Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 231140
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
640 AM CDT Sun Apr 23 2017

.AVIATION(12Z TAFS)...Southward moving cold front over northern
Wisconsin still on track to accelerate southward down Lake
Michigan and affect southeast and east central WI from late
morning through the afternoon. NAM guidance showing some low
clouds developing in surge of cold air behind front, but other
guidance remains drier in low levels. Low level convergence looks
weak so for now, wl hold off on introducing any low cigs in the
east later this afternoon. Otherwise VFR conditions to continue.

&&

.PREV DISCUSSION... (Issued 335 AM CDT Sun Apr 23 2017)

SHORT TERM...

TODAY and TONIGHT - Confidence...Medium to High.

Light winds has allowed temperatures to fall into the mid to upper
30s over parts of CWA.  Will continue to mention patchy frost threat
early this morning.  Temperatures will warm quickly after 12z into
the 40s and 50s.

Focus for today is backdoor cold front/pneumonia front that will be
sweeping southward across eastern CWA from mid-morning through early
afternoon.  GFS now in much better agreement with other short term
guidance in bringing this front southward at an accelerated pace
today.  Surface front currently over northern WI extending east
across southern Upper Michigan.  3 hour pressure rises of 1-2mb are
located upstream over northern MN in response to low pressure system
moving eastward across southern Canada.  1028mb High pressure
building in behind this low pressure will continue to push this
front southward across northern Lake Michigan through mid-morning.
Ahead of the front, west breezes will allow temperatures to warm
well into the 60s across all of southern WI this morning. Lake
Michigan surface temps are estimated to be in the 40-45 degree
range.  This will cause a large gradient in ambient temperature by
late morning across eastern WI.  This differential heating and
reduced overlake friction will contribute to the southward sagging
cold front accelerating southward across southeast WI and southwest
Lake Michigan. Both WRFNMM and WRFARW show this acceleration with
the front passing through the Sheboygan and Port Washington areas
between 15Z and 17Z. Then reaching the Milwaukee area from 18Z to
19Z, and Racine and Kenosha between 20Z and 22Z. Lakeshore areas
will cool dramatically once the wind shifts and increases to 10 to
15 knots for several hours. One to two hour temperature falls of
10 to 20 degrees will be likely, reaching the pneumonia front
criteria in many locations.

Not impossible some low clouds may accompany frontal passage in
eastern areas this afternoon, but low level convergence looks fairly
low.  For now wl continue partly to mostly sunny conditions. Western
CWA will enjoy a mostly sunny and warm day with daytime temperatures
topping out in the upper 60s to middle 70s.  By late afternoon, the
surface cold front should be in the vicinity of Madison.

Cooler temperatures will return tonight with some eastern areas
likely falling back into the mid to upper 30s.  Will hold off on
frost mention at this point due to uncertainties and small potential
for clouds.

MONDAY - Confidence...High.

Zonal flow in the upper and mid levels will gradually back to the SW
by Monday afternoon as a weak shortwave moves through the area.
Closer to the surface, low pressure will develop over the Northern
Plains and pass to our west.

There will be some upper level moisture associated with the
shortwave on Monday afternoon, but the lower levels will be bone
dry. Mostly clear skies should allow temps to reach well into the
60s across much of the area, and even as high as 70 in some spots.
We should also see plenty of mixing in the afternoon, allowing
dewpoints to drop into the mid 30s in the afternoon. Finally,
winds out of the south will pick up as the low passes to the west
on Monday afternoon. This all puts temps, RH, and winds just shy
of Red Flag Warning thresholds. Additionally, fuel moisture is
forecasted to be just shy of Red Flag Warning levels. A Red Flag
Warning is not expected for Monday at this time, but given how
close we are to meeting the thresholds of all criteria, we will be
watching closely for any changes in the forecast

LONG TERM...

TUESDAY AND WEDNESDAY - Confidence...Medium.

A series of low pressure systems will pass through the region. The
models are in generally good agreement, with a broad upper level
trof sitting over the the western CONUS, ejecting a series of
shortwaves toward the midwest.

On Tuesday, weakly cyclonic flow will persist in the wake of the low
that will pass to our west on Monday, with the attendant cold front
remaining to our west, allowing for one more day of warm
temperatures. By Tuesday night, the cold front will begin to creep
into our region as another low moves northeast out of the
Southern Plains. This stronger low should pass through the Upper
Midwest on Wednesday. At this point, model solutions begin to
diverge a bit regarding the exact timing and placement of this
stronger low. Most guidance does show some limited instability
building in Wednesday morning, but this is very dependent on the
low track. Right now, it looks like southern Wisconsin will be on
the wrong side of the low track to see much instability. However,
if the low tracks a bit farther to the NW, we may see more
instability and greater thunder chances.

THURSDAY THROUGH SUNDAY - Confidence...Low.

Some precip on the back side of the low may linger into Thursday
morning, while northerly winds will help drop temps into the mid
30s. Therefore it looks like we may see some snow mix in with any
rain. After a quiet day on Thursday, the models begin to diverge
pretty drastically. The GFS and Euro take a deep low from the
Southern Plains into the Upper Midwest over the weekend while the
Canadian has high pressure over the region. Needless to say, the
forecast confidence is quite low due to these differences.

AVIATION(06Z TAFS)...

VFR conditions tonight through Sun AM. There are small chances of
low stratus along a backdoor cold front that will sweep swwd from
ern WI into south central WI for the afternoon and evening hours.
Patchy MVFR fog may develop early Mon AM over portions of se WI
away from the lake.

MARINE...

Backdoor cold front will sweep across southern Lake Michigan from
late morning through mid-afternoon.  Westerly winds of 5 to 10 knots
through mid-morning will abruptly turn north to northeast and
increase to 10 to 15 knots with gusts to 20 knots for several hours.
Timing has front moving through Sheboygan area around 15-16Z, Port
Washington 16-17Z, Milwaukee 18-19Z, and Kenosha 21-22Z.  Gustiness
will settle down tonight as weak high pressure builds southward
across Lake Michigan as the winds remain NNE.

FIRE WEATHER...

Both today and Monday will present fire weather hazards. Today,
temperatures are expected to reach into the 70s across much of the
CWA and RH values to fall into the 20s. Additionally, the fine fuel
moisture code (FFMC) will be just below 90. This puts temps, RH,
and the FFMC just shy of Red Flag Warning criteria. Fortunately,
winds will be generally weak, and we`re also expecting a push of
cold air surging down Lake Michigan this afternoon cooling
temperatures quite a bit in our northeast and along the lake,
further limiting fire weather hazards in those areas. Fire weather
hazards will be greater on Monday, when we`re expecting very
similar conditions to today, but winds reaching near 15kts and
gusting to 25kt. A Red Flag Warning is not expected for Monday at
this time, but given how close we are to meeting the  thresholds
of all criteria, we will be keeping an eye on it.

&&

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

$$

Update...MBK
Today/Tonight and Aviation/Marine...MBK
Monday THROUGH Saturday...BSH



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