Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 koax 170910 
afdoax

Area forecast discussion
National Weather Service Omaha/valley NE
410 am CDT Wed Jul 17 2019

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 moistures 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 South Dakota 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 06z tafs through 06z Wednesday night)
issued at 1122 PM CDT Tue Jul 16 2019

An mesoscale convective system over western into south-central South Dakota as of 11 PM is forecast
to track generally east overnight with some potential for storms
to develop south into portions of northeast NE during the pre-dawn
hours. Confidence in storms affecting the taf sites is presently
too low to include in the current forecast. Otherwise, the
presence of a very moist air mass could contribute to patchy fog
overnight. On Wednesday, winds are forecast to increase from the
southeast by mid to late morning.



&&

Oax watches/warnings/advisories...
NE...excessive heat warning from 1 PM this afternoon to 7 PM CDT
Saturday for nez034-043>045-050>053-065>068-078-088>093.

Excessive heat warning from 1 PM this afternoon to 10 PM CDT
Friday for nez011-012-015>018-030>033-042.

Iowa...excessive heat warning from 1 PM this afternoon to 7 PM CDT
Saturday for iaz043-055-056-069-079-080-090-091.

&&

National Weather Service Glossary of Abbreviations