Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 231454 CCA

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
951 AM CDT Fri Mar 23 2018


23.12z NAM has backed off on precipitation across our southwest,
now only bringing 0.25 inches of liquid equivalent into far
southwest Lafayette County. 23.13z RAP and HRRR solutions are also
farther west with the precipitation through 06z Saturday, and the
HiRes ARW core keeps the precipitation completely out of our
area. Given this, no plans to introduce winter weather headlines
at this time. Will continue to evaluate the 12z model suite over
the next few hours, but trends at the moment are pointing towards
a less impactful event for our southwestern forecast area.


Winds have turned onshore this morning, and will remain so into
this weekend. Speeds will increase, with gusty conditions
developing tonight and persisting over the weekend. This will build
wave heights tonight, with high wave action continuing into Sunday.
A Small Craft Advisory remains in effect during this time.


.PREV DISCUSSION... (Issued 626 AM CDT Fri Mar 23 2018)

UPDATE...Small area of mid-clouds advanced into far western CWA
last several hours but has since thinned and dissipated. Upstream
high clouds spreading rapidly east across the northern Plains.
These clouds should spread across southern WI later this morning
and afternoon.

AVIATION(12Z TAFS)...VFR conditions expected for bulk of the
forecast. MVFR ceilings and possibly IFR will accompany snow over
southwest CWA later tonight into Saturday morning.

PREV DISCUSSION... (Issued 320 AM CDT Fri Mar 23 2018)

Today - Confidence...High.

Another quiet and cool day lies ahead due to upstream short wave
ridging and persistent dry air flow in the low to mid levels.
Expect to see increasing mid-high level clouds later today due to
increasing warm air advection spreading into the IA/MN area ahead
of short wave energy. Onshore winds will keep lakeshore areas a
few degrees cooler today, mostly in the upper 30s. Inland areas
should climb into the low to mid 40s.

Tonight and Saturday - Confidence...Medium to High.

Shortwave ejected from base of long wave trof over the eastern
Pacific will strengthen and sharpen as it moves across the central
Plains tonight and Saturday. The strengthening will be helped
along as it moves across a tightening baroclinic zone that will
be draped across the central Plains into the mid-MS Valley region.
Short term model guidance remains in good agreement on carrying
shortwave and 85H level circulation across southern IA tonight and
across central IL on Saturday. 70H circulation moves from NW IA
to around the Quad Cities late tonight and Saturday as well. Left
entrance region of upper jet favors strong synoptic forcing
remaining just to the southwest of southern WI during this period.
Column precipitable water increases to 0.5 to 0.75 inches in the
tri-state area of WI/IA/IL. Impressive layer q-vector convergence
of 20-30 units in the low levels remains just southwest of MKX CWA
but mid-level convergence of 20 units scrapes southern WI late
tonight into Saturday morning. The problem remains the increasing
low level easterly winds feeding drier air into the low levels of
this enhanced forcing. Typically, computer models do not handle
this influx of drier air all that well. 00Z ECMWF and CMC picking
up on this and has cut back severely on QPF. Meanwhile NAM and
GFS remain more consistent on 0.1 to 0.5" QPF falling in the
southwest corner of CWA, mainly from 06Z-18Z Saturday. Model
Certainty comparison continues to increase confidence in these
amounts in the SW CWA. Hence, will continue to use around 10 to 1
SLR to generate 1 to 5 inch snowfall potential in the southwest
CWA, focused on Lafayette, Green and Iowa counties. Due to
uncertainty with dry air inflow, will hold off on issuing Winter
Weather Advisory for Lafayette county for now, and will let
dayshift get one more look at dry air intrusion potential. Snow
will likely linger for a time in the far southwest on Saturday
before possibly changing over to light rain before ending.

Saturday night through Monday - Confidence...High.

Surface high pressure maintains control over our weather regime.
Mid/high level clouds will be on the increase, particularly later
Sunday into Monday. Temperatures will be seasonably cool Saturday
night and Sunday, warming to above average on Monday.

Monday night through Tuesday Night - Confidence...Medium.

00z suite of model output offers no major changes to the
forecast. There are indications of a bit more in the way of most
unstable and mixed layer CAPE to support adding a mention of
slight chance thunder. High precipitable water air supports going
forecast of 0.5" to 1" of rainfall. Above average temperatures are

Wednesday onward - Confidence...Medium.

Mainly dry conditions are expected. Temperatures will be at/just
above average.

VFR conditions expected for most of this forecast period. MVFR
ceilings will likely accompany a period of snow in southwest CWA
tonight into Saturday morning but the lower ceilings should remain
southwest to south of KMSN. Gusty east winds will develop tonight
and persist into Saturday.

Light northwest winds will turn onshore this morning as surface
high pressure ridge slides slowly off to the east. A gradually
tightening pressure gradient between this high pressure ridge and
developing low pressure in the central Plains will result in gusty
onshore winds developing tonight and continue through the
weekend. The onshore winds will cause wave heights to build and
should remain elevated into Sunday. A Small Craft Advisory has
been posted from later tonight into Sunday.


LM...Small Craft Advisory from 10 PM this evening to 1 PM CDT Sunday
     for LMZ643>646.



Today/Tonight and Aviation/Marine...MBK
Saturday THROUGH Thursday...Gagan is the U.S. government's official web portal to all federal, state and local government web resources and services.