Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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535
FXUS63 KDVN 250602
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
102 AM CDT Thu Apr 25 2019

...06z AVIATION UPDATE...

.UPDATE...
Issued at 935 PM CDT Wed Apr 24 2019

Added fog to the forecast for late tonight into early Thursday
morning, roughly over the SW two-thirds of the forecast area where
dewpoints are in the lower 40s to lower 50 F. Winds overnight
will be light and variable under an area of high pressure thereby
promoting low-level saturation.

GOES microphysics imagery showed stratus clouds from Iowa City to
Macomb and points to the southwest. These clouds may expand
northward overnight, transitioning into areas of fog late as
temperatures cool. Hi-res models are aggressive on potential for
dense fog and it`s something we`ll have to keep an eye on tonight.
As of 930 PM, fog has yet to form in our area. The closest dense
fog observation is to the south, with the visibility down to 1/4
mile in Pittsfield, Illinois.

&&

.SYNOPSIS...
Issued at 316 PM CDT Wed Apr 24 2019

While today certainly is not particularly hazardous as far as
current weather goes, it`s certainly fraught with challenging
details, including chaotic flow,  low clouds, high based narrow
swaths of measurable rain, and daytime light fog. This is resulting
in an afternoon improvement from a wet dreary day to one that may
still be quite pleasant in some locations in the west, south, and
east, while the north central, near the Mississippi River, remains
sunny, and has been in the lower to mid 60s since Noon. The weak low
level flow around this high based vort has certainly created this
chaotic flow, as it allowed the weak precipitation process to
saturate the initially dry mid levels. The shallow stratus has only
been found on the northwest flank of any rain, likely favored there
as the cool moist low levels to the southeast of it have been
advecting into that region all day. Now that rain processes have
moved to the east, that support mechanism should break down and
allow clearing.

&&

.SHORT TERM...(This Evening through Thursday)
ISSUED AT 316 PM CDT Wed Apr 24 2019

Clearing conditions should be the trend this evening, with some
potential for stratus and mid clouds to hang on in the southwest and
south, possibly through the night, as the flow increases from the
south tonight. Lows tonight are challenging with cloud cover, and
may vary from mid 40s northeast to upper 40s central and west.
Tomorrow, the cold front should move through from west to east, from
mid morning to mid afternoon, with a wind switch initially seeing the
main impact. Saturation appears mainly post frontal, with showers in
the cooler air, most likely light. This band of showers should be
less than a tenth of an inch in most areas. There is a low chance of
reaching convective temperature prior to the front hitting in the
southeast, and for those locations, I have added an isolated thunder
risk during the afternoon. This is a low threat, but at least is
hinted at by the Namnest and extended RAP model runs. Convective
temperatures of the mid 70s are possible, but clouds may keep that a
low threat.

Otherwise, look for mid 60s to lower 70s highs from west to east.

.LONG TERM...(Thursday Night through Wednesday)
ISSUED AT 316 PM CDT Wed Apr 24 2019

Weather pattern will turn quite active over the weekend and into
next week. The potential for heavy rainfall is very real. However,
there is considerable uncertainty on where and how much rain could
fall.

Thursday night
Assessment...medium to high confidence

The cold front will exit the area and rain will end along and east
of the Mississippi during the evening hours. Strong winds
immediately behind the front are very possible during the early
evening hours. Dry conditions are then expected after midnight.

Friday and Friday evening
Assessment...high confidence

Quiet, dry but windy conditions will be seen on Friday with
temperatures at or slightly below normal. Although soil conditions
are quite moist, humidity levels will become quite low late Friday
morning and afternoon which may result in an enhanced fire risk for
any grassy areas that have not yet greened up.

Late Friday night through Saturday
Assessment...high confidence on a storm system affecting the area.
Low to medium confidence on placement of and rainfall amounts.

The first storm system with the potential for heavy rain will move
through the Midwest. The models have been somewhat consistent with
this storm system in placing the heaviest rainfall from the MN/IA
border into southern Wisconsin. However, recent GFS runs have
trended slightly further north while the FV3 has trended slightly
south. Regardless of the model solution all models have been
pointing to Saturday as when the main rainfall will occur.

The model consensus has slight chance to chance pops late Friday
night and likely to categorical pops on Saturday.

Saturday night on...

Saturday night
Assessment...medium to high confidence

The early weekend storm system will exit the area Saturday evening
followed by dry conditions late Saturday night.  The model consensus
has slight chance to chance pops for Saturday evening.

Strong winds Saturday evening will usher in much colder temperatures
with a risk of freezing temperatures in the highway 20 corridor.

Sunday
Assessment...medium to high confidence

The cold front that moved through the area with the weekend storm
system will begin moving back north toward the area on Sunday. The
model consensus has mainly dry conditions Sunday due to the dry
atmosphere over the area. Temperatures will average below normal.

Sunday night through Wednesday
Assessment...high confidence that two separate storm systems will
impact the Midwest. Low confidence on storm track and potential
rainfall amounts.

The global models are highly varied on timing and tracks of two
additional storm systems. Likewise the location of and rainfall
amounts are also highly varied.

The GFS takes both systems from the IA/MO border into northern
Illinois with heavy rain over the area.

The ECMWF as a stalled front further south and takes the first
system from Missouri into central Illinois with the second system
moving from western Iowa into Minnesota Tuesday night into Wednesday.

The CMC global takes two separate systems from the IA/MO border into
central and northern Illinois with heavy rainfall.

The FV3 takes the first system from Iowa to the IL/WI border. The
second system is much further south going from Missouri into
southern Illinois.

Given all these differences in track and timing, the model consensus
has chance to likely pops Sunday night and Monday, slight chance to
chance pops Monday night, chance to likely pops Tuesday and Tuesday
night, then chance pops on Wednesday.

Although there are rain chances from Sunday night through Wednesday,
it will not rain continuously. There will be periods of dry weather
the first half of next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
ISSUED AT 1255 AM CDT Thu Apr 25 2019

With sfc ridge overhead and light sfc winds, temps cooling to sfc
DPTs will promote fog into Thu morning at most of the TAF sites.
How dense and widespread is still uncertain, but areas south of
I80 the best chance for IFR to even LIFR fog and very low level
CIGs from the fog layer. BRL already on edge of fog and MVFR
stratocu, and will have to watch for light southerly flow in the
low levels ahead of an approaching front to push it north toward
MLI into early Thu morning. most fog should clear by mid Thu
morning, then eyes turn to a cold front switching winds to strong
northwesterly direction by mid to late afternoon. Some sctrd
showers and possibly a thunderstorm may accompany this frontal
passage, and post-frontal northwest sfc winds may surge to 15 to
25 KTS and gusty into Thu evening.

&&

.HYDROLOGY...
Issued at 1117 AM CDT Wed Apr 24 2019

The Mississippi is currently rising from LD11 down to LD15. The
river will begin rising again on Thursday from LD16 down to LD17.
Downstream of LD17 the river will begin rising again Friday into
Saturday.

The new forecasts for the Mississippi have slightly lower crests
from LD11 down through LD17.

HOWEVER, the current 7 day Mississippi forecast does not, repeat,
does not take into account predicted rainfall from Friday through
Tuesday. The weather forecast models are suggesting the
possibility of heavy rainfall.

Depending upon where and how much rainfall occurs crest timing and
crest forecasts are subject to change. If the rain occurs on or
just ahead of the crest then crest forecasts have the potential to
go higher than forecast.

The weather models are suggesting the heaviest rainfall from the
early weekend rain would occur from the IA/MN border into
southern Wisconsin. If this location is correct it would occur
behind the crest and would slow the rate of fall on the
Mississippi.

There is much more uncertainty regarding the second round of
potential heavy rain late in the weekend and early next week. The
weather models continue to offer different tracks for the storm
system and potential rainfall amounts.

Individuals with interests along the Mississippi are strongly
urged to pay attention to future weather and river forecasts over
the next week.

&&

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

$$

UPDATE...Uttech
SYNOPSIS...Ervin
SHORT TERM...Ervin
LONG TERM...08
AVIATION...12
HYDROLOGY...08



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