Special Weather Statement, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
647 PM CDT FRI MAY 27 2016

...Updated for 28/00Z Aviation Discussion...

.SHORT TERM.../Tonight/
Issued at 349 PM CDT Fri May 27 2016

Negatively-tilted H300 trough axis currently over the Texas
Panhandle will lift northeast tonight into east central KS, helping
to fuel the next round of showers and storms for Iowa. At the
surface, a broad surface trough encompasses the state with multiple
embedded outflow boundaries courtesy of this morning's convection.
The break between these two rounds of precis will be short-lived,
with the next round of multi-cellular convection already developing
across eastern Kansas and western Missouri. Most synoptic and
mesoscale models are in good agreement on the timing of this precis
but are struggling with the overall areal extent and amounts. Leaned
towards the 27.18Z HRRR and GFS with the placement of the heaviest
rainfall/highest POPs. Axis of elevated H700-500 mixing ratios will
lift north through Iowa between 00 and 09Z with the best chance of
heavy rainfall over the southeast CWA. RUC/NAM/GFS soundings for Des
Moines and west are rather dry below 800mb, lending further
confidence in the heaviest rainfall falling in the east. Localized
heavy rainfall will be the biggest threat from these storms tonight
given the weak to modest instability profiles and weak flow below
600 mb.

.LONG TERM.../Saturday through Friday/
Issued at 349 PM CDT Fri May 27 2016

The primary concerns remain the slow evolution of the current Plains
long wave trough and the next northern stream long wave cycle toward
the middle of next week. Potent short wave/PV anomaly should be
right along the NE/IA border at 12z with fairly decent synoptic
scale rise/fall couplet moving through northern Iowa. The high res
models do not depict the areal coverage one might expect versus this
degree of forcing, but confidence is still there that weak
convection will be lifting toward the Minnesota border in the 09-15z
time frame so pops remain high. Peak heating convection will likely
follow, mainly over central and southeastern sections by
afternoon as well. MLCapes looks to be in the 1.5-2.5k j/g range
with only moderate deep bulk shear. Thus agree with SPC midday Day
2 outlook pulling the Marginal Risk back farther to the north and
west. None of the threat probs are particularly high, but hail,
wind and tornadoes are all still on the table depending on how
much cells organize due to limited shear. Even non-supercell
tornadoes are possible considering low LCLs and 0-3km Capes 100
j/kg or more.

The potential should decrease into the evening with the loss of
large scale forcing and heating with only low chances relegated to
far northeastern sections into early Sunday morning. This will lead
to a relative min and dry break Sunday into Sunday Night before the
attention again turns upstream. Unfortunately the evolution of the
long wave pattern next week is not clear cut with initially some
timing issues with the surface reflections into Tuesday, and the
degree of long wave phasing into Thursday. There is low confidence
in this time window with individual GEFS H5 members leaning both
toward the operational run and the ECMWF. As far as sensible
weather, this would result in relatively higher confidence in
weak warm advection convection crossing the Missouri Valley Sunday
Night into Monday. This could potentially continue into Tuesday as
well, but questions arise with regard to the proximity to the
surface trough and potential low level convergence during
afternoon peak heating. The faster ECMWF solution would be more
conducive with the slower GFS less so and favoring weak warm
advection precis lingering into the night with a farther west
genesis region. The ECMWF would suggest precis exiting with
mainly dry northwest flow while the GFS hangups up a drifting
upper low through the Central Plains. Would tend to favor more
phased ECMWF solution at this point with the GEFS and ECMWF
ensembles pointing in that direction and although neither are
great, the ECMWF has slightly better run to run continuity and
passes the eye ball test better. Thus have keep only some slights
going into the end of the next work week lending the GFS just a
little credence.

&&

.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 647 PM CDT FRI MAY 27 2016

Widespread SHRA and TSRA expected across the region tonight...as an
upper level storm system moves through. Have gone MVFR cigs and
vsbys at worst. Winds will be light from the south to southeast
through tonight.

&&

.DMX Watches/Warnings/Advisories...None.

&&

SHORT TERM...Skow
LONG TERM...Small
AVIATION...Zogg

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
408 PM CDT FRI MAY 27 2016

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-281100-
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-
408 PM CDT FRI MAY 27 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR MUCH OF CENTRAL IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THUNDERSTORMS ARE LIKELY INTO TONIGHT. LOCALIZED HEAVY RAIN
REMAINS POSSIBLE OVER MUCH OF THE AREA. THE SEVERE WEATHER RISK
IS EXPECTED TO REMAIN LOW HOWEVER WITH ONLY A MARGINAL RISK OF
LARGE HAIL AND WIND GUSTS SOUTH.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

SCATTERED THUNDERSTORMS ARE EXPECTED SATURDAY AND SATURDAY
EVENING. ALTHOUGH THE THREAT OF SEVERE WEATHER IS ONLY
MARGINAL...IF ANYTHING DID OCCUR LARGE HAIL...DAMAGING WIND AND
TORNADOES WOULD ALL BE POSSIBLE.

THUNDERSTORM CHANCES RETURN LATE SUNDAY NIGHT AND CONTINUE
THROUGH THE WORK WEEK. THE SEVERE WEATHER POTENTIAL WILL BE BETTER
DEFINED IN THE COMING DAYS.

.SPOTTER INFORMATION STATEMENT...

THE POTENTIAL FOR SPOTTER ACTIVATION IS LOW THROUGH THE
PERIOD...BUT SPOTTERS MAY BE NEEDED BRIEFLY SATURDAY AFTERNOON OR
EARLY EVENING.

SMALL

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
736 PM CDT FRI MAY 27 2016

IAZ086-097-280130-
DAVIS IA-WAPELLO IA-
736 PM CDT FRI MAY 27 2016

...TORRENTIAL RAIN AND SMALL HAIL POSSIBLE...

AT 736 PM CDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 6
MILES SOUTHWEST OF BATAVIA...OR 8 MILES SOUTHEAST OF OTTUMWA...MOVING
WEST AT 5 MPH.

HALF INCH HAIL WILL BE POSSIBLE WITH THIS STORM.

RAINFALL AMOUNTS UP TO TWO INCHES WILL BE POSSIBLE WITH THIS STORM.

LOCATIONS IMPACTED INCLUDE...
ELDON AND AGENCY.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TORRENTIAL RAINFALL IS ALSO OCCURRING WITH THIS STORM...AND MAY LEAD
TO FLASH FLOODING. DO NOT DRIVE YOUR VEHICLE THROUGH FLOODED
ROADWAYS.

TO REPORT SEVERE WEATHER...CONTACT YOUR NEAREST LAW ENFORCEMENT
AGENCY. THEY WILL RELAY YOUR REPORT TO THE NATIONAL WEATHER SERVICE
OFFICE IN DES MOINES .

&&

LAT...LON 4083 9227 4099 9239 4109 9218 4087 9218
TIME...MOT...LOC 0036Z 076DEG 5KT 4095 9228

KOTENBERG