Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 182000
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
300 PM CDT MON SEP 18 2017

.TONIGHT AND TUESDAY - Forecast Confidence...Medium.

Sct-bkn cumulus over Milwaukee county and points southward due
to lake convergence appears to be thinning and decreasing per
GOES-16 visible imagery.  Expect this trend to continue through the
afternoon.

Warm air and moisture advection during the night fairly weak over
southern WI, but does coincide for a time with enhanced synoptic
forcing from right entrance region of upper jet.  Hence need to
continue small chance pops during the overnight.  Elevated
instability marginal so wl hold off on thunder threat.

-shra threat wl continue into Tuesday but bulk of forcing wl
have slide off to the east.  Weak convergence and lingering
moisture may result in isolated -shra redeveloping.  Not alot
of confidence in this scenario however.  Also doubts about
lingering cloudiness into Tuesday afternoon as GFS showing
considerably less low level RH as opposed to NAM and ECMWF
solutions.

.TUESDAY NIGHT THROUGH THURSDAY - Forecast Confidence...Medium.

Short range guidance in reasonable agreement on weakening frontal
boundary sliding eastward into southern WI on Wednesday.  Will
further weaken and may end up stalling and transitioning to warm
front Wednesday night and Thursday as southerly low level jet
reenergizes over the upper midwest.  Best chance for more scattered
to numerous showers and storms during this period across southern WI
as front waves across the area.  Deep column moisture will be in
place with pwat values increasing to around 1.5".  GFS shows
elevated CAPE increasing to around 2000 j/kg with bulk shear around
30 kts.  Can not rule out an isolated storm approaching severe
levels Wed afternoon closer to approaching cold front but mid-level
synoptic forcing remains to the north of the area.

.EXTENDED PERIOD...

THURSDAY NIGHT THROUGH MONDAY - Forecast Confidence...Medium to High.

Medium range guidance in good agreement on nearly stationary high
amplitude weather pattern remaining across much of the CONUS for
this period.  Tropical systems meandering northward in the western
Atlantic will contribute to stationary pattern.  High amplitude
ridging will remain over southeast CONUS while long-wave trof
lingers over most of the west. Wisconsin will remain between these
two high amplitude systems with lighter southwest mid-level steering
winds.  Colder low level air associated with the upstream trof wl
remain to the west of southern WI through the period.  925H
temperatures remain mostly in the 20-25C range.  Not expecting
extensive low to mid level rh and resultant cloud cover.  Hence at
least partial sunshine and southerly winds should contribute to
daytime temps warming into the 80s but occasional lake breezes will
contribute to cooler temps at times by Lake Michigan.  Lake Michigan
water temps have cooled into the 65-68 degree range.  Dry conditions
are expected for much of the period resulting in abnormally dry
conditions possibly expanding across southern WI.  Drought monitor
available at droughtmonitor.unl.edu.  High temps should remain a few
degrees below record levels, but will need to keep an eye on those
record high minimums.

GFS 5-day 500H anomolies has downstream positive anomoly and
upstream negative anomoly slowly weakening to cooler zonal or
broadscale upper troffing across the upper midwest by 29/00z.

&&

.AVIATION(21Z TAFS)...Latest GOES-16 visible imagery showing sct-bkn
MVFR cigs over Milwaukee county, south toward KENW slowly decreasing
as low level winds become more easterly and decrease.  Also cigs not
making much progress inland due to mixing of drier air farther
inland.  Would expect this decreasing trend to continue next few
hours.  Otherwise, expect mid-high clouds to increase across
southern WI this evening with threat for sct -shra overnight into
Tuesday mrng.  Still potential for a period of lower cigs to develop
during this period as well.

&&

.MARINE...Onshore flow wl continue into Tuesday night as weak
high pressure remains just north of the Great Lakes.  Few light
showers still possible later tonight into Tue morning.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...

WI...None.
LM...None.

$$

TONIGHT THROUGH MONDAY/AVIATION/MARINE...MBK



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