Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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915
FXUS63 KOAX 212022
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
322 PM CDT THU JUL 21 2016

.SHORT TERM...(tonight through Sunday)
Issued at 322 PM CDT Thu Jul 21 2016

...Heat and humidity to continue, with some relief by Sunday ...

Current water vapor imagery and 12z upper-air analysis indicate a
low-amplitude short-wave trough over Ontario into the upper Great
Lakes, which has temporarily dampened the upper ridge over the
north-central U.S.  Meanwhile, a lower-latitude vorticity maximum
embedded within a sub-tropical air stream was observed over
central Nebraska, translating east.  At the surface, 18z
mesoanalysis revealed a surface low near KYKN with an associated
trough/weak front trailing southwest into west-central Nebraska.
This boundary then extended northeast from the low into southern
Minnesota.

The interaction of the central Nebraska impulse with ambient
steep mid-level lapse rates has fostered convection rooted in the
EML this afternoon over portions of northeast and east-central
Nebraska. The above-mentioned surface front will continue to
settle south into eastern Nebraska and western Iowa tonight owing
to surface ridging over the Dakotas. When coupled with the
eastward advance of the vorticity maximum, we will maintain the
going slight chance POPs in the vicinity of the boundary tonight.

Friday, another weak impulse will emerge into the central High
Plains, promoting a deepening lee trough, and the northward
advance of the surface front over our area. The warmest
temperatures (i.e. mid to upper 90s) are expected south of the
front, with lower 90s north of it. While not overly hot, these
temperatures will combine with dewpoints in the mid to upper 70s
at some locations, pushing heat indices into the 110+F range.
Isolated storms will remain possible with the front in the area.

Friday`s High Plains impulse will track northeast through the mid
Missouri Valley Friday night. Forcing for ascent (DCVA) related to
this feature coupled with strengthening low-level warm advection
to the north of the retreating surface front will likely yield
the formation of an MCS with the highest POPs across our northern
CWA. Residual clouds remnant from the MCS could hamper daytime
heating across the north on Saturday, while over central and
southern portions of the area, highs in the mid to upper 90s are
again expected. As such, the excessive heat warning may have to be
extended through Saturday.  We will let the next forecast shift
evaluate the situation.

A strong polar-branch short-wave trough will track along the
U.S.-Canadian border to our north Saturday into Saturday night,
driving a more substantial cold front into the mid Missouri
Valley Saturday night into Sunday. The best chance for measurable
precipitation appears to be Saturday night with slightly cooler
and a bit drier air mass filtering into the area on Sunday.

.LONG TERM...(Sunday night through Thursday)
Issued at 322 PM CDT Thu Jul 21 2016

The 12z medium-range models suggest that the mid-level high
currently centered over the Ozark Plateau will retrograde west
into the southwestern U.S. by the middle of next weak with the
north-central U.S. transitioning to a west-northwest flow regime.
Weak perturbations embedded in this air stream will support
continued chances for isolated to widely scattered storms through
the forecast period. Temperatures will be close to seasonal
normals.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1232 PM CDT Thu Jul 21 2016

VFR conditions are expected through the TAF period. Isolated
showers and even more isolated thunderstorms are possible this
afternoon near KOFK and possibly KOMA, but confidence is too low
to include more than a VCSH shower mention at KOFK in the first
hour. Have included wind shear at KOMA/KLNK late tonight...with
southwest winds around 10-15kt this afternoon becoming light and
variable to southeasterly tonight into Friday.


&&

.OAX Watches/Warnings/Advisories...
NE...Excessive Heat Warning until 8 PM CDT Friday for NEZ011-012-
     015>018-030>034-042>045-050>053-065>068-078-088>093.

IA...Excessive Heat Warning until 8 PM CDT Friday for IAZ043-055-056-
     069-079-080-090-091.

&&

$$

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



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