Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 200803
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
303 AM CDT Thu Jul 20 2017

.SHORT TERM...(Today through Saturday)
Issued at 303 AM CDT Thu Jul 20 2017

...Excessive Heat Continues Through Friday...

Existing forecast remains in good shape with only minor tweaks
here and there. Convection from earlier storms has significantly
diminished in our area, with best coverage now across north
central NE. The frontal boundary associated with that convection
remains in place today, placing most of the forecast area in the
warm sector today with another day of very hot and oppressive
conditions. Highs today will likely be a couple of degrees warmer
than yesterday, from 95-101 along and south of the front. There
will be some morning cirrus from the convection to our northwest,
but this should thin through the day. Like yesterday, models are
likely underdoing the dewpoints this afternoon, thus have continued
to trend forecast a little higher, due in large part to peak
evapotranspiration occuring from the mature midwest corn crop.
These conditions yield another day with afternoon heat indices
103-115.

The stalled frontal boundary will be a focus for thunderstorm
development this evening and overnight as a weak impulse,
currently noted on water vapor imagery across the central Rockies,
moves onto the Plains. Will have a small chance of thunderstorms
north of I80 tonight. Given the heat and instability, a marginal
risk of storms will exist. Should be another muggy night with lows
in the mid to upper 70s.

If there is any nighttime convection along the front, it may
dissipate by daybreak Friday. Also important to note that the
ECMWF generally keeps any convection north of the area tonight as
well.

The GFS hints at spotty convection in the warm sector on Friday,
but this seems overdone, given the strong cap in place across the
Midwest. Friday should be the hottest day as H85 temps remain
quite warm. Again, the afternoon model dewpoints may be slightly
low, thus trended a little higher as we have done the last few
days. This yields one more day with afternoon heat index values
103-115. The stalled front does remain in the vicinity of
northeast NE Friday, and this could trigger isolated afternoon
thunderstorms.

A better chance of storms will exist Friday night, generally
along/north of I80, as another upper impulse moves out of the
Rockies. Any convection that develops Friday night will probably
dissipate by daybreak Saturday. Meanwhile the stalled front near
I80 Saturday morning should continue to drift slowly south in
response to a fairly strong low moving through southern Canada.
While the initial air behind the front is not that cool, it is
enough to drop the humidity just a bit to be below heat advisory
criteria, except for extreme southeast NE where the heat warning
may need to be extended. There is a small chance of storms along
the front south of I80 for Saturday afternoon.

.LONG TERM...(Saturday night through Wednesday)
Issued at 303 AM CDT Thu Jul 20 2017

There remains a small chance of thunderstorms south of I80
Saturday night along the front, then dry for Sunday and Monday.
More importantly, temps and humidity return to near normal
with more typical summertime values in the upper 80s, with much
more comfortable dewpoints in the upper 50s to lower 60s. Tuesday
and Wednesday may be slightly warmer, upper 80s to near 90s, with
mostly dry conditions, although model blends generate sporadic
spotty slight chance of precip, but confidence is pretty low that
far out.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1050 PM CDT Wed Jul 19 2017

Earlier intense storms over north-central NE have since weakened
with additional, more recent development along the MO River south
of KSUX. Short-range model guidance continues to indicate a band
of thunderstorms developing across northeast NE and west-central
IA overnight, though confidence in this scenario is diminishing.
As such, will not mention any thunder in the KOFK TAF. Plan-view
VAD data indicate the strengthening of a southwesterly LLJ from
south-central NE into central IA with LLWS likely impacting KOMA
and KLNK overnight. Otherwise, prevailing VFR conditions are
expected.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Excessive Heat Warning until 8 PM CDT Friday for NEZ034-044-045-
     050>053-065>068-078-088>093.

     Heat Advisory until 8 PM CDT Friday for NEZ011-012-015>018-
     030>033-042-043.

IA...Excessive Heat Warning until 8 PM CDT Friday for IAZ055-069-079-
     080-090-091.

     Heat Advisory until 8 PM CDT Friday for IAZ043-056.

&&

$$

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



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