Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 150415
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1115 PM CDT Thu Sep 14 2017

.UPDATE...
Issued at 1100 PM CDT Thu Sep 14 2017

Band of showers continues into portions of east central and
northeast IA late this evening within low/mid level warm,
moist ascent. Veering flow also is advecting in elevated
instability with rather steep mid level lapse rates (8c/km)
leading to a few lightning strikes in this activity over
portions of northeast IA. Models continue to show this waning
overnight and refocusing more back to our west, but this
diminishing processes appearing slower than forecast thus will
extend some small precip chances into the overnight. In time later
tonight would anticipate the focus (LLJ and attendant warm/moist
advection) to shift back west perhaps as close as central IA where
may see additional development occur. Should this happen then
could envision some of this activity then moving back into w/sw
portions of cwa early Friday AM.


&&

.SYNOPSIS...
Issued at 245 PM CDT Thu Sep 14 2017

18Z surface data has high pressure over the Great Lakes and Ohio
Valley with low pressure along the SD/NE border west of KYKN. Dew
points were mainly in the upper 50s and 60s across the Midwest.

&&

.SHORT TERM...(This Evening through Friday)
ISSUED AT 245 PM CDT Thu Sep 14 2017

The dry and very warm weather will continue late this afternoon
through Friday.  Diurnal temperature swings will be quite large
given the dry ground and atmosphere.  Lows tonight should be 55 to
60 with the coolest readings east of the Mississippi and in the
favored cool areas/river valleys north of I-80. Patchy fog is
possible tonight in river valleys and low lying areas.

Very warm temperatures will be seen on Friday with readings of 85 to
90 expected.

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 245 PM CDT Thu Sep 14 2017

Highlights of the long term forecast period include hot and muggy
conditions on Saturday, followed by potential for some long-awaited
rain across the area.

For Saturday, have adjusted highs upward slightly into the 87-91
range ahead of the cold front to the west. Surface dewpoints should
creep into the 60s, somewhat uncomfortable given the recent dry
weather, resulting in heat indices a couple degrees higher than the
ambient temperature. The main cold front will move through the
forecast area Saturday night into Sunday. Coverage of showers and
storms is forecast to be highest in eastern Iowa. Average rainfall
amounts are expected to be limited to a quarter inch or less. Shear
vectors oriented nearly perpendicular to the front will mean meager
bulk shear values, so the severe weather threat will be minimal.
Cooler and drier air will filter into the area behind the front on
Sunday, with afternoon highs int the mid 70s to low 80s from NW to
SE.

Sunday night through Monday, the boundary is forecast to retreat
northward as a warm front. More scattered showers and a few storms
will be possible during this period.

Tuesday through Thursday, there is increasing divergence in the
synoptic scale models. The ECMWF is main dry through the period with
a strong upper level ridge in place. The GFS/GEM have this ridge
slightly farther east, allowing energy to ride up into the forecast
area in southwest flow. Have not strayed from the model blend pops,
which favor Tuesday night into Wednesday for additional rain.
However, confidence in any organized rain during this period remains
low. Above normal temperatures will persist through the last part of
the long term period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday Night)
ISSUED AT 1100 PM CDT Thu Sep 14 2017

Band of showers and isolated storms over portions of northeast
into east central IA near/nw of CID to DBQ is anticipated to
gradually weaken/diminish overnight with the focus shifting back
west with LLJ. While a brief shower can`t be ruled out at CID/DBQ
would anticipate limited impacts with vsbys AOA 6sm. Additional
showers may develop over central IA and if this occurs some of
this activity could move back into eastern IA early Friday morning.
Overall though coverage and impacts to terminals would appear rather
low during the TAF cycle. Otherwise, expect bouts of mid clouds
within broad warm advection regime. Some fog will be possible
again toward daybreak, but with clouds and enough BL mixing (SSE
wind around 5+ kts) confidence is too low for mention as well.
River valleys and other low lying areas east of the Mississippi
River remain most favored for fog at this time. An increasing
pressure gradient and mixing on Friday should aid in gusty south
winds 10-20 kts by late morning through afternoon.

&&

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

$$

UPDATE...McClure
SYNOPSIS...08
SHORT TERM...08
LONG TERM...RP Kinney
AVIATION...McClure



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