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-- Discussion containing changed information from previous version are highlighted. --
561
FXUS63 KOAX 211647
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1147 AM CDT Wed Jun 21 2017

.UPDATE...
-- Changed Discussion --
Issued at 1142 AM CDT Wed Jun 21 2017

An outflow boundary from convection to the north has pushed
through the northern 2/3 of the area. Showers and storms have
formed along this boundary from Crete to Nebraska City. Wind shear
is especially weak, but instability is about 1500 J/kg. This may
continue into the early afternoon, but should not be severe.
Cooler temps behind the outflow boundary will also temp highs
across the northern 2/3 of the area today, thus have backed off
temps just a bit there.

Regarding severe threat later this afternoon and evening, latest
HRRR/RAP models suggest that convection should still develop
across northeast NE through south central NE by late afternoon,
along the convergence zone with the approaching front. These
storms will push east off the boundary through the evening, but
without a significant upper level system, they may have a hard
time remaining strong the further east they get. Best threats will
be in northeast NE late this afternoon, and convection may not
reach Lincoln and Omaha until 9 pm or after, and then the strength
remains in question the further east the storms get.
-- End Changed Discussion --

&&

.SHORT TERM...(Today through Friday)
Issued at 315 AM CDT Wed Jun 21 2017

Forecast concerns in the short term will be thunderstorm
potential/evolution through Thursday night and severe weather
potential.

The h5 pattern during the period has a large high pressure system
over the desert southwest U.S. that extends toward Alberta and
Saskatchewan.  Hot temperatures...127 degrees at Death Valley,
CA...and numerous excessive heat warnings and advisories were over
the southwest U.S.  Meanwhile Tropical Storm Cindy was in the Gulf.
Through Thursday night...a broad tough will flatten the ridge with
fast flow across the Northern Plains and a couple and closed low
pressure over Ontario.

This morning, the front will lift north as a warm front and
southwest extent of elevated thunderstorms is still questionable. It
is common for storms to develop as the low level jet increase and
the warm nose returns to the region. Pooled h7/H85 moisture was
noted over parts of the Plain and a few storms developed near the
KS/Nebraska border near the surface cold front. Warmer h7 air will
spread into the forecast area and the h85 low level jet increases to
40 to 50kts. Moisture transport vectors increase this morning and
are oriented southwest to northeast across the forecast area,
however Corfidi vectors show that elevated storms that form will
travel from northwest to southeast. There are accas/mid clouds,
therefore will have to monitor...a stronger WAA signal is farther
north over the Northern Plains into Iowa. Thunderstorms can
develop southwest into the low level jet, especially if the cap is
weaker in that region and moisture is adequate. Will maintain
pops for these features...especially from northeast Nebraska into
Iowa and monitor areas farther south.

The cold front will push into central Nebraska by 21Z.  14 to 15 deg
C H7 temperatures are in place.  Very steep lapse rates over the
western High Plains will stretch from southwest Minnesota into
eastern South Dakota into southwest Nebraska and western Kansas back
toward New Mexico by 18z...shifting into western Iowa by 00Z.
Instability increases to 2000 to 4000 J/kg near the front. The
forecast soundings maintain a cap...however near the
front...isolated strong to severe thunderstorms could develop. SPC
has the area outlooked in a slight risk with all modes of severe
weather possible including isolated tornadoes and locally heavy
rain. Trimmed pop area and focused in northeast
Nebraska...although something isolated may try to get going
elsewhere. There is some pooling of moisture in southeast Nebraska
and southwest Iowa and the cap may be weaker here. The storm
coverage with the cap appears limited on the
NAM12/EC/GFS...however with the forcing from the shortwave and
convergence with the front in the 00-06Z timeframe thought it
prudent to include scattered thunderstorms during the evening. The
wave pushes east and the surface front tries to lift back north
with another round of showers and thunderstorms for thursday
afternoon and thursday night and the stronger shortwave pushes the
front south. Again we are in the slight risk as temperatures heat
up into the 80s and 90s with the area on the southern edge of a
belt of stronger winds aloft. There may be some lingering showers
Friday, however this would be behind the front.

Highs today should top out well into the 90s and more humid with
stronger south winds. Highs Thursday will again depend on the
frontal position, but have highs in the 80s north and 90s south.
Cooler for Friday with highs in the 70s

.LONG TERM...(Friday night through Tuesday)
Issued at 315 AM CDT Wed Jun 21 2017

Cooler for the extended with highs in the 70s then a return to the
80s Monday and Tuesday. We remain in a general northwest flow
aloft pattern.  There may be some showers Saturday, however the
medium range models have backed off on the coverage; although the
EC still has better coverage. Dry weather is forecast for Sunday
and Monday with some small rain chances Tuesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 627 AM CDT Wed Jun 21 2017

VFR conditions expected through the morning and afternoon hours.
Thunderstorms may impact KOFK by 23z and spread southeast
thereafter and affect KOMA and KLNK but uncertainty remains high.


&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&

$$

UPDATE...DeWald
SHORT TERM...Zapotocny
LONG TERM...Zapotocny
AVIATION...Kern