Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 201058
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
558 AM CDT Sun Aug 20 2017

.SHORT TERM...(Today through Tuesday)
Issued at 333 AM CDT Sun Aug 20 2017

A loosely organized MCS is present as of 07z from southwest IA
into south-central NE with this convection likely being forced by
a weak shortwave trough moving into the mid-MO Valley and the
presence of a nocturnal LLJ. While the bulk of this convective
system will continue east-southeast, short-term model guidance
indicates the potential for backbuilding storms through the
remainder of the morning across portions of our central and
southern CWA. Given the recent heavy rainfall across our west-
central counties, the potential for flash flooding and rapid rises
on the Big Blue River and its tributaries will exist. As such, a
flash flood watch remains in effect until 12z (7 AM CDT).

Later today into tonight, mid-level heights will rebound with the
passage of the shortwave trough to the east. However, residual
mesoscale boundaries associated with the early-morning storms may
serve as a focus for isolated to widely scattered storms. Given
the presence of a moist and moderate to strongly unstable air
mass, the potential will exist for isolated severe storms capable
of damaging downburst winds, hail and locally excessive rainfall.
Storm coverage should tend to increase tonight as warm advection
and moisture flux are enhanced by a nocturnal LLJ. Upscale growth
of storms into an MCS is possible with this activity shifting east
into IA by Monday morning.

--Eclipse Weather Outlook--

As mentioned above, it appears that the remnants of nocturnal
thunderstorm activity will shift east of the area Monday morning.
Dry conditions are then expected through early afternoon before
thunderstorm chances increase by mid to late afternoon across
northeast NE and west-central IA. Not much has changed with
respect to the cloud forecast. Latest model guidance continues to
indicate the potential for high-level clouds, the extent and
opacity of which remain uncertain. High temperatures will top out
at around 80 north with mid 80s south. Heat indicies will rise
into the lower 90s by late afternoon into early evening across
southeast NE and southwest IA.

On Monday evening and night, considerable thunderstorm activity
is expected along a cold front moving south through the mid-MO
Valley. Increasing vertical shear and the presence of a moist and
unstable warm sector will support a risk for a few severe storms,
especially from late Monday afternoon through Monday evening.
Localized flooding also appears possible.

On Tuesday, a cooler and drier air mass will filter into the
region from the north with highs in the upper 70s north to lower
80s south.

.LONG TERM...(Tuesday night through Saturday)
Issued at 333 AM CDT Sun Aug 20 2017

Medium-range guidance indicates that a high-amplitude upper-air
pattern will evolve across North America this upcoming week. We
will remain under the influence of a prominent trough situated
to our east, resulting in generally mild and dry conditions during
the middle to late part of the work week. By next weekend, there
are indications that a cold front will move into the region from
the north with an increased chance of precipitation.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 557 AM CDT Sun Aug 20 2017

Backbuilding storms atop a mesoscale cold pool will continue to
affect portions of southeast NE for the next few hours, including
the KLNK area. Currently, it appears that KOMA will remain to the
northeast of this activity, so we have only included a VCTS
mention for a couple of hours there. Convection should gradually
diminish by late morning with the potential for storm re-
development later this afternoon into tonight. Short-range
guidances offers several solutions and confidence in any one is
quite low at this juncture. Model data do depict a more
consistent signal in fog potential late tonight into early Monday
along a weak boundary which will stall across northeast NE, which
we have included at KOFK.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Flash Flood Watch until 7 AM CDT this morning for NEZ042-043-050-
     051-065-066-078.

IA...None.
&&

$$

SHORT TERM...Mead
LONG TERM...Mead
AVIATION...Mead


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