Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 142309

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


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

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 00Z TAFS through 00Z Friday Evening)
ISSUED AT 554 PM CDT Thu Sep 14 2017

Warm air advection regime next 24 hrs will promote bouts of mid clouds,
which could spawn a few stray high based showers (as evidence by
isolated activity currently over south central IA). Coverage of any
showers though likely too sparse for mention. Some fog will be possible
again tonight, 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 would appear to be
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.




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