Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 201048

Area Forecast Discussion
National Weather Service Denver/Boulder CO
448 AM MDT Tue Mar 20 2018

.SHORT TERM...(Today and tonight)
Issued at 448 AM MDT Tue Mar 20 2018

Dry and breezy conditions will remain across the plains today, but
temperatures will be a little warmer than yesterday with the
onset of warm advection aloft. We should see highs push into the
lower to mid 50s.

The main change in the forecast today is to increase PoPs and
snowfall for the mountains. Some light snow is already developing
per mountain cams and radar imagery, and should see an uptick
this morning as nose of strengthening upper level speed max moves
into the state. Mid level cloud deck was already thickening in
response to this feature over the northern Great Basin per latest
GOES-16 imagery. Low level moisture is a bit limited but still
expect light snow showers to continue off/on in the mountains
today given the mid level moisture, orographics, and proximity of
upper level speed max. Accumulations of an inch or two expected at
this time, but can`t rule out a little more as this snow seems to
be unfolding more than previously advertised.

For tonight, we would expect the moisture to gradually lift and
thin in the wake of the upper level speed max. The plains should
see partly cloudy skies remain in place through the period, while
winds will decrease early this evening with the loss of daytime
heating and mixing.

.LONG TERM...(Wednesday through Monday)
Issued at 448 AM MDT Tue Mar 20 2018

The upcoming week will feature a slow motion transition from an
upper ridge over Colorado and the rest of the Rockies to a
longwave trough over the same regions. And the transition is
currently forecast to take about six days to occur. The GFS has
the least amplitude at Day 7 and is therefore more progressive
with placement of the trough axis at that time. However, the 00z
runs of the Canadian and ECMWF show remarkable agreement through
about 168 hours and then begin to diverge with the shape and
placement of a closed low over Utah and northern Arizona.

What does it mean? The first couple days of the forecast should be
dry and quite warm as subsidence under the upper ridge axis
suppresses any shower activity over the mountains. On the plains,
temperatures will warm up as surface low pressure over western
Colorado and high pressure over the Great Plains produces
southerly flow from Texas northward across the central high
plains, including eastern Colorado. The warmest day looks to be
Friday when high temperatures will range from the mid 70s over the
I-25 corridor to near 80 over the far eastern counties. Humidities
will be low, which could raise fire danger levels, but winds are
not expected to be excessive, and with any luck the recent
precipitation will combine with warm temperatures to hasten the
green up of vegetation. Will address that as the time approaches.

Over the weekend, things begin to cool off as the upper ridge
slides eastward and a surface low develops over eastern Colorado
which begins drawing cooler air in from the north. In the
mountains, moisture from the southwest will be arriving,
increasing the coverage of rain showers and then snowfall as the
weekend continues. These moisture levels will need to be monitored
as Western Region`s Ensemble Situational Awareness Table shows
that the moisture coming ashore over California in the next couple
days is going to be 5 to 8 standard deviations above climatology.
Even though the bulk of this moisture is going to be falling over
California, Nevada and Utah, the amount that makes it to the
Colorado mountains is probably going to be a little higher than a
typical Spring storm. This will also be monitored over the next
couple days. Snow Levels from Friday into Saturday will also be
starting out quite high, at or above 10,000 feet, due to the
initial warmth of the airmass and the fact that the moisture is
moving in on a southwesterly fetch. Snow levels will then fall
through the weekend. One period of precipitation is expected
Friday night and then a second period should arrive Sunday into
Monday. Unsettled weather will spread onto the plains Monday and
Tuesday as the upper trough remains over the state.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 448 AM MDT Tue Mar 20 2018

VFR conditions will persist through the period, with only
scattered to broken mid/upper level cloudiness above 9000 feet.
Winds are expected to turn northwest and increase 17Z-19Z to
around 15-20 knots, with gusts 25-30 knots. Then winds will
subside 01Z-03Z (most likely turning easterly at KDEN), and then
eventually turn south/southwest 7-12 knots by 06Z.




SHORT TERM...Barjenbruch
LONG TERM...Dankers
AVIATION...Barjenbruch is the U.S. government's official web portal to all federal, state and local government web resources and services.