Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 251108
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
608 AM CDT Tue Jul 25 2017

.SHORT TERM...(Today through Thursday)
Issued at 345 AM CDT Tue Jul 25 2017

Forecast concerns will primarily be temperatures and heat
headlines then thunderstorm chances tonight night through
Wednesday night.

Thunderstorms developed Monday afternoon near an area of surface low
pressure in southwest South Dakota.  Good southeast inflow was still
noted over southern South Dakota as the center of low pressure was
still near Pierre, SD, however this better flow had shifted into
MN by 08Z. The storms were weakening as they spilled southeast
into the OAX cwa at 05Z, however storms continued farther north in
northeast SD and parts of MN at 05Z and southern MN at 08z as the
low level jet should continue to strengthen to 50kts through 12Z.

Early today...the shortwave over MN will continue to push into the
Great Lakes...meanwhile...a strong h3 100kt jet and the closed H5
low pressure system tracks over Manitoba. As the upper level jet
increases near the U.S./Canada border upper level divergence
increases and omega increases within the area of steep lapse rates
over SD/western Nebraska. The operational and cam models tend to
rapidly increase convection along the front this afternoon between
21-00Z northwest of the OAX forecast area. Although the low level
jet is around 25 to 45kts this morning, the flow decreases to
25kts by mid afternoon...and begins to strengthen again to 30kts
by 00Z and 40kts+ by 06z. A pocket of drier air over parts of the
forecast area should help boost temperatures to 95 to 100 degrees
over the northwest half of the forecast area...meanwhile...higher
lower level moisture returns from the southeast.

The combination of hot temperatures and returning deeper
moisture/evapotranspiration from crops should boost heat index
values for areas along the Missouri River into southwest Iowa to
around 105 degrees or higher. A heat advisory will be issued for
this afternoon.

As the mid tropospheric trough progresses across the Northern
Plains...thunderstorms will gradually sink southward. In advance
of the main area of storms, there is weak lift, thus scattered
showers and thunderstorms could develop farther south where it is
uncapped and very moist.

PWAT values were 1.32 inches on the 00Z sounding and are forecast
to increase to 2 to 2.75 inches during the evening. K-index
values of 42 to 44 are forecast over the forecast area by 12Z Wed.
Chances for thunderstorms become likely near the SD by 06Z
tonight...and periods of storms are forecast for the forecast area
through Wed/Wed night...with a slight chance in the southeast
Thursday morning. Rainfall is needed due to the recent hot weather
and for now have amounts between .3 and 1.3 inches. Should
training of storms occur, much higher amounts could be realized
due to the very moist environment.

The enhanced risk of severe storms is from SD into MN for Day 1
and a slight risk locally for day 2. There is some risk for winds
with storm outflows and locally heavy rains. 0-3km 40 to 50kt
shear vectors track across the area Wed. The risk for excessive
rainfall is moreso in iowa where thickness diffluence/forcing
lining up better with moisture parameters, however short-term
metwatch is needed for training of storms.

.LONG TERM...(Thursday night through Monday)
Issued at 345 AM CDT Tue Jul 25 2017

Cooler weather for the extended with highs in the 80s. There are
some spotty storms forecast, however nothing organized.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 605 AM CDT Tue Jul 25 2017

VFR conditions are expected the bulk of the TAF period. Axis of
low level jet oriented from central Kansas into northeast Nebraska
this morning, thus LLWS remains a concern for KOFK until surface
mixing begins in earnest around 14UTC. Increasing surface pressure
gradient and deep mixing will allow surface winds to increase by
late morning into the 10 to 20 kt range with gusts up to 25kt by
this afternoon. As frontal boundary approaches the area tonight,
thunderstorm activity across South Dakota into central Nebraska
will spread 10-25K ceilings into KOFK by evening. Current
indications are that storms will not affect KOFK until 06Z or
later, with ceilings lowering into 4-6K range. Thunderstorms likely
will not affect KLNK or KOMA until the end or after the TAF
period.


&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Heat Advisory from 1 PM this afternoon to 7 PM CDT this evening
     for NEZ034-045-052-053-067-068-091-093.

IA...Heat Advisory from 1 PM this afternoon to 7 PM CDT this evening
     for IAZ055-069-079-090.

&&

$$

SHORT TERM...Zapotocny
LONG TERM...Zapotocny
AVIATION...Fortin



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