Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 260000
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
700 PM CDT Tue Apr 25 2017

...00Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 355 PM CDT Tue Apr 25 2017

Band of warm air advection isolated light showers and sprinkles
that lifted quickly northeast across the cwa has moved out of the
dvn cwa early this afternoon. In the wake of this band of
precipitation, thicker high level clouds have spread over the
area. 3 pm temperatures were in the 70s to lower 80s.

Elsewhere, quite the temperature contrast in the middle of the
country with 3 pm readings only in the 30s in the Dakotas and nw
Minnesota. Snow was falling in the Black Hills and into Wyoming.
Farther south, temperatures were in the 80s to lower 90s in Texas
with surface dewpoints in the 60s as far north as Little Rock.

&&

.SHORT TERM...(This Evening through Wednesday)
ISSUED AT 355 PM CDT Tue Apr 25 2017

Forecast focus on increasing showers and thunderstorms.

Tonight: Low pressure will pull out of OK and lift into WI by
morning, as an upper level trough approaches from the west.
Forcing and decent low level moisture transport will lead to
increasing coverage of showers and thunderstorms later this
evening and during the overnight hours. With PWATs rising to 1.5
inches later tonight some of the storms may produce locally heavy
rainfall. With sufficient instability and shear a few storms may
approach severe levels in northeast MO. SPC has a marginal risk in
our far southern cwa. This will be a very mild night with lows in
the 50s to near 60.

Wednesday: Timing is everything when it comes to severe weather
most of the time. In this case, a strong cold front will be
pushing across the dvn cwa, reaching our far eastern counties
early in the afternoon. Showers and thunderstorms can be expected
along and ahead of the front with the instability/shear weakening
rapidly with the passage of the front. At this time, the consensus
models have the front pushing east of the dvn cwa by early
afternoon with the bulk of the severe weather from central IL
southward into AR. As of now, SPC has a marginal risk near and
east of the MS River. If the front slows just enough then
Bureau/Putnam counties would have a higher risk for severe storms.
Rain chances will also gradually decrease from the west during
the afternoon as the front pushes eastward. Colder temperatures
will be spreading into the cwa in the wake of the front. Highs
will range from the mid 50s in our far western counties to around
70 in our far eastern cwa.

.LONG TERM...(Wednesday Night through Tuesday)
ISSUED AT 355 PM CDT Tue Apr 25 2017

Wednesday Evening and Night:

Upper jet will have carved out a longwave trough over the Western
and Central U.S. by Wednesday afternoon/evening. A negatively tilted
shortwave trough and associated mid-level vorticity max is forecast
to track from Oklahoma through Arkansas and Missouri into Illinois.
By the evening hours the cold front and sfc-based instability will
be close to our far SE/E CWA border.

Precipitation:

Rain is likely, especially in the counties along and east of the
Mississippi River into early Wednesday night before sliding to the
east. The rain will be steadier and heavier in the far eastern CWA,
toward Bureau and Putnam Counties. The good news is the heaviest
band of rain of 1.50-3.00" is forecast to miss most, if not all, of
the CWA to the east, reducing the risk for widespread river flooding.

The challenging part of this forecast is whether or not some of the
convection that forms along the cold front during the afternoon and
evening impacts the far SE/E sections of the forecast area including
Bureau and Putnam Counties, possibly McDonough. The NAM is an
outlier being further NW with the front and heavy precip. It is also
much more aggressive with anafrontal precip associated with 925-
850mb frontogenesis, PVA, and right entrance region of an upper jet
streak. This would bring widespread light to moderate rain to the
entire CWA in a secondary round Wednesday night until the 500mb
trough axis and PVA move east of the area.

Thunderstorm Risk:

There is a Marginal Risk for severe storms east of the Mississippi
River, but the expected track of the sfc low and positioning of the
cold front by the evening places the best chance for severe storms
to the east of the CWA. If strong storms were to impact the DVN CWA,
they would probably be in McDonough, Bureau, and Putnam Counties.

Thursday and Friday:

High pressure ends precip chances on Thursday. Although this is a
brief break. Models already develop a closed 850mb circulation and
low-level warm front across Iowa and Illinois by Friday morning. As
a result, shower chances are back in the forecast for Friday.
Forecast PWATs and forcing for ascent are supportive of mainly light
rain.

Saturday through Tuesday:

The longwave trough that was anchored over the Western U.S. and the
Plains, finally moves through the central section of the country in
the form of a strong low. More wet weather is likely Saturday and
Sunday before we dry out early next week. Uttech

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
ISSUED AT 643 PM CDT Tue Apr 25 2017

A cold front will sag into the terminals over the next 24 hours
accompanied by increasing rain chances. Timing the rain into the
terminals is the main challenge. Expect initial surge of
at least scattered showers and a few storms late evening into
the overnight with moisture advection and elevated convergence
attendant to branch of low level jet. Due to uncertainty with
coverage I have opted to maintain vcsh wording for this initial
round. Then eyeing the potential for a linear complex of showers
and storms lifting up from the southwest late tonight through
Wed AM with much of the area on the NW side and possibly more
rain/showers with embedded thunder. Have handled this round with
a several hour period of prevailing MVFR conditions in
rain/showers, although thunder is possible have left out any
mention due to uncertainty on coverage. Then drier air attempts
to work in on westerly winds by Wed PM, but expect a renewed round
of showers/rain late PM to just beyond the end of the TAF cycle as
a wave of low pressure lifts up along the stalled frontal zone.
Bottom line, conditions VFR this evening then deteriorate to more
widespread MVFR on Wed with local IFR possible at CID and DBQ
post-frontal.

&&

.HYDROLOGY...
Issued at 354 PM CDT Tue Apr 25 2017

Potential for several rounds of heavy rainfall through this
weekend and rises on area rivers.

1) Wednesday afternoon through Wednesday night. Confidence on
widespread heavy rain with this round is low because model
consensus tracks an area of thunderstorms, and heavy rainfall of
1-3 inches, primarily to the east of the local forecast area.
There is a low chance this band of heavy rain and thunderstorms
clips the far east and southeast sections of the CWA. But again,
even if this worst case scenario verifies, the areal coverage of
heavy rainfall in our forecast area would be low.

2) Saturday through Sunday. 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 4-5 days away, confidence
on the exact placement of the heaviest precipitation is low.
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.
&&

$$

SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...Uttech
AVIATION...McClure
HYDROLOGY...Uttech



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