Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 131121
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
621 AM CDT Wed Mar 13 2024

.KEY MESSAGES...

- Unsettled weather tonight and Thursday in tandem with a shift
  from highs around 70 today to lower 50s areawide Friday.

- Semi-organized thunderstorms expanding northeast across much
  of the area tonight, mainly after 11 PM, with a risk level of
  1-2 (out of 5) for large hail and depending on how organized,
  also some threat south of I-80 for damaging winds.

- Thursday, there is a chance for showers and thunderstorms,
  where some may be strong to severe. The Storm Prediction
  Center has highlighted much of our area in a Slight Risk for
  severe weather, with all hazards in play.

- Cooler and dry through the second half of the weekend and
  into next week, with breezy conditions. Low-end chances for
  flurries or light snow in our northeast Sunday.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 325 AM CDT Wed Mar 13 2024

Last night`s disturbance that brought isolated thunderstorms as
far north as the Quad Cities was a lead impulse ahead of a
deeper western U.S. trough. Another lead impulse, this one even
stronger, will eject from this trough tonight toward the region
and be the start of an unsettled 24-hour period. Ahead of this
today, a mix of clouds and sun will be the rule. A southeast
wind rarely results in upper 60s and lower 70s for highs in
early March, but that looks to be the case given the warm
starting point and lack of thick cloud cover. One note for
afternoon and early evening precipitation chances, is that as
the flow at 800-900 mb turns more southerly, this elevated warm
advection zone may spark scattered showers and even a couple
non-severe storms in far northwest Illinois and northeast Iowa.
Convection-allow models (CAMs) do hint at this and have added a
chance (30%) into the forecast from roughly 2-8 PM.

The aforementioned impulse for tonight will be riding a well-
defined left exit region of a 100 kt upper jet, with even some
coupled structuring taking shape over our area by late tonight.
The surface low response will be well away from the region near
the KS/OK border. However, the low-level jet and associated
moisture transport overriding a warm front in central/northern
Missouri will initiate storms in the general northern
Missouri/far southern Iowa region this evening. Deep layer shear
in this region is forecast to be 30-40 kt and oblique to the
west-to-east warm front, so a potential mixed mode of semi-
organized convection is expected to enter the southern forecast
area later this evening and possibly as late as early overnight.
With forcing and the upper level wave tracking more north of
east, convection is expected to do the same, although any more
organized activity may track due east along the sharp MUCAPE
gradient. That means the greater coverage will likely be over
the southern CWA. With farther north extent, including Cedar
Rapids and the Quad Cities, there is less confidence in
thunderstorm morphology, but at least scattered or arcs of
convection or the northern extent of a loosely-defined MCS are
anticipated over/near these locations overnight.

In terms of severe risk, the more mature, sustained convection
closer to the boundary will have the chance to pose a severe
threat -- so mainly the southern forecast area. However, a
threat of hail to at least quarter size with any larger updrafts
does look like it would exist to I-80. In the southern CWA, if
convection is mature and organized, strong wind gusts to 45+ mph
would be possible, and some spotty CAM solutions last night do
indicate that possibility. A couple solutions even show evenly-
spaced convective arcs, a possible sign of gravity waves and in
turn, some of the convection along those might be able to
produce isolated damaging winds. But that`s low confidence at
this point. Some stronger storms will remain possible after
daybreak Thursday morning, especially into Illinois.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 325 AM CDT Wed Mar 13 2024

Thursday will be an unsettled day, with a deep upstream wave cutting
off from the flow over the southwest U.S, resulting in a weak
surface low developing in lee of the Rockies. Surface cyclogenesis
is forecast over parts of western KS, with the surface low tracking
northeast towards our area on Thursday. Latest trends in forecast
guidance have the low passing farther south through our area than
the previous forecast package, which may limit the northern
extent of the severe potential later in the day. The northward
progression of the warm front is going to be something that
needs to be watched closely, as it will be a key player in all
of this. Why the focus on how far north the warm front goes, you
may ask? Well, guidance still has a juiced warm sector, with
plenty of warmth and moisture, allowing instability to increase
into the 1000-2000+ CAPE range. This, coupled with 50-65 KTs of
deep layer shear and ~25 KTs LLVL shear, is more than favorable
for a severe threat Thursday afternoon. With this southerly
trend in guidance, the best environment will remain south of
I-80 at the moment. One thing to keep in mind, which may also be
a failure mode for severe in the afternoon, is the residual
cloud cover and rain/storms through Thursday morning, along with
anymore of a southerly trend in the surface low. With these
latest trends in the forecast, uncertainty has increased. As
short term guidance and observations continue to filter in
through the day today, we should get a better grasp on how this
should play out.

Along with the threat for strong/severe storms, this system will
bring another round of much-needed soaking rainfall. The
ensemble suite from the long term deterministics favor a 60-80%
chance for seeing at least a 0.50" of rain throughout the area.
The greater uncertainty comes with the higher end of the
rainfall chances, which will be determined by where
thunderstorms Wednesday night and Thursday set up, which will be
where the warm front sets up. Currently, this swath of higher-
end precipitation chances falls along Highway 34. So, as of this
forecast package, these areas are where probabilities favor the
best chance of seeing upwards to an inch of rain or more. This
is highlighted well with the WPC QPF forecast for the area,
where they have a swath of ~1.00" of rain. The latest HREF also
paints a similar picture, with it being a little more aggressive
on totals and showing some receiving upwards to 1.50"+. With
the ongoing drought, this rainfall will see a warm welcome!

Friday, we see the start of cold advection, with cooler temperatures
starting to filter in. Many, especially those along and south of I-
80, will see a noticeable change in temperatures from the previous
days. This weekend, upper level flow goes zonal for a short period,
prior to the approach of a deep wave digging in from the north.
Fortunately, we will be largely in cold advection all weekend, which
will limit moisture return. Thus, we are not expecting much on the
precipitation side. Although, if we do get some moisture in, I
wouldn`t be shocked if we see some flurries or light snow as the
wave passes. With the approach of the wave, we will see a tightening
pressure gradient over the area, resulting in gusty gradient winds
as the system passes. As was mentioned, this will bring a plunge of
cold air throughout the Midwest, with H85 temperatures hovering
between -10 to -15. Thus, a chilly end to the weekend and start to
the following work week is expected. We expect to remain dry through
at least the first half of the week as well, with temperatures
slowly increasing daily.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 615 AM CDT Wed Mar 13 2024

The main point of interest for aviation is the likelihood of
thunderstorms overnight and areas of IFR conditions on Thursday
morning within continued rain showers and embedded storms.

Conditions will largely be quiet today with a mix of VFR clouds
and sun and east-southeast winds <12 kt. There is a low chance
(20%) of showers at DBQ between 20Z and 01Z, but too low of
confidence to include in the TAF at this time.

For tonight, the approach of a stronger weather system will
result in deeper moisture advancing over the region and
thunderstorms developing near the Iowa/Missouri border and
spreading northeast. Confidence is high that the coverage of
these should be enough to impact BRL, MLI, and CID at some point
later tonight into early Thursday morning. BRL may even see
thunderstorm gusts in excess of 35 kt overnight. Confidence in
thunderstorms is lower for DBQ. IFR ceilings and possibly IFR
visibility in a combination of rain and drizzle may be seen for
much of the area Thursday morning.

&&

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

&&

$$

SHORT TERM...Friedlein
LONG TERM...Gunkel
AVIATION...Friedlein


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