Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 121114
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
614 AM CDT Tue Mar 12 2024

.KEY MESSAGES...

- Continued mild through midweek with highs 25 degrees above
  normal again today and Wednesday.

- Scattered storms (40% coverage) south of I-80 tonight, with a
  few capable of small hail and very localized 0.5+ inch of
  rain.

- Higher chance for storms Wednesday night including potential
  strong/severe storms along/south of Highway 34, where the SPC
  highlights a Marginal Risk for severe weather, with the focus
  on isolated large hail.

- Chance for severe weather Thursday is increasing with
  widespread showers/thunderstorms expected. The SPC has
  highlighted much of our area in a Slight Risk for severe
  weather, with all hazards in play.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 305 AM CDT Tue Mar 12 2024

A very mild start to our Tuesday with daybreak temperatures to
already be above normal mid-March highs. Established southwest
flow and 850 mb temperatures of 10C (upper 5th percentile for
time of year) will again result in marked daytime warming.
Upstream satellite and guidance do indicate a trend for
thickening high clouds this afternoon. This is expected to
offset full potential warming a smidge, but still have a
forecast blanket of lower 70s for highs. Southwest winds will
gust to around 25 mph to sporadically 30 mph through early
afternoon and then begin to diminish with a quickly weakening
pressure gradient. Relative humidity values are forecast a tad
higher than yesterday, which eases the fire weather threat some.
For mainly Illinois, where the gustiest winds will still
overlap peak heating and mixing is forecast to be nearly as deep
as yesterday, a more elevated fire threat will exist again.

An upper level short wave in central Colorado early this
morning will traverse the quasi-zonal flow and track eastward
across far southern Iowa and Missouri tonight. The response to
this is a 30-40 kt low-level jet and a narrow window of
associated moisture transport. Signal in model soundings and
QPF output is that this will be enough moisture for scattered
showers and some storms south of I-80 and possibly up through
just north of the I-80 corridor (low confidence in this north
area though, including the Quad Cities). Development timing
could be as early as 7-9 PM in southeast Iowa and northeast
Missouri. While mid-level lapse rates are steep (7.5-8C/km),
the inherently dry column ahead of this and limited deep layer
shear (<25 kt) will keep the severe threat low. Small hail is
still possible given elevated CAPE collocated in the -10C to -20C
layer. A pool of PWATs near one inch may supply any location
that gets a couple storms tonight to see over one half inch,
with the HREF local probability matched mean indicating spotty
values this high. Activity will diminish from west to east in
the pre-dawn hours as the wave progresses east.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 305 AM CDT Tue Mar 12 2024

Wednesday through Thursday will be an unsettled one, with a deep
upstream wave along/west of the Rockies inducing southwest steering
flow across the mid-upper MS RVR Valley by Wed night. Surface
cyclogenesis is forecast over parts of western KS, with the surface
low tracking northeast through our area on Thursday. As the low
progresses northeast, a warm front will push north through our area
between 00-09z Thursday, which will be a focus for nocturnal
convection. With instability and shear present, this will pose a
threat for strong to severe storms, focusing on elevated storms
producing hail.

As this low approaches IA late Wednesday night, it will occlude
near the NE/IA border, with a triple point pushing east across
the state through the day on Thursday. Guidance hints at the
warm sector warming up a bit during the day, with plenty of
moisture, allowing instability to increase into the 1000-2000+
CAPE range. This, coupled with 40-60 KTs of deep layer shear and
~25 KTs LLVL shear, is more than favorable for a severe threat
Thursday afternoon. At the moment, frontal placement varies
amongst guidance, which makes it hard to pinpoint an exact area
to be mindful. Also, there remains uncertainty on the amount of
instability that develops, with the NAM being the most
aggressive. The location of the triple point will be key, as
that may result in a tornado threat. Guidance has been trending
in the strong/severe direction over that last 24-36 hours for
Thursday, which is increasing our confidence.

Along with the threat for strong/severe storms, this system will
bring another round of much needed soaking rainfall. Guidance has
come into better agreement for rainfall amounts, compared to the
previous forecast package. The ensemble suite from the long term
deterministics favor a 50-70% 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 between Highway 34 and Interstate
80, but this could certainly change. 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 introduce a narrow swath of 1.00-1.25" of rain. With the
ongoing drought, this rainfall will see a warm welcome!

Friday, a wide area of mid-level vorticity will remain over the
area, which will continue to provide forcing for light
precipitation on the back end of the system. While cooler
temperatures start to filter in on Friday, we expect the main
precipitation type to be rain, with light accumulations. This
wave will be slow to depart, but will be out by the weekend.
This weekend, flow goes zonal for a short period, prior to the
approach of a deep wave digging in from the north. Compared to
last night`s forecast package, the wave has become more potent,
with it digging south into the region a bit farther west than
initially forecast. 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. Rather, we
will see a bout of cold air into early next week, with a period
of 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 -10C to -15C. Thus, a
chilly end to the weekend and start to the following work week
is expected. This follows well with CPC guidance, which favors
below normal temperatures.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 608 AM CDT Tue Mar 12 2024

The primary aviation forecast points are low-level wind shear
(LLWS) early this morning and scattered storm potential tonight.

A 40-45 kt southwesterly low-level jet in the 1,000-2,500 ft
layer will persist through 14Z, resulting in LLWS. Mixing will
ensue again by mid-morning, with southwesterly surface gusts of
20-25 kt with high confidence. Any higher should be sporadic.
Wind speeds will begin diminishing mid-afternoon as the pressure
gradient eases, with a quick drop off near sunset.

For tonight, a weather disturbance will traverse the
Iowa/Missouri border into northern/central Illinois. The signal
is fairly solid for scattered showers and isolated storms from
this between 03Z and 10Z. Confidence is highest in these south
of I-80, especially with any prior to 06Z, but the chance
(30%) does exist up to MLI.

&&

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

&&

$$

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


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