Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 280013

Area Forecast Discussion
National Weather Service Quad Cities IA IL
613 PM CST Mon Feb 27 2017


Issued at 330 PM CST Mon Feb 27 2017

A southerly wind transported unseasonably mild air into the region
during the early afternoon hours. Temperatures ranged from the
upper 40s along the Highway 20 corridor, to near 60 degrees in the
Keokuk, Iowa area. Fair weather cumulus clouds were located mainly
across northwest Illinois, while mid level clouds increased across
eastern Iowa.


.SHORT TERM...(This Evening through Tuesday Evening)
ISSUED AT 330 PM CST Mon Feb 27 2017

There are several issues to contend with in the short term period,
including storms tonight, near record temps Tuesday, and potential
for severe weather Tuesday afternoon/evening.

For tonight, high resolution model guidance is in general
agreement in bring showers and scattered storms into the forecast
area tonight, especially after 9 pm. Elevated instability, robust deep
layer shear, and low freezing levels will likely support some
hail. Potential for 1 inch or larger hail is low. Weak convergence
will favor fog development across the northern counties late
tonight, with the low clouds and fog likely lingering into Tuesday
morning. This may help suppress additional strong storms during
the morning hours Tuesday.

A strong south to southwest wind will boost afternoon temperatures
to record or near record levels again, from the upper 50s north to
near 70 degrees south. Moline and Burlington should be right
around the record highs of 66 and 69, respectively, while Dubuque
and Cedar Rapids may fall a bit short.

Attention then turns to the cold front passage Tuesday afternoon
and evening. SPC has expanded the marginal and slight risk areas
farther north to include most of the forecast area, which is very
reasonable given the latest suite of model data today. Some latest
18z runs, including the hi-res WRF, and pulling the potential
threat north to the Interstate 80 corridor. Confidence in favored
locations for severe is relatively low, but predictability will
increase with new data overnight into Tuesday morning. The main
threat is large hail, due to the prodigious deep layer shear and
low freezing levels. A secondary concern is isolated damaging wind
gusts, if strong winds off the deck can descend through the
shallow near surface stable layer. Surface winds do not appear to
be backed enough to warrant mention of a significant tornado
threat. But if timing and location become more favorable
regarding a surface low along the boundary, there may be a small
window for a tornado threat during the late afternoon. Locally
heavy rain may be an issue with repeat rounds of storms along the
boundary, and will have to monitor for impacts to current rising
river levels.

.LONG TERM...(Late Tuesday Night through Monday)
ISSUED AT 330 PM CST Mon Feb 27 2017

Late Tue night into Wednesday...As convection shifts to the east
later Tue night into early Wed morning, synoptic scale lift
continues with the approach of main upper trof acrs and east of the
MO RVR Valley. In-wrapping northwesterly low to mid level flow to
act as a cooling conveyor, as well as dynamical top-down cooling
effect acrs the CWA as the day progresses. This process to interact
with secondary def zone type precip band developed under the low to
mid level trof, for a switch over to a wintry mix or all wet snow
from west-northwest to east-southeast into Wed morning. Even taking
into account diurnal processes that battle snow accums with marginal
sfc and boundary layer temps, latest thinking suggests areas
generally along and north of HWY 30 may still get a few tenths up to
over a half inch of snow accum by early afternoon. Heavier narrow
bended snows may produce up to a quick inch in localized spots, but
would have to be on elevated surfaces with lingering mild ground
temps. The NAM continues to be bullish with almost advisory level
snows or at least several inches north of I80 on Wed, but will throw
it out for now with it`s wet bias. Otherwise a rather raw blustery
day with little or just minor temp recovery from morning values, and
lingering precip exiting out of the east by mid afternoon. With some
clearing over fresh snow cover, a cool Wed night with lows well down
in the 20s.

Thursday and Friday...freshly established broad northwesterlies
aloft will look to shuttle down a wave/clipper-like system over or
near the local area Thu into Thu evening. Both the latest run GFS
and NAM are stronger with this system, and with these models
indicated steep low to mid level lapse rates and mixing possibly up
to near H7 MB, could be snow shower or squall scenario with gusty
winds mixing with the passing showers by afternoon. Depending on the
system`s path, possible warm draw in the llvls with a further north
low track, there could be mixed precip scenario at times during the
day affecting precip amounts and impacts. It could all switch to
rain showers by afternoon especially south of I80. Not currently
sure if some thunder may occur, but can`t rule it out. Will go with
highs in the upper 30s north, to the mid 40s south unless the the
deep mixing can drive temps even higher. Passing sfc ridge later Thu
night into early Fri for a seasonably cold morning, then ridge
passes enough for return flow warming by Fri afternoon for decent
diurnal swing. WAA type precip chances Fri night, but currently low
confidence at this point if it breaks out acrs the area or just to
the north.

Saturday through next Monday...Longer range indications on the
latest run medium range models continue the idea of shunting
building upstream thermal/upper ridging east acrs the region over
the weekend. If the CWA can get under the southerly influence of
ridge-riding waves, a strongly thermal moderating weekend could be
in store.  Highs in the 50s to low 60s on Sat, may trend well up in
the 60s by Sunday, with a 70+ degree reading possible, looking at
the thermal draw of the GFS and especially the 12z ECMWF. The medium
range solutions then dig L/W troffiness acrs the Rockies into the
mid CONUS by early next week, keeping mild and eventually wetter
weather aimed at the local area until the cyclone passes for another
temporary chill down into the mid week.   ..12..


.AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening)
ISSUED AT 554 PM CST Mon Feb 27 2017

Challenges a plenty this TAF cycle and include timing of precip and
arrival of lower flight conditions. Scattered showers will be found
this evening with the best coverage north of I-80. Mainly vfr
visibilities in the showers with brief localized mvfr visibilities in
the stronger showers. Another round of showers is likely late tonight
into Tue AM with low level jet and advancing warm front. There is a
chance of thunderstorms with this round. Then persistent isentropic
lift and moisture advection will likely result in areas of rain/drizzle
from mid morning into the afternoon ahead of a cold front and low
pressure system. By late afternoon into Tuesday evening expect
scattered storms to develop ahead of the cold front. Overall, expect
mainly vfr conditions this evening into the overnight with
deteriorating conditions to mvfr/ifr and possibly lifr late tonight
through Tuesday.


Issued at 1210 PM CST Mon Feb 27 2017

Many area rivers continue to be on the rise due to rainfall late last
week and snow melt. Along the tributaries, a flood warning remains
in effect for the Cedar River near Conesville, where the river is
expected to crest just under a half foot above flood stage on
Tuesday. A flood watch has been issued for the Wapsipinicon River
near De Witt, where projected rainfall over the next 48 HRS takes
the stage there well above flood stage by Thu. If rainfall is much
less, the river may only come in around the flood stage or fall just
short. This forecast rainfall over the next 36 to 48 HRS, along with
with anticipated rapid melting of the snowpack in the upper reaches
of the river basins, will likely result in renewed rises and
possible flooding out 7 to 10 days. The Iowa and Cedar Rivers will
be more susceptible to these rises, as well as portions of the

More significant rises and possible flooding are forecast for
segments of the Mississippi River due to routed flow from upstream,
as well as some input from upcoming local rainfall. With upstream
flow input from the Iowa/Cedar Rivers, there is higher confidence
that at least Gladstone and Burlington will rise above flood stage
later this week. Thus the flood watch for these sites has been
upgraded to a flood warning. Otherwise, flood watches remain in
effect for numerous other Mississippi forecast points from Dubuque
on down to Keithsburg for potential flooding that is forecast to
begin later this week and into the weekend.   ..12..


ISSUED AT 330 PM CST Mon Feb 27 2017

Record Highs for February 28...

Moline.........66 in 2016
Cedar Rapids...64 in 1932
Dubuque........62 in 1895
Burlington.....69 in 1932




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