Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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689
FXUS63 KOAX 191035
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
535 AM CDT Sat Aug 19 2017

.SHORT TERM...(Today through Monday)
Issued at 300 AM CDT Sat Aug 19 2017

A shortwave trough --evident in water vapor imagery-- over WY
early this morning will translate east-southeast into the NE
Sandhills this afternoon before moving through our area late
tonight into early Sunday. Forcing for ascent attendant to this
feature coupled with low-level convergence along an associated
surface trough will foster a band of storms to our west this
afternoon. A strengthening nocturnal LLJ along with DCVA related
to the shortwave trough should maintain a subset of these storms
across eastern NE/wrn IA tonight into early Sunday. While a strong
storm is possible, greater severe weather potential will remain
to our west this afternoon into evening. Abundant sunshine in
conjunction with low-level warm advection will support warmer
temperatures today with values ranging from lower 90s south to mid
to upper 80s north.

On Sunday, the afore-mentioned shortwave trough will continue
east of the area with rebounding mid-level heights in its wake.
However, model guidance is suggestive that a west-to-east-oriented
boundary will be situated across our area which could serve as a
focus for late afternoon or early evening storm development.
Increasing amounts of low-level heat and moisture will yield a
moderately unstable air mass late in the day and isolated severe
storms are possible. Afternoon temperatures will again be warm; in
the upper 80s to lower 90s.

A nocturnally strengthening LLJ will likely support an uptick in
thunderstorm coverage Sunday night, especially to the north of the
above-mentioned surface boundary where warm advection is enhanced.
Deterministic model guidance is somewhat dispersive on specifically
where that preferred corridor may be, though there is some
indication it will be to our north/northeast.

--Eclipse Weather Outlook--

On Monday, it appears that any early-day storms will move east of
the area prior to the time of the eclipse. However, the models
continue to indicate the potential for high-level cloudiness
associated with a weak perturbation moving into the central Plains
from the west/southwest. At this juncture, it is difficult to
determine the extent and opacity of any cloud cover. Simply put,
it seems quite likely that some degree of cloudiness will be
present at 1 PM CDT. Afternoon highs will be impacted by the
degree of clouds and the dip in incoming solar radiation
associated with the eclipse with readings in the mid to upper
80s. Heat index values will rise into the lower to mid 90s by late
afternoon. Precipitation chances during the time of the eclipse
currently appear low with a gradual increase thereafter.

.LONG TERM...(Monday night through Friday)
Issued at 300 AM CDT Sat Aug 19 2017

Latest medium-range guidance continues to advertise considerable
amplification of a mid-level trough over eastern North America
next week. This process will result in the movement of a notable
cool front through the forecast area Monday night into early
Tuesday. Strengthening mid-level flow and forcing for ascent
should yield one or multiple MCSs along the cool front with
isolated strong to marginally severe storms possible Monday
evening/night. Locally heavy rainfall will also be possible.

The front will usher in a cooler and drier Canadian air mass which
will linger across the mid-MO Valley through much of the upcoming
work week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 535 AM CDT Sat Aug 19 2017

A surface high over central NE as of 10z will build east today
with winds gradually shifting to the southeast by this afternoon
or tonight. Thunderstorms are expected to develop to the west of
the area this afternoon before moving across portions of eastern
NE tonight. Confidence in timing and specific location of this
convection remains low, so we have only added a mention of VCTS at
all three TAF sites. A strengthening nocturnal LLJ could result in
LLWS criteria being met tonight with the highest probability of
this occurrence being at KLNK. Otherwise, expect prevailing VFR
conditions with increasing mid-level clouds tonight.

&&

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

$$

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



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