Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 181658

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1158 AM CDT Tue Jul 18 2017

Issued at 1158 AM CDT Tue Jul 18 2017

Showers and storms which affected parts of the forecast area
continued to diminish late this morning. Will keep some low POPs
for a few more hours in our far southeast counties, then attention
turns to the northwest. We could see some storms later this
afternoon and evening in northeast Nebraska. Shear and instability
suggest a few storms could be strong to severe. Experimental HRRR
and 12Z NAM are not overly aggressive with development though.
Trended POPs down a little for much of the area into mid
afternoon. Made some minor changes to temps and winds.

UPDATE Issued at 614 AM CDT Tue Jul 18 2017

Bumped up Pops in southeast NE where numerous showers/isolated
storms will exist this morning.


.SHORT TERM...(Today through Thursday)
Issued at 321 AM CDT Tue Jul 18 2017

Ongoing convection was noted in north central NE to southeast SD,
as well as in central NE. Subjective 00Z upper-air analysis
indicates broad upper-level ridging across the central US, with an
embedded weak shortwave trough in central NE. Upper-level trough
was noted in the Canadian prairie provinces. Upper-level jet up to
90kt was noted across MT-ND to northern MN. An 850mb low was
centered in northern ON, with trailing front extending toward the
ND-MN border through central SD. Ahead of the boundary, 850mb
dewpoints of 12C+ had pooled across the Plains to upper Midwest.
Elongated surface low at 07Z extended from southeast WY/western NE
panhandle through eastern CO, with another low center in northern
ON and a trough axis extending through northern MN/northeast to
southwest SD.

Main forecast concern is convective potential today, then heat
Wednesday through Friday. Ongoing thunderstorms in central NE should
move into eastern NE this morning as the associated shortwave trough
slowly ambles eastward. Activity is likely to decline diurnally in
the mid to late morning. However, have some concerns that the
morning showers/storms and remnant clouds will temper temperatures
today, offsetting increasing dewpoints and keeping heat indices
below advisory thresholds for one more day.  Surface cold front will
sag through MN/SD into IA/NE this afternoon, potentially reinforced
by convective outflow, and likely inducing a few thunderstorms along
the front in the late afternoon to evening. Northwest Iowa would be
most likely to see storms, closer to the shortwave trough in MN, but
isolated to scattered storms could extend back along the front
through eastern NE as it progresses southward through Tuesday
evening. Instability will be greatest from central into eastern NE,
but so will potential capping, while deep-layer shear around 30-40kt
is possible in northeast NE to northwest IA, closer to the upper-
level shortwave sliding across SD to MN. Thus, the potential for
strong to severe storms will be higher toward the northeast but may
skim the northernmost CWA. Given warm/moist profile and only modest
deep-layer shear, think hail will be tough to find, with gusty winds
more of a threat.

The front is progged to wash out somewhere near the KS-NE/IA-MO
borders by late Tuesday night, with reestablished southerly surface
winds across the area by midday Wednesday. Upper-level high centered
over KS-OK will extend into NE, with 500mb heights around 594-596dm.
This should drive the ridge-riding troughs north and out of the
area, with dry weather on Wednesday and temperatures able to soar.
Mixing may improve on Thursday as surface to 850mb winds veer a bit
more southwesterly, though 500mb heights may come back down a bit.
The northernmost NE counties into northwest IA may just get skimmed
wtih some convection on the periphery of the upper-level high, but
with 850mb temperatures into the upper 20s C, a few sites may reach
that triple digit mark. Convection may encroach on the northern CWA
again on Thursday night, but the southern 2/3 of the CWA, at least,
should remain just as hot on Friday.

.LONG TERM...(Thursday night through Monday)
Issued at 321 AM CDT Tue Jul 18 2017

As an upper-level low digs into the Great Lakes through the weekend,
and the upper-level ridge is pushed west, the resulting
northwesterly flow will bring lower temperatures. Also, with a
surface to mid-level boundary floating around the area through
Monday, chances for precipitation should increase for the weekend
through Monday. Temperatures should dip to near- to below-normal
readings for the weekend, responding to both the lower mid-level
temperatures and the potential for clouds and showers/storms.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1158 AM CDT Tue Jul 18 2017

Generally expect VFR conditions, outside of any TSRA. Chances are
too low to mention in TAFs at this time.


NE...Excessive Heat Watch from Wednesday afternoon through Friday
     evening for NEZ015-033-034-042>045-050>053-065>068-078-

IA...Excessive Heat Watch from Wednesday afternoon through Friday
     evening for IAZ043-055-056-069-079-080-090-091.



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