Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
916 am MST Tuesday Mar 3 2015
Synopsis...a cold upper trough will cross the region today. A
cool northerly flow will be over the area Wednesday. High pressure
will bring a drying and warming trend through the rest of the
Discussion...water vapor loop shows the trough axis approaching
with an embedded wave nearing the northwest corner of Utah. Amdar
400-250mb wind observations confirm the position of the upper
level jet axis to our northwest...along with a 125-175kt
soutwhesterly jet from The Four Corners through the Great Lakes.
GOES/GPS/rap/12z radiosonde observation indicate the precipitable water value ranges
between 0.10-0.15" mountains...to 0.30-0.35" most valleys. Blended
total precipitable water product indicates an abnormally dry
airmass across the west with the exception of the Great Basin.
With the arrival of the frontal band...heavy snowfall and low
visibilities have contributed to copious traffic accidents along the
Wasatch per udot traffic website. Going headlines in great shape and
did not make any adjustments thus far this morning. Will revisit
late morning as valley advisories expire at noon.
Did update through the evening hours. Latest rap and hrrr-3km are
more excited about upslope snow along I-15 across west central and
southwest Utah through the evening hours. Increased quantitative precipitation forecast and probability of precipitation
here...but with bulk of middle level cold air shifting east...will take
more of a Nowcast approach with the need of any short fused
adivsories for the afternoon and early evening hours.
Added mention of isolated thunder across the south per sref guidance
and BUFKIT indicating equilibruim level colder than -25c. Cant rule
out a strike off the Great Salt Lake either with lake temperatures
near +5c contributing to similar instability this afternoon.
Coverage will thin out...but scattered showers will continue through
the afternoon downstream of the lake.
Adjusted temperature curve with early morning observations and lamp
guidance through this evening.
With building high north-northwest winds will begin to increase
across east central and southern Utah late this evening.
Previous discussion follows...
The last piece of the multi-part storm system than has been
impacting the forecast area since last Thursday is dropping south
into northern Utah early this morning.
This wave has an associated cold front that extends from Wendover
northeastward to near Logan at this time. Snow has developed across the northern
County Warning Area ahead of this front with snow already falling along the Wasatch
front from about Bountiful north. Roads remain wet at this time but
should start to receive accumulation soon.
The heaviest snow for the Wasatch front will be along the cold front
that will be shifting southward through the morning. It looks to cross slc
around 800 to 900 am local time with snow turning showery by about
noon. The band of snow along the front holds together as it shifts
south into central Utah and does maintain some integrity as it reaches
southwestern Utah this afternoon. However expect it to be a fairly narrow
band of snow showers by then with little impact on travel south of
about Cove Fort outside of brief slush ups under the heaviest snow
So have cancelled the Winter Storm Warning for the southern mountains but kept
all other highlights in place. There is a small potential that southern
Utah County could still be receiving heavy snow past noon but will
allow morning crew to assess need to extend any portions of the
highlights as the event unfolds.
Snow should taper off pretty quickly late this afternoon with a few
showers lingering over the northern and central mountains tonight. Cold dry
northerly flow for Wednesday and a more stable airmass will keep temperatures
similar to today under mostly sunny skies. Temperatures warm back up to
near normal Thursday.
Not much weather of significance to note in the long term...other
than a return to stable high pressure and temperatures trending above
climatology. Made minimal changes to going forecast...retaining said
warming trend and a dry forecast through next weekend.
Regarding temperatures...bulk of the forecast area will once again climb 5-
10 degrees above climatology by next weekend as the forecast area will
remain beneath the downstream side of an amplified West Coast ridge.
Some hint exists in global guidance that a strong eastern Pacific
jet will flatten this ridge in about a weeks time...but details
remain to be seen regarding any additional significant weather
changes at that time.
Aviation...gusty northwest winds and heavy snow at the slc terminal
as of 16z are both expected to reduce significantly between 16z and
18z...though occasional gusts and periods of IFR snow showers will
still be possible at times through 22z. Ceilings will likely
improve to 7000ft or above between 21z and 00z...with only a
slight chance that these ceilings linger past 02z.
Utah...Winter Storm Warning until 4 PM MST this afternoon for utz008-
Winter Weather Advisory until 4 PM MST this afternoon for utz007-
Winter Weather Advisory until noon MST today for utz001>004-006.
Wyoming...Winter Weather Advisory until 4 PM MST this afternoon for wyz021.
For more information from National oceanic and atmospheric administration/S National Weather Service visit...
http://weather.Gov/saltlakecity (all lower case)
For frequently asked questions about the area forecast discussion
http://weather.Gov/saltlakecity/general/afd_faqs.Php (all lower case)