Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 230229
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
929 PM CDT THU SEP 22 2016
.UPDATE...Scattered showers and storms continue to fire along axis
of MUCape across northern IA into northern IL this evening in the
vicinity of low level frontogenesis. A few of these showers and
storms have crossed into far southern WI. Expect this trend to
continue but remain more scattered as low level baroclinicity
increases as low level thermal gradient tightens with increasing
northeast winds. Best instability and low level frontogenetical
forcing remains farther south. Best chance for showers and storms
across southern two tiers of counties into Sauk County. Hence wl
continue Flash Flood Watch for Iowa and Sauk counties but cancel
for Columbia, Marquette and Green Lake. Areas of fog likely with
localized dense fog until stratus becomes widespread across the
.AVIATION/06Z TAFS/...Increasing moist northeast flow should
result in MVFR and possibly IFR cigs developing across most of the
area overnight, lingering into Friday. Before the clouds fill in,
will be some patchy thicker fog the next several hours before
transitioning to lighter fog and better visibilities.
.MARINE...Transient dense fog continues to persist over the
northern marine zones from Port Washington to Sheboygan per
lakeshore web cams. Will hold off on issuing Marine Dense Fog
Advisory however as expect increasing north to northeast winds in
the next few hours to help thin and dissipate some of the fog. As
the low level winds increase from the north, some of the dense fog
may advect south and affect southern marine zones overnight.
Otherwise onshore flow to persist through the weekend with winds
and waves getting close to Small Craft Advisory levels.
.PREV DISCUSSION... /Issued 318 PM CDT THU SEP 22 2016/
TONIGHT AND FRIDAY - Confidence...Low Have decided to extend the
watch until midday Friday given how much rain has already fallen
there. However there is increasing uncertainty based on trends in
latest meso progs and what is transpiring across ern IA and the
likely consequence of these trends favoring a more southern QPF
max. Per coord with KARX feel it prudent to give this watch a bit
more time. Won`t take much to aggravate things. The mesoscale data
of the non-NAM variety does focus precip further south which is
more in line with the latest discussion from WPC and trends in
Iowa. While 500 millibar heights will slowly build during this
period, there is still some concern of where the better 925/850
millibar frontogenetical forcing sets up and whether that may
waffle back further north. Primary surface boundary is proggd to
gradually shift south of WI. Mainly the NAM progs show some banded
precip setting up through midnight and then another surge arriving
later tonight into the far west and then shifting across the area
Friday morning. With the northeast low level flow expect cloud
cover to be widespread with at least a chance of shra persisting
into the afternoon hours. However at this time the main focus for
any decent precip would be in the morning. Should see plenty of
60s for highs with the cloud cover/precip and ne winds. Better
shot at some 70s closer to Illinois border.
FRIDAY NIGHT AND SATURDAY...Forecast Confidence Medium.
Mid-upper level ridging begins to build in with the southern portion
of broad surface high pressure centered over central Ontario
settling down into the western Great Lakes. But sw flank of 925 mb
and 850 mb cold pools linger over the CWA into Saturday morning with
some 700 mb RH, and weak vorticity maxima dropping down front side
of ridge overnight into early in the day Saturday. Will hang on to
slight chance/chance PoPs over most of the CWA Friday night and
slight chance in the NE through Saturday morning.
Light easterly winds will keep lakeshore a bit warmer overnight
versus upper 50s inland areas across the northern CWA, with southern
area lows holding in the low 60s. ECMWF is a bit faster veering
winds to the southeast and subsequent 925mb warm advection than the
NAM and GFS. Given early clouds and overall slower return flow will
trend towards the cooler blended guidance for Saturday highs.
SATURDAY NIGHT...Forecast Confidence High.
Warm advection ahead of deep 500 mb trough shifts over the forecast
area after 06Z, with 925 mb temps rising to 19c to 20c by 12Z
Sunday. While better forcing with focused warm advection keeps
precipitation west of CWA through 06Z Sunday, precipitation chances
increase from west to east as the warm advection moves into the
region. Overnight lows will hold in the low to mid 60s.
SUNDAY AND SUNDAY NIGHT...Forecast Confidence Medium.
Raising PoPs to likely with a band of showers and thunderstorms to
cross the forecast area with the low-mid level frontogenetic response
to the surface cold/occluded front and associated 925-850 mb troughs
swinging through the area mainly Sunday afternoon and evening.
Surface boundary reaches the lake by 06Z Monday with pcpn lingering
back to the west until 850 mb baroclinic zone moves through.
Will see highs in the mid-upper 70s in the warm sector ahead of the
surface front, then dipping into the 50s overnight as cooler air
LONG TERM...MONDAY THROUGH THURSDAY...Forecast Confidence Medium.
While none of the mid-long range models are moving the 500 mb trough
through the region with any speed, GFS is particularly slow as it
closes off the 500 mb trough over the northern Plains Sunday night
and slowly tracks it into MN Monday then drops it south over WI Tue
into Wed. ECMWF keeps more of an open wave with the axis reaching
Lake Superior to lower MI by 00Z Tue. But it then drops a back-door
trough Tue and Tue night.
The result is cloudy cool weather with sporadic instability showers
under the persistent cyclonic flow. Blended temperatures are
trending more toward normal but may not be cool enough, especially
if the closed solution on the GFS pans out.
AVIATION/00Z TAFS/...As low level boundary sags to our south
tonight the guidance continues to support a reinforcing of the lower
cigs across more of the CWA which would linger into Friday. This is
supported by the MOS data and BUFKIT soundings. Convective trends
will be watched carefully tonight as lingering 850/925 baroclinic
zone and overrunning associated with it acts as focus for further
development tonight into Friday. Meso models show some disagreement
on placement but a little more emphasis being placed towards the
southwest cwa and even possibly further south with latest trends in
HRRR and RAP.
MARINE...Northeast winds are expected to develop tonight and
into Friday. Winds and waves are expected to remain below small
craft advisory levels, but conditions will be more elevated than
what we`ve seen over the past few days. Small craft may want to
WI...FLASH FLOOD WATCH through Friday afternoon for WIZ056-062.
TONIGHT/Friday AND AVIATION/MARINE...Collar
Friday NIGHT THROUGH Thursday...REM