Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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398
FXUS63 KOAX 210457
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1157 PM CDT Thu Jul 20 2017

.SHORT TERM...(Tonight through Sunday)
Issued at 337 PM CDT Thu Jul 20 2017

Excessive heat maintained a strong grip over the southern 3/4 of
the forecast area where 3 PM heat indices were in the 100-110
range. However, a weak slow moving MCV with thicker cloud cover
and even a few light showers has at least tempered the heat a bit
over far northeast Nebraska. Regardless, even in these areas it
has remained hot...just not as hot as it would have been in the
absence of those clouds.

Expect T/Td/Heat Index readings for the rest of this evening to
behave similarly to yesterday with temperatures increasing another
few degrees while the dewpoints also increase over much of the
area. This is likely to keep the heat index above 105 into the
evening hours before a very gradual cool down takes place. The
exception, to some extent, will be those cloudier areas in
northern parts of the forecast area. Isolated thunderstorm
development is also expected through early evening focused
immediately ahead of the slowly advancing MCV along a weak front
extending from near West Point to near Denison. If storms develop
here, there is a small chance for one or two to become strong or
perhaps briefly severe although wind shear is on the low end to
support any long-duration severe activity and it should remain
fairly isolated and relatively short lived.

A secondary chance for thunderstorms will develop between 10 PM
and sunrise over mainly areas north of Highway 30 with chances
increase as you go farther north. This will be in response to an
intensifying low level jet which will converge and focused into
northeast Nebraska and northwest Iowa. It appears that the LLJ
airmass will be quite dry though and the full amount of most
unstable energy will not be realized as cloud bases would likely
be well-elevated. Thus the potential for severe weather overnight
is very low although not completely out of the question if
moisture is a bit deeper near/above the LLJ than currently
forecast.

Friday will be hot once again, and likely very similar conditions
to today although with a better chance for the entire area to
remain primarily cloud free and hot with the thermal ridge
building back into northeast Nebraska. Have thus continued the
heat advisory and excessive heat warning areas for the previously
issued areas and the heat index forecast has changed very little
from the previous forecast. Saturday will start out hot and we`ll
have to consider extending heat products for mainly the southeast
part of the forecast area. A cold front will be making its way
through the forecast area during the daytime hours, and the timing
of this front will be the primary factor in just how hot we get on
Saturday as the post-frontal airmass should be a good bit cooler
than the existing airmass. By Sunday the front will be through the
entire forecast area with cooler air filling in. Even with the
post-frontal air being cooler, highs will still be in the upper
80s to lower 90s while dewpoints fall into the upper 50s and 60s.

Regarding precipitation, there are a few generally low-end
chances. The best chances for thunderstorms seem to focus along a
weak front and short wave trough in northeast Nebraska on Friday
afternoon/evening with another chance mainly near/south of I-80
associated with the cold front on Saturday.

.LONG TERM...(Sunday night through Thursday)
Issued at 337 PM CDT Thu Jul 20 2017

The long term forecast maintains a fairly similar weather pattern
but with a slightly weaker ridge overhead than presently exists.
The ridge is also showing tendencies to remain more focused just
west of the local area. The end result will be continued hot
weather, but the likelihood of another extreme heat event
currently appears to be on the lower end. This may allow the weak
short wave energy track to shift slightly farther to the south
than it has been this week, and while precip chances are low, we
will continue to advertise at least low-end precipitation
potential through much of next week as multiple weak waves cross
the northern Plains and may influence (mainly northern) parts of
the forecast area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1118 PM CDT Thu Jul 20 2017

VFR conditions will prevail thru the fcst pd.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Excessive Heat Warning until 8 PM CDT Friday for NEZ034-044-045-
     050>053-065>068-078-088>093.

     Heat Advisory until 8 PM CDT Friday for NEZ015-018-030>033-042-
     043.

     Heat Advisory from noon to 8 PM CDT Friday for NEZ011-012-016-
     017.

IA...Excessive Heat Warning until 8 PM CDT Friday for IAZ055-056-069-
     079-080-090-091.

     Heat Advisory until 8 PM CDT Friday for IAZ043.

&&

$$

SHORT TERM...Barjenbruch
LONG TERM...Barjenbruch
AVIATION...DEE



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