Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 221208
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
608 AM CST Fri Feb 22 2019

...12z AVIATION UPDATE...

.SYNOPSIS...
Issued at 406 AM CST Fri Feb 22 2019

00z upper air analysis and current water vapor loop showing deep
trof acrs the southwestern CONUS and northern Mex Baja, with the
circulation acrs far southern CA that will eventually roll out right
acrs the region by Sat night and be our weekend storm maker. Initial
leeside elevated warm and moist conveyor will fuel incoming precip
later tonight into early Sat, with a wintry mix concern in the
north. Then rounds of rain on Sat, followed by high winds and a
potential precip switch over into Sunday as the system exits.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 406 AM CST Fri Feb 22 2019

Today...Initial mainly mid deck with elevated returns aloft acrs the
CWA currently, should migrate off to the northeast as the day
progresses for some midday insolation. But more clouds will fill
in from the southwest as warm air advection accelerates from the
south and southwest. Will go with highs in the upper 20s to around
30 over the deeper snowpack areas of the northwest, to the mid
30s around I80, and to around 40 in the far south.

Tonight...As the upper level low in the deep trof base rolls east of
the 4-corners region, increasing LLJ of 30-40+ KTS to create the
warm moist conveyor aloft off the western Gulf. The 00z GFS and NAM
eventual PWAT feed of 0.70 to 0.90 inches up acrs the area by late
tonight may be overdone some, but even taking off a few tenths still
makes the feed unseasonably high. Embedded vort wings in increasing
amplified southwesterlies, as well as some convergent strips induced
by the LLJ itself will produce increasing lift for precip making
processes to start to produce. Some LLVL dry air to overcome, but
fcst soundings respond to the lift and moisture advection/saturation
for precip to form and reach the sfc acrs the far west and southwest
after 03-04z or so. But midnight through Sat morning will be the
main precip window, with accepted QPF values generally of 0.05 to
.10 of an inch by 12z Sat in the far southeast/east...to 0.20 to
over 0.30 tenths of an inch acrs the northwestern half of the fcst
area. Initial lower DPTS/WBZ`s and sfc ambient temps may allow for a
light fleeting initial glaze of ice as precip develops from Sigourney
IA to Aledo IL just before midnight, before sfc parameters warm for
all regular rain at the sfc in those areas.

Areas generally along and north of the Hwy 30 corridor will have the
longest residence time of freezing to subfreezing sfc temps for more
icing potentail from midnight into Sat morning. These areas may get
up to at least a tenth of an inch of ice glaze and will issue a
winter weather advisory for this threat from Midnight through 15z
Sat. Some sleet may also occur north of I80, and an initial wing of
snow or snow/sleet mix possible along Hwy 20 west of Dubuque just
after midnight before transitioning to more sleet into freezing rain
as warm wedge aloft arrives from the south. A light ice glaze may
occur from Hwy 30 down to I80 as well after midnight, but sfc temps
marginal and improving to 32+ degrees into the overnight in those
more southern areas...day shift will have to assess if the advisory
may be needed to expand southward if an ice glaze may be more
southerly in extension and problematic. Some low to mid layer CAPEs
of 100 to 250 J/KG advected acrs the CWA from the south mainly after
midnight, may support some embedded thunder especially along and
south I80. Small hail may occur from these cells adding to the
precip mix and confusion. Of more of an impact from any
thunderstorms could be brief heavier downpours for some ponding of
water on low lying surfaces. Also, if a cell makes it further north
of I80 or hwy 30 there could be localized higher ice accums.  ..12..

.LONG TERM...(Saturday through Thursday)
ISSUED AT 406 AM CST Fri Feb 22 2019

Confidence remains high on a strong storm system impacting the region
this weekend. System looks to bring a plethora of weather types and
potential for multiple hazards affecting the area that will likely
necessitate additional headlines from wind to winter Saturday
night through Sunday.

Potent shortwave trough over the Southwest CONUS is forecast to strengthen
and become negatively tilted while lifting quickly from the TX/OK
panhandles Saturday AM to the Great Lakes Sunday AM. Models coming
into better consensus on track of the compact vigorous PV anomaly
and attendant deepening surface cyclone up across the CWA, with
deviations still noted in the track of which could have
significant impact on precipitation type and amounts. Have
generally favored the ECMWF/GFS for this system, with dprog/dt of
00z NAM showing a gradual northward shift toward these models in
past several runs.

Potential hazards Sat-Sun:

Ice... Some lingering light freezing rain and threat for light ice
accumulation is possible early Saturday morning along/north of
Hwy 30 before temperatures climb above freezing. Highs by late in
the day on Saturday expected to range from mid 30s NW to mid 40s far SE.

Thunderstorms... low risk of isolated lightning Saturday AM. Isolated
to widely scattered storms possible late Saturday afternoon and
Saturday evening, especially over the southeast half of the CWA.
Main threat will be brief heavy downpours, with gusty winds and small
hail risk rather low given fairly pronounced low level inversion and
saturated aloft.

Flooding... Rainfall is anticipated around 0.25 to 0.75 inch Saturday
and Saturday night. This may lead to some ponding water in urban
or poorly drained areas. Thus it is recommended to make sure storm
drains are free of ice/snow. Snowmelt and runoff could lead to development
of some flooding on a few area rivers. In addition some break-up ice jams
are possible which could aid in flooding and rapid fluctuations in river
levels. Hopefully just a relatively short period of 36+ hours above freezing
with temperatures only in the 30s/40s will limit the break-up ice jam threat.

High winds... Winds will increase significantly on the backside of the
system with a highly tightened pressure gradient (20+ mb across IA
supportive of 50 mph gradient winds based on 5 mph/every 2 mb rule of
thumb) and deep mixing bringing blended 40-50+ kt winds to the surface.
This will be coincident with strong cold advection on Sunday enhancing
the momentum transfer, thus looks like at least a wind advisory with the
potential for a high wind warning in some areas late Saturday evening
through Sunday.

Snow/blowing snow... Snow amounts offer the greatest uncertainty at
the movement, with the track of deformation zone and timing of any
change-over and BL temperature trends all critical to amounts. Right now
any rain lingering overnight into Sunday morning looks to change to
snow from west to east. The forecast has the greatest potential of an inch
or more roughly along/NW of Dubuque to Cedar Rapids line. The pre-existing
snow field will have a crust over it due to melting and ice. However,
this could be enough snowfall along with the strong winds to create near
blizzard conditions/impacts in these aforementioned areas. Further east amounts
look to drop off considerably.

Winds and any attendant impacts look to slowly diminish Sunday night through
daybreak Monday as the storm continues to pull away.

Next week looks to generally remain colder than normal and continued unsettled
with periodic snow chances. Temperatures offer the biggest challenge early
in the week with some significant model variances on strength of cold air.
With all the weather between now and then, the forecast at this time is just
straight blend, but will need to re-evaluate this potential to be colder in
the coming days.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday Morning)
ISSUED AT 559 AM CST Fri Feb 22 2019

Passing mid deck of clouds and some marginal MVFR fog will
decrease by mid morning, making for a MVFR day with east winds of
5-10 KTs. Then tonight, areas of rain and freezing rain will
advance from the southwest and overtake the TAF sites from
Midnight into the early Sat morning hours. CIGs and VSBYs will be
reduced down to MVFR levels, and CID/DBQ will have the possibility
of having a wintry mix of freezing rain and sleet adding to the
impacts again mainly after midnight. Strong LLVL winds streaming
up acrs the region will also add turbulence into the mix later
tonight, and have added low level wind shear(LLWS) to most TAFS
with strong 35-40 KT southeast flow 2000 FT AGL.    ..12..

&&

.HYDROLOGY...
Issued at 327 PM CST Thu Feb 21 2019

Moderate to heavy rainfall Saturday into Saturday evening combined
with temperatures above freezing will result in new rises on area
rivers.

With river levels already running higher than normal, flooding is
again possible either through runoff or break up ice jams.

&&

.CLIMATE...
ISSUED AT 327 PM CST Thu Feb 21 2019

Week 2...March 1st to March 7th

There has been a consistent signal indicating that another
significant arctic outbreak will affect the Midwest into early March.

The Climate Prediction Center has a high risk for much below normal
temperatures, especially low temperatures.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Winter Weather Advisory from midnight tonight to 9 AM CST
     Saturday for Benton-Buchanan-Delaware-Dubuque-Jackson-Jones-
     Linn.

IL...Winter Weather Advisory from midnight tonight to 9 AM CST
     Saturday for Carroll-Jo Daviess-Stephenson.

MO...NONE.
&&

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...McClure
AVIATION...12
HYDROLOGY...08
CLIMATE...08


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