Area Forecast Discussion
Issued by NWS Grand Junction, CO

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480
FXUS65 KGJT 241611
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
911 AM MST Fri Feb 24 2017

.UPDATE...
Issued at 911 AM MST Fri Feb 24 2017

Radar and surface reports show snow ongoing in several of our
higher mountain locations with snow packed and icy conditions.
Expect some convective banding to set up later today that will
enhance snowfall as showers roll through. As earlier shifts were
indicating, coverage of the heavier precipitation will be spotty
but could cause quick impacts should one set up over heavily
traveled locations. Will extend winter highlights through this
afternoon with continued impacts to travel expected over the
higher passes and expand highlights into the northwest San Juans
where WNW component and ongoing showers will drop a few more
inches of snow by this afternoon.

&&

.SHORT TERM...(Today through Saturday)
Issued at 346 AM MST Fri Feb 24 2017

500mb hand analysis chart is rather chaotic this morning over the
mid latitudes. Amplified ridging over both oceans is leaving a
positively tilted long wave trough axis from the arctic to the
Desert SW. There are numerous shorter wave troughs embedded in the
westerlies from the Central Plains westward across the
intermountain west to off the left coast of Oregon. There is even
a larger Rex block over the EPAC and several smaller Rex blocks
over the northern Rockies and the Hudson Bay area to make this
pattern more interesting. What`s most important for us is the very
steep lapse rates overhead leading to elevated instability. Short
term models are fair in showing large scale pattern but very
limited in use for this unstable condition and the very isolated
but intense snow bands that have set up. This was verified in
yesterday morning`s LSR and expect more this AM south of the I-70
corridor from Collbran to Carbondale to Basalt. Little skill in
forecasting this and therefore have little confidence in nailing
it later today. The best I got this morning is correlating
gradients on the 1.5 PVU surface with radar and satellite imagery.
The HRRR and RAP are fair at best. The two areas sticking out this
morning are from SE Utah into the San Juans and draped form the
Uinta basin to the Flat Tops. POPs will be a bit generic and
overdone in many places...especially this afternoon...as the
convective element of the precipitation really shows itself. About
the only place that appears safe will be the extreme SW corner of
our CWA where mid level lapse rates will be relaxing as warm air
advection works in aloft. This more stable air works in
temporarily overnight with a downturn in most precipitation.
Orographics on the divide look to linger overnight then as an
elongated more channelized wave approaches on Saturday
afternoon...convective showers will increase once again as cold
air moves back in aloft. Confidence on placement and amounts
of heavier snow amounts extremely low. Temperatures stay well
below normal.

.LONG TERM...(Saturday through Thursday)
Issued at 318 PM MST Thu Feb 23 2017

Another vigorous upper level trough will move down the West Coast
late Friday into Saturday. This causes the flow over our region to
become west or southwesterly Saturday. The trough moves quickly
through Saturday night and Sunday morning with relatively higher
chances for snow showers accompanying and in the rear of its
passage. The NAM is an outlier with higher snowfall amounts for
the southern San Juans and adjacent lower elevations toward the NM
border Sunday morning. Have not bit off on that solution, but
opted for an ensemble approach which keeps PoPs and QPF lower for
now. This system will at least act to reinforce the colder air
over the region heading into the early part of next week.

The active pattern continues early in the week as another, but
broader, upper level trough moves through Monday night and
Tuesday. This period will have relatively higher chances of
precipitation, mainly snow though rain/snow mix possible for lower
valleys. There are considerable differences in the various long
range models on the moisture and strength associated with this
trough and the southwest flow ahead of the system. So, confidence
at this point is low. Northwest and drier flow follows for Wed
and Thur with a slow warming trend, but remaining below normal.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 346 AM MST Fri Feb 24 2017

Strong showery component to precipitation today will mean quickly
changing conditions as snow showers continue to work through in
this unstable atmosphere. VFR conditions could almost instantly
drop to IFR in showers today but this should only be temporary at
the terminal forecast areas. Confidence extremely low on when and
where these showers will occur so expect frequent TAF updates as
satellite and radar data will be best tools for forecast trends
today. More stable conditions move in overnight and besides the
potential for patchy fog much improved conditions are expected.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory until 6 PM MST this evening for COZ003-
     004-009-010-012-013-018.

UT...None.
&&

$$

UPDATE...JDC
SHORT TERM...15
LONG TERM...BEN
AVIATION...TGJT



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