Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 260824
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
324 AM CDT THU MAY 26 2016
TODAY AND TONIGHT...Forecast Confidence - Medium.
Attention early this morning on convection spreading ENE across
central into eastern IA. Convection being driven east by mid-level
short wave trof in vcnty of northwest IA and 700h warm air surge.
Both synoptic mechanisms weaken slightly but continue NE and affect
portions of central and srn WI this morning. Thinking at least sct
t-storms will return to srn WI but unsure if they will hold together
into the east. Hence trended toward from sct to more chance
wording. May bump up western CWA to numerous if convection holds
together next several hours. Bulk shear in the 30kt range with SF
Cape increasing to 1.0-1.5k joules, could not rule out isold severe
threat this mrng.
Other early morning concern is dense fog. Dense fog holding on at
KUNU and KETB but has been transient elsewhere. With thickening mid-
high clouds and boundary layer mixing just off the surface, will
hold off on Dense Fog advy but issue an SPS for several hours.
After convection ends later this morning, clouds should break up
allow warm and humid conditions to develop. Temperatures should
rise well into the 80s but a lake breeze will cool locations right
at the lake.
With dewpoints mostly in the mid 60s, afternoon capping remains
minimal with lingering instability of 1-2k joules CAPE. Trigger
appears to be lacking but need to hold onto small pops in case
something pops along weak boundary or lake breeze.
Another stronger mid-level short wave approaches southern WI late
tonight along with another surge of low to mid level moisture flux
advection. Late night shear and instability impressive. Wl
continue high pops across western CWA, even some likely wording in
the far southwest. If trend continues, likely wording may be spread
farther north and east late tonight in next forecast.
FRIDAY THROUGH SATURDAY... Forecast confidence is medium.
The closed upper low over the southwest states will progress
northeast into the upper Midwest through Saturday. There will be
repeated waves of vorticity advection, a steady feed of moisture
from the Gulf increasing precipitable water values to 1.75 inches,
and the nose of the low level jet pointing into southern WI. Expect
CAPE to be around 1000 j/kg or less, with a warm profile leading to
tall, skinny CAPE. Bulk shear will be 20 to 30 knots.
These conditions are very similar to the last couple of days except
that there is better stronger synoptic support for more widespread
thunderstorms. Parameters support the potential for a few to grow
strong. SPC may expand the marginal risk into southern WI with their
morning update today.
It is very difficult to pin down a more favorable time for showers
and thunderstorms for this whole period of Friday morning through
Saturday night. The instability will be more diurnally driven, and
Friday should have the stronger instability out of the two days. It
looks like we will be stuck in a wet pattern with warm, moist,
southerly flow that will lead to scattered showers the whole time.
Max temps should reach around 80 each day with 925mb temps around
20C, although clouds and precip could limit highs a bit.
SUNDAY THROUGH MONDAY... Forecast confidence is medium.
The weakening upper trough will slide through northern WI on Sunday
and the corresponding surface low will track across Lake Superior.
Showers and thunderstorms will be possible, but probably earlier in
the day and more isolated.
We will transition into a temporary zonal flow pattern for Memorial
Day. There are signs of a weak shortwave rippling through southern
WI, which could produce a few showers and perhaps a rumble of
thunder. The GFS continues to look overdone with its qpf. Southern
WI will still be in the mild air mass, so expect temperatures in the
lower 80s inland from the lake.
TUESDAY THROUGH THURSDAY... Forecast confidence is medium.
A closed upper low will make its way across the northern Plains. The
occluding surface low will likely bring showers and thunderstorms to
southern WI during a 24 hour period between Tue night and Thu.
However, there are some timing differences between the GFS and ECMWF
now that will need to be resolved. The GFS continues to look too wet.
Areas of fog will continue through the early morning before lifting.
Fog may yet affect KENW and KMKE taf sites next several hours along
with a period of IFR cigs. Generally VFR conditions expected today
but wl need to watch for scattered t-storms this morning. There
will be a better chance for t-storms affecting taf sites later
tonight into Friday morning. More fog is likely later tonight as
Warm and humid air will remain in place across Lake Michigan for the
foreseeable future resulting in areas of fog and occasionally dense
fog. Latest Racine Harbor webcam is showing fog over the harbor but
Sheboygan and Milwaukee harbors look fairly fog free. Lake surface
temperature in the near shore waters estimated to be in the lower
50s while mid-lake buoy measuring 49 degrees. With dewpoints in the
low 60s and lighter wind regime, fog inevitable and as winds become
onshore later this morning, areas of dense fog likely. Will wait
for after sunrise to evaluate near shore visibilities before pulling
trigger on Marine Dense Fog Advisory. No significant synoptic wind
events expected, but off and on t-storms affecting the near shore
waters may bring some gusty winds over 30 kts. Best chance for t-
storms looks to be late tonight through Friday evening.
TODAY/TONIGHT AND AVIATION/MARINE...MBK
Friday THROUGH Wednesday...MRC