Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 131616

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1116 AM CDT Fri Apr 13 2018

Issued at 1113 AM CDT Fri Apr 13 2018

The forecast has been updated to lower temperatures north of the

Data through 16z indicates the warm front is probably close to its
northern extent of travel. Observations indicate northeast winds
are slowly increasing in strength. That strengthening combined
with cloud cover increasing and lowering in height should stall
the warm front.


Issued at 314 AM CDT Fri Apr 13 2018

988 MB surface low was located over north central KS early this
morning. A strong cold front with lake enhancement was pushing
through northern IL, but showing signs of slowing and becoming
stationary as the low level flow turns easterly on the cold side
of the boundary. The stationary front then extends roughly from
Peoria, IL to Fort Madison, IA on westward to low pressure over
KS. Strong moisture transport on potent 70 kt low level jet and
elevated instability currently aiding narrow banded convection
north of the stationary front from far southern MN and northern
IA into southern WI. Reports of small hail have been received with
this activity over northwest IA.

Overall, a complex and challenging forecast is on tap for the region
not only today but through the upcoming weekend, as a very dynamic
early spring storm swings through the central CONUS accompanied by a
variety of weather.


.SHORT TERM...(Today and Tonight)
ISSUED AT 314 AM CDT Fri Apr 13 2018

All sorts of challenges in this forecast over the next 24 hours (and
beyond too). Let`s start with the front and high temperature forecast.
As low pressure over KS shifts east today, the front will begin to
return back northward as a warm front. Just how far north will be
critical to the high temperature forecast for today. Current expansion
of pressure falls over the Missouri River Valley support short range
guidance on low translation toward southwest IA by evening. This would
be on a latitude supportive of keeping the warm front south of I-80.
Therefore, I have trimmed highs most areas north of I-80, but still
may need further lowering especially on the Hwy 20 corridor where
guidance continues trending cooler keeping highs in the 40s. Meanwhile,
south of the front temperatures should be near or above 70 degrees.
In between expect quite the thermal gradient of 15-20+ degrees over
20-40 miles making for a very challenging forecast either side of the
I-80 corridor. The next challenge is precipitation chances today.
In general, expect to be under some threat for precipitation all day
especially north of the warm front with veering low level jet and
attendant strong moisture transport, and increasingly diffluent flow
aloft. But, also anticipate the focus for precip to shift/develop to
our southwest by mid to late afternoon, as an upper level disturbance
lifts up into the region. Sufficient elevated instability and dry air
aloft exists for hail with the stronger cells, with a low risk of marginal
severe hail late this afternoon.

Tonight, low pressure will continue to shift toward the region from
the Missouri River Valley. Anticipate this warm/quasi-stationary
front to lay out south of I-80. Temperatures again will be quite the
challenge and have cooled most areas a few degrees north of I-80 with
readings dipping down into the 30s to near 40 degrees. Areas north
of I-80 may see some convection tonight, especially this evening with
any threat being hail. In addition some locally heavy rain swaths of
around an inch or more can`t be ruled out near and immediately on the
cold side of the boundary, as anomalously high moisture feed (PWATs
1.25-1.4 inches) is juxtaposed over tight low level thermal gradient
aided by lake enhancement. Meanwhile, south of the front temperatures
will only dip into the 50s. The airmass south of the front will be
sufficiently unstable and mixed through the low levels for some threat
of strong wind gusts potentially all night long, in addition to the
risk for hail. 0-3km shear vectors ahead of the convection are progged
to be from the SSW at 35-40 kts, thus any northeastward moving storm
or possible cell clusters could take better advantage of the
environmental shear and rotate. Will have to certainly be watchful for
any interaction of storms with the strong warm/quasi-stationary front.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 314 AM CDT Fri Apr 13 2018

Saturday...Latest 00z run models still showing some variances, but
in general they suggest an occluding sfc low and trof complex acrs
the IA/MO border region by 18z Sat, with the closed upper low center
still northwest of Kansas City. The sfc low will then look to energy
transfer to east central IL/west-southwest IN by mid Sat evening.
Prefer the 00z ECMWF sfc front placement acrs the southern third
of the DVN CWA as a happy medium from the further north GFS and
southerly NAM. Strong east to northeast sfc winds(probably close to
advisory levels at times, gravity wave induced gust enhancement)
will continue north of the boundary, and with cooler fetch will make
for a large temp contrast from north to south acrs the fcst
area...possibly upper 30s in the north to near 60 in the far
southeast. Expect ongoing band of elevated showers or rain north of
the boundary with enough elevated instability to keep embedded
thunder going through at least midday before the CAPEs/lapse rates
wane. Some storms still capable of at least small hail Sat morning
through midday, and the precip complex acrs the northern 2/3s of the
fcst area with ongoing TROWAL feed to produce generally from a half
inch to over three quarters of an inch additional rainfall by late
Sat afternoon in these areas, adding to the ponding of water and run-
off into creeks/rivers. More of a sctrd showery occurrence along and
south of the west-to-east oriented boundary acrs the southern third
of the CWA. Will keep precip all liquid form at the sfc anyway,
through 00z Sunday.

Late Sat afternoon and into the evening, synoptic scale placement of
mid level low suggests in-whirling dry slot from the southwest may
bring about a lull in the more organized precip acrs much of the
area for a period, allowing for drizzle or spotty lighter rain
patches. Then the closed upper low will look to slow roll east-
northeastward acrs IA, bringing about an associated def zone like
precip band in acrs the fcst area from the west. Chances are that
this band will dynamically cool into a mainly wet snow maker as it
arrives after mid Sat evening...possibly a mix of sleet and rain on
it`s leading edge. But some models, especially the colder BL and low
wet bulb zero feed of the 00z NAM breaks out a freezing rain event
for a a while, before the snow transition. For now with the
uncertainties, will have to throw in this freezing rain potential
along with some light icing, but this goes against climo and ground
temps to be marginal at best to support any ice glaze. The milder
GFS at the sfc, goes from rain straight to snow without much of any
ice or sleet. With low SLR`s and mild sfc temps, have come up with 1-
2 inches of snow accum by 12z Sunday morning northwest of the Cedar
Rapids area

Sunday...the upper low will continue to progress along and just
north of the DVN CWA, with ongoing mainly snow bands or showers
overspreading most of the CWA(except maybe less coverage/intensity
acrs the southern quarter to third)...another half inch to 1.5
inches of wet snow accums along and west of DBQ-Iowa City-Fairfield
IA by 18z...mainly in grassy/elevates surfaces. The snow to continue
eastward into the afternoon, with 0.5 to 1 inch of additional snow
accums along and north of I80 into northwest IL. Brisk north to
northwest winds of 15 to 25 MPH combined with the falling snow could
make for reduced visibilties and temporary low based drifting, but
wet nature of the snow/mild pavement temps during insolation again
may be a limiting factor. The NAM continues to produce some freezing
rain acrs portions of NW IL through mid morning, but low confidence
in this at this point and see more of a rain-snow-sleet transition
to all wet snow. High temps to be held down in the 30s in the north
and west, to the low 40s in the east/southeast. Most snow should be
exiting off to the east of the CWA by Sunday evening. True storm
total snow amounts very difficult to come by with all the variables,
but early thoughts are 1-3 inches across the northwestern third of
the CWA, with an inch or less to the east. The southeastern CWA may
not see much snow at all. A clear out and ongoing cold advection to
make for a seasonably cold night Sunday night...well down in the 20s
into early Monday morning.

Monday through next Thursday...Generally a below normal temp-regime
this period in the wake of the weekend cyclone. Both the 00z GFS and
ECMWF advertise some type of wave trying to undercut a mid CONUS
blocking ridge and produce some precip acrs portions of the area by
late Tue night into Wed. Depending on timing and how far north or
south this wave tracks, more precip-type issues/headaches may be
possible with this mid week system.   ..12..


.AVIATION...(For the 12Z TAFS through 12Z Saturday Morning)
ISSUED AT 613 AM CDT Fri Apr 13 2018

Localized MVFR/IFR conditions today most likely to impact DBQ and
possibly for a time at CID, with a few showers potentially nearby
at times as well. Tonight, expecting more widespread MVFR to IFR
conditions in cigs and/or visibilities with showers and storms
as a frontal boundary remains situated across the region and a
storm approaches the area. The stronger storms will have the
potential for hail, with gusty winds possible at BRL. Have kept
mention of LLWS at most sites this morning and again for tonight
with potent low level jet.




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