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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1152 PM CDT Tuesday may 5 2015

Update...
issued at 1139 PM CDT Tuesday may 5 2015

With the surface boundary slow to move north/retreat or even showing
signs of getting pushed even further south by the Great Lakes high
pressure...have added patchy to areas of fog along and north of it
into early Wednesday morning. There may even be some locally dense fog
right in the convergent flow in the vicinity of the boundary. Low
temperatures may get cooler than earlier expected from i80 on northward.

&&

Synopsis...
issued at 340 PM CDT Tuesday may 5 2015

Nearly stationary frontal boundary still draped from near Vinton
Iowa to Galesburg Illinois. To the north of the boundary low clouds...east
winds and temperatures only in the middle 50s to middle 60s were found.
To the south of the boundary winds were from the south with partly
to mostly sunny skies and readings near 80. As expected isolated
thunderstorms have formed along this boundary this afternoon.

Shear is weak most areas and we have no short wave to focus any
organized thunderstorm development. However...moisture convergence
and better shear near/along the boundary will help to continue to
trigger isolated or scattered thunderstorms this afternoon into
the evening. Forecast soundings indicate a rather moist column so
hail does not look to be an issue. Locally heavy rainfall is
possible with precipitable waters over 1.30 inches.

&&

Short term...(this evening through wednesday)
issued at 340 PM CDT Tuesday may 5 2015

Forecast focus on a few thunderstorms into early this evening and
another chance Wednesday afternoon.

Tonight...a few thunderstorms will end early this evening with
loss of heating as heights build overnight. This will allow the
frontal boundary to slowly push northward and should be close to
or possibly north of the dvn County Warning Area towards morning. Minimum
temperatures will range from the lower 50s in far northwest Illinois to the
lower 60s south.

Wednesday...ridge continues to build in the Ohio Valley while deep
trough pushes out of The Rockies and into the plains. The stronger
forcing should remain west of the dvn County Warning Area during the day. However...
there is just enough forcing to keep a mention of a chance of
thunderstorms in our far western counties during the afternoon.
GFS seems aggressive in bringing quantitative precipitation forecast too far east into the building
ridge compared to the other operational models. Once again shear
will be weak and severe weather is not expected. Should be more
sunshine across the County Warning Area so afternoon high temperatures will push
into the upper 70s to lower 80s.

Long term...(wednesday night through tuesday)
issued at 340 PM CDT Tuesday may 5 2015

Active weather pattern looks to persist through the upcoming weekend.
A good portion of the period from late week through the weekend
will find the County Warning Area residing in moist southerly flow ahead of an
anomalously deep slow moving trough over the western Continental U.S..
disturbances ejecting from the trough will interact with the
increasing moisture for rounds of showers and storms. The main
challenge will be with trying to time the disturbances and
subsequent better rain chances. At this time it appears that the
Thursday through Friday... and late Saturday through Sunday time
periods offer the best rain chances. With precipitable water
values prognosticated to increase to 1 to 1.5 inches (1 to 2 Standard
deviations above climo) will see potential for widespread moderate
to areas of heavy rain... and anticipate most areas receiving
anywhere from 0.5 to 2 inches of rain from Thursday through Sunday
with potential for locally higher amounts where any training
occurs. This may bring renewed rises on area waterways and
potential for flooding with any training especially in those areas
which received 2-5 inches of rain past 24 hours. At this time... the
threat for organized severe weather appears low through late week.
However... severe potential looks to be on the increase over the
latter half of the upcoming weekend when the models generally show
strong negative tilt shortwave lifting from The Rockies to the
upper Midwest by early next week. This system looks to swing cold
front through the area which should bring end to active weather
early next week. Temperatures will remain generally above normal though
trending closer to normal early next week.

&&

Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1139 PM CDT Tuesday may 5 2015

With the surface boundary having trouble pushing back to the north or
even showing signs of still sagging to the south some...have gone
pessimistic with IFR to LIFR conditions into Wednesday morning at all
taf sites except brl thanks to low ceilings and visibilities north of the
front. Some locally dense fog may also be possible from mli on
northward if surface winds go lighter and variable along the front.
East to southeast surface winds of 5-12 kts overnight further north of
the front. Brl may go southeast toward morning...until then even
that site now in danger of having IFR visibilities from fog in the vicinity
of the boundary through at least 3am. During the day Wednesday...
conditions should improve by middle morning with south surface winds
increasing. A chance of showers getting into the vicinity from the west
at Cid around sunset Wednesday evening. ..12..

&&

Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&

$$

Update...12
synopsis...haase
short term...haase
long term...05
aviation...12

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