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FXUS63 KDVN 171547
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1047 AM CDT Wed Jul 17 2019

.UPDATE...
Issued at 1043 AM CDT Wed Jul 17 2019

The very short term models are not handling the current storm
complex across Iowa. Have updated the forecast to better reflect
thunderstorm chances based on current movement of the storm
complex.

The now expected rain today raises questions regarding how hot it
will get today. Will keep the current heat headlines as there may
be a quick recovery this afternoon.

&&

.SYNOPSIS...
Issued at 330 AM CDT Wed Jul 17 2019

Dangerous heat still looks on track into the weekend, but another
factor will be potential rounds of thunderstorms to go through as it
settles in. Strong storms and heavy rain a good bet with all the
instability and moisture feed looking to take place acrs the region
today into early Thu. Some uncertainty when the heat will break,
but some potential with a cool front late in the weekend or early
next week. Until then, Excessive heat headlines will persist.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Wed Jul 17 2019

Areas of showers in northwest IL should wane into sunrise. Then eyes
will be on the ongoing MCS's acrs the Dakotas. Current instability/
CAPE gradient angles southeastward toward eastern IA out of those
upstream areas. This along with accepted MCS 19-23C H85 MB thermal
gradient track drops down this way as well. Thus some chance for a
portion of the current activity to survive and propagate into the
northwest or western CWA by mid afternoon or early evening. But at
the same time, any incoming activity will have to battle building mid
level heights and an elevated mixed layer(EML)/capping inversion.
Several CAMs do indeed bring some storms down into the area by mid
to late afternoon, while other models such as the 00z GFS and ECMWF
decay the southeastward moving elements before they make it acrs our
area and thrust strong ongoing convective clusters east acrs
southern MN through early evening. If storms can make it down into
the local area and get sfc rooted, very high CAPEs of 3000-4000+
J/KG and adequate deeper layer shear would support severe storms and
high wind threat. Isolated tornadoes possible as well with discrete
cells on any kind of discontinuity boundary. Quite a bit
uncertainty but will have to expand south at least moderate chance
POPs this afternoon and early evening acrs the northwest half.

If nothing makes it into the area today, plenty of MCS parameters
coming together such as a convergent 40-50 KT THTA-E rich LLJ acrs
southern MN on lingering LLVL boundary. Thus there will be the
chance for large bowing MCS feeding south into the area off the
MN/IA border region late tonight. Timing still uncertain but more
models support midnight on into early Thu morning from north to
south and areas north of I80 more susceptible. But as the gust front
typically out paces the main line and scoops up additional
showers/storms, precip will possibly extend into the southern CWA by
Thu morning. Damaging wind threat and heavy rain will be the primary
threats for this later night storm activity. But again still some
uncertainty as how far south storms can make it against mid level
ridging and EML strength. The 00z GFS keeps the bulk of any night
time MCS to the north of the DVN CWA, the 00z ECMWF down to I80 by
Thu morning, and the 00z NAMnest south of I80 but in decaying mode.
For now highest POPs along north of I80 after midnight.

With a near 2 inch precipital water feed and strong LLJ possibly
producing repeated storm generation over the same areas on any
lingering outflow boundary, worried about some flash flood potential
and will hoist a Flash Flood Watch generally along and north of the
Hwy 30 corridor for now. A lot of these areas have been dry lately,
but a few spots such as Cedar rapids and northwest IL have received
locally heavy rain over the past 24 hours. Plus with high rainfall
rates and training potential, even the currently dry areas will be
susceptible for flooding where the line of storms sets up. The next
shift will have to assess whether to add areas further south to the
watch or not. Will extend it through at least mid Thu morning for
lingering activity until the LLJ diurnally shuts down.

Although cloud debris and storm outflow may be factors in affecting
temps at times especially north of I80, will take into account
accumulative day factor and high sfc humidity/heat on the way for
Thu-Sat and upgrade the rest of the excessive heat watch to a
warning to keep things simple and more uniform. Also, some of the
current watch may get the heavier rains which will eventually add to
the sfc moisture layer misery factor. ..12..

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 330 AM CDT Wed Jul 17 2019

Excessive Heat Warning In effect through Saturday. Many areas will
likely see warning criteria heat index values Thu-Sat, but any areas
that don't the warning is also being issued for the cumulative
effects of the heat over several days on the body.

Thursday-Thursday night: Will continue with shower and storm chances
in the morning with the best chances right now appearing to be north
of I-80 for either gradual dissipating MCS, or festering convection
within terminus of slowly waning low level jet. The afternoon
appears to be dry with capping on strengthening synoptic SW flow.
This should allow for a quick recovery on temperatures in any areas
that are impacted by rain cooled outflow. Do expect gusty SW winds,
which could provide a little heat stress relief. But for sure this
favorable warming wind direction combined with increasing amounts of
sunshine should pump highs rapidly back north of 90, topping out
largely in the mid 90s with a few upper 90s possible. Heat index
readings will likely peak in range of 100-110. Thursday night looks
to remain dry with the low level jet and upper level forcing
focusing storm chances well to our north. Otherwise, it will be very
warm and humid, with lows only settling into the mid 70s to around
80 degrees... near record warm lows in some locations. This will not
allow for much if any relief. For information on record highs and
record warm lows for the dates of the heat wave please refer to the
climate section below.

Friday-friday night: This looks like the peak of the heat wave, and
offers the best potential for hottest day given combination of low
to mid level thermal ridge overhead, SW winds and abundant sunshine.
Progged 850 mb temperatures remain around 25C, which is favorable
for widespread highs in the mid 90s to lower 100s.

Saturday-Sunday: Models continue to advertise a cold front bringing
much needed break in the heat, but vary considerably on the timing.
General consensus though would have the boundary coming through
deeper into the weekend. Feeling is a slower scenario likely more
correct given absence of any strong height rise/fall couplets aloft
and nearly parallel mid level flow. Thus, no changes with the heat
warning continuing through the day on Saturday, but if slower
scenario plays out then potential to need extending through Saturday
night, and possibly Sunday south. The boundary will also bring
a return of thunderstorm chances.

Early next week looks really nice and features dry weather with more
seasonable temperatures in the 80s, and much lower humidity
compliments of a large expanse of high pressure.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday Morning)
ISSUED AT 639 AM CDT Wed Jul 17 2019

After morning MVFR fog decreases in spots, a mainly VFR TAF day
with just higher level convective debris clouds or sctrd ambient
CU formation. Light sfc winds going south 5-10 KTs by afternoon.
Will have to watch the ongoing storm complex crossing the MO RVR
Valley into northwest IA and see if it maintains east-southeast
into the area this afternoon. This system and severe winds/
driving rains could be a big impact for 1-2 hours as it sweeps
acrs the terminal sites. Several models still want to decay it
diurnally, or drive it more east staying north of the terminals,
but again it will have to be watched if it becomes it's own sfc
rooted entity. If no storms make it into the area this afternoon,
then another chance arrives by late night as more storm clusters
develop acrs southern MN/far northern IA and possibly propagate
southward toward the TAF sites into early Thu morning. This system
may also pack strong gusty winds and heavy rain producing IFR
VSBYs at times. Passing rounds of low MVFR CIGs could be a factor,
as well as LLVL turbulence. ..12..


&&

.CLIMATE...
ISSUED AT 330 AM CDT Wed Jul 17 2019

Record Warm Lows for July 18...

Moline.........79 in 2011(+) Dubuque........76 in 2011(+)

Record Highs for July 18...

Moline.........100 in 2012(+) Cedar Rapids...101 in 1930
Dubuque........99 in 1894 Burlington.....103 in 1930

Record Warm Lows for July 19...

Moline.........80 in 2011 Dubuque........81 in 1930

Record Highs for July 19...

Moline.........101 in 1934 Cedar Rapids...103 in 1930
Dubuque........97 in 2011(+) Burlington.....107 in 1934

Record Warm Lows for July 20...

Moline.........78 in 2011 Dubuque........78 in 1930

Record Highs for July 20...

Moline.........102 in 1934 Cedar Rapids...105 in 1901
Dubuque........101 in 1901 Burlington.....107 in 1934

(+) = also occurred in previous years

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Excessive Heat Warning until 7 PM CDT Saturday for Benton-
Buchanan-Cedar-Clinton-Delaware-Des Moines-Dubuque-Henry IA-
Iowa-Jackson-Jefferson-Johnson-Jones-Keokuk-Lee-Linn-Louisa-
Muscatine-Scott-Van Buren-Washington.

Flash Flood Watch from 7 PM CDT this evening through Thursday
morning for Benton-Buchanan-Clinton-Delaware-Dubuque-
Jackson-Jones-Linn.

IL...Excessive Heat Warning until 7 PM CDT Saturday for Bureau-
Carroll-Hancock-Henderson-Henry IL-Jo Daviess-McDonough-
Mercer-Putnam-Rock Island-Stephenson-Warren-Whiteside.

Flash Flood Watch from 7 PM CDT this evening through Thursday
morning for Carroll-Jo Daviess-Stephenson-Whiteside.

MO...Excessive Heat Warning until 7 PM CDT Saturday for Clark-
Scotland.

&&

$$

UPDATE...08
SYNOPSIS...12
SHORT TERM...12
LONG TERM...McClure
AVIATION...12
CLIMATE...McClure
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