National Weather Service Forecast Discussion

000
FXUS65 KBOU 200204
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
804 PM MDT Fri Apr 19 2019

.UPDATE...
Issued at 804 PM MDT Fri Apr 19 2019

Light winds and clear skies will prevail tonight with mild
temperatures. No changes to the forecast planned. Still on track
for a warm day tomorrow with highs near 80s degrees. A weak short
wave trough is expected to produce isolated high based
showers/thunderstorms, mainly over the mountains. A few locations
in the mountains could see light rainfall, otherwise across the
lower elevations just gusty winds are expected with convective
activity.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 134 PM MDT Fri Apr 19 2019

Dry air coming over Colorado in light northwest flow aloft will
make for a quiet night. This should make for good radiational
cooling in the mountain valleys where we dropped low temperatures
a couple of degrees. Elsewhere light drainage winds should help
keep temperatures up a bit and the forecast looks good. For
Saturday it should be nearly clear in the morning, then some
moisture and a little cooling aloft should produce scattered
showers and a few thunderstorms over the mountains in the
afternoon. It looks like this forcing won`t be to the plains yet
in the late afternoon, and the very dry low levels would likely
inhibit surfaced based convection anyway. There`s a chance of some
clouds and a little cooler west wind from convective outflow
coming off the mountains near the end of the day. All this is
covered pretty well in the existing forecast.

.LONG TERM...(Saturday night through Friday)
Issued at 134 PM MDT Fri Apr 19 2019

For Saturday night into Sunday, an upper shortwave trough will
stretch from Nevada into Colorado with increasing moisture over the
western half of the state. This trough will help to increase lift
over the region into Sunday morning. By later Saturday afternoon
some convection will be possible over the higher terrain with a
slight chance of thunderstorms. PWAT values are lower during this
period so main threats will be rain with gusty winds and lightning.
A surface low over the plains will move SE with increasing westerly
winds off the mountains. Model cross sections show a drier inverted-
V pattern over the plains that would result in mainly winds and less
chance for precip late Saturday.

For Sunday morning, the main piece of energy will be pushing into
eastern Colorado and western Kansas. Moisture will increase over the
higher terrain with snow levels dropping between 9 and 10,000ft. By
late Sunday morning a shallow front will push out of the North onto
the plains turning winds more NE by the afternoon. With the front
pushing in a tad later than previous model runs, solar insolation
may be strong enough to bring highs into the upper 50s to lower 60s
across the plains and foothills. Model CAPE values responded with
returns of 300 to 1200 J/kg across the plains by Sunday afternoon
according to the NAM. This will help to bring a slight chance of
thunderstorms to the mountains, foothills and portions of the
eastern plains. Model cross sections show lapse rates in the low
levels at 8.7 C/km, however, deep bulk shear is relatively weak with
values in the 20s. PWAT values begin to increase at this time with
values approaching the climatological max for this time of year of
0.66 inches. This means we could see some thunderstorm development
across the urban corridor and foothills with the main threats being
moderate to heavy rain, small hail and gusty winds. Mean wind values
are relatively weak so these most likely will be slow movers that
could drop a decent amount of rain in a short period of time. For
the slightly higher elevations of the foothills, rain is still
expected Sunday afternoon but small perturbations in the timing of
the colder air and the influence of the lift could result in an
earlier onset of a rain and snow mixture. As we continue into Sunday
late afternoon and evening, the main focus for the ongoing
precipitation remains over the mountains, foothills and Urban
corridor to include the higher elevations of Elbert and Douglas
counties. The cool and moist airmass will push South into the
evening hours and bring the snow level down to between 6000 and 8000
ft. This will help to transition the rain to snow over the foothills
and Palmer divide as moderate NE winds continue on the plains.
Confidence continues to be low to medium on the timing and exact
locations for rain changing over to snow but at this time, will
maintain snow for the foothills above 6000 ft and the Palmer divide
with rain on the plains after midnight on Sunday. Mountains will
continue to see moderate to heavy snow for the Sunday night into
Monday time frame with models showing upwards of an inch of
liquid in a 24 hour period for the mountains mainly North of I-70.
Like previous discussions mentioned, this could impact holiday
weekend travelers that decide to travel later on Sunday into
Monday.

The upper trough will continue to push ESE across the state into
Monday with a continued unsettled pattern into Tuesday. This is
provided by an upper low that will deepen and move into the four
corners region late Monday. Snow is expected to continue over the
higher terrain into late Monday although with less upslope influence
and slightly lower PWAT values. Lower elevations will dry out by
Monday afternoon but temperatures will remain on the cooler side
with highs in the 50s due to prolonged cloudiness across the area.
By Tuesday, models diverge on the progression of the upper low so
will maintain low confidence on pops after this point but will keep
a slight chance of storms over the higher terrain for Tuesday.

The latter half of the week will see a warm up with a building upper
ridge and highs back in the 60s to low 70s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 804 PM MDT Fri Apr 19 2019

VFR through Saturday. There is a slight chance of west winds
gusting to 25 knots after 21z Saturday due to showers over the
mountains.

&&

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

$$

UPDATE...Meier
SHORT TERM...Gimmestad
LONG TERM...Bowen
AVIATION...Meier

NWS BOU Office Area Forecast Discussion