afternoon, with sfc-3km SRH values around 100 m2/s2.  Model 
reflectivity also support the strongest storm development to the 
north and northeast of Denver in the afternoon. SPC assessment of 
Marginal/Slight Risk of severe thunderstorms still looks reasonable. 
Main threats would be damaging wind and large hail, but enough 
speed/directional shear to support isolated tornadoes too. Much 
lower dewpoints over the Palmer Divide would form a dryline, with a 
Denver cyclone forming a boundary that should help initiate 
thunderstorm after 21z east/northeast of Denver. To the south of the 
line, critical fire weather conditions possible over southern 
Lincoln County similar to this afternoon. Reference the fire weather 
discussion. In the mountains of mix of rain/snow showers and 
thunderstorms in the afternoon, with the snow level above 10 
thousand feet. Higher southwest facing slopes could see 1-2 inches 
of snowfall.  

.LONG TERM...(Sunday night through Saturday)
Issued at 224 PM MDT Sat May 28 2022

Cooler unsettled weather is expected across North Central and 
Northeastern Colorado Sunday night through Tuesday as a large 
upper level trough dominates the western half of the U.S. Sunday 
night into Monday morning, a closed low within the upper trough 
will track across Southern Wyoming with a 115KT+ upper jet over 
Southern Colorado. In addition, models are showing a cold front 
moving across Northeastern Colorado during the evening hours with 
some upslope flow developing across the plains. The combination of
QG ascent from the upper trough and jet, and increased moisture 
and upslope flow should result in a continuation of scattered to 
numerous showers and storms across much of the forecast area. Some
light snow is forecasted across the mountains above 10,000 feet 
with only light accumulation expected over the higher peaks. 
Further east across the plains, Some of the models are indicating 
CAPE's over 1000 J/KG and plenty of shear which would suggest the 
potential for a few strong to severe storms during the early 
evening hours. 

Cool and showery weather is expected Monday afternoon through 
Wednesday with max temperatures in the lower to mid 60s on the 
plains. The cool and stable airmass should limit any thunderstorm 
activity both days. A potent shortwave moving across the state 
should enhance precipitation chances across much of the CWA late 
Tuesday into Wednesday with a few inches of snow possible over the 
higher mountain peaks. 

Warmer and drier conditions are expected Thursday into the weekend 
as upper level high pressure builds over the Rocky Mountain Region. 
More typical June weather is expected Friday into the weekend as 
increasing low level moisture is progged to move into the plains 
with isolated to scattered storms possible. The combination of 
increased instability, ample shear along with an occasional passing 
upper level shortwave could lead to some of the storms becoming 
strong to severe. At this time, it appears that any severe threat 
will be focused along a dry line east of Denver. However, with the 
uncertainty of outflow interactions and the location of the Denver 
Convergence Zone, can't rule out the possibility of of one or two 
stronger storms further west across the Front Range Urban Corridor. 

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 552 PM MDT Sat May 28 2022

Winds are currently out of the WNW to NW at 10-15 kts. Winds 
trend westerly this evening gradually returning to light drainage
before midnight. Sunday morning, may see a brief period of SSE 
winds at 8-11 kts before transitioning to SW. Most model guidance
shows increased chances for showers/thunderstorms aoa 18z. 
Although confidence is lower in the chances a storm may directly 
pass over the terminal, the best chances will be aoa 21z as 
showers/storms become higher in coverage. Gusty winds will be the 
primary threat with the storms. Dry conditions in the low levels 
will support virga earlier in the afternoon before better moisture
moves in, so gusty outflow winds are possible. With 
showers/storms in the area, confidence is lower in the wind 
direction for the afternoon period, but will likely have a W/WNW 
component. There will be a push of NE winds later in the afternoon
with some variation in the timing from model to model (Generally 
in the 22-00z timeframe). Will mostly see VFR conditions for the 
period with brief periods of MVFR possible in a passing shower or 
thunderstorm. 


&&

.FIRE WEATHER...
Issued at 224 PM MDT Sat May 28 2022

No changes to the ongoing Red Flag Warning this afternoon. On 
Sunday, critical fire weather conditions possible over southern 
Lincoln County similar to this afternoon. Consequently, we issued
a Fire Weather Watch for Sunday afternoon too. Cooler and
wetter weather will reduce the fire danger across the forecast
next week next week. The exception may be across extreme southeastern
Elbert and southern Lincoln Counties where low relative humidity 
and gusty winds could result in elevated fire weather conditons 
Monday afternoon. 

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch Sunday afternoon for COZ247.

&&

$$

UPDATE...EJD
SHORT TERM...Cooper
LONG TERM...jk
AVIATION...Mensch
FIRE WEATHER...Cooper/jk