Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
509 am MST Thursday Dec 12 2013
Synopsis...high pressure over the area today will give way to a
weak weather disturbance from the eastern Pacific on Friday. A dry
and warmer northwest flow will follow for the weekend.
Short term (thru 00z Monday...a strong ridge is centered over the
Great Basin early this morning with a weak closed low to the south
over the Southern California coast. The airmass aloft has warmed overnight with
mountain top sensors now warmer than they have been for at least the
Strong inversions remain in place across the basins of eastern and
western Utah and patchy ground fog has been noted in a few more
Expect the higher elevations to warm nicely today while cold
temperatures remain locked in the inverted valleys...and kept
maxes in those areas today near persistence.
The weak California low tracks into western Arizona today then east across Arizona tonight.
A few clouds from this feature could make it into southern Utah but the
low should remain too far S for any threat of precipitation for our County Warning Area.
Upstream of the ridge a weak trough is moving into the pacnw. This
feature drops southeastward through the northern rockies and Great Basin splitting
as it heads southeast...and the ridge rebounds behind it in the
eastern Pacific. Expect some airmass cooling from this trough and some
cloudiness but little in the way pf precipitation. It also will likely
not be strong enough to dislodge the cold air from the lower
valleys. So any addition of moisture to the lower levels could
bring a fairly large increase in fog and stratus.
The trough moves off to the southeast Friday night with a northwesterly flow
over the County Warning Area forecast through sun. A little moisture persists over
the north through Sat night and the airmass warms back up again through
sun. Expect valley inversions to remain in place and held temperatures
down in these areas but warmed the higher terrain back up.
Long term (after 00z monday)...high pressure is expected to
continue to build through early next week. This will result in dry
conditions with mild temperatures at higher elevations and
strengthening valley inversions. As a storm system moves into the
central United States Monday night/Tuesday morning...the latest GFS
indicates shortwave energy on the back side of this system will move
into northern Utah...increasing clouds and perhaps causing a few
showers. European model (ecmwf) keeps the system farther east...but have included
some token probability of precipitation over the higher terrain to account for the GFS
Global models continue to indicate a stronger storm system will
break through the ridge for the end of the work week. 00z ec is
faster with this system than the latest GFS...bringing a cold front
into northwest Utah as early as Wednesday night/Thursday morning. It
is also more progressive with this system...indicating it will exit
the forecast area Friday morning. In the GFS...the system does not
enter the area until during the day Thursday and it lingers through
the first half of next weekend. Both bring 700 mb temperatures as low as -
14c with the system...which would not be quite as cold as the
previous cold trough. Uncertainty remains about the details...but
models continue to be consistent with a pattern change beginning on
day 7...so have moved probability of precipitation noticeably above climatology as forecaster
confidence in the trough increases.
Aviation...at the slc terminal...VFR conditions are expected
throughout the day. However...there is a 30 percent chance of MVFR
visibilities through about 16z. There is a 10 percent chance that
IFR visibilities over the northwest runway will move across the rest
of the terminal. Light but prevailing southeasterly winds are
expected to shift to the northwest between 18z and 20z.
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)