Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 200837
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
337 AM CDT SAT AUG 20 2016
.TODAY AND TONIGHT...Forecast Confidence Is Medium.
Numerous t-storms associated with surge of warm air advection and
frontogenesis shifting north of the area. However next batch of
showers and storms already pushing into the southwest CWA. This
batch associated with approaching mid-level short wave getting
shoved northeast by main wave farther upstream over NE/SD area.
Expect these showers and storms to sweep across southern WI
through mid-morning, followed by diminishing trend. May be enough
time for atmosphere to destabilize as cold front moves through the
eastern CWA this afternoon for one or two storms to take on severe
Short term guidance now in reasonable agreement on low pressure
rapidly intensifying as it moves across WI today. GFS and NAM have
come into better consensus. Hence after early morning activity,
expect more scattered to numerous showers and t-storms to
redevelop later this morning and afternoon.
However, drier air wrapping around the strengthening low pressure
system will reduce the threat across the western area this
afternoon behind the passing cold front.
Sauk county received 1.50 to 2.50 inches of precip Friday
morning, with another three quarters inch overnight. Contemplated
issuing Flash Flood Watch, but expect this morning`s activity to
result in lighter qpf amounts, and more scattered activity along
the front late this morning and early afternoon. Sauk County
dispatch did not report any flooding issues around 07z. Hence wl
not issue FFA at this time.
Patchy fog likely to accompany lighter winds this morning, in
humid airmass as sfc low pressure passes through, and where it is
Few showers may affect parts of the north tonight, as mid-level
deformation zone associated with low grazes central WI. Otherwise,
breezy west winds will pull cooler and less humid air across the
area for Sunday.
.SUNDAY THROUGH MONDAY NIGHT...Forecast Confidence Is Medium.
Models are in decent agreement with gusty west winds slowly
decreasing on Sunday, as pressure gradient weakens. 500 mb flow
remains cyclonic over the region, as the main shortwave trough
shifts off to the northeast. Differential cyclonic vorticity
advection from another vorticity maximum shifts southeastward
across the northeast half of the forecast area during the day.
Area forecast soundings show scattered to broken cumulus
development during the day. Kept lower end POPs for light rain
showers in the north and east for Sunday, given the above
mentioned features. A cool day is expected, with highs only in the
lower to mid 70s. Cool lows in the lower to mid 50s are forecast
for Sunday night, per 925 mb temperatures.
Models then are in good agreement with showing the 500 mb
cyclonic flow transitioning into a ridge by later Monday night.
High pressure passing south of the region Sunday night into Monday
will result in dry conditions, continuing into Monday night.
South to southwest winds developing Monday into Monday night
should allow for warm air advection to develop. This should lead
to gradually rising temperatures, closer to seasonal normals.
.TUESDAY THROUGH FRIDAY...Forecast Confidence Is Medium.
ECMWF/GFS are in decent agreement with features during this
period. They shift the 500 mb ridge to the east Tuesday, with a
shortwave trough shifting through the area in southwest flow
Tuesday night or Wednesday. Warm air advection continues into
Tuesday night, with the cold front passing east through the region
late Wednesday or Wednesday night.
Kept consensus POPs for this period, and may need to raise these
in later forecasts if these models continue to show this trend.
Temperatures look to remain near seasonal normals, with more humid
Cold air advection with drier air then should work into the
region for Thursday into Friday. Thursday POPs may need removal in
later forecasts if dry look continues in models. Pleasant
temperatures are expected.
Several more periods of showers and t-storms will affect TAF
sites, as low pressure and a cold front move through the region.
Patchy stratus will continue to expand, as winds diminish and
more rain pushes through the region. MVFR cigs are expected with
patchy IFR. Fog may also reduce the visibility for several hours
Small Craft Advisory will remain in place for this afternoon and
tonight. Approaching low pressure is expected to strengthen as it
passes across Wisconsin today. This will result in increasing
south to southeast winds this morning. The winds will turn to the
west to southwest this afternoon, as a cold front passes through.
Several more periods of showers and t-storms are expected as
these weather features move through the region.
Strengthening low pressure passing through Wisconsin today will
result in increasing south to southeast winds this morning,
turning to the southwest to west this afternoon after a cold front
moves through. Waves are expected to increase to 2 to 4 feet later
this morning and afternoon, resulting in a Moderate Swim Risk at
Lake Michigan beaches into this evening.
LM...SMALL CRAFT ADVISORY from 1 PM this afternoon to 10 AM CDT
Sunday for LMZ643>646.
TODAY/TONIGHT AND AVIATION/MARINE...MBK
Sunday THROUGH Friday...Wood