-- Discussion containing changed information from previous version are highlighted. --
913
FXUS63 KDVN 210514
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1214 AM CDT Sat Sep 21 2024

.KEY MESSAGES...

- Highs in the mid 80s to near 90, or 8 to 15 degrees above
  normal, are expected Saturday

- Marginal Risk for severe storms late Saturday afternoon into
  the evening for the far NW CWA.

- Rainy and much cooler for Sunday and Monday with highs in the
  mid 60s to lower 70s, which is slightly below normal.

- Dry conditions are expected to prevail Tuesday through Thursday
  with temperatures in the low to mid 70s.

&&

.UPDATE...
Issued at 833 PM CDT Fri Sep 20 2024

Latest CAMs have become more robust with convection in the
afternoon as daytime heating destabilizes the the warm sector.
The 00z HRRR depicts a supercell that rides the sfc boundary SE
along the Mississippi River into NW Illinois in the
mid-afternoon, before bowing it out. Wind gust forecasts in the
HRRR suggests severe winds are possible with this cell. Then
later in the afternoon a wave moving across the warm sector
should lead to more strong to severe storms. Right now large
hail and damaging winds are the main threats. If we get that
supercell, then a tornado risk would exist as well. Another
wrench in the forecast are the storms out west right now. Where
do they end up and what kind of anvil shield could we see in the
AM. Regardless, environment is supportive of severe weather.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 224 PM CDT Fri Sep 20 2024

Tonight, high pressure will drift east of the area as a warm front
lifts northeast into SE IA and NE MO towards daybreak bringing
clouds and shower and storm chances to that area. In the meantime, a
pleasant night is expected, with evening temps slipping into the
upper 60s and 70s, nearly calm winds, and moonlit skies.
Temperatures will eventually settle into the upper 50s to mid 60s by
daybreak, with areas around Keokuk possibly only seeing upper 60s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 224 PM CDT Fri Sep 20 2024

Saturday through Monday night, an upper level low will slowly be
moving from northern AZ, across the plains, and into the mid MS
Valley while a surface low moves across Canada with a trailing cold
front moving across the area.  Some upper level waves will be drawn
up along this boundary during this time, bringing periods of better
rain chances to the region. This appears to be a good widespread
rainfall period of good wetting rains. Currently the WPC rainfall
forecast for the 3 days has amounts roughly of a half to 1 inch
forecast north of I-80 with 1 to 2 plus inches possible to the
south. There will be some dry periods, especially across the north
half of the CWA. The most likely chances are for late Saturday night
into Sunday morning and across the far south from Sunday evening and
overnight into Monday. SPC has a Marginal Risk area for the NW
quarter or so of the CWA. This is dependent on whether any
morning convection and debris clouds can clear out early enough
to help destabilize the atmosphere. Thunderstorms are forecast
to develop in the late afternoon into the evening with the focus
locally north of I-80, with the better potential off to the NW
where SPC has the Marginal Risk area. The main threats are hail
and damaging winds. Based on the last couple of HRRR runs, the
best timing is roughly from 5pm to 9pm.

Tuesday through Thursday, the forecast blend continues dry
conditions as high pressure builds into the region. Temperatures
will inch upwards from the upper 60s and low 70s Tuesday to the low
to mid 70s by Thursday. The GFS drops an upper low over MO and
IA mid to late week, which may result in some introduction in
POPs and cooler temperatures.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
-- Changed Discussion --
Issued at 1211 AM CDT Sat Sep 21 2024

VFR weather will continue into this upcoming morning, but it
should be noted, there is a low chance (20%) that some high
based thunderstorms may form over southeast Iowa and northeast
Missouri through 15Z today. The bulk of Saturday will be dry
with warm VFR conditions, followed by a thunderstorm chance
arriving in the evening hours. There remains rather low
confidence on placement an timing at this time, so a prob30 for
storms is included at all sites from 00Z to 06Z Sunday/22nd. Any
thunderstorm would bring IFR conditions for a brief time, and
possibly gusty winds over 35kts.
-- End Changed Discussion --

&&

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

&&

$$

UPDATE...Gibbs
SHORT TERM...14
LONG TERM...14
AVIATION...Ervin