Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 270812
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
312 AM CDT Tue Jul 27 2021

.SYNOPSIS...
Issued at 310 AM CDT Tue Jul 27 2021

High pressure was over the region early this morning with mostly
clear skies and calm or light southerly winds. Temperatures ranged
from 63 in Monticello to 72 in Fort Madison.  Dew points were mostly
in the lower and middle 60s.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 310 AM CDT Tue Jul 27 2021

Today, a light southwesterly breeze will bring warmer and slightly
more humid air into the region today, with mostly sunny skies. Dew
points will be increasing into the mid 60s to low 70s. Models have
been overdoing temps of late and with some smoke-filtered sun opted
to keep temps in upper 80s and lower 90s.  Heat indices will top out
in the 92 to 99 range.

Tonight, clouds will increase across the north as some models show a
disturbance moving across NE IA into northern IL. Have slight chance
pops for the highway 20 corridor after midnight tonight. Otherwise,
it will be a warm and muggy night with mostly clear skies elsewhere.
Lows will be in the upper 60s to low 70s.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 310 AM CDT Tue Jul 27 2021

...Heat headlines are likely needed for both Wednesday and
Thursday...

Our criteria for Heat Advisory is widespread 100 to 105 Heat Index.
This is right in the middle of the guidance spread forecast for our
area Wednesday. The south half is forecast to reach that range again
Thursday afternoon.   As often happens when we`re expecting heat
index readings to be high, there are some indications that
convection may occur, especially in the northeast Wednesday, and
area wide Thursday. While convection is a low chance of occurring,
it would certainly disrupt the heat from verifying.

For that reason, I`m planning on taking this one day at a time, and
going with only a Heat Advisory for Wednesday Noon to 10 PM, and in
all but our far north/northeast where office collaboration prefers
to wait on this. In this period, even the 25% NBM, which has
verified best over the past 2 days with the filtered smoke taking 2-
3 degrees off the NBM blend`s over forecast. For Wednesday, this
results in highs in the lower 90s east and north to mid 90s central
and west/south. Dewpoints are confidently forecast to reach the 72
to 76 range, which is well below the highest guidance, and should
occur with minimal advection into the area. The combination of
afternoon heat/humidity will allow for widespread 100 to 106 heat
index readings, which best fits an advisory product.

Thursday has the highest confidence in dewpoints in the 75 to 78
range, though it rather low confidence in temperatures exceeding 90
as AM convection debris and afternoon storms are possible. These
contrasting confidence inputs into heat index will keep us just
mentioning it in the HWO and in graphics, but not going with a
continuation into the advisory through Thursday, which is could
need!

Storms both late Wednesday night and Thursday will have access to
high CAPE pool over the region, so while flow is weak over our area,
some strong storms are certainly possible.

Friday through Monday will be dominated by cooler surface high
pressure and northwest flow aloft.  For now, the primary active warm
frontal processes appear to be taking place well to the west of our
CWA.

Highs late in the period are in the 80s, and lows in 60s, which is a
welcome reprieve from the daily heat of late.

ERVIN

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
ISSUED AT 1220 AM CDT Tue Jul 27 2021

VFR conditions will prevail with mostly clear skies and light
southwest winds.


&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Heat Advisory from noon to 10 PM CDT Wednesday for Benton-
     Buchanan-Cedar-Clinton-Des Moines-Henry IA-Iowa-Jackson-
     Jefferson-Johnson-Jones-Keokuk-Lee-Linn-Louisa-Muscatine-
     Scott-Van Buren-Washington.

IL...Heat Advisory from noon to 10 PM CDT Wednesday for Bureau-
     Hancock-Henderson-Henry IL-McDonough-Mercer-Putnam-Rock
     Island-Warren-Whiteside.

MO...Heat Advisory from noon to 10 PM CDT Wednesday for Clark-
     Scotland.

&&

$$

SYNOPSIS...14
SHORT TERM...14
LONG TERM...Ervin
AVIATION...14


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