614
FXUS63 KDVN 181917
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
217 PM CDT Fri Apr 18 2025

.KEY MESSAGES...

- A conditional chance of thunderstorms, some possibly strong to
  severe, remains for late this afternoon into the early
  evening hours, mainly along and east of the Mississippi River

- Another storm system will cross our area Easter Sunday, with widespread
  rainfall and perhaps a few strong thunderstorms along and
  south of Highway 34

- Seasonal temperatures are expected this weekend, with a warm
  up by mid-week next week

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 217 PM CDT Fri Apr 18 2025

A low pressure system, currently located over the IA/IL/WI
border, will continue to lift northeastward towards
southeastern Wisconsin late this afternoon into the evening.
This surface low will help drag a cold front across our area
from northwest to southeast, which will be focal point for the
potential for scattered thunderstorms (30 to 60% chances)
developing late this afternoon into the early evening hours.
Ahead of the front, mixed-layer CAPE is progged around 1000 to
1500 J/kg among the global models, with the GEFS ensemble
suggesting 70-90+ percent chances of 1000 J/kg or more of CAPE
this afternoon. Deep-layer shear also appears to be supportive
of organized updrafts, with values around 50 knots, thanks to a
stout 60-70+ knot southwesterly mid-level jet. Mid-level lapse
rates are also expected to be quite stout, with values progged
around 8-9 C/km ahead of potential convective initiation (CI)
per the suite of CAMs. The threat for strong to severe storms
remains conditional as there are some questions as to how much
diabatic heating/instability will build as more cloud cover
would help to hinder this. Additionally, the 18.12z DVN sounding
indicated a 14 degree C capping inversion around 700 mb level,
which could inhibit CI if it holds, and the latest guidance
shows varying degrees of cooling to erode the cap. If the cap
holds, CI could be later and farther east of our forecast area.
SPC continues to maintain a Slight Risk (level 2 of 5) of severe
weather, mainly for areas along and east of a line from
Morrison, IL to Kahoka, MO, with a Marginal Risk (level 1 of 5)
for the northwestern periphery of the Slight Risk. Severe
threats still look most likely to be large hail and damaging
winds, but we can`t rule out a tornado, albeit a more marginal
environment for tors.

Any convection that does develop will eventually shift off to the
east pretty quickly, leading to a largely dry period tonight
through Saturday. The only exception may be over our southern
areas as the cold front stalls over Missouri into central
Illinois, so there could be some showers and perhaps an isolated
storm closer to the boundary. We are not outlooked for any
strong or severe storms at this time Saturday, and temperatures
should be cooler/more seasonal, with highs in the upper 50s to
near 60.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 217 PM CDT Fri Apr 18 2025

The longwave upper-level trough that is expected to loiter over the
Intermountain West today and Saturday will finally approach the
region for Easter Sunday, becoming more negatively-tilted with time.
A pretty potent mid-level vort max should pivot through the area,
supporting large-scale forcing for ascent. An attendant surface low
pressure system will lift northward from the southern Great Plains
towards eastern Iowa by Sunday evening. This will support widespread
chances (80-100%) of showers and a few thunderstorms with it. Heavy
downpours at times will be the main story with this system, as
instability will be more limited. However, abundant moisture is
expected, with Pwat values progged around 1 to 1.5 inches, as well
as integrated water vapor transport per the ECWMF ensemble
percentiles giving values over 97% of climatology. NBM exceedance
probabilities of one inch of total rainfall for Sunday through
Sunday night range from 40 to 70% for most locations, so between 1
to 2 inches of total rainfall appears likely. SPC also has a
Marginal Risk (level 1 of 5) for strong to severe storms for
areas along and south of Highway 34, so we will need to watch
for that potential.

For Monday through Thursday, the pattern remains somewhat active
despite zonal flow aloft. Periodic shortwaves will translate through
the region, which could spark off some additional showers and
storms, but exact timing and location details remain uncertain
this far out. Temperatures are expected to gradually warm up,
particularly by Tuesday through Thursday, with highs returning
to the 70s for most locations.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1231 PM CDT Fri Apr 18 2025

An area of low pressure continues to lift northeastward over
east-central Iowa early this afternoon. VFR conditions were
observed east of the low, with MVFR to IFR ceilings west of it.
The MVFR/IFR ceilings are located along a cold front that will
gradually make its way eastward this afternoon. Some scattered
showers and even a few storms are possible later this afternoon,
most likely for the MLI and BRL TAF terminals, but uncertainty
remains on the timing of storm development as it could be
delayed and develop east of these locations. Confidence remains
high for MVFR to IFR ceilings moving in from the west behind
the front, as well as a wind shift from the southwest ahead of
the front to more northwest behind the front. Ceilings should
gradually improve late this evening into the overnight hours
tonight.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...None.
MO...None.

&&

$$

SHORT TERM...Schultz
LONG TERM...Schultz
AVIATION...Schultz