Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
948 am MDT Monday Apr 27 2015
Synopsis...high pressure will build in from the west today and
remain in place through middle week. A weakening boundary is
expected to settle into the area Thursday.
Short term...the hard freeze warning for west central and
southwest Utah was cancelled earlier as all temperatures had climbed
above freezing by 830 am MDT.
Morning water vapor and 500 mb analysis indicate a low amplitude
ridge building into the eastern Great Basin states...axis
stretching from central California northeast to the Idaho
Panhandle. The old closed low from this past weekend has slowly
shifted east with center of circulation now over the Texas
Panhandle. Resultant pattern locally leaves the area beneath a
weak northeasterly flow aloft with a weakening north-S oriented mslp
gradient across the state.
Aforementioned building stability can be noted in the 12z kslc
radiosonde observation as subsident inversion has lowered from roughly 600 mb to 700
mb over the last 12 hours. Remnant low level moisture beneath this
cap and some low level instability continues to promote stratus
across the northeast from the Wasatch back through SW
Wyoming...and to a point along the Wasatch Plateau. Made minor
adjustments to sky grids to reflect this. Feel daytime heating
will aid to thin/evacuate this stratus and promote some shallow cumulus
those areas...but limited if any precipitation. Removed probability of precipitation for this
morning across the northeast and lowered scattered afternoon mountain
spine probability of precipitation to isolated this latest update. Hard to imagine much
more than sprinkles/flurries however.
Ridge axis will settle overhead over the next 24 hours as the middle
level high circulation shifts to around Dixie by 00z Wednesday. This
increasingly subsident environment will aid warming both aloft
and at the surface...with 700 mb temperatures prognosticated to climb roughly 10
degrees through that time...current forecast handles this well.
This ridge axis will continue to shift east Wednesday as the next
pacnw trough begins to carve inland. An even warmer southwesterly
flow aloft will develop as such and will yield near 80 f temperatures
along the Wasatch front...pushing 90f in Dixie.
Previous long term discussion below...
Long term (after 12z thursday)... Pacific northwest trough splits
as it moves onshore Wednesday night. Models in fairly good
agreement that the northern branch stays well north of the area as
it tracks east on Thursday. It does...however...push a frontal
boundary into northern Utah during the day Thursday that then
stalls and weakens over central Utah. 700 mb cooling is
modest...only a few degrees at best...but the boundary does appear
to have just a bit of moisture with it that will help with the
development of convection...primarily over the higher terrain.
Behind the system...a somewhat unstable zonal flow is expected to
hang around over the weekend before the southern branch of the
system finally moves onshore over Southern California/northern
Mexico on Monday. Models in better than usual agreement this far
out...keeping the system south of the area through day 7 but
bringing associated moisture and instability into the forecast area.
Have raised probability of precipitation just a bit for Monday to account for this.
Aviation...operational weather concerns will remain minimal at
the kslc terminal through the valid taf period. Northwesterly
surface surface winds will remain in place through this evening
before switching to a light southeast between 03/04z. Skies will
remain largely clear with VFR conditions holding.
Fire weather...a warming and drying trend is forecast into middle
week. Northerly winds will be locally gusty across portions of
southern Utah through this evening. A few showers and isolated
thunderstorms are possible across the eastern mountains the next
couple of afternoons. Snow level near 9kft today rises to 10kft
Southerly winds will increase a bit Wednesday afternoon ahead of the
next cold front. This front is forecast to cross northern Utah
Thursday...stalling across central Utah Friday. Winds will shift to
the north with slight cooling and moistening. Isolated to scattered
showers will be a threat across the north.
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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)