Snowmelt Runoff into Small Streams and Creeks will Drastically Increase Over The Weekend

Hydrologic Outlook
National Weather Service Riverton WY
1233 PM MDT Thu May 4 2017

...Warm basin temperatures across Western and Central Wyoming
through Saturday will cause steady rises in small creeks and
streams Friday afternoon through Sunday afternoon...

...Rain expected across Western and Central Wyoming Tuesday
through Thursday of next week will increase flood potential...

Snowmelt runoff into small streams and creeks will drastically
increase due to warm basin temperatures across Western and
Central Wyoming through Saturday. Small streams and creeks will
see steady rises Friday afternoon through Sunday afternoon with
the increased snowmelt runoff.

Afternoon temperatures at the 9000 foot elevation are forecasted
to be into the lower 60s Friday and Saturday with overnight lows
Friday night staying between 35 and 40. Temperatures are expected
to cool down into the lower to middle 50s by Sunday afternoon.

After the warm temperatures, the next main concern will be how
much rain may fall across the area in the early to middle part of
next week. A large upper level low pressure system is expected to
develop over the Desert Southwest Sunday into Monday before
gradually moving east to northeast into Colorado Wednesday or
Thursday of next week. Some lighter amounts of rain in the form of
showers and isolated thunderstorms will fall in spots late in the
weekend into early next week but the most significant rain
potential will likely hold off until later Tuesday night through
Thursday. How much rain falls during this period is the bigger
question. The computer models are differing on timing by up to a
day and by quite a bit on total rainfall. The potential for a
couple inches of rain do exist in the foothills of Central and
Southwest Wyoming with with less in the northwest mountains. The
lower elevations of the same area could see up to an inch of rain
but these are just very preliminary indications. Lesser amounts of
rain are possible late Sunday through Monday before the more
significant rain potential begins. The bottom line is that
significant rainfall could fall on the snowpack in the early to
middle part of next week. Snow levels will be quite high and
mostly in the 9000 feet and above level with some lowering
Wednesday into Thursday.

Tributary creeks and streams may reach bankfull by Sunday morning
through Monday morning due to excess snowmelt runoff and rainfall
runoff. Minor flooding of low lying areas is possible due to the
elevated stream levels. Main stem rivers will see noticeable rises
by Sunday morning with continued rises possible on Monday. Main
stem rivers are expected to remain below flood levels through
Monday.

The forecasted rain Tuesday through Thursday will increase flood
potential across Western and Central Wyoming. Stay tuned for
updated outlooks, advisories, and warnings as we get closer to
this developing rain on snowmelt event.