Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 272032
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
331 PM CDT Thu Apr 27 2017


.SYNOPSIS...
Issued at 330 PM CDT Thu Apr 27 2017

18Z surface data has high pressure from the northern Plains into the
lower Missouri Valley with strong low pressure over the upper Great
Lakes. Dew points were in the 20s and 30s from the northern Plains
into the mid-Mississippi Valley with 40s and higher from the Ohio
Valley into the lower Mississippi Valley.

&&

.SHORT TERM...(This Evening through Friday)
ISSUED AT 330 PM CDT Thu Apr 27 2017

Cloudy and brisk conditions will continue through sunset with any
patchy drizzle or flurries ending.

Dry conditions look to be in store for the evening hours as the high
moves across the area. Return flow developing after midnight will
allow light rain to break out across Missouri and move north into
the southern half of the area. The amount of dry air does raise
questions on whether or not there will be any precipitation reaching
the ground. Several solutions suggest the potential of the entire
area remaining dry until sunrise Friday.

Cloud cover is the big unknown regarding the potential for any frost
tonight in the highway 20 corridor. Based on satellite trends the
cloud cover may remain intact which would reduce the potential for
any frost. For now will maintain the current headlines for frost in
the highway 20 corridor.

Friday, if light rain is occurring across the southern half of the
area at sunrise it will slowly overspread the area during the
morning. Light rain should be seen across the entire area during the
afternoon hours with the best chances across the northwest half of
the area.

The combination of cloud cover, rain, and east or east northeast
winds is expected to keep roughly the northwest half of the area in
the 40s Friday. The southeast half of the area should see
temperatures in the 50s which is below normal for late April.

.LONG TERM...(Friday Night through Thursday)
ISSUED AT 330 PM CDT Thu Apr 27 2017

Active weather will continue through the weekend with the threat of
renewed flooding and possibly some severe weather.

Periods of showers and thunderstorms, heavy at times, will persist
through Sunday before rain chances decrease early next week.
Saturday and Sunday are most favored for heavy rain. PWAT values
running 2-3 standard deviations above normal support widespread 1 to
3 inch amounts, with the heaviest axis most likely across west
central into northwest Illinois. The most extreme rainfall totals
still look to stay southeast of the area. Nonetheless, some renewed
rises are expected into next week. The longer term river flooding
situation is discussed below.

Most of the period is expected to be free of severe weather with
little or no thunder. However, recent synoptic model trends,
indicate a conditional severe weather threat Sunday afternoon and
evening, especially along and east of the Mississippi River. This
scenario would discount the 12km WRF as a fast outlier. Depending on
the timing and track of the surface low, a decent portion of the
forecast area could be in the warm sector with a warm front/triple
point nearby. This would put all modes of severe weather into play.
With the increasingly saturated soils, also cannot rule out some
isolated flash flooding Saturday night into Sunday in areas affected
by multiple rounds of storms.

On Monday, a well developed TROWAL will support lingering showers
and perhaps some wet flakes depending on the timing of the colder
air. Have dropped Monday`s highs into the 40s most areas and
additional downward adjustments may be needed. Lack of model
consensus means low confidence in additional rain for Tuesday
through Thursday. Temperatures will be slightly below normal, with
highs in the upper 50s/low 60s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
ISSUED AT 1240 PM CDT Thu Apr 27 2017

Widespread MVFR conditions will continue across eastern Iowa and
northern Illinois through 00z/28. After 00z/28 conditions will
improve to VFR as weak high pressure builds into the Great Lakes.
Conditions will slowly deteriorate to MVFR after 12z/28 as the
next storm system moves into the area.


&&

.HYDROLOGY...
Issued at 330 PM CDT Thu Apr 27 2017

Forecast confidence is now high enough at New Boston LD17 to warrant
an upgrade from flood watch to flood warning this morning.
Minor flooding also continues at Keithsburg, Gladstone, and
Burlington.

Expect periods of showers and thunderstorms Friday through the
weekend. Widespread rainfall amounts of 1 to 3 inches are possible
through the period. Parts of west central and northwest Illinois are
currently favored for the higher end of that range. Confidence
remains low on specific rainfall amounts and placement, but details
will become more clear as the weekend approaches. The most likely
scenario in response to this rainfall is renewed rises on some
points with some minor flooding into next week. The faster
responding LaMoine River at Colmar would be most susceptible to more
significant flooding.

Those with interests along area rivers, streams and creeks should
check back for updates over the next several days.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Frost Advisory from 1 AM to 8 AM CDT Friday for Buchanan-
     Delaware-Dubuque.

IL...Frost Advisory from 1 AM to 8 AM CDT Friday for Jo Daviess-
     Stephenson.

MO...NONE.
&&

$$

SYNOPSIS...08
SHORT TERM...08
LONG TERM...RP Kinney
AVIATION...08
HYDROLOGY...RP Kinney


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