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000 
FXUS63 KDVN 201742
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1242 PM CDT Fri Sep 20 2019

...AVIATION UPDATE...

.UPDATE...
Issued at 937 AM CDT Fri Sep 20 2019

Nocturnal convection continues to persist over the area. Outside 
of the band in eastern Iowa there is a decrease in coverage east 
of the Mississippi.

Internally, the RAP is suggesting the potential of convection 
persisting through early afternoon before new diurnal convection 
develops. Given the saturated state of the atmosphere this seems 
reasonable as any weak convergence or lift would be enough to 
initiate an isolated shower or storm.

An updated forecast with this thinking will be available shortly.

&&

.SYNOPSIS...
Issued at 422 AM CDT Fri Sep 20 2019

Stalled boundary just south of Interstate 80 and weak moisture 
transport from the south has ignited scattered thunderstorms roughly 
all along this boundary. Shear/instability weak but these storms 
have been producing heavy rainfall in spots. These storms are on the 
gradient of SBCAPE of 1000 J/kg in our southern cwa.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 422 AM CDT Fri Sep 20 2019

Today: Scattered thunderstorms should diminish this morning as 
overrunning weakens. Then scattered storms should re-fire this 
afternoon with the heating of the day, especially in our northern 
counties as the boundary lifts northward. Forecast soundings 
indicate very weak shear so no severe weather is expected.
However, rather slow movement of the storms and plenty of moisture 
available so isolated flash flooding is possible, especially if 
storms can form along Highway 20 where soils are extremely 
saturated. Highs will be in the 80s.

Tonight: Mainly dry this evening then increasing pops after midnight 
as deepening moisture arrives, and strengthening southerly LLJ 
provides low level convergence/forcing. There may be localized heavy 
rainfall but the more widespread heavy rains should hold off until 
this weekend. Another warm/muggy night with lows around 70.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 422 AM CDT Fri Sep 20 2019

Signal still strong for the potential for heavy rain this weekend, 
as an upper level trough and attendant surface front encounter an 
anomalously moist atmosphere with connections to Gulf, remnants of 
Imelda and possibly even a little connection to tropical systems off 
the Baja of CA. Model soundings show impressive PWAT fetch of 2-2.3 
inches with warm cloud depths just over 14 kft agl supportive of 
extremely efficient rainfall production of which could be quite 
torrential. The heaviest rain looks to focus mainly from Saturday 
evening through Sunday evening with the potential for widespread 1-3 
inch amounts. The heaviest rain amounts are being suggested south of 
I-80, but this axis could still shift. In addition, couldn't rule 
out seeing locally higher totals in excess of 3 inches in some 
locations as models support potential for repeated activity with 
cell motion nearly parallel to Corfidi vectors. All this taken into 
account have collaborated a Flash Flood Watch for Saturday evening 
through Sunday evening for the entire area - north to account for 
the saturated soils and very sensitive antecedent conditions, and 
central/south to account for high rainfall rates and possibility of 
repeated activity. Depending on where the heavy rain occurs there is 
the potential for also seeing rises on some rivers. If you have 
interests on area rivers or live in an area susceptible to flooding 
be sure to keep updated to this heavy rain threat for the weekend.  
Aside from the heavy rain, the Storm Prediction Center does have a
slight risk for severe storms into a small portion of eastern Iowa 
for Saturday/Saturday night, with a marginal risk nearly 
encompassing the rest of the cwa. Overall, the severe threat looks
low given the abundance of atmospheric moisture limiting cold pool 
productivity, and anomalously high freezing level limiting any hail
potential.  

Front passes late Sunday-Sunday night and should bring cooler 
conditions early next week, with near normal temperatures then for 
the remainder of next week. Initially lower and more comfortable 
humidity is expected, however by the mid to late part of next week 
signs of another slower moving front exist which will likely bring 
back the humidity and rain chances. 

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
ISSUED AT 1237 PM CDT Fri Sep 20 2019

VFR conditions will be seen through 06z/21. Isolated diurnal
SHRA/TSRA will be possible through sunset. After 06z/21 the next
push of tropical moisture moves into eastern Iowa and northern
Illinois associated with an upper level disturbance. VFR
conditions will start the period but will deteriorate to VFR/MVFR
with SHRA/TSRA developing. Brief IFR conditions are possible in
the strongest TSRA.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flash Flood Watch from Saturday evening through late Sunday 
     night 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.

IL...Flash Flood Watch from Saturday evening through late Sunday 
     night for Bureau-Carroll-Hancock-Henderson-Henry IL-Jo 
     Daviess-McDonough-Mercer-Putnam-Rock Island-Stephenson-
     Warren-Whiteside.

MO...Flash Flood Watch from Saturday evening through late Sunday 
     night for Clark-Scotland.

&&

$$

UPDATE...08

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