Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Milwaukee/Sullivan WI
1129 am CST sun Dec 28 2014
Sunshine today with a high pressure ridge moving across southern WI.
Clouds over northern Wisconsin along a cold front will slide down
through southern WI this evening and overnight. Timing of the clouds
is a little earlier than previous forecasts. There is less certainty
about clouds over southeast WI... although models are persistent in
developing them overnight. The other question is whether or not
there will be flurries with the clouds. Given upstream
observations... I added flurries north of Madison for this afternoon
and am still debating about tonight. Moisture will be very shallow.
Weak ridge of high pressure slides through the region today...with a
cold front sagging into southern Wisconsin late this afternoon into
tonight. MVFR cloud deck will slide into southern WI with the cold
front. There is uncertainty about cloud base height... especially
over southeast WI. It may be 2500 feet above ground level all night rather than
dropping to 1500 feet above ground level like I have in the tafs. Based on
observations in northern WI this morning... there may be some
flurries associated with the low clouds/cold front.
Previous discussion... /issued 333 am CST sun Dec 28 2014/
Today...forecast confidence high.
Clouds have finally pushed southeast out of forecast area with weak
ridging nosing over region...bringing some rare sunshine to the
region today. Clouds and a few flurries well north along cold front
across northern Minnesota/Lake Superior that will be sagging south today.
GFS fastest with bringing cold air into southern WI...so went with a
slower consensus blend that allows high temperatures to reach the
lower to middle 30s...with upper 20s far northwest...early this afternoon
then slowly cooling through the rest of the daytime hours. Will see
an increase in middle-hi level clouds late this morning/afternoon as
weak short wave crosses the state...with lower clouds moving in with
the cold front.
Tonight... forecast confidence high.
Colder air begins to spread in on north winds behind slow-moving
cold front that models take just south into northern Illinois by 12z Monday.
The low level clouds along and behind the surface cold front will
help hold lows in the teens...with low 20s along the Illinois Border.
Lake water temperature/850 mb temperature differential somewhat
favorable for lake-effect snow. But no little to no convergence on
west side of lake...except over NE Illinois for a short time
overnight...and shallow cloud depth that does not reach into the
dendrite growth zone so no lake-effect expected.
Monday - confidence...medium
increasingly confluent flow across the area with elongated
sheared vorticity to our south and other shortwave affecting northern
WI. Airmass looks very dry with NAM showing some middle level
saturation potential at or above 8k feet but parched below. Cold advection
continues with 925 temperatures across northern County Warning Area getting into the negative
teens celsius. Lake effect potential looks better closer to Middle
Lake and points south and east but consensus probability of precipitation still brushes
far eastern Kenosha County Monday night so left that as is for now.
Tuesday and Wednesday - confidence...medium
main story will be the cold airmass in place this period. Center
of high pressure drops from the northern plains Tuesday into the
Southern Plains Wednesday. With low pressure moving through Canada
this will tighten up a decent pressure gradient across WI by
Wednesday into Wednesday night. Most highs in the teens and
morning lows in the single digits.
Thursday - confidence...medium
rather strong northwest upper flow persists. Any vorticity within this
flow looks largely sheared. Weak front is proggd to sag into the
area with the European model (ecmwf) showing light quantitative precipitation forecast potential. Other models are
dry. Have retained the dry look of the superblend probability of precipitation at this
time as overall forcing looks weak and moisture quite minimal.
Expecting highs to moderate back into the 20s as low level
westerly flow moderates 925/850 cold pool.
Friday and Saturday - confidence...low
the 00z European model (ecmwf) has trended towards the GFS solution with respect
to bringing northeastward moving southern stream shortwave energy and merges
this with northern branch wave. This results in a surface low developing
in a similar fashion to the GFS. European model (ecmwf) solution is colder with a
more eastward track and keeps precipitation all snow while GFS suggests
some mixy potential for a time. On the flip side the Gem and
parallel GFS show high pressure and dry scenario. So this far out
like the superblend approach of having some chance probability of precipitation introduced
especially with the European model (ecmwf) trending towards the GFS solution...but still
some question Marks with the dry Gem/parallel GFS.
Aviation/12z tafs/...weak ridge of high pressure slides through
the region today...with a cold front sagging into southern Wisconsin
late this afternoon into tonight. VFR conditions with increasing
middle-hi level clouds spreading in this afternoon. MVFR cloud deck
will then move in late this afternoon/early this evening as the
cold front slowly moves through. Light west winds will turn north
with cold front passage.
today/tonight and aviation/marine...rem
Monday through Saturday...collar