Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 140440
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1140 PM CDT Wed Sep 13 2017

.SHORT TERM...(Tonight through Saturday)
Issued at 312 PM CDT Wed Sep 13 2017

The main highlights of the forecast are a cold front moving into our
area on Saturday, with warm temps and sporadic precip chances
ahead of, then cooler with better precip chances behind, the
front.

Mid level shortwave extending from Minnesota into south central
Nebraska was triggering isolated showers over parts of eastern
Nebraska this afternoon. A few showers could linger in far eastern
Nebraska or southwest Iowa this evening before diminishing.
Attention then turns to increasing low level jet later tonight as
another minor impulse works west to east across Nebraska, producing
modest theta-e advection on 35kt southwest 850mb flow pointing into
eastern Nebraska. Resultant weak elevated CAPE on the order of 500
J/kg may be enough to trigger widely scattered showers or rumbles
of thunder in southeast Nebraska after midnight, continuing east
through mid Thursday morning.

Pattern changes very little through Thursday afternoon as weak warm
advection regime remains in place. Thus cannot rule out a stray
shower or storm through the afternoon, especially over southern
parts of the CWA where lift is maximized.

Mid level flow regime will undergo changes Thursday night through
Saturday as a trough deepens to our west, placing much of the
Central Plains under southwest flow aloft. Induced lowering surface
pressures in the High Plains will lead to increasing southerly flow
and thus moisture return. When that process begins Thursday night,
low level jet will again provide the ingredients for isolated
elevated convection. Activity should wane a bit during the day
Friday as weak mid level impulse moves away and low level jet
decreases.

By Friday night and Saturday, cold front attendant to deepening
western trough will push toward northeast Nebraska by Saturday
morning, then ushered southeast through much of our CWA Saturday
afternoon behind another shortwave riding through southwest mid
level flow. Again, overnight convection is possible Friday night
with theta-e advection, but favoring areas in northeast Nebraska
nearer frontal boundary. Then better chances for more widespread
showers/storms will come Saturday afternoon as front moves through
an increasingly unstable atmosphere (MUCAPE 1500-2000 J/kg), but
lingering warm air aloft may cap things off much of the day.

Temperatures the next couple of days should reach the 85 to 90
degree range, but could be hindered by lingering cloud cover in some
areas. Saturday highs will drop most in northeast Nebraska where
cooling behind front is more robust, but still warm in our south
where warm sector air should be in place through the afternoon.
Highs likely will range from the lower 70s north to upper 80s
south.

.LONG TERM...(Saturday night through Wednesday)
Issued at 312 PM CDT Wed Sep 13 2017

Off-and-on thunderstorm chances are expected through mid week, with
temperatures rebounding as well.

Upper flow pattern should remain largely unchanged over our area
through Wednesday, with a general southwest flow pattern ejecting
periodic impulses overhead. And each of these could trigger
scattered convection just about any time during the longer term
period.

Saturday cold front will have slipped south of southeast Nebraska
and southwest Iowa by Sunday morning. Continued chances of
thunderstorms are forecast along the front overnight, but should be
far enough south for a dry Sunday morning. Front retreats back to
the north rather quickly on Sunday, providing a focus for afternoon
storms in our south, then spreading north overnight as significant
shortwave rolls into the Northern Plains. Broad southerly low level
flow will commence during that time, effectively moistening boundary
layer for later convection. The next potent shortwave moving in from
the southwest is scheduled for a Tuesday arrival, bringing perhaps
the best chance for widespread showers/storms across our area during
the 7-day period.

Otherwise temperatures should start the longer term period cool with
highs in the 70s Sunday behind Saturday cold front. Persistent
southerly flow should push highs back into the 80s Monday through
Wednesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1140 PM CDT Wed Sep 13 2017

VFR conditions are expected thru the fcst pd.

&&

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

$$

SHORT TERM...Dergan
LONG TERM...Dergan
AVIATION...DEE



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