Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 181905

Area Forecast Discussion
National Weather Service Quad Cities IA IL
205 PM CDT Fri May 18 2018

Issued at 200 PM CDT Fri May 18 2018

At 2 PM CDT, the area was under mostly cloudy skies of generally
mid to high clouds with light sprinkles and showers to the southeast
under a closed upper low. Temperatures are in the 70s with light
easterly winds. Upstream energy shows upper low to move east with
partly cloudy skies ahead of a ejecting short wave in the southwest
CONUS Saturday which will bring showers and storms Saturday night
into Monday.


.SHORT TERM...(This Evening through Saturday)
ISSUED AT 200 PM CDT Fri May 18 2018

Short Term Forecast Confidence...Good or above average with little
sensible weather issues as any lingering light precipitation ends
by early evening. Impacts of low clouds later tonight could have
an impact on low temperatures with possible light fog.

Tonight...skies to become mostly cloudy with areas of light fog,
mostly with visibilties above 2 miles. Area mins should be in the
upper 50s to around 60F with light northeast winds of 5 to 10 mph.

Saturday...mostly cloudy skies and light fog should become partly
sunny by mid day with highs upper 70s northeast to the lower 80s
southwest with light northerly winds of 5 to 15 mph and moderate
humidity for a nice late May day.

.LONG TERM...(Saturday Night through Friday)
ISSUED AT 200 PM CDT Fri May 18 2018

Saturday night will see a threat for thunderstorms, along with
potential a severe weather risk if the convective allowing models are
correct in taking the surface low northwest of our CWA with the
surface warm front/triple point moving through the central CWA or
southeast CWA. The ECMWF is vastly different from prior runs, and
now takes the low over central Missouri, compared to earlier runs
over northwest Iowa. That`s a huge difference in a convectively
favored earlier run, and a cold rain on the new run.  For now, we`ll
go with the idea of earlier EC runs and the CAMs which bring a line
of storms, possibly supercells, into the southwestern CWA Saturday
night and lift it northeast, with some chance for rotating storms as
far north as Interstate 80 through Midnight, and a lower threat for
them over the northern sections of the area after Midnight. As the
models converge on timing, we can begin to more accurately pin down
the timing and placement of severe threats, but for now, we broadly
say shear supports supercells and bowing line segments, and if the
low level shear along the warm front remains accessible through the
evening, tornadoes could be possible.

By Sunday, the system remains over the Midwest, but loses winds
aloft. There may still be shear in the lower levels that supports
weak tornadoes, but for now, the threat appears more isolated and
weaker than Saturday night`s event.

Temperatures Saturday night through Monday are mild, but are cooler
in the north than past forecasts due to blending in the cold ECMWF
run.  The balance of the forecast is also mild and early summer
like, with highs in the lower 80s each day through Friday. The pops
remain spread over many days in this unsettled pattern, though
Wednesday into Thursday seems to be the best potential for another
convective event.


.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
ISSUED AT 1215 PM CDT Fri May 18 2018

Partly to mostly cloudy skies with VFR conditions will become mostly
MVFR and possibly high end IFR conditions as ceilings drop by late
evening and overnight to 1-3K AGL. Some 500 to 1000 ft ceilings are
possible with visibilities AOB 3 miles possible toward morning. East
and northeast winds will become northerly by morning at 5 to 10 mph.





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