Area Forecast Discussion
Issued by NWS Springfield, MO
FXUS63 KSGF 170112 AAA
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SPRINGFIELD MO
812 PM CDT Sat Aug 16 2014
Issued at 812 PM CDT SAT AUG 16 2014
Forecast updated to adjust PoPs and account for hourly trends.
Initially robust convection late this afternoon has quickly
become more tame in the past hour or so. Continuing to see
redevelopment in a west to east fashion from the Rolla/Vichy area
back toward Stockton. This activity has been sustained along a mid
level shear axis and ahead of a surface cold front. Individual
cells will move east, while the axis of rainfall slow shifts to
the southeast with time.
High resolution, convection allowing models are a bit overdone
with the current situation, in all likelihood feeding off of
robust CAPE values. In addition, these models seem to be overdoing
moisture a bit, especially in the mid levels. The precipitable
water value from the 00z sounding is 1.76", while these models
insist on values exceeding 2.1". Lift continues to be marginal in
spite of a shear axis passing through the area. Low level
convergence is broad, though certainly enough to support scattered
showers and storms. Deep layer shear remains quite weak, as a
result, as we continue to spend our CAPE budget the prospects for
stronger storms is dwindling. There is still an outside shot at a
strong storm or two this evening capable of 40-50mph localized
wind and small hail, but this should be the exception rather than
Expectations for the rest of this evening are for lift to remain
best along the incoming front and generally along/east of the
Highway 65 corridor where weak isentropic upglide will remain best
collocated with elevated instability. Heading into the overnight
hours, isentropic downglide will continue to spread over the
region, with rain chances shunting to the east.
Will still need to watch for fog potential in western/northern
areas later tonight.
.SHORT TERM...(This Evening through Tonight)
Issued at 306 PM CDT SAT AUG 16 2014
Main forecast concern will be with storm development and trends
for this afternoon through tonight. The cold front is making
slower than expected southward progress and currently extends from
Kirksville to Sedalia to Emporia Kansas. The airmass ahead of the
front has gotten very unstable with LAPS showing lifted indices
around -7 and CAPE over 3000 j/kg. Dewpoint temps in the lower to
mid 70s were pooling just ahead of the front. The latest radar
images shows storms beginning to develop just to the northwest of
the forecast area.
Storm coverage will increase ahead of the front through the rest
of the afternoon as the lower levels continue to destabilize and a
subtle 700mb trough moves across the area. Freezing levels will
remain high limiting hail growth potential. However unusually tall
CAPE profile on NAM Bufr soundings show that cloud heights may be
sufficient for at least some marginally severe hailstones. Steep mixed
layer below cloud height may also allow a few storms to produce
wind gusts to 60 mph. Am getting concerned about higher
precipitable water values showing up on forecast soundings so may
need to add limited flood potential to our HWO.
Storm development will gradually shift southeast through tonight
as the front makes its way toward the I-44 corridor...so will keep
pops going through the night. Severe threat should diminish with
loss of afternoon destabilization.
.LONG TERM...(Sunday through Saturday)
Issued at 306 PM CDT SAT AUG 16 2014
Short wave to exit eastward and approach LSX by 12z Sunday. On
going storms should be exiting region as well as front passes
through as well.
Weak ripples currently topping the upper ridge and then descending
into the plains to then be key for redevelopment of thunderstorms over
the eastern CWA on Sunday and then again on Monday. While POPS are
in the forecast...confidence in any organized rain is somewhat
limited after tonight into early next week.
Models then advertise a series of shortwaves to travel across the
northern tier of the nation...with variation in how they are
handling a split flow. Of particular interest is a stronger wave
that both the GFS/ECM advect across the northern tier to reach the
Great Lakes on Wednesday. There is the potential that this wave
will push a weakening front into the Central Plains that will
focus convergence as weak ripples top the ridge. At this time
though...will downplay rain chances while noting that some of the
warmest conditions of the summer will occur as the ridge builds
into the Central Plains.
Toward the end of the week...temperatures rise to above normal as
an upper ridge builds into the central U.S. Heat indices will
likely reach near triple digits Thursday and Friday afternoon.
We will need to address potential impacts on residents in our area
who have become acclimated to below normal temperatures so far
.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
Issued at 632 PM CDT SAT AUG 16 2014
Scattered storms developed a couple of hours ago and currently
extend from Warsaw to Lamar to Baxter Springs. Storms and
associated trough are making fairly steady eastward progress so will
be carrying tempo thunder early in the forecast for Joplin and lag
a couple of hours for Springfield and Branson.
The front is expected to stall near the Arkansas border Sunday
morning and will likely focus additional convection after 18z.
Will wait and let later runs get a better handle on storm
development location...but would expect some addition of TSRA in