Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 270241
AFDDVN

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

.UPDATE...
Issued at 924 PM CDT Wed Apr 26 2017

Forecast looks to be on target with rain expected to continue
increasing in coverage and intensity from south to north late this
evening and overnight, as upper forcing attendant to amplifying
upper trough and right entrance region of jet streak overspread
strong low to mid level thermal gradient. Induced circulation will
lift north and aid in backing flow drawing in plume of high
moisture characterized by PWATs 1-1.5 inches or 150-200 percent.
This moisture coupled with the forcing will likely lead to areas
of moderate to perhaps locally heavy rain at times, mostly near
to east of the Mississippi River within strong 925-850 Frontogenetical
forcing where rainfall amounts of 0.25 to 0.75 inches is possible.
Thunder threat looks quite small due to moist soundings, but can`t
be completely ruled out and should it occur would be isolated and
confined to eastern CWA.

&&

.SYNOPSIS...
Issued at 245 PM CDT Wed Apr 26 2017

Surface analysis at 2 PM CDT showed an area of low pressure near
KISW in Wisconsin ,with a cold front extending south into
Illinois just east of the Mississippi to near KUIN. Temperatures
ahead of the front, were in the 60s with dewpoints in the 50s.
Behind the front, temperatures struggled to rise much with
readings west of a Monticello to Mount Pleasant line, only in the
upper 40s and lower 50s. Next wave of energy to impact the area
this evening was tracking over Oklahoma.

&&

.SHORT TERM...(This Evening through Thursday)
ISSUED AT 200 PM CDT Wed Apr 26 2017

Forecast focus in the short term is on precipitation chances this
evening and overnight.

Surface low currently in northwest Arkansas will lift northeast
along the frontal boundary into east central Illinois by 03z this
evening. Latest 12z model solutions show strong low level
convergence and upper air support with this wave to bring
scattered showers to the area late this evening and overnight.
As far as thunder potential, 700-500 mb theta-e lapse rates off
the 18z RAP, go negative just to the southeast of the CWA after
00z. Can`t rule out an isolated thunderstorm over the far SE
portions of the CWA, but most of rain should be more stratiform
tonight. There is also a possibility that areas north and west of
a Oskaloosa to Manchester line, may see little to no rain
overnight tonight.

This system will also have plenty of moisture to work with as it
lifts into Illinois. 12z observed DVN sounding showed 1.31" PW
this morning, which is almost 200% of normal. This fact, combined
with model progs of moisture transport suggest that rainfall may
be heavy at times overnight, especially east of the Mississippi.
Rain amounts east of the Mississippi, are expected to be between a
quarter and three quarters of an inch by 12z Thursday. Precipitation
to end across the entire area by 15z, with the rest of the day
remaining dry.

Cooler air filters into the area on Thursday, as 850 mb
temperatures drop below 0C. This will keep afternoon highs in the
lower 50s north of highway 30, to the upper 50s south.

.LONG TERM...(Thursday Night through Wednesday)
ISSUED AT 200 PM CDT Wed Apr 26 2017

Thursday Night and Friday:

Light winds and initially clear skies late Thursday night could
result in patchy frost before mid-level clouds increase into
Friday morning in the counties along highway 20. Forecast lows
are in the mid 30s in this area. For Friday, models develop a
closed 850mb circulation over eastern Nebraska and SW Iowa which
will force an elevated warm front and zone of theta-e advection to
the north and east. Scattered showers are expected to move from
south to north through the CWA from the morning through the
evening. Forecast PWATs under 1" and modest forcing for ascent
are supportive of mainly light rain. Max temps will be cool in the
50s, although a little warmer over the SE third of the CWA in the
lower to mid 60s.

Saturday and Sunday:

Models continue to advertise a rapidly deepening sfc low tracking from
Kansas into Iowa and Wisconsin with a central pressure possibly
below 990mb. A 125 kt jet streak is forecast to round the base of
a deep trough over the Southern Plains before approaching the
Upper Mississippi Valley. The end result is strong and expansive
upper divergence beneath a coupled jet structure. Furthermore, this
system is forecast to intensify a low- level baroclinic zone as it
tracks into the Midwest. Thus, expect a dynamic system with
severe weather in the warm sector and snow possible to the NW of
the low track. For E Iowa/NW Illinois, widespread moderate rain is
likely from Saturday midday through Sunday. There is also the
potential for thunderstorms on Sunday. However, it is too early to
assess the risk for severe storms.

At this time, the signal for heavy, possibly flooding rain, is to
the SE of the local area (across central Missouri into central
Illinois) where deterministic models and the NAEFS are placing
the best deep layer moisture transport. Integrated water transport
values from the NAEFS are already over 2 standard deviations
above the avg for late April in the aforementioned area. We`ll
have to see if the models trend NW with this feature which would
place heavier rain into at least the SE portion of the CWA.

Monday through Wednesday:

Lingering showers and breezy behind the strong low on Monday.
Finally drying out and quiet for Tuesday through most of
Wednesday. Uttech

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
ISSUED AT 639 PM CDT Wed Apr 26 2017

Generally expecting mvfr conditions tonight through mid AM Thu
with periods of rain/showers (mainly light with some moderate
intensity periods along/e of the Mississippi River as a low
pressure system lifts up along a frontal zone over IL. Drier
air will filter in behind the exiting system late Thu AM
through Thu PM and should lead to decreasing clouds /vfr
conditions/ from southwest to northeast on gusty westerly winds.


&&

.HYDROLOGY...
Issued at 356 PM CDT Wed Apr 26 2017

Widespread rainfall expected Saturday through Sunday leading to
rises on area rivers into next week.

A strong area of low pressure is forecast to track through the
Midwest. Heavy rain on the order of 1-3 inches is possible over
portions of Iowa, Missouri, and Illinois. However, since this
system is still several days away, confidence on the exact
placement of the heaviest precipitation is low. At this time, the
favored location for amounts closer to 3 inches is to the
southeast of E Iowa/NW Illinois - through central Missouri and
central Illinois.

Please check back for forecast updates through this week as we
try to zero in on the region of heaviest rainfall.

&&

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

$$

UPDATE...McClure
SYNOPSIS...Gross
SHORT TERM...Gross
LONG TERM...Uttech
AVIATION...McClure
HYDROLOGY...Uttech



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