Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 162347
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
647 PM CDT Fri Jun 16 2017

.MESOSCALE DISCUSSION...
Issued at 647 PM CDT Fri Jun 16 2017

SUPERCELL THUNDERSTORMS THAT HAVE PRODUCED BRIEF TORNADOES,
DAMAGING WINDS, AND LARGE HAIL ARE BEGINNING TO BECOME OUTFLOW
DOMINANT OVER CUMING, STANTON, AND PLATTE COUNTIES. FURTHEREST
WEST SUPERCELL IN PLATTE COUNTY MAY STILL BE A CANDIDATE TO
PRODUCE A TORNADO AS THERE IS AN INTERSECTION OF AN EAST WEST
TROUGH AND NEAR A SURFACE MESOLOW. THIS IS ALSO WHERE THE 0-1 KM
HELICITY VALUES ARE AROUND 150 M2/S2.

EXPECT STORMS TO BECOME PRIMARILLY A DAMAGING WIND AND LARGE HAIL
THREAT WITH TIME AS THEY DRIVE SOUTHEAST OVER PLATTE, COLFAX,
DODGE AND WASHINGTON COUNTIES AND EVENTUALLY INTO THE OMAHA METRO
AREA. STORMS ARE MOVING INTO A HIGHER MOISTURE ENVIRONMENT AND
FAVORABLE DOWNDRAFT CAPES AROUND 1200 J/KG. EXPECT STORMS TO REACH
THE OMAHA METRO AREA AROUND 8 PM CDT WITH THE THREATS OF DAMAGING
WINDS AND LARGE HAIL.

&&

.SHORT TERM...(Tonight through Monday)
Issued at 336 PM CDT Fri Jun 16 2017

Severe thunderstorm threat through this evening remains the primary
forecast concern.

Atmosphere was taking its time recovering this afternoon from
Thursday evening convection, however the process was slowly
occurring. Mid level shortwave as shown by enhanced water vapor
imagery was progressing into central Nebraska at mid afternoon,
ushered along by 90kt upper level jet knifing into the western
Dakotas. Surface front was sharpening in central Nebraska as well,
with 60-70F dew points streaming north ahead of it into south
central Nebraska. 850 moisture was also slowly increasing in this
area as per RAP analysis, noted by 12C dew point temp just ahead of
surface front. Northward extent of moisture return was less than
previous model solutions, but HRRR continued to initiate
convection in north central Nebraska, and that has occurred as of
330 PM.

As convection moves across northeast Nebraska as per HRRR,
strongest activity is likely to develop/move southeast with time
this afternoon and evening into plume of higher moisture and
instability across south central and southeast Nebraska. However
high effective bulk shear is in place now and will continue across
all of eastern Nebraska into southwest Iowa through the evening.
Thus even where instability is somewhat lacking, severe storms are
still possible.

While hail is likely with any storms given combination of shear and
instability, wind threat is also enhanced where inverted-v soundings
are prevalent in our north, and cold pool acceleration in the south.
There is a tornado risk as well, especially with initial development
of storms over the southern half of the state where low level
moisture is in place, and also as supercellular structures maintain
themselves as scattered line progresses southeast and interact with
mesoscale surface boundaries.

Expect line of storms to progress south and east of our area late
this evening, leaving most of the rest of the night dry. Another
stronger mid level trough is still forecast to drop into the Dakotas
Saturday, enhancing lift over cooler air behind surface front. Thus
scattered showers are possible during much of the day in our north.
To the south, most model output suggests cold front and thus surface
instability will be well to our south during the afternoon. However
there is plenty of spread suggesting southeast Nebraska and
southwest Iowa may be close enough for strong storms during
afternoon heating. A slight to enhanced risk is outlined by SPC Day
2 outlook there, but will have to see how far front progresses
before getting overly concerned.

Otherwise cooler conditions are forecast Saturday and Sunday when
northerly low level flow keeps highs in the 70s to lower 80s. Highs
rebound back into the lower 80s on Monday when westerly low level
flow brings slightly warmer air into the region.

.LONG TERM...(Monday night through Friday)
Issued at 336 PM CDT Fri Jun 16 2017

Northwesterly mid level flow will begin the longer term period, with
a gradual return to a more zonal pattern by the end of the week. No
major storm system are forecast to affect our area during this time,
so precipitation chances will be confined to impulses rolling
through the faster mid level flow. Timing of these features is
impossible to pin down this far out, and model output offers varying
opinions on timing and magnitude. Suffice it to say there will be at
least random chances for convection beginning Tuesday night and
continuing through Friday. Temperatures are likely to rebound back
into the upper 80s to lower 90s most spots Tuesday through Thursday,
and perhaps a bit cooler on Friday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 628 PM CDT Fri Jun 16 2017

Line of convection in northeast Nebraska will affect the KOMA TAF
site between 01Z and 04Z with IFR conditions and will have the
potential for wind gusts over 50kt and large hail. Storms will
likely just skirt KLNK area, but could produce similar
IFR/wind/hail between 02Z and 04Z. Storms are south of KOFK and
will remain that way. North winds will overtake all TAF sites
later tonight and will continue into Saturday with mainly mid and
high level clouds.


&&

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

$$

MESOSCALE...Smith
SHORT TERM...Dergan
LONG TERM...Dergan
AVIATION...Dergan



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