National Weather Service Forecast Discussion

000
FXUS65 KBOU 252018
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
218 PM MDT Sat May 25 2019

.SHORT TERM...(This evening through Sunday)
Issued at 215 PM MDT Sat May 25 2019

Southwest flow aloft ahead of an upper trough pushing into the
Great Basin has brought another nice seasonable day to the area
today. Southeasterly surface flow into the plains this afternoon
and tonight will aid in keeping a chance for thunderstorms over
the northeastern plains, where CAPE values will still be elevated
and shear still around 40 kts. Gusty winds to 45 kts and small
hail up to penny size may occur from a stronger storm. These
storms will continue pushing northeast tonight and should be done
and east of the forecast area by midnight. An upper low over the
OR/WA coast will drop south into the upper trough tonight to lower
surface pressure over the western US. High surface pressure over
the Great Plains will aid in southeasterly surface flow advecting
higher moisture into our plains tonight with dewpoints in the 50s.
Low clouds and patchy fog are expected to form and spread north
and west into the rest of the plains and urban corridor in the
early morning hours. Forecast soundings show a pretty shallow
layer, so at this point not expecting much drizzle, but can`t rule
it out.

A surface low will form near the Palmer Divide Sunday then begin
to push northeast forming a dryline. A speed max in the southwest
flow will move over southeastern Colorado to put our forecast
area into the left exit region by the afternoon. Once the low
clouds and fog burn off, warmer temperatures and dewpoints in the
50s and 60s east of the dryline will aid in CAPE values of 2500
J/kg or more. This line is expected to form somewhere along and
east of a line from the WY/NE/CO border south to Limon. With shear
values of 40 to 60 kts, there is an enhanced probability of
seeing severe strength storms in the area described above. Strong
damaging winds and large hail, up to 2 inches at least, will be
possible, with an outside chance of a tornado. Further west of
this line, over the urban corridor and mountains, weaker isolated
to scattered storms are expected in the afternoon causing little
but gusty winds and small hail.

.LONG TERM...(Sunday night through Saturday)
Issued at 215 PM MDT Sat May 25 2019

For Sunday night, the far northeast plains of Colorado
will remain under a severe weather threat with sufficient low
level moisture with dewpoints in the 50s to around 60 and sfc
based CAPES in excess of 2000j/kg. SPC has upgraded the day 2
outlook to enhanced over the far northeast corner. Thunderstorm
activity will be more isolated further west with much drier low
level flow.

For Monday, the Great Basin low will move into southeast Utah by
late in the afternoon with a continued strong southwest flow aloft
over Colorado. There will also be a strong 100+kt jet streak which
will slice across central portions of Colorado. Models are in
general agreement with the track, with the NAM being the quickest
and a bit further north of other model players as the low moves
northeast across central Colorado. Best chance for showers and
storms will be over the mountains and far northern plains with best
moisture and QG ascent. There will be a drier, low level south to
southwest flow on the plains. Temperatures will be cooler on
Monday as the colder air mass works in from the west as 700mb
temperatures cool to around +8c on the plains.

An associated cold front will push southward across the plains late
Monday night with cooler temperatures with a better chances of
showers, again, especially over northern sections of Colorado. The
I-25 corridor will see some local downsloping from the northwest
which could limit shower activity. A secondary surge of colder air
poised to drop southward Tuesday night with temperatures dropping
into the mid and upper 30s on the plains.

The storm system will track into Nebraska by Tuesday evening but
then lingering troughiness across of the west will remain through
the end of the week. Across Colorado, we will have weak high
pressure ridge under a moderate westerly flow aloft. Temperatures
by Thursday and Friday will return to near normal for this time of
year with only isolated late day showers and storms. Best chances
for showers will remain over the mountains.


&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 215 PM MDT Sat May 25 2019

There is the potential for isolated thunderstorms, but these are
expected to remain north of the terminals at this time, so will
not be mentioned in the TAFs. Some high resolution models
indicate some convective activity between 22-00z, however
ceilings/vis should remain above ILS. Southeast winds will
continue with gusts 20-25 kts this afternoon. A cyclone will
remain around the KDEN overnight, with moisture increasing over
the plains. Areas of fog are expected to advect in as well, but it
will depend on the wind direction on whether it will impact the
terminals. Best chance will be at KDEN and KBJC, after 10z, but
should be short-lived as drier southwest flow is expected to push
off the Palmer Divide early in the morning. Another day of strong
southeast winds are expected Sunday early on before the
cyclone/dryline pushes east. Isolated thunder possible for the
terminals Sunday afternoon.

&&

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

$$

SHORT TERM...Kriederman
LONG TERM...Entrekin
AVIATION...Kriederman

NWS BOU Office Area Forecast Discussion