National Weather Service Forecast Discussion

000
FXUS65 KBOU 190939
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
339 AM MDT Wed Jun 19 2019

.SHORT TERM...(Today and tonight)
Issued at 301 AM MDT Wed Jun 19 2019

Another wave of showers and thunderstorms is slipping across the
Wyoming border at this time. Will keep the mention of this in the
grids until around 12z, then these showers/thunderstorms are
expected to dissipate as the short wave exits the cwa. Patchy fog
will persist as well until around 15z mainly north of Denver and
east of I-25. For today, the mid and upper levels will becoming
drier and more subsident by this afternoon. Temperatures today
will climb back to near normal. Thunderstorm coverage will be
isolated across most of the forecast area. Fairly healthy CAPES
still exist however over the far northeast plains. SPC still
keeps a marginal risk of severe thunderstorms along the
Nebraska/Kansas border this afternoon, with a better chance of
thunderstorms east of Sterling and Akron line. CAPES still around
1500-1800 j/kg there this afternoon with the stronger storms
capable of producing moderate to heavy rainfall, hail up to nickel
size and wind gusts in the 50-60 mph range. A stronger
northwesterly flow aloft will negate any flooding threat. In the
mountains, it will be windy especially above timberline. Late
tonight, NAM12 spatial cross-sections show some mountain wave
amplification so stronger winds expected to occur in the Front
Range mountains and higher foothills of Boulder and Larimer
counties. Gusts around 50 mph range may develop in those areas
after 06z.

.LONG TERM...(Thursday through Tuesday)
Issued at 301 AM MDT Wed Jun 19 2019

On Thursday, a large upper level low will be over the Northern
Rockies with several short wave troughs rotating around it. Over
Colorado, westerly flow aloft will prevail. At the surface, a low
pressure trough will be east of the foothills. West of the trough,
gusty westerly downslope winds will prevail. East of the surface
trough, southerly flow will transport moisture northward. Surface
based CAPE east of the trough will be up to 500-700 J/kg, so a few
strong storms will be possible. Precipitable water values are
expected to range from a half inch over the higher terrain to
three- quarters of an inch across the plains, somewhat higher than
expected given the westerly flow. Temperatures will warm to near
normal with highs in the 80s across northeast Colorado. A jet at
base of the low is expected to provide lift over northern parts of
the area. This is where the most showers and storms are expected
to be.

The main upper level low tracks east across Montana Thursday
night and Friday. One piece of energy rotates south across the
Great Basin Friday and strengthens into a deep trough or closed
low over Nevada. Flow aloft turns southwesterly across Colorado.
Models show a cold front pushing south through eastern Colorado
sometime Friday. The timing is still unclear. Upslope flow behind
the front and lift from the jet, combined with precipitable water
values nearing an inch along the Front Range should result in
numerous showers and thunderstorms. May be a marginal severe
threat as well Friday. Biggest challenge for this...will it be
unstable enough for severe storms. Plenty of shear will prevail
with the strong flow aloft.

Models still trying to resolve what happens to the upper level
low/trough over the Great Basin. There is a good amount of
uncertainty on the strength and timing of this system as it tracks
east across the Central Rockies. On Saturday, there will be lift
from the jet and approaching upper level low/trough. Good moisture
will remain in place with precipitable water values near an inch
across northeast Colorado. A cooler airmass and cloudy skies is
expected to result in a chilly day. Highs may struggle to reach
the 70s. If there is enough clearing for temperatures to climb
into the 70s, there should be enough instability for a chance of
severe thunderstorms.

Another thing to watch is the cold air over the mountains with
this system. There is enough cold air to drop snow levels below
10,000 feet MSL Saturday night on the ECMWF. The NAM is quicker
with the snow levels falling below 10,000 feet MSL by Friday
night. Most models indicate the potential for snow over the north
central mountain this weekend. If the cold air arrives sooner, a
good amount of snow could fall above 10,000 feet. At this time,
best precipitation is expected to occur before the cold air
arrives.

Sunday`s forecast is still unclear. If the low/trough is moving
over Colorado or still to the west, would expected another round
of numerous showers and thunderstorms. If the low/trough is east
of the area, subsidence behind it should limit convection to
scattered at most. Either scenario should produce another cool day
with highs in the 70s.

For Monday and Tuesday, an upper level ridge starts to build over
the Southern and Central Rockies. This will start a warming trend
with highs reaching the 80s by Tuesday. Models indicate moisture
will decrease, but enough should be around for at least isolated
convection.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 301 AM MDT Wed Jun 19 2019

Generally expected VFR conditions over the next 24 hrs. Some fog
north and northeast of Denver this morning and not expected to
move into the terminals this morning. Drainage wind this morning
should keep this out of the terminals. Wind will transition to
west/northwesterly late this morning and afternoon with speeds in
the 8-12 kt range. Only isolated thunderstorm coverage today
mainly near the higher terrain and not expected to impact the
terminals at this time.

&&

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

$$

SHORT TERM...Cooper
LONG TERM...Meier
AVIATION...Cooper

NWS BOU Office Area Forecast Discussion