240 
FXUS65 KBOU 261508
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
908 AM MDT Tue May 26 2020

.UPDATE...
Issued at 903 AM MDT Tue May 26 2020

Only minor adjustments to the grids. No updates needed at this
time.

&&

.SHORT TERM...(Today and tonight)
Issued at 312 AM MDT Tue May 26 2020

WNW flow aloft will be over the area today as some mid and high 
level moisture move across this aftn. Only some clouds will 
accompany this moisture.  Highs will be warmer as readings reach 
the mid 70s to lower 80s over nern CO.

For tonight, a weak disturbance embedded in the flow aloft will 
move across overnight. There could be a a few high based showers, 
over the nrn mtns, late tonight with this feature. 

.LONG TERM...(Wednesday through Monday)
Issued at 312 AM MDT Tue May 26 2020

On Wednesday the deep cutoff low slowly moves across the Arklatex 
region while the blast furnace ridge builds across CA/AZ. That 
leaves us in between the two with northwest flow aloft. A decent 
short wave trough moves across the northern Rockies into the high 
plains late Wednesday into early Thursday. The GFS and NAM are 
very aggressive with moisture availability associated with the 
short wave trough. PW values go to 1.0-1.2" across the plains by 
midnight Thursday. EC isn't too far behind with 0.80-1.0", which 
is over 2 standard deviations above normal for that date. QG lift
from the trough is weak, but there is a 65 kt jet out of the 
northwest that places NE colorado in the left exit region, 
favorable for lift. Some convective instability is available 
Thursday afternoon via diurnal heating, and continues into early 
Thursday morning and as the cold pool aloft moves across northern 
Colorado. Am not buying the significant rain scenario seen on the 
GFS for late Wednesday into early Thursday yet given all forcing 
is weak and we believe the moisture content is a bit overdone. 
Nevertheless, thunderstorm chances are in place from Wednesday 
afternoon first over the high country, then spreading east and 
continuing past midnight Thursday given the presence of the 
trough. Instability and shear are both limited, so not expecting 
any strong to severe thunderstorms at this time. The warming trend
continues Wednesday with low 80s across the plains. 700 mb temps 
warm to +10 degC by Wednesday afternoon and will support temps in 
the mid to upper 60s in the mountain valleys and close to 50 at 
treeline.

On Thursday the blast furnace ridge over the desert southwest shifts 
slightly east, a tad closer to Colorado. This will usher in drier
air, and only isolated thunderstorms are possible across the high
country given the limited moisture, and then moving east across 
the plains. A surface cold front moves across the plains early 
Thursday with northeast flow near the surface, which will hold 
dewpoints in the upper 40s so it's not out of the question for a 
sprinkle or two across the northeast plains Thursday afternoon. 
There is a good shot of cold advection on the backside of the 
trough, resulting in 700 mb temps around +5 degC. Thus, highs 
across the plains will remain in the low to mid 70s, with low to 
mid 60s in the foothills and mountain valleys.

On Friday an impressive late season extratropical cyclone approaches 
the Central California coast, which will act to strengthen the 
downstream ridge and push it further east. By Friday afternoon 
the ridge axis is across the Four Corners. Flow aloft will be weak
out of the northwest. There is enough mid-level moisture for 
scattered thunderstorms in the afternoon. Across the plains, 
strong southeast return flow advects dewpoints around 50 deg into 
our area. Instability will thus respond accordingly with SBCAPE 
500-1000 J/kg along the I-25 corridor. Wind shear is weak, likely 
limiting severe potential but nevertheless thunderstorms are 
possible, with the best chances across Park County and the Palmer 
Divide. With the ridge axis in our state, temperatures will warm 
back into the low to mid 80s across the plains, and 70s in the 
mountain valleys and foothills.

Saturday through Monday the ridge axis moves over Colorado during
the weekend and into the Central plains by Monday. There 
continues to be moisture advection across the top of the ridge, 
especially Saturday and Sunday and Monday when subtropical 
moisture works it's way north out of old Mexico on the backside of
the ridge. Ensemble based PW values Sunday and Monday look to be 
2 standard deviations above normal for this time of year, as each 
afternoon values are forecast to be 1-1.25". Thus, afternoon 
thunderstorms will continue to be in the forecast, especially for 
the high country (Park County especially), and those storms will 
move off the mountains each afternoon. On Saturday and Sunday they
stand a better chance of surviving east of the mountains with 
good southeast return flow and mid 50s dewpoints possible. Overall
not buying the far above normal PW values because it's unusual 
this time of year in the middle of a ridge. Wind shear is weak 
Saturday through Monday with the ridge close by so do not expect 
severe thunderstorms during this period, but if that much moisture
makes it's way into Colorado we'd have to watch out for isolated 
heavy rain producing storms. At this time we have low confidence 
in that scenario playing out. Much more confidence in hot 
temperatures this weekend into early next week, with upper 80s to 
low 90s expected across the plains.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 903 AM MDT Tue May 26 2020

VFR with no significant impacts expected. West/northwest winds
this morning will become more northerly after 18z.  By early evening,
winds will become more east/southeast and then transition to 
drainage by 06z.


&&

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

$$

UPDATE...Cooper
SHORT TERM...RPK
LONG TERM...Schlatter
AVIATION...Cooper