Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 220329
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
929 PM MDT Thu Mar 21 2019

.UPDATE...
Issued at 929 PM MDT Thu Mar 21 2019

No changes needed at this time. This evening a band of snow
showers brought what looks like a quick inch of snow in South
Park. This is lifting NNE and weakening as it approaches I-70, but
there are more showers developing down around Salida that should
take a similar path. There`s a bit of a dry slot further west, but
not sure this will move much. Current forecast of light snow
showers with some decrease later tonight still looks alright.
These showers will try to drift a bit off the mountains but will
be fighting low level dry air, so while a few sprinkles are
possible later tonight on the plains it shouldn`t be much. Gradual
moistening on tap for Friday morning with the main lift and
destabilization in the afternoon, which seems to be well covered.

&&

.SHORT TERM...(This evening through Friday)
Issued at 321 PM MDT Thu Mar 21 2019

Current satellite imagery shows an elongated upper level trough
stretching across the Desert Southwest toward the Four Corners
area. Moisture and instability was leading to shower and
thunderstorm development to our west. The main batch we`ll have to
contend with tonight is the current band of showers and
thunderstorms stretching from near Grand Junction into northwest
New Mexico. This band, fairly well handled so far by the HRRR and
NAMNest, is advertised to reach the northern mountains 8-11 PM. We
have therefore bumped up PoPs in this time frame when we could see
a quick inch of slushy snow over the mountains, with up to 2 or 3
possible on some slopes around the Mosquito Range.

On the plains, the low levels are still fairly dry and we have
deep southerly flow sheltering us, so mainly virga is expected. We
can`t rule out a couple showers due to mid level instability, so
we`ll maintain a slight chance of precipitation.

On Friday, shower coverage will expand over the entire forecast
area by afternoon as the upper level low begins to reorganize over
the Colorado/New Mexico border, and we destabilize further with
daytime heating. CAPE values increase to 200-500 j/kg, so will
mention isolated to scattered thunderstorm coverage as well. A
couple thunderstorms may produce small hail, especially over
Lincoln county where CAPE may approach 800 j/kg by late afternoon.
Snow levels will hover near 7000-8000 feet most of the day, with
the lower levels west of the Front Range. Accumulations of 2 to 4
inches can be expected above 9000 feet during the bulk of the snow
showers during the afternoon. Snow may be quite heavy at times
due to the convective nature of the snow, so despite the
relatively mild temperatures road impacts will be possible along
the I-70 corridor with some slush/snow accumulation during the
periods of heavier snowfall.

.LONG TERM...(Friday night through Thursday)
Issued at 321 PM MDT Thu Mar 21 2019

Tomorrow evening will see areas of rain showers and thunderstorms
moving over the plains as a negatively tilted trough continues
on its path toward western Kansas. By Friday morning the closed
upper low will be over western Kansas with northerly flow aloft
over northeast Colorado. Quasi-geostrophic diagnostics shows only
modest dynamic forcing with this trough, so only marginal cooling
of the airmass is expected. Evaporative cooling may be enough for
the tail end of the showers on the plains to begin changing over
to snow, probably after about midnight. In the mountains, evening
snow showers may produce an additional inch or two of snowfall.

Most of Saturday should be dry as weak upper level ridging moves
over the state. Models then show moist zonal flow across state
Sunday with an embedded shortwave trough in the ECMWF model.
Either way, this should bring more snow to the mountains, but keep
the plains dry. Temperatures should be right around seasonal
normals.

The rest of next week shows strong upper level ridging dominating
the weather across the western United States. This will bring dry
and warm weather to the state for the Monday through Wednesday
time period. During the latter half of the week, flow aloft will
become more southwesterly as the upper level ridge axis slides
eastward and over the Central Plains. Moisture aloft should begin
to increase after Wednesday. Afternoon highs on the plains through
much of the week will be in the 60s, if not into the lower 70s on
Wednesday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 929 PM MDT Thu Mar 21 2019

VFR conditions will persist through most of this period with only
increasing mid and high level moisture. There is a slight risk of
a passing rain shower after 06Z tonight. Showers and scattered
thunderstorms will develop after 20z and become likely by 00z with
localized MVFR conditions. Wind gusts to 25kts will be possible
at KDEN and KAPA, while KBJC will keep lighter winds.

&&

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

$$

UPDATE...Sullivan/Gimmestad
SHORT TERM...Barjenbruch
LONG TERM...Dankers
AVIATION...Sullivan/Gimmestad



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