Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 272356
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
656 PM CDT WED JUL 27 2016

...00Z AVIATION UPDATE...

.SYNOPSIS...
Issued at 305 PM CDT Wed Jul 27 2016

18Z surface data has low pressure near KMSP with a frontal boundary
across northern Wisconsin. A cold front ran southwest from the low
into central Nebraska. Dew points were in the 60s from the Great
Lakes into the northern Plains with 70s from the Ohio Valley into
the central Plains and on south to the Gulf Coast.

&&

.SHORT TERM...(This Evening through Thursday)
ISSUED AT 305 PM CDT Wed Jul 27 2016

Based on radar trends, some isolated showers may develop across the
far northwest and west areas by late afternoon. Otherwise, expect a
mix of clouds and sun with dry conditions through late afternoon.

This evening, isolated showers and possibly a couple of
thunderstorms should slowly develop across the northwest half of the
area and move southeast with a passing upper level disturbance. Due
to the overall weak forcing, more showers than thunderstorms should
be seen.

Late tonight, slightly stronger forcing arrives as the cold front
begins moving through the area. Although the forcing is a bit
stronger, there should still be more showers than thunderstorms with
the passing front.

Thursday plenty of wrap around clouds should be seen across the area
along with scattered showers and some thunderstorms. Temperatures
should average below normal. Depending upon the cloud cover and
precipitation coverage, high temperatures may be much cooler than
forecast.

.LONG TERM...(Thursday Night through Wednesday)
ISSUED AT 305 PM CDT Wed Jul 27 2016

Thursday Night...Vorticity max forecast to move through during the
day, then linger, especially along and east of the Mississippi
River, into the evening and nighttime. Isolated to scattered showers
and thunderstorms that exist in the aftn should decrease in coverage
into the evening/nighttime period as the mechanism for their
development will be mainly diurnal heating. Decreasing 850mb temps
into the lower teens and a northerly component to the sfc winds will
result in a comfortable night with lows in the low/mid 60s.

Friday through Sunday...Northwest mid-level flow dominates through
this time. The models are showing a few vort. maxima crossing
through the Mid/Upper Mississippi Valley. However, this occurs with
a background environment of cooler or near normal temps, light NE
sfc winds, and dewpoints in the 60s...implying less fuel for storms
due to less instability.

The one consist message I see from the models is for better storm
organization and coverage to remain south of the CWA...down across
Missouri eastward into the Ohio Valley. POPs are only in the 20-30%
range locally which is a good representation of lower end coverage
or many areas staying dry.

Monday through Wednesday...Yet another pattern change indicated by
the models. The culprit is a seasonally strong upper-low progged to
track through Saskatchewan and Manitoba. Low-level mass fields
responding to this synoptic area of low pressure would result in an
south-southwest flow from the sfc-850mb and significant warm air
advection in the Central U.S. Latest Model-blend temps, beyond
Monday, are in the lower 90s as 1000-500mb thickness values increase
to levels comparable to the prolonged very muggy period which ended
this past Monday. The GFS is near 586 dam while the ECMWF is lower
at 582 dam.

Examining the NAEFS, do not see a strong signal for 850mb temps
exceeding 24 C which is where this ensemble had values peaking at
during the last extremely humid period. At this time, 850mb temps
are not forecast to become excessively high.

The cooler ECMWF is more favorable for MCS development from
Minnesota southeastward into Iowa/Illinois - along the northeast
periphery of the heat dome. If this scenario plays out Model-blend
temps may be too warm for some areas. For now, there is higher
confidence in the potential for oppressive dewpoints in the mid to
upper 70s, possibly near 80 F, than there is in max temps.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
ISSUED AT 644 PM CDT Wed Jul 27 2016

Chances for showers and a few storms will exist through the TAF
cycle, as a weak low and cold front pass through the region to be
followed by an inverted surface trough lingering through Thursday
afternoon. Forcing is fairly weak thus very difficult to pin down
timing and location of any precipitation. As a result, I have left
out any precipitation mention in the TAFs for now, but will
continue to monitor radar and short term trends and amend as
needed. Winds will generally become northerly late tonight and
Thursday. The weak cool advection coupled with abundant low level
moisture may promote patchy fog late tonight, and eventually mvfr
cigs across portions of the area on Thursday. Have held off on
mvfr cigs for now as largely have yet to develop and opted instead
for lower vfr cigs, but will also continue to monitor satellite
and ob trends and amend if needed.

&&

.DVN Watches/Warnings/Advisories...
IA...None.
IL...None.
MO...None.
&&

$$

SYNOPSIS...08
SHORT TERM...08
LONG TERM...Uttech
AVIATION...McClure


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