Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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230
FXUS63 KOAX 212049
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
349 PM CDT Fri Jul 21 2017

.SHORT TERM...(Through Saturday)
Issued at 256 PM CDT Fri Jul 21 2017

At 3 PM on Friday afternoon, conditions were quite hot once again
with heat indices ranging from near 100 in Knox county to several
110-115 degree readings in southwest Iowa and southeast Nebraska.
An area of scattered thunderstorms had developed and moved east
from Thurston and Burt counties while another stray cell was
moving across Dodge county. These were in response to a compact
short wave trough that moved across the area while also providing
subsidence over the remainder of northeast Nebraska for the past
few hours.

Farther west, a somewhat diffuse surface boundary extended from
near McCook to Lexington to Oneil. This convergent zone was
nearly stationary but perhaps making a bit of eastward
progression. Some convection had been developing between 3-4 PM
especially over SW Nebraska, but also now with signs of a
developing cumulus field from Boone/Antelope counties west. Hi-Res
short term models continue to favor this area for robust
development in the next few hours, and this seems a plausible
solution based on observations. The real kicker though will be the
strength of an area of relatively weak upper level support
entering central Nebraska coincident with cooling aloft and a
weakening of the cap. Current indications are that this should
help initiate scattered storms in the vicinity of Boone county
with a general eastward progression from there. Any storms that
develop will have ample instability available and wind shear
supportive of modest storm organization. This in combination with
very steep low-level lapse rates and relatively high LCLs suggests
potential for damaging wind with any stronger storms that
develop. The cap should strengthen again fairly quickly after
sunset and put an end to severe storm potential.

Should also note minimal inhibition and extreme instability in SW
Iowa and southeast NE through this evening. At this time there is
no appreciable lifting mechanism to initiate a storm, but should
one manage to develop along a weak convergence zone, it could
become intense for a brief period of time before dissipating in
weak wind fields aloft.

Maintained a slight chance for elevated thunderstorms overnight
but do not expect any strong storms at this time and coverage
should be on the low end. Then on Saturday a cold front will
finally move across the forecast area but not until temperatures
warm significantly, and have thus extended the heat products
through Saturday afternoon for roughly areas along/south of I-80
where max heat indices should be in the 100-110 range. Scattered
storm activity will be possible across mainly the southern half of
the area through the day, with some low-end severe potential near
the Kansas/Nebraska border by late afternoon before the front
shifts well south of the area.

.LONG TERM...(Saturday night through Friday)
Issued at 256 PM CDT Fri Jul 21 2017

The remainder of the weekend into the first part of next week
looks to be dry and cooler with highs in the mid 80s to lower 90s
and dewpoints much lower than we`re currently experiencing. The
ridge builds back north a bit for the second half of the week,
although indications continue to point to temperatures not quite
as hot as this week has been. With the forecast area being on the
northeast flank of the upper ridge will also see occasional storm
chances as weak upper level waves move through the faster flow
aloft and develop occasional thunderstorm complexes.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1208 PM CDT Fri Jul 21 2017

VFR conditions are expected thru the fcst pd. There is a chance
for isold TSRA though developing along a weak sfc boundary
drifting swd thru the area late this afternoon/evening. Given
areal coverage is in question...have opted for VCTS at all
terminals.


&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Excessive Heat Warning until 8 PM CDT this evening for NEZ034-
     044-045-050>053-065>068-078-088>090.

     Heat Advisory from 8 PM this evening to 7 PM CDT Saturday for
     NEZ045-052-053-066>068-078-088>090.

     Excessive Heat Warning until 7 PM CDT Saturday for NEZ091>093.

     Heat Advisory until 8 PM CDT this evening for NEZ011-012-015>018-
     030>033-042-043.

IA...Excessive Heat Warning until 8 PM CDT this evening for IAZ055-
     056-069-079.

     Heat Advisory from 8 PM this evening to 7 PM CDT Saturday for
     IAZ055-056-069-079.

     Excessive Heat Warning until 7 PM CDT Saturday for IAZ080-090-
     091.

     Heat Advisory until 8 PM CDT this evening for IAZ043.

&&

$$

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



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