Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 201741
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1241 PM CDT Thu Apr 20 2017

.AVIATION(18Z TAFS)...

Low pressure will continue to push off to the east, but ample low
clouds associated with the low remain well upstream of southern WI.
Models in good agreement showing the low clouds lingering at least
through the night, though there are some differences regarding
just how quickly clouds clear out Friday morning. Most guidance
keeps cigs at all TAF sites just above 2kft through the night.
That said, IFR cigs will be just to the north. At this time, I do
not expect IFR cigs to reach as far south as the TAF sites, but
given the proximity of potential IFR cigs, will have to keep an
eye on cigs through the night.

The center of the low has moved out of the area, so winds have
picked up. While gusts will fall off overnight, the pressure
gradient will remain tight, resulting in sustained winds around 10
kts through the night.

&&

.PREV DISCUSSION... (Issued 1045 AM CDT Thu Apr 20 2017)

UPDATE...

Previous forecast remains largely on track. Tweaked temperatures
slightly to account for frontal placement, but still expect the
far SE to get into the 60s while the rest of the CWA stays in the
50s.

MARINE...

Low pressure currently over the CWA has caused winds to calm over
the nearshore waters. The low will move off to the east later this
morning, causing winds to turn offshore and quickly increase. SCA
conditions, mainly winds, will return later this morning and into
the afternoon, before diminishing through the night as the low
moves out of the region and the pressure gradient weakens.

PREV DISCUSSION... (Issued 731 AM CDT Thu Apr 20 2017)

AVIATION(12Z TAFS)...

IFR CIGS and some fog cover all but far southern Wisconsin early
this morning. This is due to a weak pressure pattern under low
pressure moving across southern Wisconsin. Once the low moves
east later this morning, increasing westerly wind will improve
conditions to MVFR levels by early afternoon. These clouds will
then linger through a good portion of tonight with clearing
moving in from west to east later tonight.

PREV DISCUSSION... (Issued 254 AM CDT Thu Apr 20 2017)

TODAY AND TONIGHT...Forecast confidence is high.

Low pressure will track across southern Wisconsin this morning,
exiting to the east by noon. Any lingering rain will end by early
to mid morning. Cooler and drier air will filter into the area in
the wake of the exiting low. The southeast won`t see this cooler
air as quickly and should still be able to achieve highs in the
mid 60s. Look for gusty westerly winds by afternoon. High pressure
building in tonight brings us clearing skies and lows in the mid
to upper 30s.

FRIDAY THROUGH MONDAY - Confidence...Medium
Cyclonic flow will persist Friday with positive tilt 500 millibar
trough passing Friday night. Expecting this feature to come
through dry due to dry column and lack of any lower level
features. Mid level ridging and influence of lower level surface
high will then dominate over the weekend with quiet weather
expected. By Monday we should see our winds turn more southerly
ahead of an approaching low pressure system in the Plains. The
models keep the precipitation with this system to our west but the
warmer flow ahead of this feature will boost temps.

MONDAY NIGHT AND TUESDAY - Confidence...Medium
The low will lift to our west and north this period. A strong 850
LLJ will translate eastward across the area. On Monday night
there will likely be a combo of waa/moist advection with some DCVA
associated with the arrival of a slightly negatively tilted mid
level shortwave. This should lead to shra/tsra chances. Some
lingering cold frontal shower potential may continue into Tuesday.

TUESDAY NIGHT AND WEDNESDAY - Confidence...Low
Weak ridging is expected for a time Tuesday evening. Some
uncertainty with respect to evolution of next low riding northeast
out of the central Plains. The 00z GFS and 12z ECMWF both showed
mid level energy riding northeast with a surface low tracking to
our south. A decent shot of rain would arrive Wednesday in this
solution. However the GEM shows a higher amplitude pattern with a
trough out west and a large ridge holding sway in the center of
the country. This would keep the dry look intact this period. And
now the 00z ECMWF has come in showing a drier look for Wednesday.
Given the uncertainty in this scenario will ride with the blended
guidance at this point.

AVIATION(06Z TAFS)...The main window for the showers and thunderstorms
should be until around 10z Thursday from west to east across the
area. Ceilings and visibilities may drop down to below alternate
minimums in any stronger storms, along with a risk for small hail
and gusty winds.

Some showers and isolated storms may linger until 13z or so in
the east, before moving out of the area. Low ceilings to IFR
category are possible late tonight into Thursday morning.

There should be a period of low level wind shear across the area
from around 09z to 13z Thursday, with southwest winds around 40 to
45 knots at 2000 feet above ground level. This is borderline to
mention in TAFs, with surface gusts approaching 20 knots at times.

Surface winds should gradually veer to southwest by later tonight
into early Thursday morning. Winds should then veer west behind a
cold front later Thursday morning into the afternoon. Gusts to
around 25 knots are expected in the afternoon.

MARINE...Increasing westerly winds in the wake of a passing low
pressure system will bring small craft advisory conditions
through tonight.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 4 AM CDT Friday for LMZ643>646.

&&

$$

Update...BSH
Today/Tonight and Aviation/Marine...Davis
Friday THROUGH Wednesday...Collar



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