Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 191754
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1254 PM CDT Fri May 19 2017

...AVIATION UPDATE...

.UPDATE...
Issued at 945 AM CDT Fri May 19 2017

Mesoscale convective system (MCS) that pushed into the cwa earlier
this morning has formed a mesoscale convective vortex (MCV) in
western IL. Rainfall so far has been up to one inch. This vortex
was wrapping moderate to locally heavy rain back across much of
the cwa. With a brisk northeast wind coming off Lake Michigan,
combined with the rain, this has lowered temperatures into the
40s across the entire cwa. This has allowed the airmass to become
stable so the thunder threat has ended for today. Feels more like
March rather than the middle of May. Models struggling with this
very cool airmass and how far south it has gotten so this will
play a role in the upcoming storm system for tonight and Saturday.
If anything, it should enhance the rainfall.

The rain should gradually diminish and end from southwest to
northeast during the day, with nw IL having the rain linger for
much of the afternoon. Will continue to monitor temperature and
radar trends and update as needed.

&&

.SYNOPSIS...
Issued at 312 AM CDT Fri May 19 2017

Showers and thunderstorms associated with a shortwave trough from
the central Rockies closed low and stretching from eastern Iowa
south to Arkansas are moving through the area this morning.
However strong low-level easterly flow is advecting dry air with
dew points around 40 in the eastern part of the CWA, and this is
limiting the intensity and amount of precip generated by the
storms. A surface frontal boundary across northern MO into central
IL is the focus for somewhat stronger storms, while the 850mb
boundary over the CWA helps focus our precip.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 312 AM CDT Fri May 19 2017

Two forecast concerns in this timeframe are round one of showers
and thunderstorms this morning and round 2 later tonight.

Convective-allowing and short-term models are in general
agreement on moving the first wave through the CWA mainly this
morning with precip chances diminishing temporarily this
afternoon and early evening. The next wave looks a little move
vigorous with higher PWs, so rain amounts should be a tad heavier
with this system compared to this morning. This should not be
enough to seriously impact rivers, and the severe risk looks to
remain in our extreme south and points further south closer to the
surface front.

With a dry easterly flow fighting the advancing precip, the wet
bulb effect will keep temps mainly in the 50s across the CWA,
perhaps a little warmer in northeast MO and nearby where rain
should end first. Extensive cloud cover will limit diurnal
variation with min temps tonight only a few degrees cooler than
max temps today.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 312 AM CDT Fri May 19 2017

Saturday and Saturday Night:

Deep mid and upper-level trough will become negatively tilted as it
swings through the Midwest. This is the same trough that brought
heavy snow to parts of the central and northern Rockies the past few
days. The attendant sfc and 850mb lows are forecast to follow along
a rather tight baroclinic zone from the Texas Panhandle
northeastward into Minnesota and Wisconsin. Periods of showers are
likely and there are chances for thunderstorms as well. The first
round of showers and possible storms will be elevated as positive
theta-e advection increase MUCAPE atop easterly flow at the sfc.
Saturday morning PoPs are between 60-90%, highest W/NW sections of
the CWA.

There is a risk for severe thunderstorms, mainly during the
afternoon and evening. The latest outlook from the Storm Prediction
center has a marginal risk for severe weather along and east of the
Mississippi River. However, with a northward lifting warm front
through the afternoon, highs back into the 70s, and a sfc low likely
tracking west of the area, there is potential that this risk area is
either shifted westward or upgraded. Stay tuned to the latest
forecasts today and into Saturday.

Sunday and Monday:

Brief high pressure follows on the heels of the large synoptic low
bringing drier and cooler air into E Iowa/NW Illinois. Forecast max
temps are in the lower to mid 60s on Sunday with overnight lows in
the 40s. Temps rebound into the 70s for Monday when a shortwave is
progged to drop out of the NW into the Upper Mississippi Valley
which could result in periods of showers and isolated storms from
Monday afternoon through Monday night.

Tuesday through Thursday:

Temps avg below normal in cyclonic mid-level flow pattern. Any
precipitation amounts will be light and in a showery form. Uttech

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
ISSUED AT 1254 PM CDT Fri May 19 2017

IFR/ocnl low MVFR conds through the taf cycle. Several rounds of
showers and embedded thunderstorms will be spreading from southwest
to northeast across the taf sites beginning this evening through
Saturday morning. Northeast to east winds 10 to 20 knots.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

UPDATE...Haase
SYNOPSIS...Wolf
SHORT TERM...Wolf
LONG TERM...Uttech
AVIATION...Haase



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