Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 220148
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
848 PM CDT WED SEP 21 2016

.UPDATE...Showers and thunderstorms have continued to regenerate
and affect portions of Sauk, Columbia and Marquette counties
during the evening. Some locations in these counties received 2 to
3 inches earlier today, and an additional 1-2 inches has fallen in
parts of the counties this evening near/over the same area.
Vigorous upstream short wave over northwest IA expected to move
northeast into central WI overnight. With upstream convection over
northeast IA expected to lose its severity but track northeast and
low level frontogenetical forcing expected to line up across
central WI, went ahead and issued an Areal Flood Warning for these
three counties until around 13z Thursday. May not get flash
flooding, but expect more gradual urban and rural flooding
expected from the prolonged and persistent moderate to heavy
rainfall. General ponding or buildup of water in low-lying, flood
prone areas as well as small creeks and streams is expected. Will
keep Flash Flood Watch going as is for now.

&&

.AVIATION/06Z TAFS/...Expect bulk of showers and storms to remain
north of TAF sites tonight but possible a few could sneak into the
TAF vicinity. Better chance later Thursday into Thursday night for
more widespread showers and storms returning. Mostly VFR
conditions expected into Thursday.

&&

.MARINE...Showers and storms likely to affect northern marine
zones overnight with decreasing chances farther south. Few gusty
winds are expected with storms, but should remain below 33 knots.

Expect north to northeast winds to become more southeast overnight
and remain mostly 5 to 15 knots. Main concern is burst of winds
associated with passing back door cold front sagging south through
near shore waters Thursday night. Northeast wind gusts could
approach Small Craft Advisory levels.

&&

.PREV DISCUSSION... /Issued 317 PM CDT WED SEP 21 2016/

SHORT TERM...

TONIGHT - Confidence...Medium

LLJ will continue to impinge on 850 baroclinic zone situated across
southern Minnesota into wrn WI. Surface warm front across central WI
with MCS modified cooler airmass/outflow to our southwest. In
addition water vapor/models show shortwave energy riding northeast
from the Plains. Some divergence associated noted tied to upper jet
riding nearly west/east across US/Canada border. This will result in
the continuation of tsra development through the night. Ongoing
convection traversing the Flash Flood watch area in the northern
CWA. The latest meso progs develop more of a line deeper into the
night but they have trended this further south into the axis of
better MLCAPE that is set up to our west. Rather impressive buildup
of CAPE across parts of central Iowa with temps into the 90s/dew
points in 70s. Looks like the best 850 forcing will be across the
northern CWA closer to better baroclinicity and surface warm front.
The stronger line that draws closer to WI later in the night may end
up diving more across ern IA where aforementioned surface based
instability/instability gradient is better aligned. However still
expect potential for elevated activity to traverse parts of the area
and perhaps weaker linear system arriving later. The better focus
for training storms tied to LLJ looks better set up where the Flash
Flood Watch is in place. So see no need to expand this any further
to the southeast at this time.

THURSDAY - Confidence...Medium

LLJ and shortwave are proggd to shift east by afternoon. A surface
trough/boundary takes shape across central Wisconsin and this shifts
south during the day. Southwest 850 winds maintain gradual waa.
While primary shortwave shifts east by midday there are
indications that additional ripples in the flow will be possible.
Consensus of meso progs suggests northern/western CWA stands by the
best potential for seeing the better precip. Temps again tricky
given precip, cloud, boundary positions so for now stayed pretty
close to blended numbers.

THURSDAY night and Friday...Forecast Confidence...Medium

The upper zonal flow begins to break down as a ridge builds over
the northern plains and the strong jet across the upper great
lakes moves east. Upper level divergence and 700 mb upward motion
weakens by midnight. Deep moisture will remain in the low levels
through 700 mb. 850 mb winds weaken with the strong low level jet
well west across the plains. zero to 1 km mixed layer CAPE
diminishes and is around 500 Joules/kg mainly southwest of
Madison with the surface boundary just to the southwest. GFS QPF
is rather light.

Friday night and Saturday...Forecast Confidence...Medium

The upper ridge builds across the Upper Mississippi River Valley
as a strong trough moves into the Rockies area. Little in the way
of upper divergence with 700 mb upward motion increasing Saturday
afternoon.

700 mb RH decreases but 850 mb moisture remains. the low level jet
weakens as it moves east toward the Mississippi River valley.

Surface dewpoints rise over south central Wisconsin. Little in the
way of precipitation on the GFS until Saturday afternoon, west of
Madison.

LONG TERM...

SUNDAY THROUGH Wednesday...Forecast Confidence...Low

The GFS and ECMWF all have a trough over the Central U.S, but the
GFS cuts of an upper low earlier and much farther north. Both
models take a band of moderate to heavy precipitation across
Southern Wisconsin Sunday. Then the surface pattern diverges with
the GFS bringing a dry slot into the area, while the ECMWF
continues the potential for moderate to heavy rainfall with a
strong surface low pushing north from the mid Mississippi valley
into Eastern Iowa and towards the northern plains. By wednesday
both the GFS and ECMWF are fairly dry.

1000 to 500 mb Thickness values are quite low with much cooler
temperatures expected.

AVIATION/00Z TAFS/...

Patchy MVFR cigs noted but by and large
expecting VFR conditions to prevail. Expecting an active period to
persist into Thursday with several bouts of convection. Many of the
models focus the better action north or west of the TAF sites but
some models showing potential for another MCS to arrive in closer
proximity to TAF sites very late tonight or into Thursday
morning,but latest runs have the strongest portion of this line
shifting more to our south and west vcnty of surface instability
axis. At this time expecting only the usual potential for MVFR
cigs/vsbys associated with hvy rain/convection and nothing too
widespread.

MARINE...

Northeast winds are expected to develop thursday night and
into Friday which may reach or exceed Small Craft Advisory
thresholds.

&&

.MKX Watches/Warnings/Advisories...
WI...FLASH FLOOD WATCH through Thursday evening for WIZ046-047-051-
     052-056>058-062-063.

LM...None.
&&

$$

UPDATE...MBK
TONIGHT/Thursday AND AVIATION/MARINE...Collar
Thursday NIGHT THROUGH Wednesday...Hentz



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