Special Weather Statement, NWS Omaha, NE

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1225 PM CDT MON JUN 20 2016

.SHORT TERM...(today through Wednesday)
Issued at 345 AM CDT Mon Jun 20 2016

The chance and strength of thunderstorms over the next several days
are the primary forecast concerns.

Mid level heights have begun lowering this morning as potent
shortwave progressing through the Northern Plains has suppressed
sprawling upper ridge to our south, extending from northwest Mexico
through Kansas and Missouri. Heights will continue to fall across
eastern Nebraska and southwest Iowa with southwest segment of
shortwave diving into the mid Mississippi Valley. Shortwave has
ushered cold front into our northern CWA this morning, with wind
shift expected close to Interstate 80 by sunrise. Warm mid level
temperatures and lack of forcing above boundary have kept
convection squashed in our area so far. However short-range hi-res
model output is still suggesting isolated showers or storms could
fire this morning before front stalls out in northern
Kansas/Missouri this afternoon.

Mid 60s to near 70 dew points will be common near and just north of
the front this afternoon, with surface-based CAPE increasing over
1500 j/kg in southeast Nebraska and southwest Iowa. Bulk shear in
the 30 to 40kt range is forecast as well. However mid level lapse
rates are relatively low, only approaching 7 C/km for brief time
this afternoon along frontal zone. Would expect at least a few
storms to fire during the late afternoon in or close to our southern
areas, with a slight risk of severe hail/wind.

Convection should lose intensity/coverage through sunset. At that
time, front will begin working back north overnight as southerly low
level jet kicks in and increases isentropic upglide leading to
scattered elevated convective potential over much of eastern
Nebraska and southwest Iowa. Forecast soundings from NAM/GFS show
1000-1500 j/kg of elevated CAPE and decreasing CINH in central and
northern sections of our CWA. Severe threat looks minimal as
freezing levels near 15kft limit large hail potential and stable
boundary layer suppresses wind gusts.

Overnight convection should be waning or lifting northeast Tuesday
morning. But more storms are possible in the afternoon as warm front
retreats farther north. Tough to say exactly where that front will
lie by time of max heating as GFS suggests northeast Nebraska
through west central Iowa while NAM is farther south, closer to the
Omaha Metro area. Morning convection will play a role in this as
well. Wherever the front sets up, pooling of moisture and high
instability will reside along it. Turning of winds surface to mid
levels and low level helicity will be maximized as well, with Bulk
Shear reaching 40 to 50kt. Warm mid level temperatures may limit
potential during the afternoon when front is in our CWA, but if
storms do fire, all modes of severe are possible as supercell storm
structures rule. Then chances diminish from southwest to northeast
Tuesday night as warm front lifts well northeast of our area.

By Wednesday layer moisture will be decreasing markedly as surface
low pressure moves east along South Dakota border and into northern
Iowa by the afternoon. Trailing wind shift will bring southwest then
northwest winds to the CWA, helping temperatures warm back into the
90s for most spots.

.LONG TERM...(Wednesday night through Sunday)
Issued at 345 AM CDT Mon Jun 20 2016

Upper pattern will favor zonal flow or weak ridging in the Plains
for the end of the work week. Then a strong shortwave is forecast
to roll east along the US/Canada border this weekend, bringing
slightly cooler temperatures aloft and pushing a cold front into
the region. Thus a generally dry period is expected through Friday
before an increase comes for the first half of the weekend.

One caveat is a weak impulse shown by ECMWF/GFS drifting through the
Central Plains Thursday night, and both models kick off a few areas
of QPF. Will maintain our small precipitation chances for this
potential, then increase chances Friday night into Saturday with
shortwave and cold front. Front should be east of our area by
Sunday.

Temperatures will average the mid 80s to lower 90s Thursday
through Sunday.

&&

.AVIATION...(18Z TAFS for KOMA...KLNK...KOFK through 18Z Tuesday)
Issued at 1223 PM CDT Mon Jun 20 2016

Showers are in the vicinity of KOFK at TAF issuance, and could
possible see a thunderstorm there for an hour or two. Trajectory
of showers/storms could bring them into the KOMA area by 20-24z.
Initial showers/storms probably staying north of KLNK. Could see
additional convective activity later tonight and tomorrow morning,
in the 09-15z period.

MVFR clouds at KOMA, but those ceilings should lift to VFR within
an hour or two.

&&

.OAX Watches/Warnings/Advisories...
NE...None.
IA...None.
&&

SHORT TERM...Dergan
LONG TERM...Dergan
AVIATION...DeWald

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
1235 PM CDT MON JUN 20 2016

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-210745-
MONONA-HARRISON-SHELBY-POTTAWATTAMIE-MILLS-MONTGOMERY-FREMONT-
PAGE-KNOX-CEDAR-THURSTON-ANTELOPE-PIERCE-WAYNE-BOONE-MADISON-
STANTON-CUMING-BURT-PLATTE-COLFAX-DODGE-WASHINGTON-BUTLER-
SAUNDERS-DOUGLAS-SARPY-SEWARD-LANCASTER-CASS-OTOE-SALINE-
JEFFERSON-GAGE-JOHNSON-NEMAHA-PAWNEE-RICHARDSON-
1235 PM CDT MON JUN 20 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST
IOWA...WEST CENTRAL IOWA...EAST CENTRAL NEBRASKA...NORTHEAST
NEBRASKA AND SOUTHEAST NEBRASKA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THERE IS A CHANCE FOR THUNDERSTORMS THIS AFTERNOON ACROSS MOST OF
EASTERN NEBRASKA AND SOUTHWEST IOWA AS A COLD FRONT CONTINUES TO
SETTLE SOUTHWARD THROUGH THE AREA. STRONG STORMS COULD OCCUR...WITH
A MARGINAL RISK OF LARGE HAIL AND DAMAGING WINDS.

THE COLD FRONT WILL REMAIN ALONG THE KANSAS AND NEBRASKA BORDER
REGION OVERNIGHT. SCATTERED THUNDERSTORMS ARE POSSIBLE ACROSS THE
OUTLOOK AREA NORTH OF THIS BOUNDARY...MAINLY AROUND AND AFTER MIDNIGHT.
WHILE THESE STORMS ARE NOT EXPECTED TO BE SEVERE...ALTHOUGH SOME
HAIL AND GUSTY WINDS WILL BE POSSIBLE...ALONG WITH BRIEF HEAVY RAIN.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

THUNDERSTORMS ARE POSSIBLE MOST OF THE DAY TUESDAY AS THE FRONTAL
BOUNDARY TO OUR SOUTH BEGINS TO LIFT NORTHWARD THROUGH THE AREA.
SEVERE STORMS ARE POSSIBLE IN THE AFTERNOON...MAINLY NEAR AND
NORTH OF INTERSTATE 80 WITH LARGE HAIL AND DAMAGING WINDS THE
PRIMARY EXPECTED HAZARDS. THE THUNDERSTORMS SHOULD MOVE NORTHEAST
OF THE AREA TUESDAY EVENING.

ANOTHER CHANCE FOR THUNDERSTORMS ENTERS THE FORECAST THURSDAY
NIGHT AND FRIDAY BEFORE ENDING SATURDAY AS A COLD FRONT MOVES
THROUGH THE REGION.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL PROBABLY NOT BE NEEDED TODAY OR TONIGHT.

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