Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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695
FXUS63 KDVN 261816
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
116 PM CDT Wed Apr 26 2017

...18z AVIATION UPDATE...

.UPDATE...
Issued at 1133 AM CDT Wed Apr 26 2017

Extensive clouds and west winds are causing temperatures to rise
slower than expected today. Lowered highs a few degrees as I do
not anticipate much more warming given the cold front currently
east of MS RVR. Large temperature gradient still on track over
CWA this afternoon. Updated forecast out shortly.

&&

.SYNOPSIS...
Issued at 250 AM CDT Wed Apr 26 2017

Analysis at 3 AM CDT shows a cool front entering from the west with
decent winds perpendicular to lines of pressure or ageostrophic
flow and cooling supporting this front to be more progressive than
most solutions. Areas of rain and rain showers with a few strikes
of lightning moving in from Missouri. Area temperatures are mostly
in the the 60s with 50s in western 1/3 of area. Upstream energy
supports rounds or showers and some brief storms next 24 hours
with front to pass east by mid to late PM.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 250 AM CDT Wed Apr 26 2017

Short term forecast confidence...fair to poor or average to below average.
Main challenge is temperatures which may still be up to 5 degrees too
warm in many areas as cooler air and clouds with rain may tend to keep
temps lower. Rain amounts will be challenge with heavier amounts along
and especially east of the Mississippi River.

Today...cloudy and turning colder with temperatures along and especially
west of the Mississippi River nearly steady as colder air filters in.
Have lowered highs many locations by 3+ degrees with possibility still
3 degrees or more too mild for day shift to reassess. Areas of rain
showers expected with some embedded thunder over mostly the SE 1/2
of the region. High temperature gradient may approach 20 degrees with
lower 70s possible far east and maybe lower to mid 50s far west counties.
Mostly light rain amounts with moderate amounts possible along and
especially east of the Mississippi River.

Tonight...Colder and cloudy with areas of rain and some embedded thunder
east of the Mississippi as weak wave moves along the front. Low clouds
and NW winds of 10 to 20 MPH will make for a cold and brisk night. Lows
with low clouds and winds may be a few degrees too cold with lows mostly
in the rough 40 to 45 range from NW to SE. Additional rain amount again
mostly light west of the Mississippi River and Moderate amounts mostly
east of the Mississippi River.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 250 AM CDT Wed Apr 26 2017

Active pattern still on forecast for the long term period.  Guidance
into next week progs another H5 system to roll across the area and
lead to precipitation.  The beginning of the long term period will
be quiet.  Before a storm system approaches the area for the
weekend.  Early next week will be quiet until the end of the period
when another system is forecast.

Attention turns to the system starting Friday through the weekend as
repeated rounds of rain and possible thunderstorms are forecast.
Heavy rain is forecast for the area and may affect area rivers as
well.  Overall pattern remains unchanged from previous forecasts.  A
deep H5 trof will lead to the development of a H85 low Friday.  This
H85 low will track across the area.  With it, the chance for rain.
What this system does is primes the moisture return for Sunday`s
system.  The heaviest rain is forecast to fall south and east of the
area on Friday and into the Saturday as the baroclinic zone stays
south of the area.

00Z Sunday, the deep trof across the SW US ejects out across the
area.  The trof becomes negatively tilted as it track across the
Upper Mississippi River valley.  Return flow is still suspect across
our area, nonetheless, Sunday will be the day with the best chances
for thunderstorms and rain across the area.  Current QPF forecasts
bracket the CWA with heavy rain on each side.   This may not hold
true as the 00z ECMWF has come in slower that the 12Z run.  If the
system slows down, our CWA could be right in the middle of the heavy
rain.

Sunday will see little CAPE but, a lot of shear and a backed surface
winds.  The amount of shear associated with the occluding surface
low and forecast triple point moving through the CWA suggests that
severe weather is a possibility.  If the current shear forecasts
hold, strong winds and tornadoes could be a threat.  The main
limiting factor will be instability.  Another issue with the
possible storms will be any affects from ongoing precip or
convection.  Since the low is right on top of us, any small shift
east or west could have huge differences for the convective
environment.  Therefore, have low confidence in severe weather
occurring at this time.

Past this, a dry out is forecast for early week before another
system is forecast.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
ISSUED AT 105 PM CDT Wed Apr 26 2017

MVFR conditions will continue through much of the TAF cycle. An
upper level disturbance will bring a surface low up across
Illinois this evening and overnight. Precipitation will lift
across the area causing IFR conditions at several of the terminals
for a few hours. There is very low confidence in any mention of
thunder for tonight and have opted to leave out of the TAF for
now. Precipitation will end at all sites by 15z with conditions
improving to MVFR.

&&

.HYDROLOGY...
Issued at 250 AM CDT Tue Apr 25 2017

Potential for heavy rainfall the rest of this week and weekend could
lead to rises and flooding on area rivers.  Strong forcing and PWAT
values from 1 to 1.5 inches suggests the possibility exists for heavy
rain. Main question is where does this rain fall.  Models have not
keyed onto a solution, so location of rainfall is hard to determine.
That said, those with interests around local rivers should pay
attention to future forecasts

&&

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

$$

UPDATE...Gross
SYNOPSIS...Nichols
SHORT TERM...Nichols
LONG TERM...Gibbs
AVIATION...Gross



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