Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
353 PM MDT Sat Aug 1 2015
Synopsis...moisture will spread northward across the region
late this weekend. A drier southwesterly flow will follow for
early next week.
Short term (through 12z tuesday)...high pressure remains over the
forecast area this afternoon...though the ridge axis has oriented
itself more north/south as a trough off the Pacific coast moves
northward. Monsoonal moisture over southern Utah has moved little
this afternoon...with precipitable waters of around 1.0 inch as far north as
I-70...and values approaching 1.3 inch near the Utah/Arizona border.
Showers and thunderstorms have been a bit slow to develop over the
forecast area due to the extensive cloud cover this morning...but
coverage is expected to continue to increase over southern Utah
into the evening.
A shortwave developing over southern Nevada will track northward
across eastern Nevada/western Utah tonight before moving across
northern Utah tomorrow afternoon. This will weaken the ridge and
allow the flow aloft to become more southerly...drawing the
moisture over southern Utah across the rest of Utah and southwest
Wyoming. With the moisture and instability...at least isolated
showers and thunderstorms are possible across the majority of the
forecast area...with scattered to numerous showers and
thunderstorms over northern and central Utah.
As the trough exits Sunday night/Monday morning...a drier and more
stable airmass will start to move into the forecast area from the
southwest. A threat of showers and thunderstorms will remain over
northern Utah during the day Monday...diminishing overnight.
Long term (after 12z tuesday)...the primary shortwave trough will
continue to exit to the north through the day Tuesday...with a drier
airmass moving into much of the area on the heels of the shortwave.
However...enough moisture could linger in the northern portions of
the County Warning Area to allow isolated storms to persist Tuesday and
Wednesday...aided by weaker disturbances pushing through the region
in a mild southwesterly flow. After the last of these waves exits
Wednesday night...even drier air should move into the entire County Warning Area as
a ridge builds over the region...with precipitable water values
dropping below 0.5 inches areawide.
This drying may be relatively short lived. A Pacific low is forecast
to move into California on Friday and...depending on the details of
placement and strength of this low...could help draw moisture into
southern Utah from the south on Friday or Saturday. Have maintained
the general trend of increasing probability of precipitation across the south starting
Friday afternoon/evening...and then into more of the County Warning Area on
Saturday. However...with some inconsistency in the models...the
details of this potential moisture return remain low confidence at
Aviation...west-northwest winds at the slc terminal will become
southerly after 03-04z. Otherwise...VFR conditions are expected
through the night under high clouds.
Fire weather...deep moisture remains confined to southern Utah this
afternoon under high pressure aloft. The ridge will weaken tonight
and tomorrow as a weather disturbance moves northward across Utah
and Nevada. This will allow southerly flow to develop that will
spread the moisture northward across much of the fire district. As
a result...coverage of showers and thunderstorms will increase
noticeably tomorrow. Drier air will start to move back into the
state beginning Monday as the weather disturbance exits the area.
Gusty winds are possible Tuesday and Wednesday.
Short term/fire weather...traphagan
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