Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 261743

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1243 PM CDT Wed Jul 26 2017

Issued at 1236 PM CDT Wed Jul 26 2017

Overall the severe threat is relatively low across the area this
afternoon and evening. The main threat now appears to be locally
heavy rains in slow moving thunderstorms. Have received a couple
reports of 1.85 to 2.25" of rain in the Columbus area with some
minor street flooding. Thus, just recently issued an urban and
small stream flood advisory for areas either side of the Platte
River through the afternoon. These storms appear to be developing
to the north of the inverted surface trough, with relative warm
cloud depths, within a 2 to 2.3 inches of PW.

Regarding the flash flood watch that is in effect for extreme
southeast NE and southwest IA, we debated whether to cancel this
due to the absence of strong convection this afternoon. However,
highres CAMs suggest an uptick in convection in that area this
evening, thus decided to leave the watch intact at this time.

Also increased cloud cover from previous forecast and knocked down
highs a little, but may not have knocked them down enough. Will
reevaluate that for a short term forecast update before the top of
the hour.


.SHORT TERM...(Today through Friday)
Issued at 345 AM CDT Wed Jul 26 2017

Forecast concerns will continue to be thunderstorm chances and
placement for best rain chances/potential for heavy rain through
this evening...then with cooler temperatures.

Thunderstorms erupted over South Dakota, Minnesota, and western
Nebraska Tuesday afternoon and through 05Z the line had
progressed 90 mi to the southeast. At 0830Z stretched from SUX to
York with more storms developing southwest of BIE in northern

Water vapor satellite imagery and h5 heights/vorticity revealed a
tropical moisture connection across Mexico/NM/CO into the midwest.
Closed h5 low pressure was over northern CA with several
shortwaves embedded in the stronger westerly flow across the
northern half of the U.S. with the Canadian closed low over

Our 00Z PWAT was 1.18...however through 12Z is forecast to
increase to 2 inches...remaining between 2 and 2.5 inches across a
large part of the area through 00Z...with the PWAT max shifting
toward southern Iowa and northern Missouri through 06Z.

The operational models are in good agreement that the forecast
area will be affected by two embedded wave as the flat longwave
flow transitions with ridging over the Rockies through tonight.
The models vary on the heavy rain signal with some pointing to
parts of west central Iowa into northeast Nebraska with the first
wave and southern Iowa into southeast Nebraska and northern
Missouri with the wave this afternoon and this evening.
The low level jet this morning of 35 to 45kts weakens to 30kts by
18Z weakens and redevelops this afternoon in northeast Kansas.

The frontal boundary in northeast Nebraska northeast of the
surface low in southwest Nebraska is forecast to move east with
surface low pressure somewhere near southeast Nebraska by 00Z.

Will maintain fairly high pops this morning with the shortwave and
higher qpf values in the northeast part of the CWA and less
coverage farther south. This afternoon the convection is re-
invigorated in western Iowa and parts of eastern Nebraska and it
develops southeast during the late afternoon and evening.

The clouds and precipitation should hold temperatures down today,
however should some clearing/heating take place, this would
increase the severe weather potential. Locally heavy rain will be
possible due to the high efficiency of storms/favorable thickness
diffluence/re-development and training of storms. The 3hr flash
flood guidance is 2 to 3 inches and storms could surpass these

SPC has the slight risk for severe storms over southeast Nebraska
and southwest Iowa this afternoon. WPC has included southeast
Nebraska and southwest Iowa in the moderate risk for flash
flooding. It is always tough to pin down where the heavy rain
producing storms will set up. The forecast sounding supports heavy
rain as the sounding becomes saturated with 2000-3000CAPE and
decreasing storm motions. For now includes parts of southeast
Nebraska and southwest Iowa in the flash flood watch for this
afternoon and tonight.

Thursday through Friday night is fairly dry and cooler, although a
weak impulse in the northwest flow could result in a few isolated
storms Friday night.

.LONG TERM...(Friday night through Tuesday)
Issued at 345 AM CDT Wed Jul 26 2017

The chance for spotty thunderstorms continues into the weekend and
early next week, with no strong signal for widespread
precipitation. Temperatures remain cooler with highs in the 80s.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1236 PM CDT Wed Jul 26 2017

Generally VFR conditions at the TAF sites. Thunderstorms could
still affect KOMA/KLNK 19-22z.


NE...Flash Flood Watch through late tonight for NEZ091-093.

IA...Flash Flood Watch through late tonight for IAZ080-090-091.



SHORT TERM...Zapotocny
LONG TERM...Zapotocny
AVIATION...DeWald is the U.S. government's official web portal to all federal, state and local government web resources and services.