Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 271740
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1240 PM CDT Thu Apr 27 2017

...HYDROLOGY UPDATE...

.UPDATE...
Issued at 924 AM CDT Thu Apr 27 2017

The forecast has been revised to lower max temperatures today.

Cloud cover to persist into the afternoon hours. As such, max
temperatures have been lowered across the board 5 to 7 degrees
with 40s now expected across roughly the north half and 50 to 55
across roughly the south half.

UPDATE Issued at 841 AM CDT Thu Apr 27 2017

Forecast has been updated to reflect drizzle occurring behind the
main band of precipitation and to keep the morning cloudy.

Satellite shows clouds all the way back to the Missouri river in
western Iowa and Missouri. Given the strength of the CAA
occurring, clearing this morning is unlikely and clouds may
persist through much of the afternoon. Radar returns and
observations indicate patchy drizzle all the way back into
central Iowa.

&&

.SYNOPSIS...
Issued at 336 AM CDT Thu Apr 27 2017

Early this morning, a surface low tracked just south east of the
CWA. Wrap around moisture was leading to light to moderate rain
across the CWA. As the low slides north and east through the day,
the rain will follow suit. This low will be the main weather
producer for the short term period.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 336 AM CDT Thu Apr 27 2017

Main forecast concern for the short term are the chances for rain
as the surface low moves out of the area. Another forecast concern
is the chance for frost developing across the far north tonight.
This chance for frost has prompted a frost advisory for the area.

TROWAL associated with the mature midlat was leading to anywhere
from 0.25 to an inch of rain in the heavier bands this morning. As
the warm conveyor continues to feed the storm, expect this rain to
continue. Favorable jet placement is leading to even more upper
level divergence and moderate to heavy rain across the area. The
jet streak should move out of the area after 12z, so between 12z
and 16z expect a rapid drop off in precip intensity. After this
time, high pressure attempts to build into the area before the
flow turns SW and another warm advection wing marches towards the
CWA for tomorrow morning. With this system, there is another
chance for rain early in the day.

Cold H85 temps ushered in with this low will lead to temps
dropping near freezing across the northern CWA tonight. Winds will
slacked and surface diffluence across the area should lead to the
development frost across the far north. One major question
remains, when do the warm advection clouds make it into the north
CWA. Frost development and these clouds will dance to see who
wins. Regardless, decided with the low temps and clouds moving in
later in the period it was safer to go with the frost advisory. It
is very possible that frost will be gone around sunrise if the
clouds move in. Regardless, those with sensitive plants should
plan to keep them safe tonight.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 336 AM CDT Thu Apr 27 2017

Friday and Friday night...Models show re-alignment of upper flow to
southwesterly ahead of broad western trough. An ejecting wave
ahead of a digging shortwave over the Four Corners region will zip
across the region. Attendant mid level circulation will follow along
elevated warm front with subsequent isentropic lift and theta-e
advection contributing to the likelihood of showers during the day
tapering off by mid afternoon through early evening from SW to NE.
Rain amounts are expected to be fairly light and generally around
0.25 inch or less with weak elevated instability thunder chances
look quite low, but not zero given 850-500 mb theta-e lapse rates
approaching zero. Clouds and rain will keep temps quite cool, and
potential to be a few degrees colder than forecast for highs with
some sites possibly staying in the 40s across northeast IA into
far northern IL.

Saturday through Monday...Models remain in good agreement with
strong closed low tracking from the Four Corners region into
the Great Lakes by the end of the period. Deepening surface
cyclone eventually occludes while moving across our region Sunday
into Monday. Main signal for heaviest rains is still being
suggested to our S/E from portions of the Southern Plains to the
Ohio Valley where best juxtaposition of ingredients depicted
including stalled frontal zone co-located with deep southwest
flow and associated wave train, and strongest integrated water
vapor transport with teleconnections to Caribbean atmospheric river.
Rain will be increasing from south to north across the region
Friday night into Saturday attendant to elevated warm, moist
advection with some contribution from main precip processes to our
south. Eyeing Sunday as having potential for heavy rain
for our area, as strong dynamics with diffluent flow ahead of
approaching closed low and additional lift from right entrance
region of departing northern Great Lakes H25 jet interact with
tightening mid level baroclinic zone. Attendant circulation aids
in backing flow and advecting in anomalously warm, moist conveyor
with PWATs of 1 to 2 standard deviations above average for late April.
This could result in the risk for a more widespread 1+ inch of rain
on Sunday. Potential also exists for thunderstorms on Sunday but
still too early to assess the threat for severe weather due to
uncertainties with degree of instability and timing. Monday looks to
transition to much cooler and windy conditions with light rain/showers
in wrap-around as system jettisons into the Great Lakes.

Tuesday through Wednesday...Flow pattern shifts to northwest and
supports generally a drier period and continued cool.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
ISSUED AT 543 AM CDT Thu Apr 27 2017

Rain is quickly pulling out of the area this morning. With it CIGS
and VSBYS should start to improve. Some areas of IFR should become
MVFR shortly after rain ends. Then expect sites to improve to VFR
around noon with clouds breaking in the afternoon. Winds will
remain in the low teens before slackening overnight as high
pressure moves in.


&&

.HYDROLOGY...
Issued at 1240 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.

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.
&&

$$

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


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