Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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365
FXUS63 KOAX 191804
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
104 PM CDT Wed Jul 19 2017

.SHORT TERM...(Today through Friday)
Issued at 251 AM CDT Wed Jul 19 2017

...Excessive Heat Expected Through Friday...

The main concern over the new few days will be the excessive heat
across the region, with afternoon heat index values 105-113 each
day.

Early this morning, the remains of a weak frontal boundary were
across eastern NE and central IA. Some convection has bubbled up
along/east of the Missouri River, where the air remained quite
unstable with up to 2000 J/kg of CAPE, along the nose of the low
level jet, within a PW maximum. These may have some small hail
this morning, but freezing and wet bulb zero values remain very
high thus severe storms seem unlikely. Brief downpours will be the
main hazard. These should continue move slowly east of the area
through daybreak, although there could be some spotty convection
in our extreme southeast counties for an hour or two past
daybreak.

Otherwise, highs today in the mid to upper 90s, and may even hit
100 at a couple of favored locations. Models seem to be underdoing
dewpoints especially in the afternoon, with corn/crop
evapotranspiration at peak efficiency. Should easily reach heat
advisory criteria today, with heat index readings around 110 in
the Missouri River valley in favored locations.

A new front tries to push into northeast NE tonight, which may
trigger spotty convection along it, but storms probably don`t make
it too far into the heat further south. Much more substantial
convection will be possible to our north overnight.

This boundary likely remains stationary on Thursday, may even
dissipate or lift north slightly. This sets us up for another very
oppressive day with highs again very hot, in the 95 to 103 range.
Afternoon heat index values again 103 to 112 across the forecast
area.

Strong convection again appears likely north of the forecast area
Thursday night, and may sneak into the NE/SD border area late
Thursday or early Friday, but should not make much southeastward
progress. Nighttime lows remain quite muggy, in the mid to upper
70s.

One more oppressive day on Friday, which may be the hottest day of
the week for us. Again, 96 to 103, with heat index values 103 to
111. Finally forecasting a high of 100 in Omaha on Friday, which
we haven`t hit officially since May 2013. There is that stalled
frontal boundary, which remains near the NE/SD border, which may
trigger isolated strong thunderstorms Friday afternoon/evening
north of I80.

.LONG TERM...(Friday night through Tuesday)
Issued at 251 AM CDT Wed Jul 19 2017

Aforementioned frontal boundary finally gets a slow push southward
into the area Friday night into Saturday. There may be some
overnight convection that could linger into Saturday morning. This
does help to lower temps just a little, and maybe enough to allow
the excessive heat warning to drop in some areas, although may
have to extend it along the KS/NE border region where afternoon
heat index values could still be near 105. Still plenty of time to
make headline adjustments as we get closer.

A stronger frontal push finally arrives by Sunday, which finally
brings our temps back down to normal for the remainder of the
extended period. Sunday and Monday look mostly dry, but more
organized precip chances return Monday night into Tuesday as the
next wave moves out of the Rockies.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 100 PM CDT Wed Jul 19 2017

VFR conditions will prevail through the bulk of the TAF period at
all three TAF sites. There is a brief period KOFK may experience
convection per CAM and parameterized models, centered around 06
UTC. Frontal boundary moves into northeast Nebraska this evening,
and essentially stalls. Evening and early overnight convection
will be sustained by several weak disturbances and ULJ moving
through northern plains. Confidence on timing or location isn`t
great, and likely will need to be adjusted. The only other
aviation concern is with LLWS. LLJ of 35- 45kt establishes by 03
UTC, while simultaneously surface winds slacken as frontal zone
moves into northeast Nebraska. As upper level jet moves east,
atmospheric kinematic field will slacken, so LLWS threat expected
to diminish by 09-12UTC.

&&

.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 NEZ011-012-015>018-
     030>033-042-043.

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

     Heat Advisory until 8 PM CDT Friday for IAZ043-056.

&&

$$

SHORT TERM...DeWald
LONG TERM...DeWald
AVIATION...Fortin



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