Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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903
FXUS63 KDVN 231758
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1158 AM CST Thu Feb 23 2017

...AVIATION AND HYDRO UPDATE...

.UPDATE...
Issued at 1056 AM CST Thu Feb 23 2017

Have sent update to lower highs a bit most areas due to clouds and
northeast winds, with general range from the mid 40s to the
lower 50s. In addition, have fine tuned pops for the area of
light rain over far northeast MO into southeast IA (aided by 850
warm advection and upper level divergence) as it continues to
lift northward rest of today. Expect temperatures to drop into
the lower to mid 40s within the rain area... thus highs may still
be a bit warm far south. Will continue to monitor and update as
needed.

&&

.SYNOPSIS...
Issued at 330 AM CST Thu Feb 23 2017

If yesterday felt like mid May, today will feel like mid November.
As of 2 AM, cold advection with stratus is filling in in roughly
the northwest 1/2 of the CWA, and this should continue to spread
clouds and chilly northwest winds over the entire area by sunrise.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 330 AM CST Thu Feb 23 2017

While winter headlines are ruling the forecasts to the northwest of
the CWA, our forecast will be dominated by elevated thunder
potential through tonight. The low levels will continue to cold
advect through the day, and under cloud cover this morning, this
means we`ll be stuck in the lower to mid 40s through much of the
morning. There is some potential that as winds switch to the
northeast later this morning, some temporary break up in stratus
could occur, and for this I have allowed for highs to climb back to
the lower to mid 50s in the south half, while holding in the upper
40s north.

By mid afternoon, the cyclone in the plains will rapidly develop a
strong warm front near our southern counties. Winds will increase to
15 to 25 mph northeast to east. The lighter winds will be found int
the far south, where we will have to watch for fog development due
to moisture convergence. There is not a clear signal that this will
develop yet, but could be added on an update this morning.

MUCAPE/ elevated instability will increase into the south this
afternoon, and spread over the entire CWA this evening. Forcing for
rain will increase and with stable low levels, stratiform rains are
likely, but there will certainly be bands of elevated showers and
thunderstorms moving northeast over the area. Some small hail
seems likely in stronger storms, and we can`t completely rule out
large hail producing storm, but that threat most certainly is
going to be isolated. Rainfall through tonight should be on the
order of 0.25 to 0.75 for most locations. The higher threat for
the totals over a half inch seem to be in the north half, well
north of the warm front. Though any convective cell tonight could
produce a quick 1/2 inch. Despite the strong northeast winds this
evening, conditions should continue to become moist at lower
levels, resulting in drizzle and possible fog. In short, this will
be a classic early spring system passing directly over the CWA.

ERVIN

.LONG TERM...(Friday through next Wednesday)
ISSUED AT 330 AM CST Thu Feb 23 2017

Friday...Assessing the latest 00z model trends, the GFS has trended
further southeast to the current and earlier ECMWF runs, with a sub-
995 MB sfc low placement toward the Ottumwa IA area by 12z Fri.
Both models then roll up the low in occluding fashion toward
southeast WI or southern LK MI by Fri evening. Both models have
trended more bullish with brisk llvl northeast flow producing
freezing rain or sleet soundings acrs the HWY 20 corridor west of
DBQ or even further south Fri morning, but with saturated profiles
and warm ground don`t quite buy it yet especially the freezing rain
and will keep it all rain for much of the day in the northwest for
now, except mid to late afternoon mixing with wet snow northwest of
DBQ and CID.

Will walk out embedded thunder out of the east by mid morning, with
in-whirling dry slot taking over the southeast half of the CWA.
Breezy and unseasonably mild conditions in the dry slot for a good
part of the day, while the northwest stays in cool stratiform precip
and little temp recovery from values at 12z Fri(mid/upper 30s to
near 40). With current accepted storm evolution path and strength
(mainly leaning toward the more consistent ECMWF), still feel bulk
of midday to afternoon convective re-development will blossom mainly
east/southeast of the DVN CWA. of course, if system continues to
trend a bit more southeast, lowering thicknesses and dynamical
cooling on it`s northwest flank may cause a quicker switch over to
wet snow in the northwestern CWA Fri afternoon with accumulations
possible, but mild ground temps and diurnal processes will battle
snow accums until later Fri night. Also a more wrapped up system
should pull back to the northwest closer to earlier GFS runs of the
past day or two. Convective feedback could also eventually be a
player.

Friday night...Bulk of the latest medium range solutions wrap in
robust cold conveyor into in-sweeping def zone from west-to-east
this period. Rain continues to switch over to wet snow, but
strength and QPF still varying quite a bit between the runs. The 00z
GFS is the wettest an furthest south with it`s snow algorithm going
with 1-2 inches along the I80 corridor by 12z Sat, 2-4 inches from
Hwy 30 to HWY 20, and 4-6 along the HWY 20 corridor west of DBQ.
the ECMWF`s algorithm is less than half the GFS, generally half
inch along I80 to near 2 inches in the northwest. The 06z NAM says 1-
2+ inches north of I80, and an inch or less south of I80. For now
with a general blend but closer to the ECMWF, will advertise total
snow amounts from late Fri afternoon through mid Sat morning when
the snow exits to the east, of 1 to 1.5+ inches of snow along and
northwest of a line from Fairfield IA...to Davenport...and to
Freeport in NW IL. Less than an inch to the south/east of that
line. 2 to 2.5 inches from west of Cedar Rapids, to northwest of
DBQ. Ongoing mild ground temps to be a player in true snow accums,
as well as strong northwest winds of 20-30 MPH Fri night which could
really reduce visibilties in heavier falling snow bands. Low temps
well down in the 20s by 12z Sat morning.

Saturday and Sunday...Snow exits Sat morning with near normal or
actually a bit below normal temps and continued raw breezy condtions
into the afternoon. If clear skies accompany passing ridge and over
fresh snow cover, guidance lows Sat night will be to mild. But then
return flow an back side of passing ridge to bring about some temp
recovery back into the upper 30s to low 40s on Sunday. The model
still varying on strength and precip amounts with overrruning
isentropic event along llvl baroclinicity later Sunday and into
Sunday night, with the ECMWF suggesting just flurries or light
rain/snow mix, and the 00z GFS producing 1-2+ inches of snow south of
I80 Sunday afternoon and evening.

Monday through next Wednesday...Model descrepancies continue for
lowered confidence next week, but the general idea is reloading west-
southwest flow acrs the mid CONUS for continued temp moderation.
Any WAA type system should be mainly rain during the day or a rain-
snow mix if commencing at night such as late Mon night into Tue AM.
Longer range indications suggest a stronger cyclone with a pre-
system warm draw into the mid part of next week.   ..12..

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
ISSUED AT 1158 AM CST Thu Feb 23 2017

Tricky aviation forecast this period with the chance of precip,
thunder, IFR and possibly LIFR cigs and vsbys. The next two to
four hours will be the best as far as flying goes through the next
24 hours. Heavy rain and thunderstorms are expected a cigs
decrease to IFR and LIFR tonight. Tomorrow a wind shift will occur
as cooler temps make their way into the area.

&&

.HYDROLOGY...
Issued at 1158 AM CST Thu Feb 23 2017

Forecast rainfall from the event today and tomorrow along with
routed flow north of the area will lead to rises on area streams
and rivers. The Iowa and Cedar rivers are forecast to see rises
that are dependent on forecast rainfall through this event.
Conesville and Marengo are forecast to reach flood stage this
weekend. With low confidence in total rainfall amounts, these
sites have been placed in a Flood Watch. Columbus Junction,
Wapello, Oakville and DeWitt are forecast to reach flood late this
weekend and into next week. With the low confidence in rainfall
totals and these rivers forecast to reach flood past 48 hours,
flood watches were not issued at this time.

Forecast rises on the Mississippi River are expected through the
period as routed flow moves through the system. Some of this flow
in contingent on rainfall through Saturday. Regardless of this,
the river is going up. Some sites could see flood warnings in the
next week or two.

As confidence increases in the potential for river flooding,
additional watches and warnings could be issued.

&&

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

$$

UPDATE...McClure
SYNOPSIS...Ervin
SHORT TERM...Ervin
LONG TERM...12
AVIATION...Gibbs
HYDROLOGY...Gibbs



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