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Area forecast discussion 
National Weather Service Salt Lake City Utah
811 PM MDT Friday Mar 27 2015

Synopsis...high pressure overhead will move off to the east
Saturday ahead of a weak storm system. This system will send a
cold front into northern Utah Saturday afternoon and south through
the area Saturday night.

&&

Discussion...water vapor loop shows a ridge over the
intermountain west...with a system running over the ridge across
the Pacific northwest. Amdar 400-250mb wind observations show a
100-140kt anticyclonic jet over western Canada into the
Mississippi River valley. GOES/GPS/rap/00z slc radiosonde observation indicate the
precipitable water value ranges between 0.15-0.25" mountains to
0.30-0.40" most valleys. Blended total precipitable water product
indicates an abnormally moist airmass over the northern
rockies...and an abnormally dry airmass over the deep southwest.

Rap 850-700mb thickness/saturated equivalent potential
temperature/streamlines indicate that Utah will be in the thermal
ridge overnight ahead of an approaching cold front. The boundary
will likely slip into the west desert toward sunrise.

Ahead of the boundary temperatures should remain warmer than
guidance due to a decently mixed boundary layer. Warmed overnight
lows closer to lamp guidance. Also tweaked winds with latest high
resolution guidance. Rest unchanged.

Previous discussion follows...

Strong middle level ridging centered across the Great Basin this
afternoon will shift east tonight...downstream from a weak shortwave
trough currently approaching the Pacific coast. This wave will move
onshore tonight before traversing the northern rockies Saturday. The
brunt of this wave will pass well north of the forecast area...with
the trailing surface front forecast to cross northern Utah Saturday
afternoon before stalling across southern Utah Saturday night. Pre-
frontal mixing should be sufficient to once again push temperatures
15 or more degrees above climatology Saturday...which would be encroaching
on record territory in a few locations (the record high for kslc
Saturday is 77). With limited moisture and weak dynamic support only
isolated convection is expected as this feature crosses the north
Saturday afternoon through Saturday evening.

A portion of this wave is forecast to split as it moves ashore
tonight...then gradually cross the southern Great Basin during the
day Sunday. This feature will interact with the stalled surface
boundary across southern Utah Sunday afternoon into Sunday evening
bringing a somewhat better threat for convection...and have raised
probability of precipitation across the higher terrain accordingly. Meanwhile somewhat
cooler air behind this boundary will bring a modest cooldown to most
areas for the latter half of the weekend.

Middle level ridging is forecast to rebound across the region Monday
with perhaps a small threat for convection across the southern
mountains owing to lingering moisture.

Ridging will be ongoing at the start of the long term portion of the
forecast as a Pacific trough approaches the coast Monday evening.
The 12z global models have become fairly consistent with the
evolution of this system...bringing the associated cold front across
the County Warning Area late Tuesday through Wednesday morning. This is a bit slower
than previous runs...so warmed the temperatures for Tuesday for most
locations a bit.

A majority of the model guidance depicts this front as mainly
dry...but felt there was enough dynamics associated with this front
to at least increase the risk of precipitation across the higher
terrain into the slight category. Both the ec and the GFS depict
700mb temperatures falling to near -10 to -12c Post frontal
Wednesday afternoon/evening.

Yet another wave embedded in the northern jet will cross the state
Thursday. The models are considerably different during this time
period...so kept probability of precipitation near climatology for days 6 and 7. Confidence during
this portion of the forecast is fairly low.

&&

Aviation...north winds will switch to the southeast at the kslc
terminal between 03z and 05z this evening. Winds will increase out
of the southeast around sunrise ahead of an approaching cold
front.

&&

Slc watches/warnings/advisories...
Utah...none.
Wyoming...none.
&&

$$

Short term...rogowski/Seaman/loeffelbein
aviation...rogowski

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