Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 232037

Area Forecast Discussion
National Weather Service Quad Cities IA IL
337 PM CDT TUE AUG 23 2016

Issued at 300 PM CDT Tue Aug 23 2016

Southwest mid-level flow apparent on WV imagery, emanating from
the southern Rockies, beginning to transport significant moisture
northeastward into the Midwest. The PWAT gradient is situated over
Central Iowa where it jumps to over 1.5 inches. Warm air advection
aloft has lead to increasing low to mid-level clouds, helping to
cap sfc temps in the upper 70s to near 80 F. Aside from a few isolated
showers, dry conditions are forecast into the early evening.


.SHORT TERM...(This Evening through Wednesday)
ISSUED AT 300 PM CDT Tue Aug 23 2016

This Evening and Tonight...Isolated showers may give way to
sct shower and embedded thunderstorm development after 9 or 10 pm
near as 925-850mb nocturnal low-level jet and attendant WV
transport ramp up. Ascent tied to convergence NE of the jet max
may aid the small pop-up showers and storms. Then, increase POPs
after midnight to 60-70%, but uncertainty exists regarding
evolution and eastward progression of ongoing MCS currently over
NW Iowa.

Thunderstorm Potential:

Current thinking is for the MCS to move in with a weakening trend,
riding the instability/1000-500mb thickness gradient. It does not
have particularly high levels of instability to feed off of and
environmental shear (0-6 km) is less than 30 kts. Nonetheless, isolated
strong wind gusts are possible.

As the atmosphere becomes anomalously moist, showers and storms
will transition into efficient rain producers, so the threat for
heavy rainfall rates is there along with backbuilding of cells.
NAM forward/backward propagating Corfidi vectors nearly oppose
one another late tonight. And both are under 10-15 kts,
representing slow moving meso-beta elements.

Wednesday...An active weather day is on tap. High confidence in
strom redevelopment during the afternoon into the evening. POPs
increase gradually from north to south through the forecast area.
Best chances for heavy rain producing thunderstorms are along/south
of I-80 as mid level wave rides up a low-level boundary, possibly
interacting with pre-existing sct convection and enhancing rainfall
totals via 2" or higher hourly rates.

Thunderstorm Threats: Definitely some potential for
localized areas of flash flooding with PWATs near 2 inches and
threat for training of storms. In addition to the heavy rain, SPC
has a slight risk for severe storms over the southwest DVN CWA -
primary risk being sct severe wind gusts from bowing segments.

.LONG TERM...(Wednesday Night through Tuesday)
ISSUED AT 300 PM CDT Tue Aug 23 2016 The weather pattern will be
turning quite active through the middle of next week. The
probability is medium to high for above if not well above normal
rainfall that might result in river flooding.

Wednesday night the first upper level disturbance moves through the
area. Areal coverage of the convection will increase during the
evening with it reaching maximum coverage after midnight. Areas
south of I-80 have the best chances of rain and areas south of an
Ottumwa, IA to Galesburg, IL line could see locally heavy rainfall.

On Thursday the first upper level disturbance exits the area during
the morning as the front slowly moves southeast. Thus precipitation
should slowly end from northwest to southeast during the day as high
pressure builds into the Midwest.

Thursday night mainly dry conditions will be seen across the area as
high pressure moves into the Great Lakes. The extreme south may or
may not see isolated showers/thunderstorms with the front in central

Friday on...

Dry conditions will be seen across the area on Friday as high
pressure moves into the eastern Great Lakes. Temperatures should be
close to normal.

Friday evening, most of the area will remain dry due to the
proximity of the high over the Great Lakes. The far southwest areas
may or may not see some showers or thunderstorms prior to midnight.
Late Friday night the next surge of moisture associated with another
upper level disturbance moves into the area. Convection will develop
or move into the area with the southwest half favored for the better
rain chances.

Saturday, the model consensus has chance to likely pops for the
entire area. The nocturnal convection will move across the area
during the morning and boundaries left over from this convection
will provide the focus for new convection Saturday afternoon and

Sunday through Tuesday, the model consensus has chance pops for each
day across the entire area. Several additional upper level
disturbances will move through the Midwest and some model solutions
are suggesting a boundary stalling out across the area.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
ISSUED AT 1230 PM CDT Tue Aug 23 2016

Deteriorating conditions through this TAF period as increasing
moisture advection leads to lowering ceilings to MVFR during the
afternoon/evening. Shower chances are low through the day, so
kept out of TAFs at all sites but KBRL. Low-level jet forecast to
ignite sct showers and storms tonight - most likely to affect KMLI
and KBRL. Periods of IFR ceilings are possible.

Forecast uncertainty increases into early Wednesday
morning when a weakening MCS may move in from the W/NW. To cover
for this potential, included PROB30 groups. Greatest threat from
storms is torrential rainfall and VFR visibilities/ceilings. Stay
tuned to updates this evening and tonight. Uttech


.DVN Watches/Warnings/Advisories...


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