Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
307 PM CST Monday Dec 22 2014
Tonight - confidence...medium
water vapor/rap animation shows primary circulation center across South Dakota
with southwest upper flow ahead sending in ripples of energy. Mild and
moist flow with precipitation type becoming all rain. Vulnerable thermal profile
for a time has resulted in some mixiness. Airmass becomes warm enough
to support all rain as warm conveyor strengthens ahead of developing
surface/850 low in Iowa. With the cloud cover and sustained mild
airflow not expecting temperatures to drop off much if at all.
Tuesday - confidence...medium
occluded low waffles into southern/central WI with dry slot shoving rain to the
north and northwest. This results in a gradual lowering of the probability of precipitation from
southeast to northwest. Mild airmass will be in place...so expect temperatures in
the 40s despite the persistent cloud cover.
Tuesday night...forecast confidence is high.
We/re still looking at a decent dry slot across the area as the
first low pressure center lifts off to the northeast. The far
northwest forecast area will continue to have the best chance for
precipitation...and even that looks fairly low at this point. The
trailing cold front will gradually drift east with time. Look for
the light rain to gradually transition to rain/snow then all light
snow from west to east overnight. Little accumulation is expected.
Wednesday and Wednesday night...forecast confidence is medium.
Yesterday the 12z parallel run of the GFS...followed by the 18z
through the 12z today runs of the operational GFS showed a backing
to the west of the secondary low forecast to move out of the
lower Mississippi Valley and into the Great Lakes. The European model (ecmwf) has
also trended farther west now. The two versions of the Canadian
model are also showing a more westerly track as well. Therefore
precipitation chances have increased again across the southeast for
Wednesday. Still...the axis of best quantitative precipitation forecast is still southeast of
Wisconsin...we/re just getting into the western shield of it.
Temperatures will be near threshold levels for snow. In the
absence of strong dynamics...the temperatures would suggest rain with
some snow mixed in. However...we could see some dynamic cooling
of the column and this might result in a period of more snow than
rain. This would be a rather wet snow with very low snow/liq
ratios. Surface temperatures will likely be running in the middle 30s.
Given that and the fact that this will be occurring during the day
suggest the impact should be low as we will likely get decent
melting...if snow occurs. The brisk northeast flow off the lake
will also help keep the boundary layer warm.
The precipitation will pull out quickly to the east Wednesday evening
with dry weather arriving. I have about an inch or less of snow
accumulation in the forecast for now. Stay tuned for updates.
Thursday...forecast confidence is high.
All the models are in good agreement that Christmas day will be
dry with a high pressure ridge briefly moving overhead. We might
even see a little sunshine. The last time we saw widespread
sunshine was over two weeks ago.
Friday...forecast confidence is high.
The GFS and the European model (ecmwf) are in better agreement in bringing a fast
moving...and weakening...low through here on Friday. The track at
this time is across central/south central Wisconsin. The precipitation
looks light and given the temperature profile would likely be a mix that
transitions over to all light rain on Friday into Friday evening.
Saturday and Sunday...forecast confidence is high.
High pressure is still on tap for the weekend. Look for dry but
colder weather with temperatures at or below normal.
Aviation/00z tafs/...IFR ceilings expanding across southern WI as rain
shield moves in. Trended many ceilings down to LIFR values with moist
baggy regime evolving tomorrow with weakening low pressure in the
area. Airmass continues to modify so expect any mix potential to
be north of taf sites by taf issuance. Shortwave energy pivots
into southern WI later tonight after initial wave arrives towards 00z.
Surface low occludes with aforementioned baggy pressure gradient
and wind field evolving Tuesday. Improvement in ceilings noted later
Tuesday from southeast to northwest as dry slot works in and precipitation shifts north
and northwest of taf sites.
Marine...a Small Craft Advisory is in effect through early Tuesday
for breezy east-southeasterly winds and high waves as low pressure over the Great
Plains strengthens and moves to eastern Iowa by 12z Tuesday. Subsiding winds
and waves are expected on Tuesday and Tuesday nt as the low weakens northeastward
across WI. Tweeked the northern zone a bit later due to lingering
higher waves there.
Lm...Small Craft Advisory until noon CST Tuesday for lmz643>646.
Tonight/Tuesday and aviation/marine...collar
Tuesday night through Monday...Davis