Hail and Damaging Winds in Iowa, July 11, 2020

Area Forecast Discussion
National Weather Service Quad Cities IA IL
623 AM CDT Sat Jul 11 2020

...12z AVIATION UPDATE...

.SYNOPSIS...
Issued at 300 AM CDT Sat Jul 11 2020

High pressure was in control over the Upper Mississippi Valley
with NW flow aloft. Temperatures were in the mid 60s to lower 70s
and conditions were fairly humid. The area has been convection
free so far tonight as the organized activity has stayed across
the western part of Iowa and into Nebraska. Latest RAP analysis
has the mean steering vectors and 1000-500mb thicknesses aligned
from NW to SE, which should guide the western Iowa convection to
the southeast across south-central Iowa.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 300 AM CDT Sat Jul 11 2020

Main Message:

*Slight risk for severe thunderstorms today across the entire
 area. Scattered storms are likely to develop between the mid
 afternoon and the evening, some of which could become severe. The
 main threats with the strongest storms are damaging wind gusts,
 hail, and frequent lightning. The current forecast has the
 highest chances for showers and storms across the north and east
 (50-70%).

Today and Tonight

A mid-level vorticity max currently over North Dakota will drop to
the southeast today, reaching NE Iowa by this evening. Ascent from
DCVA, and the left exit region of an upper jet, should provide
sufficient lift for scattered storm development as early as the
mid afternoon, but more likely during the late afternoon and
evening.

Today's environment will consist of very warm and humid conditions
with moderate to high instability (SBCAPE between 2000-3500 J/kg)
and low to moderate deep layer shear (30-40 kts). This setup
should provide an instability/shear balance supportive of
organized updrafts and a few supercells. An isolated wind and
large hail threat within a few hours of initiation will transition
to more of a wind dominant threat as cold pools merge and the
convection grows upscale.

The potential for scattered damaging winds, and microbursts from
the strongest storms, is corroborated by high DCAPE (1300+ J/kg)
and theta-e index values (30-35+) on model forecast soundings,
which are a manifestation of dry mid-level air. Due to veered and
weak low-level winds, the overall tornado potential is very low.

Based on HREF members, the most likely timing for storms is
between 3 and 9 PM, before shifting east of the forecast area.
Uttech

.LONG TERM...(Sunday through Friday)
ISSUED AT 300 AM CDT Sat Jul 11 2020

Key Messages:

1. Dry and pleasant conditions Sunday and Monday.

2. Temperatures next week have been lowered some each day in the
extended, with any heat issues likely to remain south of CWA. Best
chance of appreciable rain will be Tuesday night-Wednesday.

Discussion:

Sunday-Monday...any lingering precipitation from overnight will be
just to the east of the area by 12z Sunday. Northwest flow aloft and
a surface high will usher in lower dewpoints resulting in more
comfortable summer conditions. Deep mixing and plentiful sunshine
will help boost highs into the lower 80s, which is near normal for
the middle of July. A nice day outside for sure. There is some
potential for some diurnal showers and storms Sunday afternoon and
evening as hinted by some of the 00z CAMs. However, I feel that this
is overdone, as forecast soundings show quite a bit of mid level dry
air aloft and thus have no mention in the forecast.

Similar conditions are expected Monday with temperatures a few
degrees warmer than Sunday and dewpoints remaining tolerable in the
60s.

Tuesday-Thursday...active zonal flow sets up with several waves
expected to impact the region. Latest 00z model solutions show that
the best chance of rain will be Tuesday night-Wednesday when a cold
front is progged to drop south over the area. Increasing theta-e
advection and pooling moisture ahead of the front will bring a heavy
rain threat. Placement and magnitude of rainfall is still uncertain
and currently with the 00z runs is favored just north of the CWA.
This front will drop south and stall somewhere over northern MO and
eventually lift north as a warm front Thursday and Friday with more
rain chances. Model blend currently has chance PoPs across the CWA
which will be further refined in later forecasts. Many areas in our
IL counties have seen less than 75% of normal rainfall in the past
30 days and could really use some rain.

Friday-Saturday...Increasingly warm and humid conditions will return
to the area as a warm front lifts north into MN/WI. Above normal
temperatures can be expected and is likely to continue beyond the 7
day forecast.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday Morning)
ISSUED AT 614 AM CDT Sat Jul 11 2020

VFR conditions expected through at least early afternoon at all
TAF sites. Scattered thunderstorms will be possible after 21z.11
with MVFR cigs/vsbys. Confidence in storms hitting terminals
remains low at MLI/BRL and thus kept PROB30 wording there until
better timing and location of storms is realized. Brief IFR is
possible in any of the stronger storms. Conditions will return to
VFR after sunset at all terminals.

&&

.CLIMATE...
ISSUED AT 300 AM CDT Sat Jul 11 2020

The Climate Prediction Center 6-10 day and 8-14 day outlooks
continue to show high probabilities of above normal temperatures
across the area. This would be through the 4th full week of July.
With the area already 4-6 degrees above normal for the month of
July, it is quite possible that the month will end up well above
normal.

The latest US Drought Monitor released this past Thursday shows
abnormally dry conditions (D0) developing over portions of
eastern Iowa and central Illinois. These areas have received
50-75% of normal rainfall in the past 30 days.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

SYNOPSIS...Uttech
SHORT TERM...Uttech
LONG TERM...Gross
AVIATION...Gross
CLIMATE...Gross

Hazardous Weather Outlook
National Weather Service Quad Cities IA IL
349 AM CDT Sat Jul 11 2020

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-120900-
Buchanan-Delaware-Dubuque-Benton-Linn-Jones-Jackson-Iowa-Johnson-
Cedar-Clinton-Muscatine-Scott-Keokuk-Washington-Louisa-Jefferson-
Henry IA-Des Moines-Van Buren-Lee-Jo Daviess-Stephenson-Carroll-
Whiteside-Rock Island-Henry IL-Bureau-Putnam-Mercer-Henderson-
Warren-Hancock-McDonough-Scotland-Clark-
349 AM CDT Sat Jul 11 2020

This Hazardous Weather Outlook is for portions of north central
Illinois...northwest Illinois...west central Illinois...east
central Iowa...northeast Iowa...southeast Iowa and northeast
Missouri.

.DAY ONE...TODAY AND TONIGHT

Scattered thunderstorms are expected to develop this afternoon
and evening mainly between 3 PM and 9 PM.

The Storm Prediction Center has a slight risk for severe storms
across the entire outlook area. The primary threats are damaging
winds, large hail, and frequent lightning. Localized heavy
rainfall is also possible along with a low potential for flash
flooding.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

Thunderstorms will be possible Tuesday evening through Friday. At
this time it is too early to determine any severe risk.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon and evening.

Uttech/Gross