Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 181149
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
649 AM CDT Sat Mar 18 2017

...12z AVIATION UPDATE...

.SYNOPSIS...
Issued at 320 AM CDT Sat Mar 18 2017

The latest sfc analysis was indicating low pressure center acrs
northern LK MI, while a 1028+ MB ridge axis extended down acrs the
plains and nosing into the mid MS RVR Valley. In between these two
regions, rather tight cyclonic flow continued acrs much of the
western GRT LKS and upper MS RVR Valley, including the local area.
This llvl gradient continued to drive blustery sfc winds overnight
acrs much of the CWA, while a stratocu cloud deck spiraled
southeastward acrs the upper Midwest around the GRT LKS cyclone. To
the west, a large ridge was amplifying acrs the Rockies, while a
closed upper low continued to roll southeastward acrs the western
GRT LKS. Channeled vorticity overhead embedded in the cyclonic
northwest flow aloft.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 320 AM CDT Sat Mar 18 2017

Best support for some spotty light precip in the cloud deck should
remain off to the northeast of the CWA acrs WI this morning and
will keep the fcst dry. Western fringe of H85 MB cold pool is acrs
the CWA now and aided by a northwesterly 40+ KT LLJ, but this
pool to seep east as the day progresses. LLVL northwesterlies will
actually start to warm air advect later today with H85 temps
recovering to positive values acrs most of the western 2/3`s of
the CWA by late afternoon. Stratocu deck will start to edge east
of the MS RVR by 18z to 19z today, and possibly mix out to sctrd-
bkn coverage on it`s western fringe as it migrates east as well.
So improving sky cover by afternoon. The northwest winds will
continue to be raw and blustery from the northwest 15 to 25 MPH
with higher gusts this morning into midday, before the llvl
pressure gradient relaxes this afternoon from the west as the sfc
ridge slips east acrs central IA. Highs mainly in the 40s today,
except a few spots to hit 50 south of I80 in the afternoon
insolation and airmass modification.

Tonight...The 00z run model guidance in good agreement of suggesting
the upstream sfc ridge axis to continue to settle east acrs the area
tonight for light to calm winds. Dry airmass/sfc dpts in place
should allow for chilly overnight lows in the 20s acrs mush of the
fcst area. But upper ridge-riding cirrus may stream down acrs the
region(much like what is ongoing seen on various IR imagery from the
Dakotas, down the MO RVR Valley, and to the mouth of the OH RVR
Valley) and limit a complete temp bottom out.   ..12..

.LONG TERM...(Sunday through next Friday)
ISSUED AT 320 AM CDT Sat Mar 18 2017

Typical late March weather, with a couple of light to moderate
rainfall episodes.

Long Term Forecast Confidence Assessment...fair or average, main
challenge is location and intensity of convection late Sunday night
and risk of any large hail.  Limited instability and forcing
profiles suggest this is a low confidence event until several hours
before initiation. Low freezing levels and dry air aloft continue to
support a decent risk of isolated storms with large hail up to
around size of golf balls in strongest updrafts.

Sunday...minor changes.  Warmer with south winds and fair skies with
highs in the 50s to around 60F in the south.

Sunday night and Monday...kept chance POPS all but far southeast
with frontal passage around daybreak Monday.  Still indications of
weak upper forcing and no surface based instability.  Mid level
instability of 800 to 1500 J/KG from I-80 corridor to Missouri
border.  This supports only chance showers and isolated to scattered
thunder.  Limited moisture continues to suggest light precipitation
amounts mostly below a quarter inch and scattered.  Low WBZ of 8-9K
AGL and dry air still favorable for risk of large hail.  The HELP
tool shows for 900 J/KG continue to suggest max hail sizes of 1.25
or half dollar with 1600 J/KG suggestive max hail size potential
over golf ball size to near 2 inches or size of hen eggs.  Local
forcing tools suggest highest risk to be along and south of highway
34 for large hail attm.  Otherwise...lows in the 40s with highs
Monday 55 to 65 degrees and possibly a few degrees higher in south
sections.

Monday night through Wedneday...Minor changes made.  Fair skies as
next Canadian high pressure moves in.  Slightly below normal
temperatures with maxes mostly in the 40s to the lower 50s south
with lows 25 to 35.

Thursday through Friday...unsettled weather of rain, rainshowers
with embedded storms as large disturbance ejects northeast from the
southern plains.  Still significant variance in timing and location
of surface low track for at best moderate confidence with trend for
low track further north.  Risk of severe weather, if any, will be
better ascertained next 24 hours.  Most locations to receive
moderate rain totals with locally 1 inch possible.  Temperatures
support highs in the 50s Thursday and mostly 60s on Friday.  Lows
mostly in the 40s.

Saturday...clearing and cooler with suggestion of highs mostly in
the 50s and lows in the lower/mid 30s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday Morning)
ISSUED AT 638 AM CDT Sat Mar 18 2017

MVFR deck of wrap around clouds will continue through at least
midday at most the TAF sites. Most of the time the CIGs will
range from 2-3K FT AGL, but a sub-2K FT AGL MVFR deck will affect
the DBQ and CID sites through 15z. Then some clearing or break up
of the deck from the west this afternoon, except possibly hanging
on at DBQ through mid afternoon. But by then the CIGs may rise to
VFR levels in the north. Brisk northwesterly SFC winds gusting up
to 25 KTS this morning, will then diminish to 10-15 KTS this
afternoon before going light north to northeast overnight. Just
passing high clouds or a mix of clear skies tonight. A few of the
models want to produce fog tonight toward dawn Sunday morning
under clear skies and light winds, but feel they are overdoing it
and the sfc layer will be drier than they give it credit for.
   ..12..

&&

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

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...Nichols
AVIATION...12



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