FXUS65 KBOU 240301

Area Forecast Discussion
National Weather Service Denver/Boulder CO
801 PM MST Tue Jan 23 2018

Issued at 752 PM MST Tue Jan 23 2018

Overnight, clearing will allow for radiational cooling with
snowcover to bring temps into the single digits for mountain
valleys and teens elsewhere. GOES-16 water vapor shows high level
clouds moving in over the ridge with increasing moisture from the
next disturbance currently over the Pacific. I expect these
clouds to increase over the region through the early morning hours
on Wednesday. The increasing moisture combined with wave- induced
stability near mountain top will allow for a building and
persistent mountain wave clouds over the Metro area and north.
This will affect high temperatures so kept what the previous shift
had, which captures this well. Also added a slight increase of
winds over the higher terrain with gusting through the afternoon
up to 60 mpg over the higher mountain passes. Some blowing snow
will be possible with the increased wind gusts. Elsewhere,
conditions will be partly cloudy with highs reaching into the
upper 50s.


.SHORT TERM...(This evening through Wednesday)
Issued at 306 PM MST Tue Jan 23 2018

Flat upper level ridge will build across the forecast area through
Wednesday. Warm advection occurs and the airmass will remain dry.
Moderate westerly flow remains in place, and with a mountain top
stable layer developing there will be some gusty winds in/near the
Front Range Mountains and Foothills. Cross sections show flow
increasing to around 35 knots so the wind prone areas will likely
see peak gusts reach 45-55 mph, mainly over the higher peaks and
higher wind prone ridges in the foothills. Some gusts will also
work out onto the nearby adjacent plains, but overall gradient is
rather weak so they won`t make it very far eastward.

Temperatures will be tricky again. Have generally undercut
guidance for tonight in most locations with snow still on the
ground and mostly clear skies. On Wednesday, a wave cloud will
likely thicken along the Front Range, so despite warm advection,
temperatures will likely be held down mainly from the northern
suburbs of Denver to the Fort Collins and Greeley area where
shallow inversions will hold in place. Have adjusted the forecast

.LONG TERM...(Wednesday night through Tuesday)
Issued at 306 PM MST Tue Jan 23 2018

A progressive upper air pattern is forecast to continue across
the United States through the upcoming week with a series of open
troughs and upper level ridges passing over Colorado. Wednesday
night will start out with the upper level ridge axis over eastern
Colorado, on the move eastward. Thursday will see increasing
southwesterly flow aloft ahead of an approaching trough.
Temperatures should be mild across the forecast area under the
southwesterly flow. Moisture with the upper trough looks like it
will arrive Thursday evening with an increasing chance of snow in
the mountains through Friday morning. The GFS and ECMWF are in
fair agreement with the amplitude and strength of the approaching
trough. This system should be moving out of the state by Friday
afternoon after producing a few inches of snowfall in the
mountains. The plains should remain dry. Gusty winds over mountain
ridges will also be possible.

Northwesterly flow aloft should continue through the weekend and
early next week as ridging builds over the southwestern United
States. Subsidence under the ridging will be enough to cut off any
mountain snow shower activity resulting in dry conditions through
the weekend. Any moisture coming in off the Pacific should be
shunted well to the north of Colorado.

The next chance of precipitation after that appears to be the
middle of next week, but the ECMWF and GFS are now showing the
next trough to be an open wave, without much amplitude. Will need
to watch some more model runs before getting a handle on how much
amplitude and moisture this system will contain.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 752 PM MST Tue Jan 23 2018

VFR conditions will prevail through the period. Winds will
gradually move SSW between 04 and 06z with BJC being the
predominant terminal to stay more westerly. Speeds will range
from 8 to 14kts and continue to hold from the SW through the day.
BJC could see occasional gusty winds from the west between 25 and
30kts by the afternoon on Wednesday due to increased mountain




SHORT TERM...Barjenbruch
LONG TERM...Dankers/Sullivan

NWS BOU Office Area Forecast Discussion