Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 231118

Area Forecast Discussion
National Weather Service Omaha/Valley NE
618 AM CDT Sat Jun 23 2018

.SHORT TERM...(Today through Monday)
Issued at 315 AM CDT Sat Jun 23 2018

The primary forecast concerns are thunderstorm chances through
Monday, especially Sunday into Sunday night, and potential for
heavy rain.

A general wavy northwest 500 mb pattern was in place last
evening. Several weak disturbances were noted, one over central
NE, one over western SD and another near the MT/ND border. A
stronger system was near the ID/MT border. Expect some chance of
showers and thunderstorms today as the disturbance to our west
moves east. Temperatures will be a bit warmer today, reaching the
upper 70s and lower 80s. Afternoon heating should result in some
boundary layer CAPE values peaking in the 1500-2000 J/kg range. A
few strong storms are possible mainly late afternoon and early
evening in northeast NE.

Tonight, storm chances will decrease the first part of the night
from west to east, then increase toward daybreak. Chances seem
highest west of a line from Norfolk to Lincoln. Storm chances are
higher Sunday into Sunday night and so is the risk of severe
storms. The closed low currently back over western MT will drop
down to northwest NE or southwest SD, with diffluent mid level
flow across our area. Highest instability stays to our
south/southwest, in KS, and that is where SPC has an enhanced
risk. A slight risk extends into parts of eastern NE. The 00Z GFS
is again very aggressive with precipitable water (PW) increasing
it to over 2 inches in parts of southeast NE/southwest IA Sunday
night. It also shows potential rain amounts of 1 to 4 inches in
that area. We will be monitoring this area the next 24 hours or
so, because of the heavy rain that saturated parts of southeast
NE earlier in the week.

The severe risk should main push mostly east of our Nebraska
counties for Monday, based on current expected timing, but there
will still be a chance of storms in western IA.

Highs both Sunday and Monday should reach the upper 70s to the
mid 80s.

.LONG TERM...(Monday night through Friday)
Issued at 315 AM CDT Sat Jun 23 2018

Precipitation chances continue Monday night but should decrease
for most of the area Tuesday as the system up over MN moves east
and weak ridging develops aloft in our area. By Tuesday evening,
a ridge at 500 mb should cover much of the southern 1/3 of the
US. The flow should be fairly zonal in our area through mid week
then turn to the southwest as a trough moves into the western US.

Highs from Tuesday through Friday should be 85 to 95 with lows
moderating from the 60s Tuesday to the lower and mid 70s by
Thursday and Friday.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 610 AM CDT Sat Jun 23 2018

Spotty showers will move through the forecast area this morning,
while areas of patchy fog persist through the early hours of the
TAF period. Winds will stay light and southerly throughout the
day. Another round of showers and thunderstorms will develop this
afternoon and evening, mainly across northeast Nebraska and
western Iowa. Otherwise, generally VFR conditions are expected.


Issued at 315 PM CDT Fri Jun 22 2018

River flood warnings continue on the Missouri River downstream
from Plattsmouth. Elevated river flows just below flood stage are
expected at both Blair and Omaha. This is in large part due to
the uncontrolled water coming out of eastern SD and northwest IA
from the heavy rains a couple of nights ago. To help mitigate the
impact of the flooding slightly, the Corps of Engineers has
lowered the releases out of Gavins Point Dam temporarily to 24,000
cfs, down from 35,000 cfs a few days ago. These lower releases
won`t eliminate the flooding though. The current river forecasts
on our AHPS webpage factor in 24 hours of forecast rainfall, which
is expected to remain on the light side. What is not factored in
this the potential for heavy rains in the Missouri River basin
Sunday through Tuesday, which could range an additional 2 to 4
inches in some locations. The bottom line, expect elevated river
levels and possible flooding south of Omaha on the Missouri River
for at least the next week.

Long range forecasts from the Corps suggest that Gavins Point
releases could increase to 50,000 cfs by the end of the month to
accommodate water upstream into South Dakota and North Dakota.
While this is well outside of our forecast window, it is unclear
how these increased flows will impact the river, which will be
highly dependent on summer rainfall.




LONG TERM...Miller
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