569
FXUS63 KDVN 260801
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
301 AM CDT Thu Jun 26 2025

.KEY MESSAGES...

- A heat advisory has been issued for much of the area this
  afternoon into early evening. The heat and humidity will
  continue through the weekend. Some relief may occur next week.

- Strong to severe storms will again be possible late this
  afternoon and evening. Damaging winds from wet microbursts is
  the primary risk.

- With a wet pattern across the area and a daily risk of showers
  and thunderstorms capable of producing heavy rainfall, area
  rivers are expected to see rises. Refer to the hydrology
  section for more information.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 259 AM CDT Thu Jun 26 2025

The LLJ is very weak and mid-level lapse rates are fairly stable. As
a result, quiet but humid conditions will be seen through sunrise.
The exception is the Highway 20 corridor where an errant shower or
thunderstorm might occur.

Hot and humid conditions will be seen across the area today. A heat
advisory has been issued for a good chunk of the area. Dew points
will drop somewhat during the day as deeper mixing is promoted
through wind gusts this afternoon.

Mid-level lapse rates continue to remain fairly stable during the
day. Some weak diurnal cumulus may develop from thermals this
afternoon.

Attention then turns to the approaching cold front. The hi-res
models have been suggesting a pre-frontal trof well in advance of
the front which is suggested in the current observations in the
Plains. Several of the hi-res solutions have a line of scattered
storms developing along the pre-frontal trof with a secondary line
along the cold front.

Although there are differences between the hi-res models, timing
suggests late afternoon/evening for the pre-frontal storms in
eastern Iowa. Most areas east of the Mississippi will remain dry
into the early evening but a few isolated diurnal storms cannot be
ruled out.

The storms moving into eastern Iowa late afternoon/early evening
would have the best chances of being strong/severe. If severe storms
develop, the primary risk is damaging winds in the form of wet
microbursts and heavy rainfall.

Tonight the stable mid-level lapse rates east of the Mississippi
suggests storms will struggle and weaken as they move east. Storm
dynamics will modify the mid-levels of the atmosphere with time
allowing storms to move east of the Mississippi later tonight. The
trailing cold front will also aid in another round of storm
development in eastern Iowa that moves east of the Mississippi well
after sunset. However, this second round of storms has the potential
to be more scattered in nature.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 259 AM CDT Thu Jun 26 2025

Friday through Monday
Assessment...Very high (>90%) of heat and humidity continuing.

The cold front moving through the area late Thusday night and Friday
will push temperatures down to around normal on Friday. The heat
and humidity builds back in for the weekend with Sunday being the
hottest day. This far out there is a 50% probability of heat
headlines for Sunday.

Rain chances are more questionable. The proximity of the front to
the area on Friday indicates this day has the best chances of seeing
some rain. The front looks to stall out and dissipate Friday night
just south of the area. If the front does stall just south of the
area, the remnants of the front would provide a focus for mainly
diurnal showers and storms across the far southern areas on Saturday
but coverage would be in the 20-30% range.

With the heat dome back into the area for Sunday, the question
becomes will a weak upper level disturbance approaching the area
generate diurnal convection. The model consensus suggests this with
a 40% scattered coverage Sunday afternoon/evening.

An approaching front on Monday (associated with the pattern change
aloft) raises questions regarding the rain potential. Several
deterministic model runs suggest very little in the way of rain.
However, there are several members from the respective ensemble runs
that generate rain. Thus the model consensus is biased toward the
ensembles but the areal coverage for any rain is only 20-40%.

Monday night through Wednesday
Assessment...medium (40-60%) confidence on near normal temperatures.
Low (<25%) confidence on rain chances

The pattern change to west northwest flow aloft will help keep
temperatures around or slightly above normal. With the heat dome
suppressed southward, the more tropical moisture that would fuel
storms is not present. Thus the deterministic model runs and nearly
all of their respective ensemble members have dry conditions Monday
night through Wednesday.

However, there are weak disturbances in the flow aloft moving
through the area Tuesday and Wednesday. Thus I cannot fully rule out
the possibility of a rogue convective storm developing during the
diurnal heating cycle on Tuesday and Wednesday. If this were to
occur, areal coverage would be under 10 percent.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1235 AM CDT Thu Jun 26 2025

The low level jet is weak at 25 knots. That combined with
stable mid-level lapse rates raises the question if nocturnal
convection will occur. Based on data available, areas
along/north of the Highway 20 corridor appears to be favored
through 12z/26. After 12z/26 daytime heating will push density
altitudes to or above 3kft. A pre-frontal trof will initiate
convection that moves into eastern Iowa after 21z/26 bringing a
risk of TSRA before they fall apart. More SHRA/TSRA can be
expected with the cold front after 05z/27.

&&

.HYDROLOGY...
Issued at 655 PM CDT Wed Jun 25 2025

Tributary rivers in east central Iowa are having a minor crest
into early Thursday from earlier week rainfall, and then should
see a temporary drop. Bouts of rain through Thursday night over
central to northeast Iowa (i.e. headwater regions of the Cedar,
Iowa, and Wapsi Rivers) will see water gradually come down the
channel and additional rises by late weekend into early next
week. Confidence in that general, slow-evolving expectation is
fairly high. However, in terms of how high of water levels
reached next week, that is much lower. That is due to
uncertainty on where exactly the heaviest rain will fall with
each bout through Thursday night, and timing of the water as it
is channeled in upstream rivers channeling into the Cedar River.

For now, we continue Flood Watches on the Cedar River, even
though flood stage currently is not probable in the next 48
hours, and more so late in the weekend into next week. A main
reason we continue the watches are that heavier rainfall could
fall southeast of where it is predicted through Thursday night,
and there are multiple models (albeit a minority of model
membership) that do show that. The predicted response on the
rivers with those 10-15% of higher models show a couple points
on the Cedar River, including Cedar Rapids, jumping all the way
to major flood stage late in the weekend into early next week.
The greater model membership would favor upper end minor stage
to lower end moderate stage for the city, and coordinating with
the North Central River Forecast Center (NCRFC), that is where
we collectively felt most comfortable with the forecast.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Heat Advisory from noon today to 7 PM CDT this evening for
     IAZ052-053-064>068-077-078-087>089-098-099.
IL...Heat Advisory from noon today to 7 PM CDT this evening for
     ILZ009-015>018-024>026-034-035.
MO...Heat Advisory from noon today to 7 PM CDT this evening for
     MOZ010.

&&

$$

SHORT TERM...08
LONG TERM...08
AVIATION...08
HYDROLOGY...Friedlein