Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 172055

Area Forecast Discussion
National Weather Service Denver/Boulder CO
255 PM MDT Wed May 17 2017

.SHORT TERM...(This evening through Thursday)
Issued at 236 PM MDT Wed May 17 2017

Current satellite imagery showing frontal push from the NE firing
off storms over the CO and WY border. Storms will continue on the
plains through the afternoon and early evening with some storms
producing showers, lightning and small hail. Some funnels may be
possible as rotation increases along the boundary. For the
mountains increasing moisture ahead of an upper low pressure
system will bring snow across the higher elevations through the
evening. A cold front will drop down with a secondary push of
cooler air by this evening bringing rain to the plains.
Precipitation will increase overnight with easterly winds on the
plains starting early Thursday. This will aid in favorable upslope
set-up along the foothills for Thursday. Snow levels will drop to
7000ft Thursday to bring accumulating snow to the foothills. As
winds increase with the circulation of the low pressure system
snow intensity could increase to 2" per hour at times over
mountain passes by Thursday afternoon. Hazardous driving
conditions will exist for the mountains tonight through Friday
afternoon. With the amount of moisture in the system aided by a
700mb low spinning over the Denver area will continue to push
moist ENE flow into the northern foothills. This will cause higher
snowfall accumulations for the mountains and northern foothills.
Rain and snow will continue on Thursday with temperatures staying
in the 20 and 30s in the mountains and foothills and 30s and 40s
on the plains.

.LONG TERM...(Thursday night through Wednesday)
Issued at 236 PM MDT Wed May 17 2017

Models have an upper low centered over Colorado from 00Z Thursday
night well into Friday. The upper low lifts northeastward at 00Z
Friday night with the trailing trough getting to the eastern
Colorado border by 12Z Saturday morning. Northwesterly flow aloft
will dominate on Saturday, becoming more zonal by Sunday morning.
There is strong upward synoptic scale energy over the forecast
area Thursday night and Friday. Downward motion is progged Friday
night through Saturday night. The low level pressure and wind
fields show upslope over most of the plains Thursday night into
Friday night. Some of the models have an inverted trough over the
plains, causing some downsloping over the far western plains near
the foothills. By Saturday, northwesterly low level winds are
progged. There is deep moisture in place for all the CWA Thursday
night and Friday. Moisture decreases somewhat Friday night through
Saturday night but there is still some around. The QPF fields show
vast amounts of precipitation including snowfall. There is
certainly decent energy and moisture with the storm. Winter storm
warning highlights look good for the high mountain zones 33 and
34, same for the foothills zones 35 and 36. Soundings look cold
enough for snow for the western plains so will go with a watch for
the Urban Corridor and Palmer Ridge. There are still concerns
with this including the downsloping low level winds in some areas
and the latest ECMWF moved the upper feature a bit further north.
We`ll see? For temperatures, Friday`s highs are 2-4 C colder than
Thursday`s. Saturday`s warm up 6-10 C from Friday`s. There is
certainly the potential for readings to be below 32 F both Friday
and Saturday mornings over the much of the plains. For the later
days, Sunday through Wednesday, models have zonal flow aloft
Sunday, with more upper troughiness Monday and Tuesday. North and
northwesterly flow aloft is progged on Wednesday. Temperatures
pretty much stay below seasonal normals through the period.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 236 PM MDT Wed May 17 2017

West winds will turn more NW then North with the frontal push by
23z as winds increase with gusts to 25 mph. Thunderstorms will be
in the vicinity with APA and DIA expected to only get rainshowers
between 00 and 02 with BJC seeing the possibility of TS. Another
round of showers will be possible until 06z with winds continue to
push gusts up to 25 mph from the NNE through Thursday morning.
Ceilings will drop to MVFR by 06z and continue to decrease through
Thursday morning with increasing showers and moisture behind the
frontal push. Ceilings will fluctuate between IFR and MVFR through
Thursday with increasing shower intensity through the day.


Winter Storm Watch from Thursday evening through Friday
afternoon for COZ038>041.

Winter Storm Warning from midnight tonight to 6 PM MDT Friday
for COZ035-036.

Winter Storm Warning from 6 PM this evening to 6 PM MDT Friday
for COZ033-034.



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