Severe Thunderstorm Warning 62, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
1232 PM CDT Sat Jun 15 2019

.DISCUSSION.../Today through Friday/
Issued at 333 AM CDT Sat Jun 15 2019

The primary concern this morning will be convective trends with
likely events later today into this evening, around
Tuesday/Wednesday, and then a few others later into the extended
forecast. The current situation has a short wave/MCV pushing
through KS with associated convection attempting to blossom across
northern MO and far southern IA in an axis of 0-2km moisture
convergence. The typical nocturnal support is not impressive
however with rather weak warm/theta-e advection this far north,
and the northern MO convection will likely struggle to get too far
north based on Corfidi vectors pulling cells south and the better
H85 flow and moisture convergence staying to our south. Thus will
keep some low PoPs south this morning. Whatever does materialize
should likely stay below severe limits. Although MUCAPEs are 1-2K
j/kg, effective shear is minimal.

Attention will then turn upstream to our NW with synoptic scale
lift increasing ahead of the approaching MT/ND short wave/PV
anomaly. Although much of it will stay to our north, this feature
will increase our QG forcing to some degree and likely increase
convection NW into peak heating. Both NAM and GFS upstream
dewpoints are overdone versus 07z obs, especially the NAM, so will
stay closer to lower GFS expectations and 2-3K j/kg MLCAPEs by
afternoon. Expect convection to develop along the weak surface
front/trough reflection by early afternoon at the latest and
progress slowly south and east into the evening before exiting
toward midnight. Deep shear is initially weak, but does increase a
bit by 00z-03z so the potential for organization and supercells
does increase a into the day. Even so the shear is never too much
so the severe potential will likely stay toward a low end Slight
Risk per the current Day 1 outlook. The HREF calibrated severe
guidance reflects this thinking as well. Nevertheless there will
be some large hail and damaging wind possible and even a minimal
stretching/thermodynamically dominate tornado potential,
especially if the higher end of the instability spread is realized
even though the low level shear is weak. The heavy rain parameter
space is not overly impressive and near seasonal normals, but
there could still be some locally heavy rains, mainly due to storm
motions no better than 20kts as shown by the mean wind and
Bunkers supercell motion.

Although it should be quite warm and humid today, the weekend
warmth and humidity should drop off again somewhat as we start a
few days of dry weather into early next week. Our next precip
window will be Tuesday into Wednesday, but confidence here and
beyond is not great due to subtle features. However both the
ECMWF and GFS show large scale forcing into IA during peak heating
Tue, and another following wave Wed. The weak surface flow will
not really allow for much preceding return flow however so both
instability and shear will be low keeping the severe weather
potential minimal. The flow will remain somewhat weak in the
extended although the pattern will change somewhat as brief
ridging transitions to some degree of SW flow aloft.
Predictability is low because of this persistent weak flow and
ill-defined short waves and associated surface features, but the
overall pattern supports a prolonged period of low end PoPs. The
potential for strong to severe convection may increase somewhat
again toward the end of the period however as a bit stronger SW
flow will increase our deep shear and allow for a return to
climatological instability.

&&

.AVIATION.../For the 18Z TAFS through 18Z Sunday afternoon/
Issued at 1231 PM CDT Sat Jun 15 2019

Weak boundary situated over central/eastern sections aiding in
development of iso thunder at 17z and expect some convection to
pop and recycle through mid afternoon. More organized convection
expected aft 22z over central/northwest areas as larger portion of
the region realizes CAPE release. Have mainly VCTS/VCSH for now
but will monitor for potential better timing of categorical
chances. Winds rather light except near convection. MVFR/IFR cigs
move into northeast sections at KMCW/KALO/KFOD from 12-18z Sunday
as southern sites KDSM/KOTM generally VFR through period. /rev

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

DISCUSSION...Small
AVIATION...REV

Hazardous Weather Outlook
National Weather Service Des Moines IA
436 AM CDT Sat Jun 15 2019

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-160945-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun-
Webster-Hamilton-Hardin-Grundy-Black Hawk-Crawford-Carroll-Greene-
Boone-Story-Marshall-Tama-Audubon-Guthrie-Dallas-Polk-Jasper-
Poweshiek-Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union-
Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-
Appanoose-Davis-
436 AM CDT Sat Jun 15 2019

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Non-severe thunderstorms are possible through this morning across
southern Iowa.

Strong to severe thunderstorms are possible this afternoon and
evening. The main threats are lightning, large hail, and damaging
winds.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

Thunderstorms are possible Tuesday through Thursday. At this time,
the predictability of severe weather is too low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon and evening.

Kotenberg