Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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690
FXUS63 KOAX 232050
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
350 PM CDT SAT JUL 23 2016

.SHORT TERM...(tonight through Tuesday)
Issued at 350 PM CDT Sat Jul 23 2016

12z Upper-air analysis and early afternoon water vapor imagery
revealed a polar-branch short-wave trough from Saskatchewan into the
northern High Plains with downstream ridging present from Manitoba
into Ontario. Meanwhile, a lower-latitude perturbation, embedded
within a sub-tropical moisture plume was progressing from the mid
Missouri Valley into upper Midwest. Expect the former impulse to
track across the Canadian Prairie Provinces late today and tonight,
effectively flattening the antecedent mid-level ridge over the
north-central states. Meanwhile, an associated cold front
stretching from the central Dakotas through north-central into
southwest Nebraska as of 20z will advance southeast through much
of the mid Missouri Valley tonight, with this feature eventually
clearing our southeast Nebraska and southwest Iowa counties Sunday
morning.

Persistent mid and high-level cloudiness has stunted daytime
heating, especially across our southern CWA today with 20z temperatures
commonly in the upper 80s to lower 90s. However, given heat
indicescurrently hovering around advisory criteria at many
locations, we will maintain the going excessive heat warning until
7 PM. Otherwise, consensus of latest model guidance is suggestive
that the strongest large-scale forcing for ascent and associated
pre- frontal thunderstorm development will remain to our northeast
tonight. However, recent visible satellite imagery shows a growing
ACCAS field ahead of the front from north of YKN to near ONL to
BBW. As such, we will maintain slight chance POPs along the front
tonight.

Mid and high-level clouds will increase across the area Sunday in
advance of a short-wave trough amplifying from the upper Mississippi
Valley into central South Dakota. Weak vorticity advection and some
frontogenetical forcing may be sufficient to promote a few mid-level
showers and storms across our far northern counties Sunday
afternoon. Meanwhile, in the south, weak warm advection atop a
shallow frontal surface will maintain a chance for isolated showers
and thunderstorms there as well. The increased clouds and slightly
cooler, post-frontal air mass should yield highs largely in the mid
80s.

A surface high will develop southeast through the mid Missouri
Valley Sunday night with the subsequent deepening of a lee trough
over the northern High Plains on Monday. Aloft, mid-level heights
will build over the northern Plains during that time frame, ahead of
low-amplitude disturbance which will emerge into the northern High
Plains Monday afternoon.  Warm advection will strengthen over
southeast Nebraska Sunday night in conjunction with the nocturnal
LLJ, where we have maintained the going slight chance to chance
POPs.  Conditions will generally be dry Monday with highs in the
mid to upper 80s.

The aforementioned short-wave trough moving into the northern High
Plains Monday afternoon will be the first in a series of
disturbances tracking east-southeast through the Dakotas and mid
Missouri Valley Monday night through the middle part of this
upcoming week. This pattern will favor multiple rounds
thunderstorms over the region with a risk for flooding rains and
possible severe weather, namely in the Tuesday night to Wednesday
night time frame.

.LONG TERM...(Tuesday night through Saturday)
Issued at 350 PM CDT Sat Jul 23 2016

As mentioned above, the polar-branch of westerlies will become
increasingly active around midweek as the prevailing flow
transitions to northwest over the north-central CONUS. By the end of
next week into early next weekend, the 12z deterministic runs of the
ECMWF and GFS indicate pronounced ridging over western North
America with a broad downstream trough near or east of the
Mississippi Valley. This large-scale pattern configuration will
continue to support a chance of thunderstorms with temperatures
near or slightly below seasonal normals.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1218 PM CDT Sat Jul 23 2016

VFR conditions are expected through the TAF cycle, with scattered
to broken ceilings largely at or above 15kft. Winds will change
from south to southwest today to northwest tonight and Sunday,
with speeds remaining below 10kt. Isolated showers and even more
isolated thunderstorms are moving away and should stay out of the
TAF sites this afternoon, with potential too low yet to mention
tonight.


&&

.OAX Watches/Warnings/Advisories...
NE...Excessive Heat Warning until 7 PM CDT this evening for NEZ012-
     015-018-033-034-044-045-052-053-067-068-091-093.

IA...Excessive Heat Warning until 7 PM CDT this evening for IAZ043-
     055-056-069-079-080-090-091.

&&

$$

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



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