Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43
FXUS63 KOAX 240037

Area Forecast Discussion
National Weather Service Omaha/Valley NE
737 PM CDT Wed May 23 2018

.SHORT TERM...(Tonight through Saturday)
Issued at 332 PM CDT Wed May 23 2018

Thunderstorm chances tonight and especially Thursday afternoon and
evening are the primary forecast concerns.

Showers and thunderstorms that had pretty much dissipated this
morning in central Nebraska had reformed this afternoon along mid
level theta-e axis working into northeast Nebraska. Hi-res model
output had not captured this activity in afternoon hourly runs.
Storms are expected to continue tracking north-northeast this
afternoon, and may linger in parts of northeast Nebraska during the
evening before dissipating with loss of daytime heating.

Second area of convection is possible late today and this evening,
tied to weak mid level impulse lifting northeast from western NE/KS
shown on water vapor satellite imagery and RAP 500mb analysis. Hi-
res models were becoming more insistent on scattered storms
developing in northwest Kansas and south central Nebraska, and
tracking activity into our western CWA this evening. While shear is
weak, modest instability should support storms through sunset before

Both these areas of storms are in an environment with weak shear,
but instability on the order of 2000-2500 J/kg of MLCAPE may aid
in low-end severe hail potential.

Attention then turns to later tonight when low level jet increases
to near 40kt from central into northeast Nebraska under southwest
mid level flow regime. Nose of that jet is forecast over north
central and northeast Nebraska between 06Z and 12Z in area where
MUCAPE increases to 1500 J/kg based on NAM forecast soundings.
Expect scattered convection to fire by 09Z and gradually work north
and northeast through northeast Nebraska through mid morning.

A lull in the action is likely a few hours either side of 18Z
Thursday, allowing atmosphere to recharge from central into
northeast Nebraska. Models suggest surface dew points in the mid
and upper 60s combined with cooling mid level temperatures with
approach of shortwave will push MLCAPE values potentially north of
3000 J/kg. Bulk shear looks modest at best, maybe around 25kt
0-6km, and low level convergence appears to lag instability. SPC
has elevated our severe risk into the Slight category, and given
instability, think that is reasonable if storms fire in our CWA.

Convection is expected to continue much of the night Thursday night
as shortwave gradually works through eastern Nebraska and southwest
Iowa by Friday morning. Storms may linger a while longer in
southeast Nebraska and southwest Iowa, and could re-fire Friday
afternoon if instability is not swept southeast as per latest GFS

Otherwise a mainly warm forecast is in order as 850 temps climb into
the lower and middle 20`s C range for Friday and Saturday. Many
spots should reach 90 one or both of those days.

.LONG TERM...(Saturday night through Wednesday)
Issued at 332 PM CDT Wed May 23 2018

A fairly active setup appears to be forming for next week, at least
in terms of chances for thunderstorms. Potential severity of
convection will have to be determined at a later time, but it
looks like we`ll have chances for storms much of the period
Monday through Wednesday.

Upper low moving through the western U.S. on Sunday will eventually
open up and send several impulses through the Plains, with the
timing of each impossible to time this far out as solutions are
widely variable between model to model and run to run. However low
level southerly flow should maintain a moist and warm atmosphere
conducive for convection with each impulse.

As far as temperatures are concerned, Sunday looks like the warmest
day of the long term period under mid level ridging ahead of
approaching low. Monday through Wednesday temperatures should
average 85 to 90, but could vary based on convection and cloud cover
day to day.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 728 PM CDT Wed May 23 2018

Isolated thunderstorms over northeast Nebraska to the west of KOFK
at the start of the period are located on the eastern edge of
instability axis in place across the west half of the state.
This instability pocket is forecast to shift east by the end of
the period with an increasing chance of storms at TAF sites.
VFR conditions will prevail outside of convective areas during the
period with more widespread convection likely after 18Z.




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