Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 171700
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1200 PM CDT Thu May 17 2018

...18z AVIATION UPDATE...

.SYNOPSIS...
Issued at 310 AM CDT Thu May 17 2018

The latest sfc analysis was indicating a ridge of high pressure
continuing to occupy areas from the MO RVR Valley on eastward to
the southeastern GRT LKS(including the local area). A stronger
ridge was located just north of the GRT LKS, pushing a backdoor
cool front down acrs northern WI into the northeastern plains. To
the south, a weak closed upper low continued to gyrate acrs MO,
part of a Rex type block acrs portions of the central into eastern
CONUS. Generally a fair weather pattern will look to continue to
round out the week, before a wave breaks loose out of a western
CONUS upper trof and bring about the next chance of organized
precip for the second half of the weekend.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 310 AM CDT Thu May 17 2018

Today...The local area may just have rounds of cirrus filtering the
insolation at times, while sctrd instability showers and storms
continue under the closed upper low acrs MO. Fcst soundings suggest
another deep mixing day to at least H85 MB, making for widespread
highs in the low to mid 80s and sfc DPTs maintained down in the 50s.
Backdoor cool front/tightening high pressure gradient will squeeze
down the western GRT LKS and into the northeastern CWA by late in
the day, producing an uptick in northeast to easterly sfc winds acrs
the northeastern third or so of the local fcst area. Will keep the
fcst dry, although the 00z GFS wants to develop some precip on this
incoming lake fetch front acrs NW IL into far east central IA this
afternoon and early evening.

Tonight...The incoming east to northeast winds will continue to
overspread the area, with extent of the pressure gradient
maintaining them at 10-15+ MPH even into the overnight. Cooling
northeast fetch will make for lows down into at least the lower 50s
acrs portions of northwest IL by early Friday morning. As the closed
upper low acrs MO starts to gyrate eastward toward southern IL, a
few of the models want to try and whirl some sctrd showers and
thunderstorms on it`s north end, toward the southeastern CWA before
dawn Friday morning. For now, will bank on the strength of the LLVL
ridge jutting southwestward off the GRT LKS to maintain a dry fcst
through 12z Friday anyways. Widespread lows in the 50s, with varying
bouts of high clouds again, maybe some AC into the southeastern CWA
toward dawn.  ..12..

.LONG TERM...(Friday through next Wednesday)
ISSUED AT 310 AM CDT Thu May 17 2018

The weather pattern will turn active for late weekend and will
continue into next week. Temperatures should average slightly above
normal.

Friday and Friday night
Assessment...medium confidence

Quiet and dry conditions will be seen across the area Friday
morning. However, the models disagree as to what will occur Friday
afternoon/night. These differences can be traced to where each model
places an upper low in the Midwest.

The CMC global has the upper low near the IL/IN border. This
location keeps Friday afternoon dry with a risk of showers over the
far eastern areas Friday night. The GFS has the upper low over the
Missouri bootheel but generates considerably more precipitation
along and east of the Mississippi Friday afternoon/night. The ECMWF
has the upper low near the Ohio river in southern Illinois and keeps
Friday afternoon and night dry.

Based on these differences, the model consensus has slight chance
pops for rain showers east of the Mississippi Friday afternoon and
night.

Saturday
Assessment...medium confidence

Dry flow coming around the high over the Great Lakes should slow the
arrival of the next storm system. The model consensus has slowed
down the arrival of the system with Saturday now being mainly dry.

Saturday night
Assessment...low to medium confidence

The models generally agree that the next storm system will affect
the area the second half of the weekend. However, they differ in the
positioning of frontal boundaries across the area which will have an
impact as to how warm it will get.

A reasonable guess is that the frontal boundary will stall out
somewhere in the vicinity of I-80 given the cooler than normal Great
Lakes. Such a stall would set up an east west boundary with the
potential for some locally heavy rainfall.

Right now the model consensus has chance to likely pops Saturday
night with the highest pops after midnight and north of I-80.

Sunday on...

Sunday and Sunday night
Assessment...low to medium confidence

As mentioned in the Saturday night section, where the front stalls
will be important to the overall sensible weather. An I-80 stall of
the boundary would set up the potential for some locally heavy
rainfall as the surface low moves through the area.

Right now the model consensus has chance to likely pops Sunday with
slight chance to chance pops Sunday night.

Monday through Wednesday
Assessment...low confidence

The global models are offering different opinions in regards to what
will happen with the sensible weather. What the global models
loosely agree upon is that several weak upper level disturbances
will be moving through in the flow aloft, any of which could
generate diurnal convection.

As a result of these differences, the model consensus has a daily
slight chance to low chance risk of rain for the area. Of the three
days, Wednesday may have a better signal for a risk of showers and
thunderstorms.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
ISSUED AT 1157 AM CDT Thu May 17 2018

VFR conditions will be seen at all terminals through the TAF
period as high pressure over the northern Great Lakes slowly
moves eastward.

&&

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

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...08
AVIATION...Speck



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