Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 171115
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
615 AM CDT Mon Apr 17 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 334 AM CDT Mon Apr 17 2017

06Z surface data had high pressure over the mid-Mississippi Valley.
Dew points were in the 30s and 40s from the Great Lakes into the
central and northern Plains. Dew points in the 50s and higher ran
from the Ohio Valley into the southern Plains.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 334 AM CDT Mon Apr 17 2017

Through sunrise, scattered light showers or sprinkles will end
across west central Illinois south of a Burlington to Galesburg line.

Today and tonight, quiet and dry conditions will be seen as high
pressure slowly moves into the Great Lakes. High temperatures will
average a little above normal. Low temperatures will average close
to or slightly below normal.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 334 AM CDT Mon Apr 17 2017

Active pattern through midweek with a few rounds of showers and
storms accompanied by potential for some severe weather and heavy
rain.

Tuesday and Tuesday night...
Compact, low amplitude PV anomaly is progged to shift from the
Northern Plains to the Great Lakes on Tuesday. Attendant cold
front is shown to decelerate and appropriately sag into the
CWA Tuesday night being well displaced from stronger mid level
flow with departing Great Lakes perturbation. Late Tuesday AM
through PM will see a chance of showers and perhaps a few
storms, but stayed modest on pops with best kinematics north and
thermodynamics south. Tuesday night the front is likely to turn
stationary over the CWA as the boundary becomes parallel to the
mean mid level flow. In addition, heights aloft will begin to
lower to our west ahead of a more potent shortwave ejecting from
the Great Basin, with developing surface cyclone emerging into the
Plains by 12z Wednesday. Branch of LLJ and attendant elevated
convergence and moisture advection will likely lead to uptick in
coverage of showers and storms late Tuesday evening and overnight.
Main threat with storms will be hail, and also heavy rain with
PWATs increasing to near 1.5 inches. Believe some areas of 1+ inches
of rain is possible as southwesterly LLJ favorable for potential
of repetitive cells leading to enhanced rainfall amounts. Just
where the heavier rains occur remains a challenge, but of
critical importance given the high river levels and ongoing
flooding in some areas and will be dependent on placement of the
front. With the anticipation of convection remaining elevated
I would expect areas along and especially north of the front to
be favored for the storms with hail and heavy rain. Given the
elevated nature also favor a more northerly frontal position
initially Tuesday night, thus feeling is areas near/north of I-80
may be most at risk but confidence is low on location of stalled
front and subsequent threat area as strength of incoming high
pressure into the Upper Midwest also a factor and where models do
show some larger variance.

Wednesday and Wednesday night...
Convective trends from Tuesday night will loom large in evolution
of frontal placement and mesoscale details on Wednesday. Overall
though this period looks potentially quite unsettled/active and
wet as vigorous shortwave and attendant surface cyclone shift
eastward interacting with stalled front. If Tuesday nights
convection were to grow upscale into MCS then potential exists to
shove effective frontal boundary further south through much if not
all of the CWA, with assistance also from N/E fetch off Lake
Michigan in response to high pressure shifting across the Great
Lakes. This scenario would likely limit severe risk to just far
south and lead to much cooler temperatures. However, if convection
does not grow upscale then frontal boundary likely to reside
further north across the CWA, and this scenario seems to be the
general consensus amongst the models with the boundary somewhere
between Hwy 30 and Hwy 34, with potential for heavy rain and
severe weather over about the southern 2/3rds of CWA. Severe
potential will have to be monitored closely Wednesday
afternoon/evening as strong shear aided by impressive LLJ brings
threat for large hail and damaging winds, while enhanced 0-1 km
SRH with veering low level hodographs in vicinity of front would
support risk of tornadoes. Continued moist axis residing over
portions of the CWA with PWATs of 1.5 inches along with the threat
for repetitive storms will lead to additional threat for heavy
rains of 1+ inches, which depending on where this falls could have
impact on already rising rivers. Also, no doubt temperatures will
need to be refined depending on boundary location, as expect a
decent 20-25+ degree thermal gradient across the boundary (50/70s).

Thursday and Friday...
Cool high pressure builds in, with northerly flow leading to
near normal temps with mainly highs upper 50s/lower 60s and
lows upper 30s/lower 40s. May also have some potential for patchy
frost Friday morning north of I-80 in sheltered areas where winds
can decouple.

Saturday and Sunday...
Models continue to show another significant storm system shifting
across the central CONUS over the weekend, with still plenty of
differences on the track. ECM and UK offer a more southerly
track across the Lower Mississippi Valley Saturday into Sunday,
while the GEM and GFS are further north into the Mid-Mississippi
Valley although GFS has trended a bit south. Overall splitting
the difference and thus have maintained rain chances with the
idea we may be on the northern edge of the rain shield with best
chances across the south. Wouldn`t totally rule out a more
southern shift and most if not all of CWA missed based on the
dprog/dt of medium range models. Temps seasonable over the weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday Morning)
ISSUED AT 614 AM CDT Mon Apr 17 2017

VFR conditions will be seen through 12z/18 as high pressure moves
into the Ohio Valley.

&&

.HYDROLOGY...
Issued at 334 AM CDT Mon Apr 17 2017

Recent heavy rainfall has led to rises on some area rivers, mainly
between Highway 30 and Highway 34 where some minor to moderate
flooding is occurring or is forecasted to occur on portions of the
Wapsipinicon, Iowa, Rock and Cedar basins. Please see the latest
Flood watches (FFA), Flood warnings (FLW) and Flood statements (FLS)
for details. Additional heavy rain is is forecast around the midweek
timeframe and could result in more rises and an increased potential
for flooding on area rivers.

&&

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

$$

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



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