Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 301735
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1235 PM CDT Thu Mar 30 2017

...AVIATION UPDATE...

.UPDATE...
Issued at 1022 AM CDT Thu Mar 30 2017

New convection has developed across eastern Missouri over the past
hour which had been indicated from RAP trends using the LIFT tool.
This new convection will spread north over the next several hours
and likely stratify out as it moves into more stable air. The
larger area of rain across central Illinois is slowly stratifying
out as it also moves north into more stable air.

RAP trends through mid-afternoon suggest the negative theta e
lapse rates across the area will become neutral to slightly stable.

Rain with embedded convection will continue to develop/expand
across the southern and eastern parts of the area during the
afternoon as forcing increases with the arrival of the next vort
max. If the RAP is correct, the more unstable air will remain just
south of the Hancock/McDonough county lines and thus so would the
stronger storms. However, small hail cannot be ruled out from any
convection that moves across the far south during the mid to late
afternoon hours.

High temperatures were lowered slightly across the southeast half
of the area to account from the larger areal coverage of rain
expected this afternoon.

&&

.SYNOPSIS...
Issued at 259 AM CDT Thu Mar 30 2017

GOES-16 mid level water vapor...WOW!  This storm continues to show
an impressive upper low spinning over Kansas, with a dry sloT
positioned from south central Iowa through much of Missouri and
Arkansas as of 2 AM. In our CWA, the dry mid level air is apparent
as the widespread nature of the rains are now mainly along and
east of the Mississippi River, with small scale convection now
showing up in the eastern Iowa counties.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 259 AM CDT Thu Mar 30 2017

Today`s forecast will continue the progression of the surface low
east and northeast through Illinois, while at least 2 spokes of
energy interact with the edge of the mid level moisture on the
eastern edge of the dry slot to bring rain, showers, and some
thunderstorms to the area. Temperatures should remain in the 40s
to low 50s today, as the air will remain close the wetbulb temp,
and any rise will be due to the low moving up closer to our
southern counties. Pops will remain very high in the Illinois
counties today, as the rains should be quite frequent in waves,
while the pops lower to chance in western counties where rainfall
should be far more sporadic. The first wave of energy riding up
over the area is already seen on radar in our far southwest
counties, this will progressively lift northeast, causing
additional showers transitioning to rain, along with a few small
storms. Short term guidance suggests this will reach the Quad
Cities area around 7 AM.

The next wave should ride up northward mainly through the Illinois
counties late this morning toward early afternoon. If a strong storm
occurs today, it seems that small hail is the most likely hazard.
Otherwise, the temperatures will be very cool today, as winds
continue to draw in chilly temperatures to the northeast. By late
morning, a transition from strong east winds to lesser north
winds is anticipated as the low moves into central Illinois.
Models are split on whether mid level moisture will be sufficient
for light rain on the back side of the low, this could either be
spotty light rain or drizzle. In any case, as we go through
tonight, only minor QPF is expected. Temperatures should fall to
the mid to upper 30s under clouds and cold advection. ERVIN

.LONG TERM...(Friday through Wednesday)
ISSUED AT 259 AM CDT Thu Mar 30 2017

Active long term forecast to continue with this forecast package.
Northwest flow will quickly turn back to southwest flow with the
next upper level system approaching the area for late Saturday and
into Sunday.  A short lull on Monday night before another system is
forecast across the area for midweek.  All of these systems bring
with them renewed chances for rain and even thunderstorms.
Temperatures will remain near average through the period.  Polar jet
still across the northern CONUS through this time.

The system on Sunday has shifted north of where it was yesterday
morning.  Consensus between the guidance is for the heaviest precip
to occur Sunday just south of the CWA and spread north along another
warm air advection wing.  The sfc low will track to the NE through
the day on Sunday and with it the chances for precip.

The more impressive system is the one for Wednesday, when guidance
has a strong to moderate intensity sfc low passing over the CWA.
This looks to be the next best chance for thunder across the area.
With this system over the Pacific Ocean still, will not get into
specifics.  This system will need to be watched for potential severe
weather in the mid Mississippi River valley next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
ISSUED AT 1232 PM CDT Thu Mar 30 2017

IFR/LIFR conditions with rain will continue through 06z/31 as a
storm system moves through the Midwest. Stable air is helping to
cause any thunderstorms to dissipate with time. KBRL is most at
risk for a TSRA through 00z/31. After 06z/31 IFR/LIFR conditions
will continue with slow improvement to MVFR after 12z/31.

&&

.HYDROLOGY...
Issued at 330 PM CDT Wed Mar 29 2017

Have gone ahead and issued a River Flood Watch for the Iowa River at
Marengo, with early rainfall and routed water from upstream
projections supporting it hitting flood stage there by Sunday. But
with lower confidence in this, again have went the Watch route as
opposed to an early warning. If widespread 1 to near 2 inches of
rainfall do indeed occur acrs much of the local area, a few other
fcst points on area tributaries will have to be watched for rising
near or even above bankfull by this weekend.
..12..

&&

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

$$

UPDATE...08
SYNOPSIS...Ervin
SHORT TERM...Ervin
LONG TERM...Gibbs
AVIATION...08
HYDROLOGY...12


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