Area Forecast Discussion
Issued by NWS Quad Cities, IA IL
FXUS63 KDVN 211757
Area Forecast Discussion
National Weather Service Quad Cities IA IL
1257 PM CDT Tue Mar 21 2017
Issued at 1256 PM CDT Tue Mar 21 2017
Mid-level frontogenetic band of rain and snow, triggered by a
short wave moving across Iowa, has continued to weaken as it
tracks eastward into the dvn cwa. Earlier this morning, this band
was intense and produced thundersnow in extreme eastern Nebraska
and into the Des Moines area where 1 to 3 inches of snow fell in
one hour! However, radar indicated a general weakening trend and
HRRR suggests this should continue through the afternoon, with
most of the precipitation in the form of scattered light rain.
However, there may be some snow mixed in with the rain early this
afternoon. The bulk of the precipitation will be south of
Interstate 80 and should be ending by late afternoon, as the short
wave shifts off to our east.
Issued at 330 AM CDT Tue Mar 21 2017
At 2 AM CDT...the upper midwest under a thickening canopy of mostly
mid/hi clouds as cold canadian high pressure moves into the northern
and central plains and the midwest. A fast moving broad trough will
bring more clouds from high plains into the area today with isolated/scattered
light rain or sprinkles south sections. Upstream energy shows warming
trend and weak zonal flow to return by Thursday with little or precipitation.
.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CDT Tue Mar 21 2017
Short Term Forecast Confidence Assessment...Fair to good. Two issues
are...first if we see any measurable rain south today versus more
sprinkes and second clouds and cold north winds on high temperatures.
Today...generally mostly cloudy to cloudy by mid day with light sprinkles
or patchy very light rain along and south of highway 34 in Iowa. Using
persistence and airmass modification supports highs today 45F to 55F
north to south with highs possibly off by 3+ degrees if have more or
less sunshine today. Trends support any precipitation today, if any,
should be trace amounts.
Tonight...Skies to become mostly to partly clear from north to south
with winds becoming northeast to east at 5 to 10 MPH. This supports
BL decoupling and lows at lower end of guidance of around 20 to near
30 degrees with isolated upper teens north of highway 30 possible
for a hard freeze tonight.
.LONG TERM...(Wednesday through next Monday)
ISSUED AT 330 AM CDT Tue Mar 21 2017
Wednesday...Seasonably strong sfc high pressure lingering acrs the
western GRT LKS and upper MS RVR Valley, should deflect/erode
overrunning warm air advection type precip bands trying to move in
from the west/plains and will keep the fcst dry. Just see mid and
high clouds and possibly decaying virga into the west. Cold start to
the day and the high debris clouds filtering the insolation will
make for a chilly day for this time of year with highs only around
40 or in the low 40s acrs much of the area. Elevated warm air
advection machine and lower level boundary layer southeasterly flow
to gather more steam Wed night into Thu morning acrs the central
plains into the upper MS RVR Valley. Again will bank on lingering
dry llvls in wake of llvl ridge axis to keep the CWA precip-free(at
the sfc any way) through 12z Thu with just increasing/thickening
Thursday...The GRT LKS ridge slated to edge eastward enough for
increasing warm air advection in many layers up along and west of
the MS RVR Valley this day, and depending on initial moisture
advection and saturation, the CWA will be at risk for at least some
spotty areas of WAA induces precip while the main sfc warm front
organizes to the south acrs KS into MO. Feel bulk of precip will be
a cold rain or sprinkles possibly mixed with a little wet snow on
the northern fringe as it develops and moves north acrs the area.
But blended data also throws in sleet with developing warm wedge
aloft. Not confident the sub-inversion cold layer adequate to
refreeze, but will leave in for now for the morning as precip
initially develops. Late afternoon highs in the mid 40s to around 50.
30-40 KT SSW LLJ progged to advect an elevated plume of 200-300 J/KG
mid layer MUCAPES north of the llvl warm front by Thu evening, and
may be enough to fuel at least isolated elevated thunderstorms north
of convergent H85 MB ribbon north of I80. But the 00z run medium
range models in good agreement of suggesting the main elevated
precip show will occur from the central plains and arching up acrs
MN and WI Thu night...mainly north and northwest of the local area.
Warm front retreat up acrs the local area to keep temps milder Thu
night into Fri morning and even some non-diurnal trends.
Friday through Sunday...The 00z medium range models and ensembles
suggest that a closed low will slow-roll eastward acrs the central
plains and toward the southern MO RVR Valley Fri into early Sat. A
good portion or all of the CWA may become under the influence of
this system`s warm sector on Fri, with temps warming well up in the
60s and 70s especially if incoming precip can hold off until later
in the afternoon. Current synoptic feature and forcing progs,
especially the 00z run ECMWF, suggest more substantial precip and
stronger convection potentail to occur further south acrs the lower
to mid MS RVR valley late Fri and Fri night. But at least moderate
rainfall with some thunder will still look to make it acrs portions
of the DVN CWA Fri evening, with the latest thinking targeting the
southeastern third to half of the fcst area.
Closed system utilizing a TROWAL moisture feed to keep areas of
showers and rain acrs much of the area Sat into Sat night, before
the low pulls away from the region and starts to fill by Sunday.
Some initiation of llvl cool conveyor in-wrapping into the system may
make for a large temp contrast from north to southeast on Sat and
Sat night. Low confidence on exit speed of system and potentail of
wrap-around lingering rain on Sunday. The 00z ECMWF mainly dry
Sunday while the 00z GFS lingers areas of rain into Sunday evening.
Next Monday...Longer range indications suggest broad west-
southwesterlies acrs much of the CONUS maintain an active pattern
into early next week, with another rain-making low possible on
Monday. Near normal temps appear will be in store early next week as
.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
ISSUED AT 1256 PM CDT Tue Mar 21 2017
VFR conds through this taf cycle with most cigs aoa 8k ft agl.
Scattered light rain this afternoon, mainly south of Interstate 80
will end by late this afternoon. Generally north winds 10 to 15
knots this afternoon and tonight then becoming east on Wednesday.