Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
310 PM CDT Thursday Oct 8 2015
Rest of this afternoon and tonight - confidence...medium
Surface low shifts into the eastern lakes with cold front swinging
through this evening. Considerable cooling/drying noted upstream
across southern Minnesota and this will work in as the evening wears on. Scattered
rain showers to affect southeast 1/2 of County Warning Area for balance of afternoon with some mesoscale
models lingering the potential into early this evening. Cold
advection then kicks in with plenty of low cloud cover poised to
head into southern WI within the Post frontal cold advection regime.
In fact 925 temperatures head from the teens celsius this evening to 5-7c
by late tonight.
Friday - confidence...medium
Middle level trough axis shifts southeast of southern WI early...with ridging
taking hold. Surface pressure gradient tightest in the morning with some relaxing
of the gradient during the afternoon as surface ridge axis draws closer. Low level
relative humidity forecasts suggest highest relative humidity in the morning so cloud cover likely to be
more widespread then. Some drying noted in the afternoon and this is
reflected in MOS sky from both the mav and met data. Only a subtle
uptick in in 925 temperatures to 8-10 celsius. So upper 50s/low 60s look
reasonable with greater 60 potential in western County Warning Area.
Friday night and Saturday...forecast confidence is high.
500 mb ridging will protrude eastward from the Great Basin into
the Central Plains. This will support surface ridging across the
area...with its axis sliding southeast into the Ohio Valley and
eastern Great Lakes. Low-level flow turns southwesterly Saturday
afternoon with pronounced warm advection and rising 925 mb
temperatures. Lows Friday night will remain on the cool
side...mostly in the 40s. Expect afternoon highs in the 60s on
Saturday...perhaps nearing 70 in the west.
Sunday and Monday...forecast confidence is medium.
Middle-level ridge axis slides southeast of the area on Sunday as
upstream troughing advances from the northern rockies into the
northern and Central Plains. At the surface...high pressure remains
in control locally as troughing extends from the Canadian rockies
into the northern High Plains. Sunday is shaping up to be a fine
day...with continued low-level warm thermal advection and weakly
subsident conditions aloft. 925 mb temperatures in the upper teens
to lower 20s support afternoon highs well into the 70s...and it/S
not out of the question that portions of the area could crack the 80
degree mark. Westerly 30-35 knots 850 mb winds should Transfer
sufficient momentum into the surface layer to result in some
afternoon gustiness on Sunday.
Shortwave trough continues east on Monday with its axis crossing
Wisconsin during the morning to early afternoon. Associated
strong cold front will progress steadily through the
area...likely clearing southern Wisconsin by late morning. Biggest
question during this period is precipitation chances. While
earlier indications were to keep things dry...the 08.00z European model (ecmwf)
brings some Post-frontal showers into southeast Wisconsin during
the afternoon and evening. This idea has some support from the
08.12z global Canadian model...which brushes the NE County Warning Area with some
light precipitation. Forcing for ascent appears quite weak...with better
forcing to our north. Will keep consensus model blended
probability of precipitation...which yield slight chances for most of the County Warning Area. 925 mb
temperatures support highs in the upper 60s to lower 70s prior to
the frontal passage. Temperatures will tumble thereafter with
strong cold advection commencing.
Tuesday through Thursday...forecast confidence is medium.
Upper level winds increase for Tuesday and beyond with a few low
amplitude disturbances riding the mean flow. The first wave should
pass through largely unnoticed Tuesday night given only weak
cyclonic vorticity advection and relatively limited available column
moisture. Another...slightly stronger...wave should approach by
Wednesday night or Thursday with an accompanying cold front swinging
through. Temperatures during this period should be near to slightly
above seasonal normals.
Aviation/00z tafs/...surface cold front swinging through into early this
evening triggering a few rain showers. These will exit southeast WI this evening along
with the front. Plenty of IFR and MVFR stratus upstream poised to come
on south as nearly flow develops in cold air advection regime in wake of frontal passage. Low level relative humidity
forecasts show this spreading in tonight and lingering into Friday morning
within proximity of low level thermal trough.
Marine...brisk northerly winds in the wake of a passing low
pressure system will bring Small Craft Advisory conditions for late
tonight into Friday evening. Expect northerly winds to 15 to 25
knots and waves building to 4 to 6 feet. Highest waves toward
Kenosha...lower toward Sheboygan.
Lm...Small Craft Advisory from 5 am to 10 PM CDT Friday for lmz646.
Small Craft Advisory from 7 am to 7 PM CDT Friday for lmz644-645.
Small Craft Advisory from 7 am to 4 PM CDT Friday for lmz643.
Tonight/Friday and aviation/marine...collar
Friday night through Thursday...spm