Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 191707
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1207 PM CDT Tue Sep 19 2017

.AVIATION(18Z TAFS)...Lingering influence of low level
anticyclonic flow will maintain a favorable fetch off the lake to
support the continuation of stratus/cumulus and some fog
development overnight. MOS is leaning a smidge more towards a
stratus scenario than dense fog while SREF vsby prog says a better
shot at some sub 1 mile vsbys in the eastern counties more towards
KUES. Meso models are keying on the eastern portion of the CWA
for more of the fog development, which makes sense given the more
slack gradient will reside there longer. Shower and thunderstorm
potential is proggd to stay largely to our west and northwest
overnight and then best chances on Wednesday/Wednesday evening
appear to be in the 20-03z time frame as a frontal boundary
approaches.

PC

&&

.PREV DISCUSSION... (Issued 917 AM CDT Tue Sep 19 2017)

MARINE...Weak pressure gradient across the area with surface
ridging extending from northeast WI into northern lower MI. So
this sets up an overall weak onshore flow. Southerly winds will
pick up on Wednesday as a trough of low pressure.

PC

PREV DISCUSSION... (Issued 652 AM CDT Tue Sep 19 2017)

UPDATE...

AVIATION(12Z TAFS)...

May see a period of lower clouds come in from the east this
morning, with a surge of deeper low level moisture. Still hard to
tell what is going on over the lake at the moment, due to
extensive high cloud cover. If low clouds do move in, there
should be an improvement in ceilings by late morning and early
afternoon due to daytime mixing.

There could be a few more showers in the southeast this morning,
but this activity will wind down by late morning as the currently
overhead shortwave moves on. Dry weather is then expected for the
remainder of the day and tonight.

PREV DISCUSSION... (Issued 327 AM CDT Tue Sep 19 2017)

SHORT TERM...

Today And Tonight...Forecast Confidence Is High.

A shortwave overhead early this morning will exit to the east by
late morning. Shower chances will hang on in the southeast this
morning until the wave departs. There should be gradually
decreasing clouds behind the wave, allowing temperatures to warm
back to a few degrees above normal most places by the afternoon.

The pressure gradient will tighten overnight between departing
high pressure and the next approaching trough, resulting in winds
not dropping off much tonight. There will likely be an increase in
clouds from the west later in the night too. Opted to keep out
mention of fog due to the winds/clouds. Temps will stay on the
mild side too, with well above normal lows expected.

Wednesday Through Thursday Night...Forecast Confidence Is Medium.

Models are in decent agreement with showing the south
southwesterly low level jet shifting across the area Wednesday,
before weakening Wednesday night. Warm air advection continues
across the area as well Wednesday morning, keeping the warm
airmass in the area during the afternoon. The cold front and
associated low level frontogenesis response slide east into
western portions of the area Wednesday afternoon, then into the
rest of the area Wednesday evening. Not much support for upward
vertical motion aloft.

Area forecast soundings show a good amount of elevated CAPE over
the area Wednesday into Wednesday evening, above a fairly strong
cap. It may be tough for mean layer parcels near the surface to
break cap and persist. The low level jet may give the best
chances for storm development. Deep layer bulk shear is 25 to 30
knots at best, which combined with the elevated CAPE may bring
some stronger storms with hail. For now, continued the chance PoPs
for showers and thunderstorms for Wednesday into Wednesday night.
A warm and rather humid period is expected.

High pressure will pass by to the north Thursday, which should
bring drier air into the area. There is still some gradual warm
air advection during this time over the region. The low level jet
is west of the region as well. Not much forcing for upward
vertical motion seen aloft.

GFS and Canadian models seem to want to generate showers and
storms with the surface warm front Thursday, which then slides
north across and north of the area Thursday night. There is a good
amount of elevated CAPE, but a large cap exists. Given a lack of
good upper level support and a fairly strong cap, went dry for
Thursday into Thursday night over most of the area. Warm and humid
conditions should continue over the area.

LONG TERM...

Friday Through Monday...Forecast Confidence Is Medium.

Models continue to agree with the amplified 500 mb ridge over the
eastern part of the country lingering Friday into Sunday night.
Thus, most of the low pressure systems miss the area to the
northwest. This should keep southerly winds over the region Friday
into Sunday night, with dry conditions expected. Warm and humid
conditions are expected to remain over the area during this
period.

The ridge weakens just enough to allow for low pressure and an
associated cold front to slide eastward into the region Monday.
This should bring the next decent chances for showers and
thunderstorms. Warm conditions should remain during this period.

AVIATION(09Z TAFS)...

May see a period of lower clouds come in from the east this
morning, with a surge of deeper low level moisture. Hard to tell
what is going on over the lake at the moment, due to extensive
high cloud cover. If low clouds to move in, there should be an
improvement in ceilings by late morning and early afternoon due to
daytime mixing.

Lingering showers will exit the southeast by late morning as the
currently overhead shortwave moves on. Dry weather is then
expected for the remainder of the day and tonight.

MARINE...

Southerly winds will increase on Wednesday ahead of approaching
low pressure. Gusts and resultant waves could approaching or reach
Small Craft Advisory levels.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$
Today/Tonight and Aviation/Marine...DDV
Wednesday THROUGH Monday...Wood



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