Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 080549
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1249 AM CDT Sat May 8 2021

...06z AVIATION UPDATE...

.UPDATE...
Issued at 958 PM CDT Fri May 7 2021

Influx of cool air on the northeasterlies off lake Michigan may
allow frost as far south as the I-80 corridor just east of the
Quad Cities later tonight. Have thus expanded the frost advisory
into Henry County Illinois.

&&

.SYNOPSIS...
Issued at 300 PM CDT Fri May 7 3001

A cold front has moving into northern Missouri and central
Illinois early this afternoon. There is little temperature change
associated with the front with temperatures generally in the lower
to mid 60s. However, far northwest Illinois and in adjacent parts
of Iowa temperatures were in the mid 50s. Dewpoints range from
the lower 40s ahead of and along the front to the mid 20s along
the Highway 20 corridor early this afternoon. It was also breezy
behind the front with sustained speeds of 15 to 25 MPH and a few
gusts around 30 MPH.

&&

.SHORT TERM...(This Evening through Saturday)
ISSUED AT 300 PM CDT Fri May 7 3001

The primary forecast concerns were temperatures early Saturday
morning then chances of precipitation for the remainder of the
long term period. There are some differences between the models
on the timing and northern extent of precipitation on Saturday.

Winds and diurnally driven cumulus will diminish with the loss of
daytime heating early this evening resulting in clearing skies
and light winds. A broad area of high pressure will move from the
Northern Plains this afternoon into the Middle Ohio River Valley
by 12 UTC Saturday morning. This will keep skies clear overnight
along with dewpoints in the upper 20s. This will allow
temperatures to drop quickly this evening into the overnight
hours. Models do show 850 temperatures falling below zero
overnight primarily north of a Independence to Monticello to
Princeton Illinois line. Have lowered temperatures across this
area into the mid 30s for the overnight period. These values are
within 3 to 4 degrees of record low temperatures for May 8th.
Please see the Climate section below. This results in the
potential for widespread frost across this area. Thus we have
issued a frost advisory for this area for midnight to 8 AM CDT
Saturday. Counties along the advisory may see patchy frost in
favored colder locations.

Temperatures and dewpoints will begin to rebound after sunrise as
winds begin to turn to the southeast ahead of a developing surface
low that will move into central Kansas by 00 UTC Sunday. The
storm system approaching the area from the southwest will allow a
slow southwest to northeastward expansion of precipitation late
Saturday morning up to 00 UTC Saturday as moisture overspreads the
area ahead of it. A complicating factor is that models show
frontogenetical forcing expanding into the northern half of the
area after 21 UTC Saturday which would expand precipitation
northward faster. The Canadian is farther south with this feature
and limits precipitation as far north as Interstate 80 during the
day. While other models expand precipitation eastward to the
Mississippi River in Iowa and everywhere but far northwest
Illinois. Elevated CAPE will ad thunderstorms to the forecast
south of Interstate 80 during the afternoon. Severe weather is not
expected at this time. SPC has the area in a general risk for
thunderstorms for Saturday.

.LONG TERM...(Saturday Night through Friday)
ISSUED AT 300 PM CDT Fri May 7 3001

Key Points:

Cold and wet to start the period.

Moderate to heavy rain amounts expected across the area Saturday
night into Sunday but some uncertainty on location of heaviest rains.

Below normal temperatures through much of the next 7 days, nearing
normal by next weekend.

Details:

Cool air is in place to begin this period. At 00Z Sunday much of the
forecast area will have 850mb temperatures in the 0C to 5C range,
with the far southern counties having a bit warmer air in place as a
low pressure system moves near from the southwest bringing up some
warm air ahead of it. The surface low at 00Z Sunday is expected to
be over western Kansas with an upper level shortwave trough pushing
out of the Four Corners region which will drive the system to the
northeast and impact the forecast area over the next 24 hours.

A longwave upper level trough centered from Hudson Bay into the New
England states will keep the aforementioned shortwave from traveling
too far northward and is currently looking to move across northern
Missouri and into central Illinois into the day on Sunday. This
track will keep the track of the surface low just to the south of
the forecast area, however there has been a few models that do
meander the track northward a bit. Looking at pretty strong moisture
advection in the 925-850mb layer ahead of the surface low which
brings precipitable water values of 1.00 to almost 1.50 inches into
the area. Rain and possibly some thunderstorms will be on an
increasing trend through the evening hours (Sunday 00Z to 06Z),
while the bulk of the stronger forcing comes into the area between
06Z and 12Z as the shortwave passes. As mentioned, there are some
discrepancies with the exact track of the system, and where the
areas most likely to get the heaviest rains are still along and
south of the Interstate 80 corridor, there are a few models that
track the upper level shortwave and surface low further north and
would have the heaviest rains bisect the I-80 corridor.
Precipitation chances have increased a bit, especially for the
central parts of the forecast area to account for the potential in
that northern shift. The far northern parts of the forecast area
will see the lowest QPF totals, but even looking at cross-sections
from the Dubuque, IA area, confidence has increase on raising rain
chances. Now, how much rain is going to fall? Areas ahead of the
surface low will have a bit of instability to work with, which
currently looks to at least get into the southern third of the
forecast area. So, could see some heavier bands and cells amongst
the precipitation area Saturday evening producing some heavy rain.
The strong forcing will keep the rain moderate to heavy at times
through the remainder of the night so amounts of 1 to 2 inches are
not out of the question on the north side of the surface low track.

Will have to monitor for any localized water issues Saturday night
and into Sunday, but with the heavy amounts looking to span a 6 to
12 hour time-frame, not anticipating a high chance for any flash
flooding or even rapid rises on creeks and rivers at this time.

Also for Saturday night, strong winds and cold temperatures will
make it quite brutal. Lows in the 40s with 15-20kt winds will drop
wind chills into the 30s for much of the area.

The system will move east through the day Sunday, with rain
intensity dropping through the morning and ending by early/mid
afternoon for much of the area. Clouds may persist through the
evening though and with the cool airmass remaining in place (850mb
temps 0C to 5C) high temperatures will likely stay in the 50s.

The next thing to watch will be low temperatures Sunday night. If
the skies clear out and winds do indeed drop allowing radiational
cooling to take place, lows will likely drop into the 30s. Will have
to monitor these trends to see if there will be potential for frost.

Cool high pressure will be in place through mid week, keeping
temperatures below normal, but dry conditions until Wednesday when
an upper level trough approaches from the plains to bring some rain
chances to the area for mid-week. After this passes, longer range
models are showing ridging building in for the weekend so may see
temperatures getting back to normal or even above normal for next
weekend.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
ISSUED AT 1248 AM CDT Sat May 8 2021

Predominantly VFR conditions expected today. A chance of showers
will exist by mid morning into this afternoon within elevated
theta-e advection mainly near to southwest of CID and BRL
terminals. Anticipate the coverage of rain/showers to increase
later this afternoon through this evening with an upper level
wave and lower level theta-e advection, with areas of MVFR to
local IFR (mainly for VSBY) conditions. Winds will generally be
from an easterly direction throughout the period. They will
become sustained at or above 10 kts today, and tonight when
further strengthening and gusts over 20 kts to near 30 kts will
be possible at times with a tightening pressure gradient and winds
increasing aloft.

&&

.CLIMATE...
ISSUED AT 300 PM CDT Fri May 7 3001

Record Lows for May 8...

Moline.........32 in 1976
Cedar Rapids...32 in 1925
Dubuque........31 in 1976
Burlington.....35 in 1960

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Frost Advisory until 8 AM CDT this morning for Buchanan-Clinton-
     Delaware-Dubuque-Jackson-Jones.

IL...Frost Advisory until 8 AM CDT this morning for Bureau-Carroll-
     Henry IL-Jo Daviess-Putnam-Stephenson-Whiteside.

MO...NONE.
&&

$$

UPDATE...Sheets
SYNOPSIS...Cousins
SHORT TERM...Cousins
LONG TERM...Brooks
AVIATION...McClure
CLIMATE...Cousins


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