Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 171730
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1230 PM CDT Wed Jul 17 2019

.UPDATE...
Issued at 1224 PM CDT Wed Jul 17 2019

Outflow from early morning convection made it all the way to a
line from Seward to western Omaha to south of Harlan. This is
clearly evident on satellite imagery where a broken deck of clouds
have set up north of the boundary, with cooler temperatures in
the lower 80s. Just to the south of the boundary, it`s quite
steamy in the upper 80s to lower 90s. This boundary will certainly
have an impact on the previously expected heat index this
afternoon north of it, where we`ll struggle to meet the heat
criteria today. But the heat warning will continue since it
extends through the remainder of the week, and into the weekend
south of I80. South of the boundary, the excessive heat is already
building, with dewpoints in the lower to upper 70s.

Also had quite a bit of what we think is downburst damage across
Shelby county in northwest Iowa, from 70 to 75 mph winds. A survey
crew is enroute take a closer look though, and we`ll have that
survey information available later today.

&&

.SHORT TERM...(Today through Friday)
Issued at 345 AM CDT Wed Jul 17 2019

The primary short term forecast concerns will be how the
convection to the north will evolve and if storms can develop
farther south on the leading edge of the warmer air and heat
headlines.

The current water vapor satellite imagery with lightning shows the
subtropical moisture across Mexico streaming northward across
Colorado into Nebraska. Several clusters of convection per the
WSR-88D radar mosaic were noted especially in the southwest flow
aloft across South Dakota, farther south across eastern Colorado
and to the east over southern Wisconsin. In addition, a few
isolated storms were forming in central and northeast Kansas. A
35kt low level jet is feeding into the convection across SD and
this is where there is some vorticity advection lifting northeast
aloft, there is upper level divergence with a 70kt jet, strong h7
and h85 warm air advection is occurring, a surface boundary is
draped north of PIR. Farther south, into Nebraska and Kansas,
there is a 40 to 50kt low level jet and are on the gradient of the
warm 12-14 deg C h7 temps.

The low level jet strengthens to 40kts through 12Z across the area
then to around 35kts through 18Z as it gradually slides east. Will
continue to monitor trends, but expect isolated storms to continue
to try to develop in the warm air advection environment with some
moisture pooled in the area. In addition, the most recent cluster
of storms have some elements that are moving southeast. The
propagation vectors support this along with cold pool development
into northeast Nebraska. Farther south, the cap is weaker in
southeast Nebraska into southwest Iowa. This area also has deep
moisture. Not sure on the coverage, but will mention isolated
storms this morning.

The guidelines for excessive heat warnings are issued for when heat
index values are forecast to reach 110 degrees for 48hrs with a
minimum heat index at night of 75 or when you are expecting four or
more days of heat index of 105 degrees.  There is some wiggle room
due to collaboration with offices that have slightly lower or higher
criteria and a range of values. Will go ahead and convert the
excessive heat watch to a warning and match up with Sioux Falls.
FSD does have lower criteria and do not expect HIs to be as high
today compared to Thursday and Friday. Farther south extended the
EHW to fit the forecast HIs for Sat and this encompasses the multi
day high heat better for the EHW.

A boundary will push south into northeast later this afternoon and
this evening and may provide a focus for storm redevelopment at
peak heating in the steep lapse rate environment. 2" precipitable
water is forecast to be pooled here. in addition, shortwave
trough energy will push through tonight and the low level jet re-
develops and we should see a few storms.

We remain in the warm sector Thursday and Friday.. With the
boundary near northeast Nebraska a few isolated storms may try to
form, however the blends are mostly dry.

Temperatures are forecast to be in the 90s each day with HIs
discussed above.

.LONG TERM...(Friday night through Tuesday)
Issued at 345 AM CDT Wed Jul 17 2019

Thunderstorm chances Friday night through Sunday morning with
cooler highs for Sunday. The ridge is still in place with the
storm track across the northern Plains and parts of the central
Plains. Some of the storms should push into the area. Temperatures
closer to normal Monday-Wednesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1224 PM CDT Wed Jul 17 2019

Convective outflow boundary will allow for an easterly wind at
KOFK, becoming southeast. The boundary never made it to KLNK/KOMA,
thus southerly winds there. Otherwise, VFR through the period.
LLWS develops at KLNK/KOMA 03z-14z.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Excessive Heat Warning until 7 PM CDT Saturday for NEZ034-
     043>045-050>053-065>068-078-088>093.

     Excessive Heat Warning until 10 PM CDT Friday for NEZ011-012-
     015>018-030>033-042.

IA...Excessive Heat Warning until 7 PM CDT Saturday for IAZ043-055-
     056-069-079-080-090-091.

&&

$$

UPDATE...DeWald
SHORT TERM...Zapotocny
LONG TERM...Zapotocny
AVIATION...DeWald



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