Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 210129
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
729 PM MDT Fri Apr 20 2018

.UPDATE...
Issued at 729 PM MDT Fri Apr 20 2018

Precipitation has been rather disorganized so far. The first
batch of convection this afternoon into early evening was less
than anticipated especially in the mountains. On the plains, there
has been a development of downslope flow from about 9,000 to
12,000 feet MSL per KFTG Vad Wind Profiler. That has really
squashed the earlier convective development, but there are some
trends showing up of lighter downslope and eventually this will
turn around to weak upslope later this evening into the overnight/
early Friday morning hours when more widespread rain/snow should
develop across the plains and I-25 Corridor. Overall, the
orographic forcing is quite weak with this storm despite the
favorable mid level storm track. Q-G diagnostics also show weak
forcing so overall have cut back on precipitation amounts.
Therefore, the Winter Storm Warning for the mountains has been
downgraded to a Winter Weather Advisory, while snow accumulation
numbers have been cut across the board for the mountains and
foothills.

On the plains, we still see some potential for accumulation in the
grass. In fact, the snow level in the lower elevations has
actually been lower than forecast so far as mid levels cooled and
saturated. It will still be a struggle to get surface wet bulb
temperatures down since there`s little evidence of low level
cooling or drying through the rest of this event. However, with
nightfall we should still be able to get a mix or changeover
across the higher elevations and ridges of the plains. Going
forecast looks good there with light accumulations from Denver
metro east and southeast toward Akron and Limon.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 1218 PM MDT Fri Apr 20 2018

Current WV satellite shows the low center spinning over southern
Utah with the def zone moving over the central mountains. Another
branch of moisture moved over the eastern portions of the state
bringing isolated thunderstorms and a mix of rain and graupel.
Drying to the south of the vort max will pull the system to the SE
over northern NM. At this time snow is increasing in coverage and
intensity over Park county and will continue to through the
evening hours. Coverage is still expected to increase into the
Northern mountains as wind upslope improves through the evening
and overnight hours. At the surface rain is expected to move into
the Denver area between 4 and 5 pm and change over to snow around
midnight and continue through the early morning hours.

By Saturday morning the system is expected to push ENE across CO
with wrap around continuing to bring some rain and snow mix to the
plains and light snow in the mountains that will gradually taper
off. Models indicate another push of snow to the northern
mountains and foothills with increased ENE flow Saturday late
afternoon. Overall, did not make any major changes to amounts with
8 to 14 inches over the mountains with the higher elevation
getting close to 16 inches. On the plains areas could see a trace
to an inch on grassy surfaces with a few inches of wet snow
possible over portions of the east. Temperatures started out
warmer in the mid to upper 50s across Denver and cooler to the
east but will continue to drop through the day with the
precipitation. Lows will hover around freezing overnight with
upper 40s to low 50s on Saturday.

.LONG TERM...(Saturday night through Friday)
Issued at 1218 PM MDT Fri Apr 20 2018

The closed upper low will continue to move eastward away from
Colorado Saturday evening with drying and more subsident airmass
settling in behind it.There may still be some lingering showers
over the mountains but any additional accumulations would be
minimal. High pressure ridge aloft will be centered over Colorado
by Sunday afternoon with continued dry and warming conditions,
though could still be some showers over the higher mountains with
lingering mountain level moisture.  700mb temperatures rise to
+4c over the Front Range which will put temperatures back into the
60s across lower elevations.

Next fast moving disturbance and associated cold front will sweep
across Northern Colorado on Monday night and Tuesday will cooler
temperatures. Best chance of showers will be over the far
northeast plains with some upward ascent noted and possible
thunderstorms Monday evening with some low CAPES. Stronger
subsident flow develops behind the trof by Tuesday afternoon with
windy conditions on the plains. Could be some showers over east
slopes/foothills on Tuesday in post front environment and some
shallow upslope flow creating the showers.

The next fast moving system moves across the state on Thursday
with the next chance of showers, windy conditions and cooler
temperatures. Dry and warmer again by Friday as ridge of high
pressure builds over the region.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 729 PM MDT Fri Apr 20 2018

Rain and snow is still expected to develop and become more
widespread late this evening into the overnight hours.
Temperatures should turn just cool enough by 06Z-08Z for mostly
snow, although if precipitation is lighter then could see a
rain/snow mix. Nonetheless, IFR conditions will be developing
through 04-06Z with low level flow turning more easterly and more
widespread rain/snow developing. Light precipitation may linger
through 15Z, and with conditions gradually improving thereafter.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon MDT Saturday for COZ031-
033>036.

&&

$$

UPDATE...Barjenbruch
SHORT TERM...Bowen
LONG TERM...Entrekin
AVIATION...Barjenbruch/Dankers



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