Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 151023

Area Forecast Discussion
National Weather Service Grand Junction CO
323 AM MST Wed Feb 15 2017

.SHORT TERM...(Today through Thursday)
Issued at 105 AM MST Wed Feb 15 2017

An amplified ridge over the Intermountain West continued to bring
drying to the area overnight. Except for patchy fog in the
vicinity of Pagosa Springs in the south and Steamboat Springs to
the north, skies were clear over the region. Strong radiational
cooling resulted in temperatures which were, on average, about 5
degrees cooler than the night before. Craig and Gunnison were the
outliers, running 11 and 12 deg F colder than last night,

The ridge axis will drift eastward today bringing a couple of
degrees of warming at the 7H level. The 00Z/Wednesday sounding at
KGJT indicated mixing reached the 7H level yesterday. Therefore,
there`s no reason to think that this warming won`t be reflected
in higher surface temperatures for most locations this afternoon,
especially given 10+ hours of sunshine unspoiled by clouds.

The same holds true for Thursday as the flattened ridge axis moves
overhead bringing another degree of warming at 700 mb.
Consequently, continued the warming trend throughout the period
with a couple of exceptions, despite muddled GFS numerical
guidance. However, GFS MOS does appear to be on point with sub-
freezing highs in the Gunnison Basin as the stagnant, snow covered
valley continues to radiate energy away tonight. This applies to
a lesser degree along the Craig to Steamboat Springs corridor of
the Upper Yampa River Basin.

.LONG TERM...(Thursday night through Tuesday)
Issued at 105 AM MST Wed Feb 15 2017

High clouds will begin to stream over eastern Utah and western
Colorado Thursday evening as unsettled weather moves onto the
west coast. The first in a series of weather makers will pass
through the Utah-Colorado region Friday morning. This system has
trended weaker in today`s forecast guidance, with only a brief
period of light snow indicated over the northeast UT/northwest CO
mountains Friday morning. Valleys south of I-70 will stay dry,
with a few rain showers over the valleys to the north. Guidance
has trended drier for Friday afternoon and evening with barely
any precipitation, even in the mountains, from noon through
midnight Friday. Temperatures will stay warm in the afternoon
with highs in the valleys in the mid 50s to near 60 in the lower
valleys of southeast Utah.

As mentioned in previous discussions, the weather pattern from
Friday evening through the weekend is complex, with a rather
high degree of uncertainty in timing and amounts of precipitation.
A deep trough comes ashore along the California coastline Friday
afternoon, directing a stream of Pacific moisture into the central
and southern Sierra. As this trough digs southward flow will shift
to the south over eastern Utah and western Colorado Saturday. The
trough will eventually cut off over the northern Baja Saturday
evening. Exactly where and when this trough becomes cut off from
the main flow will dictate impacts over the Four Corners region
this weekend. According to the 12Z/Tuesday guidance, light
precipitation will most likely move back in over the central
Rockies after midnight Friday night as a weak warm front pivots
north around the area of low pressure. Scattered light
precipitation is likely during the afternoon on Saturday before a
break Saturday night into Sunday. Saturday`s temperatures are
expected to be warm enough for rain in the valleys with light
snow in the mountain areas over 8000 feet. 700mb temperatures are
expected to range from -1 to -3 deg C range during the afternoon
hours Saturday, warming to near 0 deg C area-wide on Sunday.

After a break in precipitation on Sunday, the cutoff low will head
eastward through Arizona and New Mexico late Sunday night into
Monday morning. Guidance is split as to whether or not we will see
a second round of precipitation during this time frame. The GFS
keeps the low pressure suppressed to the south, with only the San
Juan mountains seeing a mix of snow in the higher terrain and rain
in the valleys. In contrast, the ECMWF lifts this storm northward
through the central Rockies bringing snow to all mountain zones
from Sunday night through Monday. This forecast package reflects
a wetter solution for the Sunday night/Monday timeframe.
Temperatures will once again be warm with this event, with snow
levels likely to be above at least 7000 feet through late weekend
and early next week.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 105 AM MST Wed Feb 15 2017

Expect VFR conditions with CIGS above ILS breakpoints at all TAF
sites across eastern Utah and western Colorado to continue through
the next 24 hours.






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