Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
341 am CDT Wednesday Apr 16 2014
Today and tonight...forecast confidence is medium.
Low pressure will move from the north Central Plains to north
central Iowa today...and into north central Wisconsin tonight. Warm
air advection will continue across the area during this time.
Initial focused warm air advection/850 mb frontogenesis response
fields bringing snow into west central Wisconsin...with more
scattered activity to the south of this area. The southern edge of
this precipitation may clip the far northwest counties through the
morning hours...though most models are dry there as low levels
remain fairly dry. Kept very low probability of precipitation in the far northwest into this
Otherwise...middle level clouds will gradually shift eastward
through the area...most concentrated in the northwestern counties.
Tight pressure gradient will bring gusty southeast winds today into
tonight...becoming more southerly later tonight. Should see gusts in
the 25 to 30 knot range this afternoon...highest toward the
southwest counties. Highs today should reach the lower to middle 50s
inland...with 40s near Lake Michigan.
500 mb shortwave trough slides northeastward through the area
tonight. Some upper level divergence noted as well...in favorable
jet streak quadrant. Good upward vertical motion fields from q
vector convergence and warm air advection. Main issue is moisture in
the low levels. Most short term models bring light quantitative precipitation forecast through the
northern portions of the area...with the NAM showing the lowest quantitative precipitation forecast.
Decent low level moisture is only a few thousand feet thick...with a
fair amount of dry air in the middle levels.
For now...will continue the chance probability of precipitation across the north half of the
area. Lows tonight should only drop into the middle to upper 30s
with the warm air advection.
Thursday and Friday...forecast confidence high.
The middle level shortwave over northern WI Thursday morning will lift
northeast through the day. The corresponding surface low will be
over central WI at 12z Thursday morning and lift into Eastern Lake
Superior by late afternoon. A surface trough will drop southeast
through southern WI by middle afternoon. Winds will shift from south to
northwest during the day. It looks like there will just be some
clouds with this trough because profiles appear very dry in the middle
levels. Temperatures are expected to rise into the lower to middle 50s
most areas before the trough moves through.
All models are in agreement that the precipitation with the next shortwave
over the plains riding up into Illinois will remain south of the WI border
Thursday night and Friday. Carried slight chances in far southeast WI Thursday
night for now.
Meanwhile...a cold front will slip Down Lake Michigan Thursday night into
Friday morning as high pressure drifts across the region. This back
door cold front could generate low clouds...but it looks too dry for
any precipitation. Not expecting cold enough temperatures aloft to generate lake
effect either. The European model (ecmwf) is the warmest of all model guidance and
does not bring sub-zero 850mb temperatures to southern WI. Went with the
consensus approach for min/maximum temperatures but favored the colder majority
of the models.
The European model (ecmwf) is also faster than other models with bringing the warmer
air back into south central WI Friday afternoon. Still...we could hit
50 in Madison before the day ends if there is enough sunshine. An
easterly breeze will keep Lakeshore temperatures cool in the lower 40s and
falling temperatures in the afternoon. It will be another cold night Friday
night with lows in the lower 30s.
Saturday through Sunday...forecast confidence medium.
The next middle level shortwave trough will cross south central Canada
on Saturday. Warm frontal precipitation with this system is expected to
remain to the northwest of the mkx forecast area. Another middle level
trough over the center of the country will gradually shift east over
the weekend. The surface trough with that northern shortwave will
begin to interact with a surface trough from the southern shortwave
and begin to draw in moisture from the Southern Plains Saturday
night through the rest of the weekend. The GFS is showing stronger
shortwaves than the ecwmf and thus produces heavier precipitation.
The best chance for rain will be over central WI on Sunday rather
than far southeast WI. By Sunday night...that better chance will
slip into southern WI. Depending on how long clouds and precipitation can
hold off for Sunday...parts of far southern WI could approach 60 for
Monday and Tuesday...forecast confidence medium.
Any lingering precipitation should end by Monday afternoon. Temperatures
will gradually moderate to seasonable temperatures early next week
as middle level ridging sets up over the center of the country.
VFR conditions are expected across taf sites today and tonight. Main
precipitation area will remain to the north of taf sites during this
time. May see light rain occur briefly tonight...but confidence is
low so left precipitation mention out of tafs. Broken middle level
clouds will push into the area this morning...lingering this
afternoon and tonight. May see breaks at times...especially at the
Gusty southeast winds are expected to develop by middle
morning...and linger this afternoon and tonight. Gusts of around 30
knots are expected at Madison this afternoon...to around 20 knots at
Milwaukee and Kenosha. Strong low level winds are expected for a
time tonight at Madison...but left out low level wind shear as
surface gusts to around 25 knots will linger.
Small Craft Advisory continues across the nearshore waters of Lake
Michigan from 15z Wednesday until 12z Thursday. A tight pressure
gradient will occur over the area during this time...allowing for
gusty southeast winds. Frequent gusts to 22 to 25 knots are
expected. High waves of 5 to 8 feet are expected during this time.
Winds and waves will subside below criteria by 12z Thursday...as the
pressure gradient relaxes with the low moving out of the region.
Several area rivers will continue to be above flood and bankfull
stages for the next several days. Most of the fast responding and
smaller rivers in the area have crested or are near crest...and are
forecast to slowly subside over the next several days. The slower
responding rivers...like the Rock River and Fox River near
Berlin...will continue to rise for several days before cresting. For
the rivers above flood stage...most of the crests have been or will
be in the minor flood stage area.
Lm...Small Craft Advisory from 10 am this morning to 7 am CDT
Thursday for lmz643>646.
Today/tonight and aviation/marine...wood
Thursday through Tuesday...mrc