353
FXUS63 KDVN 181752
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1252 PM CDT Fri Sep 18 2026

.KEY MESSAGES...

- The wet weather pattern will continue through the weekend with
  rounds of rain which may be heavy at times. There will be
  periods of dry weather between each round.

- There is a Marginal Risk, Level 1 out of 5, for isolated
  severe storms along the I-380 corridor this afternoon and for
  areas south of Highway 20 on Saturday. Primary severe hazard
  each day will be damaging winds.

- A Flood Watch has been issued for portions of east-central
  Iowa and far northwestern Illinois for late tonight through
  Saturday evening. Rainfall totals of 1-3 inches are likely
  (60-80%) in these areas with the potential (10-20%) for
  localized areas of 3+ inches.

- The repeated rounds of rain will keep the risk of flash
  flooding around through Sunday. Rapid rises on small creeks
  and streams and the flooding of low-lying areas are possible.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 219 AM CDT Fri Sep 18 2026

A mid-level trough over the Northern Plains is forecasted to pull a
low pressure over Nebraska eastward towards Iowa. WAA and F-gen in
the 850-to-700 mb layer will support scattered showers and
storms (30-60% coverage) to develop late this morning across
eastern Iowa and far northwest Illinois and last into the
afternoon. The quick motion of this rain band should keep
rainfall totals low, ranging between 0.1-0.25 of an inch, with
isolated spots over half an inch. There is a Marginal Risk,
Level 1 out of 5, for an isolated severe storms near the I-380
corridor. While storms are expected to be elevated, a few storms
near the warm front over central Iowa may be able to produce
surface gusts where DCAPE is able to exceed 750 J/kg.

By tonight, the low moves into western Iowa, lifting the warm front
towards the I-80 corridor in eastern Iowa. Another round of heavy
rain and thunderstorms north of I-80 is expected to develop
after midnight in response to the enhanced surface convergence,
low-level isentropic upglide, and near record level PWATs
around 2 inches. A Flood Watch has been issued for portions of
east-central Iowa and far northwestern Illinois where 1-3
inches of rainfall is likely (60-80%) with localized areas of
3+ inches possible (10-20%). This Watch could be expanded to
the southwest if CAM guidance continues to show storms
backbuilding along the WAA wing.

Heading into Saturday, a shortwave trough moves into the Northern
Rockies, pulling another weak subtropical trough northeastward
towards Iowa. The low pressure continues to trek eastward into our
outlook area, keeping scattered showers and storms (50-80% coverage)
around. With dew points in the low-to-mid-70s areawide and slightly
steeper mid-level lapse rates, SBCAPE will likely (60-80%) exceed
1500 J/kg along and south of Highway 30, enabling stronger
storms to potentially produce water-loaded downbursts. The SPC
has a Marginal Risk, Level 1 out of 5, for isolated severe
storms south of Highway 20 with damaging winds as the primary
hazard.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 219 AM CDT Fri Sep 18 2026

Saturday Night-Sunday...After sunset, a developing high
pressure over central Canada nudges the surface trough
southeastward into Illinois Saturday night. Despite the low-
level CAA, another band of moderate-to-heavy rainfall will
likely (70-90%) develop and persist into Sunday. While there is
still uncertainty among the ensemble models on placement of the
heaviest axis, general consensus is showing rainfall totals of
0.25- 0.75 of an inch (50-80% chance) across a broad area with a
swath of 1-2 inches possible (30-50%). The coverage and
intensity of these showers should begin to decrease by Sunday
afternoon as dry air advection occurs near the surface.

Sunday Night-Tuesday...The main trough over the Northern
Rockies finally reaches the Northern Plains as low-to-mid-level
ridging over south-central Canada continues to push the surface
trough further south into the lower Ohio River Valley. Despite
the cold air advection, CVA ahead of the trough keeps scattered
light-to-moderate showers (50-70% coverage) around Sunday night
into Monday. By Monday night, the trough finally reaches Iowa
as cold-core showers form underneath, keeping PoPs around
through Tuesday morning. As subsidence sets in on the backside
of the trough and high pressure builds in from the north, the
outlook area should be rain-free by Tuesday evening.

Wednesday-Thursday...Fall-like weather is likely (70-90%) to
return for the middle of next week. Confluence aloft and surface
high pressure is forecasted to keep Wednesday and Thursday dry
as CAA keeps temperatures below average with highs in the
mid-60s to low 70s and lows in the mid-40s to low 50s.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1245 PM CDT Fri Sep 18 2026

Active weather is expected today into Saturday morning with
periods of MVFR/IFR ceilings and rounds of showers and
thunderstorms. After some improvement in ceilings this
afternoon/evening, conditions will deteriorate into tonight with
MVFR/IFR likely north of BRL. Scattered showers and isolated
storms are then expected late tonight into Saturday AM, most
favored at DBQ and CID. Heavy downpours are likely with the
strongest cells which could lead to brief visibility reductions
under 1 mile. A return to VFR/MVFR is anticipate by mid/late
Saturday morning as rain coverage decreases across the area.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flood Watch from late tonight through Saturday evening for
     IAZ040>042-054.
IL...Flood Watch from late tonight through Saturday evening for
     ILZ001-002-007.
MO...None.

&&

$$

SHORT TERM...Delaune
LONG TERM...Delaune
AVIATION...Uttech