Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 182045

Area Forecast Discussion
National Weather Service Omaha/Valley NE
345 PM CDT MON JUL 18 2016

.SHORT TERM...(tonight through Thursday)
Issued at 344 PM CDT Mon Jul 18 2016

Early afternoon water vapor imagery and 12z upper-air analysis
indicate building mid-level heights from the central High Plains
into the lee of the Canadian Rockies, downstream from an upper low
over the northeast Pacific. In the low levels, weak warm advection
atop a composite boundary (combination of outflow and the synoptic
front) has maintained regenerative thunderstorm development over
portions of east-central and southeast Nebraska into southwest
Iowa. These storms have not been well handled by short-term
numerical guidance, casting uncertainty as to how long they will
persist. Current thinking is that low-level flow will become
increasingly divergent late this afternoon into evening owing to
the continued deepening of a lee trough over the High Plains,
potentially signaling an end to this convective activity.

Tonight into Tuesday, a low-amplitude perturbation will emerge
into the central High Plains from the Rockies, contributing to an
increase in thunderstorm coverage from southwest South Dakota into
northeast Colorado. The interaction between a nocturnally
strengthening LLJ and active cold pools associated with this
convection should promote MCS formation which will likely impact
northeast Nebraska after midnight where we will maintain likely
POPs. Storms could linger across portions of the area on Tuesday
(analogous to today), before dissipating or shifting to the

Wednesday and Thursday, pronounced ridging will exist from an
upper high over the Ozark Plateau into north-central CONUS with
the warmest low-level air mass initially over the High Plains
migrating into the mid Missouri Valley. Highs on Wednesday will
be in the mid to upper 90s, with around 100 degrees expected at
many locations on Thursday. When combined with dewpoints in the
mid 60s to lower to mid 70s, heat indices will approach 105-110F
Wednesday and possibly exceed 110F along the Missouri River on
Thursday. Given these expected conditions, we will issue an
excessive heat watch which will be valid from late Wednesday
morning to Friday evening.

.LONG TERM...(Thursday night through Monday)
Issued at 344 PM CDT Mon Jul 18 2016

By Friday, 12z medium-range guidance suggests that mid-level
heights will be suppressed by the first in a series of low-
amplitude short-wave troughs translating through the northern
Plains. An associated cold front will progress through the
northern High Plains into the mid Missouri Valley with our CWA
remaining in the warm sector through the peak of the diurnal
heating cycle. As a result, we will likely see high temperatures
in the upper 90s to around 100 with heat indices approaching

Friday night into Saturday, the aforementioned cold front
will settle south into the area, resulting in slightly
cooler temperatures and a chance of thunderstorms. Thereafter,
model guidance begins to diverge on the evolution of the upper-
air pattern and the movement of the associated cold front. The
12z ECMWF depicts a much more amplified pattern, effectively
driving the cold front into the Ozarks. In contrast, the 12z GFS
stalls the boundary over our area Sunday before lifting it north
on Monday. As such, we will only include off-and-on slight-chance
POPS Saturday night into Monday.


.AVIATION...(18Z TAFS for KOMA...KLNK...KOFK through 18Z Tuesday)
Issued at 1219 PM CDT Mon Jul 18 2016

MVFR cigs will continue at KOFK for the next couple hours before
mixing increases sufficiently to scatter this layer out. Otherwise
the TSRA have stayed between KOMA and KLNK and this should
generally be the rule into the early afternoon before this
activity dissipates. Otherwise VFR conditions are expected at
these sites. We did include a tempo for some showers to move into
the KOFK TAF late tonight and into Tuesday morning. If confidence
increases in this scenario thunder may need to be added later.


.OAX Watches/Warnings/Advisories...
NE...Excessive Heat Watch from Wednesday morning through Friday
     evening for NEZ011-012-015>018-030>034-042>045-050>053-

IA...Excessive Heat Watch from Wednesday morning through Friday
     evening for IAZ043-055-056-069-079-080-090-091.



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