997
FXUS63 KDVN 191753
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1253 PM CDT Thu Sep 19 2024

.KEY MESSAGES...

- There is a Slight or level 2 out of 5 Risk of severe
  thunderstorms late Thursday afternoon and into the evening
  west of a line from Delaware County southwestward to Keokuk
  County. A Marginal or level 1 out of 5 Risk of severe
  thunderstorms extends east of that line to the counties along
  the Mississippi River.

- Above normal temperatures remain in the forecast through
  Saturday with near to slightly above normal temperatures from
  Sunday onward.

- An active pattern will continue into next week.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 218 AM CDT Thu Sep 19 2024

There are pockets of showers and thunderstorms in a zone of 850
theta-e advection region that extends from southern Minnesota
southwestward into eastern Nebraska and northern Kansas.
Temperatures are warmer this morning and at 3 AM range from 58
degrees at Freeport to 68 degrees at Cedar Rapids.

At 500 MB, a negatively tilted trough and vertically stacked
closed low sit across North Dakota, Saskatchewan and Manitoba
early this morning. This trough and vertically stacked closed
low are forecast to lift into northeast Manitoba by 12 UTC
Friday. At the surface, a cold front is forecast to move from
central South Dakota and Nebraska this morning eastward and
into east central Iowa by 12 UTC Friday. Dewpoints will be on
the increase this afternoon into this evening with widespread
dewpoints in the mid to upper 60s. High temperatures today will
be similar to previous days and be in the mid to upper 80s.

Pockets of scattered showers and storms associated with the
theta-e advection are forecast to move into parts of east
central Iowa this morning but slowly weakening as they move into
a drier environment this morning. There are chances of showers
and storms west of a Manchester to Cedar Rapids to Sigourney
line 9 AM through 1 PM but expecting any of these to be
weakening as they move into the area.

The focus of the forecast then shifts to an approaching
shortwave and midlevel jet streak that is forecast to move along
the Iowa and Minnesota border later this afternoon and into this
evening. After 00 UTC Friday, a 30 to 35 knot low level jet is
forecast to develop across central Iowa and then veer into our
area in the 3 to 06 UTC timeframe and think that most of the
shower and thunderstorm activity will be associated with this
feature with showers and storms sinking southeastward across the
area through 12 UTC Friday.

If thunderstorms can develop during the late afternoon and
early evening associated with the approaching jet streak,
Supercells are possible with 30 to 40 knots of 0 to 6 km shear
and most unstable CAPE values of 1000 to 2000 J/KG. Model
soundings show mainly elevated CAPE across the area with high
LCLs expected. In the far western edge of CWA, northwest of
Cedar Rapids model soundings show LCLs around 2000ft. Hodographs
show good low level curvature with 0 to 1 km shear around 30
knots and SRH around 200 M^2/S^2. Although it appears that LCLs
may be too high for a tornado threat there is a 2% tornado
threat across pat of our area. It would seem that the developing
low level jet may be able to aid in lowering LCLs resulting in
a brief 1 to 2 hour threat for tornadoes mainly west of a
Manchester to Cedar Rapids to Sigourney Iowa line before
instability decrease this evening. Outside of the tornado
threat, the primary threats will be damaging winds and hail.
The Storm Prediction Center has a slight risk of severe
thunderstorms west of a Manchester to Cedar Rapids to Sigourney
line. There is a marginal risk of severe storms east of this
line to the Mississippi River.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 218 AM CDT Thu Sep 19 2024

Active weather continues Friday through Monday with zonal west
to east flow across North America. There are two closed 500 MB
lows that will bring chances of showers and storms to the area
during this time period. The first passes to our north Saturday
into Saturday night. The second will lift from the southern High
Plains and across the area Sunday through Monday when it is
followed by another 500 MB trough. Models continue to disagree
on the timing and placement of these storm systems and any
interaction between the three late this weekend into early next
week. This continues to result in broad brush POPS across the
area through the period. This will also result in cooler high
temperatures especially Sunday into early next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1240 PM CDT Thu Sep 19 2024

Scattered showers and thunderstorms have remained and persisted
west across central IA today. These have formed along an
instability gradient and are expected to  before reaching
eastern IA, as they slowly lift northeast through the afternoon.
Attention then turns to storm potential ahead of a cold front
progged to move east across IA this evening. Have delayed onset
of thunder and lower VFR/MVFR conditions a few hours and
continued PROB30 wording after 03z. Behind these storms, low
clouds are expected to develop and have trended the TAFs with
MVFR cigs. The 12z HREF and RAP guidance is even suggesting some
brief 1-2 hr IFR conditions are possible, but did not go that
low on cigs with this issuance due to lower confidence. Winds
will switch to the west late this evening and eventually
northwest just beyond the TAF cycle.


&&

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

&&

$$

SHORT TERM...Cousins
LONG TERM...Haase
AVIATION...Gross