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000 
FXUS63 KDVN 171146
AFDDVN

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

...12z AVIATION UPDATE...

.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 from 1 PM this afternoon to 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 this evening through Thursday morning for 
     Benton-Buchanan-Clinton-Delaware-Dubuque-Jackson-Jones-Linn.

IL...Excessive Heat Warning from 1 PM this afternoon to 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 this evening through Thursday morning for 
     Carroll-Jo Daviess-Stephenson-Whiteside.

MO...Excessive Heat Warning from 1 PM this afternoon to 7 PM CDT 
     Saturday for Clark-Scotland.

&&

$$

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