Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
245 am MDT Tuesday Sep 30 2014
Synopsis...a weak disturbance will cross the northern portions of
the forecast area today. A colder storm system will affect the
region tonight through Wednesday before a ridge gradually builds
in for the end of the week.
Short term (through 00z friday)...
water vapor loop shows shortwave ridging entering the eastern
Great Basin ahead of the next disturbance approaching the Pacific
northwest. Amdar 400-250mb wind observations reveal a cyclonic 75-
105kt jet over the eastern Great Basin and rockies. A second
cyclonic jet of similar magnitude is nosing into northern
California. GOES/GPS/rap/00z radiosonde observation indicate the precipitable water
value ranges between 0.25" northeast mountains to 0.60"-0.75"
Despite the shortwave ridge moving in...relatively cool air aloft
with the Pacific jet beginning to nose in from the west are
supporting showers across northern Utah this morning. Have indicated
threat of thunder downstream of the Great Salt Lake. 700mb
temperature near 0c and lake surface temperature near 21c are
supplying greater than 1000 j/kg cape with an equilibrium level near
28kft and ncape near 0.13.
Have continued to trend probability of precipitation higher across northern Utah starting
this afternoon. Short range ensembles indicate decent
destabilization takes place with the exit region of the upper level
jet in the area.
Cold front associated with upstream disturbance is forecast to cross
northern Utah late this afternoon through about midnight. Sharpening
trough and baroclinicity should support a band of convection...so
bumped probability of precipitation higher. Snow levels are expected to drop to about 8500
feet...but could end up being lower due to intensity. With warm ground
not so concerned about accumulation...rather visibility restrictions
for the higher passes...and maybe some slush.
This activity continues across east central Utah overnight and into
tomorrow morning as the cold front crosses the remainder of the
state. Kept mention of showers across northeast Utah and southwest
Wyoming due to pocket of instability and lift supplied by the wave
itself translating overhead tomorrow.
Show gusty winds in downslope/canyon sections of Washington County
later Wednesday and especially Wednesday night...with strengthening
northeasterly pressure gradient and solid 700mb cold advection
Long term (after 00z friday)...
high pressure will continue to build into the area...amplifying
further over the weekend and remaining in place through at least
early next week. Temperatures will average near to slightly below
normal Friday...but will warm to near to above normal levels by
early next week.
Aviation...a shower or two may impact the slc terminal this
morning...briefly lowering ceilings to around 6000 feet above ground level and
causing erratic winds. Southerly winds are expected to shift to the
northwest between 18-20z. Additional showers/thunderstorms may
develop this afternoon in the vicinity of the terminal. These may
cause the winds to become briefly erratic.
A cold front is expected to cross the terminal between 01-
03z...reinforcing the northerly winds.
Fire weather...a cool and moist pattern remains in place into middle
week. Scattered showers and isolated thunderstorms will continue
during this period...with high elevation snowfall a threat as well.
Strong gusty winds are possible late Wednesday and Wednesday night
behind a cold front...especially across downslope/canyon portions of
Washington County. A drying and warming trend is forecast for the
second half of the week.
Short term/fire weather...rogowski
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http://weather.Gov/saltlakecity/general/afd_faqs.Php (all lower case)