Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 081550
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1050 AM CDT Sat May 8 2021

...HYDROLOGY UPDATE...

.SYNOPSIS...
Issued at 336 AM CDT Sat May 8 2021

Surface ridge extends into northeast Iowa and northwest Illinois
early this morning. This is leading to an ideal radiational
cooling setup in these areas allowing temperatures to drop into
the 30s, with some lower 30s in favored cold drainage sites.
Further south temperatures were holding in the 40s into far
southeast Iowa and northeast Missouri with mid level cloud cover
moving into that portion of the service area. Aloft, a shortwave
trough was located over the Rockies. In the low levels, a surface
low was over Wyoming with a secondary low forming along the
Colorado front range. The low is forecast to consolidate and
deepen while emerging into the Central Plains today, and then
track eastward along a warm front to our south over the next 24+
hrs, as the upper level shortwave shifts east and eventually
traverses the Midwest. This will eventually lead to widespread and
much needed rain for the region by tonight into early Sunday.

&&

.SHORT TERM...(Today through Sunday)
ISSUED AT 336 AM CDT Sat May 8 2021

Confidence is high that many areas will see rain, with the period
by tonight into early Sunday harboring the most widespread
coverage and subsequent greatest PoPs. This rain will be driven
by several features including... 1) an upper level shortwave
moving eastward from the Rockies through the Midwest inducing
increasing upper level divergence... 2) Right entrance region of
Mid Atlantic to Great Lakes jet, with strong mid level
frontogenetical response and a Fgen circulation traversing near to
just south of the service area... 3) low to mid level warm, moist
advection... and 4) convergence on the nose of SSW low level jet.

Where confidence is lower is with rainfall amounts and location
of the heavier amounts. Factors contributing to the lower
confidence rain amount forecast include lower dew points in the
30s and 40s and elevated nature of the precipitation well north
of the surface warm front, both of which could work in tandem to
temper rainfall rates some. In addition, if surface based
convection forms south of the warm front there is some potential
for disruption of the moisture feed. This all said, precipitable
water values increasing to 1.2 to 1.5 inches combined with the
strong forcing should support the potential for at least a 1-2
inch swath of rain. With the mid level low tracking near to
just south of the area these higher amounts may be favored from
Hwy 34 corridor to near I-80. Again though confidence is low on
exact placement of the higher amounts, it looks likely that much
of the area is in line for a soaking rain. Some embedded thunder
is also anticipated, especially south of I-80 with some elevated
instability suggested. Given the fairly dry stretch of weather
over the past couple of weeks, and the largely stratiform nature
of the precipitation (some embedded convection), flooding
potential appears to be low with rises on area rivers likely to
be within bank. This will be a chilly rain as well with
temperatures in the 30s and lower 40s tonight into early Sunday
morning. In fact, forecast soundings show a deepening nearly
isothermal layer from near surface to 700 mb developing late
tonight and early Sunday AM with a marked increase in northeast
winds through this layer. This could support some potential for a
few snowflakes to mix in with the rain in some areas north of
I-80. Speaking of the winds they will be rather gusty at times
tonight into Sunday perhaps 20-30 mph at times in the tightening
pressure gradient and ramping of winds just off the surface.

More forecast details...

Today, will foster some shower chances late morning through
afternoon west/southwest portions of the service area in
theta-e advection with likely burgeoning coverage by this
evening. The many dry hours and some solar insolation should get
highs back into the 50s with a few areas around 60/lower 60s where
sun is out longer... this appears favored from QC and northeast.
Where the rain occurs temperatures should drop down through the
50s.

Tonight, a developing widespread chilly rain... possibly mixed
with snowflakes north, with lows generally in the upper 30s and
lower 40s amidst gusty northeast winds and chills in the 20s and
30s.

Mother`s Day... unfortunately not the best looking of days for
area Moms. Rain should be tapering off through midday Sunday.
This may be followed up by some sun peaks in the afternoon,
especially north/west of Quad Cities. This may allows highs to
recover into the mid/upper 50s in this portion of the service area
with lower 50s elsewhere. Winds will also remain brisk throughout
the day from the E/NE at 15 to 30 mph making it feel more like the
upper 30s and 40s at times.

.LONG TERM...(Sunday night through Friday)
ISSUED AT 336 AM CDT Sat May 8 2021

Key Messages:

1) Dry conditions favored for early to mid next week with
temperatures on a moderating trend.

2) Chance of precipitation near the end of the period.

Sunday Night through Tuesday Night...

Any rain showers leftover from the short term period will be exiting
the area to the east Sunday evening. This will be followed quickly
by high pressure, which will be settling into the upper and middle
Mississippi River for this period. Dry and quiet conditions will
dominate, which will be welcomed after our rains from the weekend.

Overall, any weather concerns this period will be how cold we can
get during the nights, which could lead to some favorable
development for patchy frost. In this package, have overnight lows
forecast to fall into the low to mid 30s for areas mainly north of
Interstate 80 Sunday and Monday night. However, other fine details
like cloud cover and winds are low confidence right now, and could
significantly impact potential.

Wednesday on...

Guidance remains quite varied beyond Wednesday, with a mix of
solutions offering either continued dry weather or another soaking
rain. The ECMWF/CMC are in the first camp, and maintain a fairly
strong surface high pressure over the Midwest through Thursday
before it eventually moves into the Mid Atlantic states Friday.
Meanwhile, in the second camp the GFS is more robust with a potent
shortwave bringing widespread rain and storms to the area beginning
Wednesday. The first camp does bring the same shortwave across the
area, but its impacts do not occur until Friday. Based on this, our
chances of seeing measurable rain for late in the short term are
fairly reasonable, but timing remains in question. NBM does a good
job of handling the uncertainty with broad `slight chance` to
`chance` POPs, and will continue to use this for the forecast.

The good news is our advertised warming trend is still holding
strong, with most guidance hinting at temperatures returning to the
70s in time for next weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday Morning)
ISSUED AT 528 AM CDT Sat May 8 2021

VFR conditions anticipated largely today, with a chance of PM
showers. Tonight, rain/showers look to become widespread with
conditions lowering into predominantly MVFR with some IFR.
Scattered storms are also possible. Winds will be predominantly
from E/NE increasing to at or above 10 kts later today and further
strengthen tonight with gusts 20-30 kts possible.


&&

.HYDROLOGY...
Issued at 1037 AM CDT Sat May 8 2021

A river flood watch has been issued for the La Moine River at
Colmar due to the current forecast of 1 to 2 inches falling in the
basin. There is lower confidence at this time in the exact
placement of heavy rain as well as rainfall amounts. While strong
lift will be in place north of the warm front tonight into Sunday
across Iowa and northwest Illinois, severe thunderstorms across
Missouri late this afternoon into this evening may disrupt the
flow of moisture into the area and limit the amount of rain that
we receive. Given the current dry conditions, the placement of the
highest rainfall amounts will dictate which points see within
bank rises.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...McClure
SHORT TERM...McClure
LONG TERM...Speck
AVIATION...McClure
HYDROLOGY...Cousins


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