Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
235 PM CST Tuesday Jan 27 2015
Tonight - confidence...medium
main issue will be cloud cover and impact on temperatures. Low level
relative humidity forecasts suggest a lot of this deck erodes fairly quickly. Starting to see
this take place but it is quite gradual. Will stick to a more pessimistic
cloud forecast especially with proximity of high with light wind regime and
BUFKIT soundings showing low level inversion hanging tough for much of the
night. The clearing trend from the east has slowed as well with more clouds
dropping south along the lake. Appears best potential for sustained clearing
will be in eastern sections so have lows a bit lower there. Should clouds
clear further temperatures will need to be bumped down a bit more in the west.
Wednesday - confidence...medium
middle level ridge axis translates east across WI during the day. Approaching
shortwave in the plains leads to surface low development across Iowa by
days end. Low level jet ramps up with 925 millibar winds increasing to
30 to 40 knots straight out of the south. Both GFS and NAM show mixing
will be limited with low level inversion based around 930-940 millibars.
This results in significantly colder maximum temperatures than what is forecast.
Leaning more towards MOS for now or a smidge higher. Precarious forecast
though as upstream temperatures in the sunshine and no snowcover are well into
the 40s across western Iowa into northwest MO.
Wednesday night and Thursday...forecast confidence is medium.
Looks like a decent setup for a period of light freezing rain and
drizzle for a good part of the forecast area Wednesday night. The
boundary layer/surface temperatures will be hovering close to or just
below freezing while a strong low level jet punches a warm layer
aloft...exceeding 4c in some places...into southern Wisconsin.
Models are in pretty good agreement with the track of the surface
low from just south of Dubuque to south of Chicago between
midnight and sunrise on Thursday. A complex merging of middle level
short wave energy will occur at that time as well. So far precipitation
amounts look on the lighter side...but it could be enough for the
freezing rain to result in some sort of advisory during this time.
Won't issue one at this time...just something to consider going
Cold air wrapping in behind the low will transition the mix over
to all snow...if we can get enough ice crystals...as it ends
quickly from west to east on Thursday.
Thursday night through Friday night...forecast confidence is
Looks like high pressure is still on tap for this period...
keeping it dry with temperatures a bit below normal.
Saturday and Sunday...forecast confidence is medium.
The GFS and the European model (ecmwf) both show a low passing to our south
Saturday night and Sunday. This could drop a few inches of snow.
If the track sneaks farther north...we would need to increase snow
amounts a few more inches. Right now it doesn/T look like a big
storm...even if it comes farther north. But it has potential for
generating more than our usual 1 to 2 inches we/ve seen this
winter. Don/T get too excited about this one.
Monday and Tuesday...forecast confidence is medium.
Cold Canadian high pressure will arrive in the wake of the
departing low. A much colder period of weather is expected through
the first half of next week. These will be some of the coldest
temperatures we/ve seen since our cold blast back in November.
Aviation/00z tafs/...influence of surface high dominates through
the night. Low levels proggd to gradually dry out though appears the
drying trend is too quick especially for central and western WI.
Seeing some clearing in the east though this is filling right back in
again with another batch of clouds trying to move south from ksbm area.
Areas of IFR fog/LIFR ceilings in parts of SC WI expected to gradually improve.
As surface high shifts east on Wednesday southerly flow develops with low level
relative humidity increasing into western County Warning Area during the aftn/eve. Surface low arrives for
Wednesday night with increasing potential for mixed precipitation.
Marine...increasing south/southeast winds are expected with tightening
pressure gradient ahead of low pressure approaching from the plains. There
will be a period when winds will reach small craft levels. With the flow
being onshore some higher waves are likely as well.
Lm...Small Craft Advisory from noon Wednesday to 4 am CST Thursday
Tonight/Wednesday and aviation/marine...collar
Wednesday night through Tuesday...Davis