Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
918 PM CST Friday Feb 12 2016
Wind Chill Advisory remains in effect.
Added freezing spray warning for ice free areas. Not sure of the
ice extent due to the brisk northwest winds. However heavy
freezing spray would occur in ice free areas...especially toward
Northwest wind gusts of 25 kts are expected into the night.
High pressure will slide across southwest WI late tonight
reducing the winds early morning and keeping clear skies into Saturday.
The tight pressure gradient will continue through tonight with
high pressure over the northern plains and low pressure over the
eastern Great Lakes. Expect winds gusts of 25 to 30 kts. Winds
are expected to drop below Small Craft Advisory levels Saturday
morning. Not sure of ice extent due to the brisk northwest winds so
added heavy freezing spray warning for ice free areas.
Previous discussion... /issued 320 PM CST Friday Feb 12 2016/
Today and tonight...forecast confidence is high.
High pressure will drop south across Minnesota and Iowa tonight and move
southwest of WI on Saturday. The strong wind gusts will diminish
late tonight but winds will remain elevated through the night. There
is some uncertainty with low temperatures tonight as skies will be
clear but the wind will promote mixing and warmer temperatures.
There is better agreement amongst guidance indicating 925 mb temperatures
bottomming out around -20 or -21 c tonight which translates to
around -2 to -10 f. Still looks like we are on track reaching low
end Wind Chill Advisory criteria late tonight and early Saturday
Sunny skies are expected for Saturday with highs in the single
Saturday night through Sunday night...forecast confidence high
Surface high pressure will quickly slide off to the east-southeast Saturday
evening...allowing a return southerly flow to kick in ahead of an
approaching trough of low pressure from the northwest. Clouds
should begin spreading into the western forecast area by
midnight...reaching the east by morning. The southerly flow will
trigger warm air advection...thus min temperatures Saturday night should
occur during the evening with steady or slowly rising temperatures after
Have made only incremental changes to probability of precipitation and snow amounts for
the snow expected to spread across the forecast area Sunday
morning. There is deep...but not impressive warm air advection
associated with a similarly deep trough moving through the area
Sunday/Sunday night. The best/focused warm air advection is south of our area.
Isentropic analysis shows quick saturation from west to east with
the dendrite region still looking very deep during the early hours
of the snow event. The isentropic lift is gentle. Warmer air
flowing into the lower levels will shorten that dendrite growth
zone up with time Sunday afternoon. Favorable Delta T/S...about
17...over the lake could help moisten up the low levels across
the east /I.E. Lake enhancement/ ahead of the wave approaching.
Thus...we may not see too much lost to the usual early evaporation
process in the low levels. The deep trough and warm advection
continues into Sunday night...so will bump up probability of precipitation from what we
had. Snow accums were tweaked but amounts still range from about
2.5 to 4 inches. Highest west...lower northeast. We could see
locally higher amounts given the high snow/liquid ratios expected.
This will be a very dry snow.
Monday and Monday night...forecast confidence is high.
We/ll probably have some light snow or flurries lingering for a
time on Monday...but the trough will be moving out with short wave
ridging moving in. Highs Monday will be close to freezing...so a
bit milder than the past few days.
Tuesday and Tuesday night...forecast confidence is medium.
A quick clipper may hit US on Tuesday. There are differing
opinions between the GFS and the European model (ecmwf)...with the GFS showing a
much more amplified low than the European model (ecmwf). This should remain more of
an open trough...so will carry small probability of precipitation of light snow
Tuesday...tapering off Tuesday evening.
Wednesday and Thursday...forecast confidence is medium.
High pressure moves across the area...sliding to the east by
Thursday. Highs Monday will be colder under the high with temperatures in
the lower to middle 20s. But...southerly winds on the back side of
the high on Thursday should push highs back into the lower 30s.
With the warm air advection on Thursday...we could see a small
chance of light precipitation. For now it looks like light snow...but the
thermal structure will be getting more iffy and precipitation type could
become questionable. Either way...amounts/pops look very low. So
impact is minimal.
Northwest wind gusts of 25-30 kts are expected through the evening
with the highest gusts in far southeast WI. High pressure will slide
across southwest WI late tonight reducing the winds early Saturday
morning and bringing clear skies through Saturday.
Marine... the tight pressure gradient will continue through tonight
with high pressure over the northern plains and low pressure over
the eastern Great Lakes. This evening expect winds gusts of 25 to 30
kts with a few gusts to 35 kts possible toward the open waters.
Winds are expected to drop below Small Craft Advisory levels
Saturday morning. The Small Craft Advisory may need to be cancelled
a little early since the latest guidance shows winds diminishing a
little quicker than previously noted.
WI...Wind Chill Advisory until 9 am CST Saturday for wiz046-047-051-
Lm...heavy freezing spray warning until 9 am CST Saturday for
Small Craft Advisory until 9 am CST Saturday for lmz643>646.
tonight/Saturday and aviation/marine...marquardt
Saturday night through Friday...Davis