Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Milwaukee/Sullivan WI
928 am CST Sat Feb 6 2016
Updated the sky cover to trend cloudier for the remainder of the
day given latest models and current cloud cover. Could see some
breaks in the afternoon with daytime mixing...but otherwise
expecting clouds to hang around. Even with clouds...temperatures are
trending milder than GFS/NAM suggest under southwest winds...more
along the lines of European model (ecmwf). Current forecast high temperatures are toward
the milder model solutions...so not expecting much change there.
MVFR ceilings will likely hang around into the afternoon...and
possibly into the evening. Seeing mixed signals in models as to
when conditions might improve as southern Wisconsin will be under
the influence of warm advection and a shortwave tonight into
Sunday. Discounting the typically overdone NAM near surface
saturated relative humidity layer...does seem that some VFR ceilings may return by
May see a few snowflakes tonight...but still seeing a good amount
of dry air in models soundings. Probably will see mainly
flurries...with little to no accumulation expected.
Previous discussion... /issued 330 am CST Sat Feb 6 2016/
Today and tonight...forecast confidence is high.
A middle level short wave will be exiting the area by 12z this
morning...but clearing is lagging well behind this wave. Any
clearing of the low clouds widespread across the area early this
morning will be difficult to come by...since it may bet hung up
under the low level inversion showing up on the soundings. Even if
it clears...it would be short lived as elevated warm air advection
ahead of the next...and much stronger...middle level wave will bring
increasing middle and high clouds during the afternoon. Highs today
look to recover in the middle 30s...and if we happen to get a bit
more sunshine...it may be a notch or two higher with 925 mb
pushing -1c by 00z sun.
The warm advection kicks in fairly strong this evening. Soundings
show a decent dry layer of about 7-8kft just above the low level
inversion...during the peak of the warm air advection. But...it seems plausible
that we could see a few flurries come out of the advancing and
gradually lowering cloud deck. Nothing accumulating though. Lows
should occur in the early evening...with temperatures steady or rising a
bit overnight due to the warm advection.
Sunday through Monday night...forecast confidence is medium.
Models are in pretty good agreement with features during this
period. They take a surface low southeast from far northern
Minnesota to the far Western Upper Peninsula of Michigan
Sunday...with a cold front moving through southern Wisconsin. The
low then weakens as it continues to the southeast Sunday night
into Monday night.
At 500 mb...a lead shortwave trough slides southeast through the
area Sunday afternoon. The 500 mb low then slides southeast across
southern Wisconsin Sunday night into Monday morning...before
sliding southeast of the area in the afternoon. Another vorticity
maximum slides southeast through the area Monday night.
Area forecast soundings are showing more dry air in the air
column on Sunday...which would limit precipitation chances. For
now...cut back on probability of precipitation Sunday to slight chances...and may be able
to remove them in later forecasts if dry trend continues.
Continued with high end chance to low end likely probability of precipitation for Sunday
night and Monday...when the upper low crosses the area. Area
forecast soundings are showing a relatively deep layer of
saturation during this time and into Monday night. There is also a
deep dendrite snow Crystal growth zone.
Probability of precipitation may need to be raised more in later forecasts Sunday night
and Monday...as sref probability of precipitation are trending upwards into the likely
range. May see a one to two inch snow accumulation total from
Sunday night into Monday night across the area. The snow would be
light in intensity and accumulation rate.
Mild temperatures ahead of the cold front Sunday will trend
downward into Monday night...with cold air advection behind the
front later Sunday into Sunday night. Northwest winds may be brisk
at times during this period...helping reinforce the colder
Tuesday through Friday...forecast confidence is medium.
Hung onto low end probability of precipitation in the far east Tuesday into Tuesday
night...though these may need to be removed in later forecasts if
drier air continues to work into the region. Otherwise...weak high
pressure would keep the area dry...with colder temperatures
European model (ecmwf) brings a swath of quantitative precipitation forecast southeastward through southwest
Wisconsin Wednesday...while the GFS is dry and keeps this further
west. Kept dry forecast for now...until better agreement between
the models can be reached. Another high then slides southeast
through the region Wednesday night into Thursday night...with
quiet weather and cool temperatures expected.
Models disagree with timing and placement of next system for
Friday...so kept consensus blend of probability of precipitation and temperatures for now.
There is a lot of uncertainty with respect to the large MVFR
cloud shield cover the upper Midwest. Many of the low level relative humidity
forecasts show it scouring out later this morning in the wake of the
passing middle level short wave early this morning...with VFR
conditions through the remaining taf period.
However...rap/NAM soundings Show Low level relative humidity hanging on all
through the day...likely getting hung up under the low level
inversion expected. Given satellite trends...I would have to favor
the more pessimistic approach...but will watch trends over the
next few hours before deciding. Some of these low clouds could
spit out flurries at times...but not an issue for Airport Ops.
Small Craft Advisory conditions are likely Monday night through
Tuesday night...due to brisk northwest winds in the wake of a
strong low pressure system moving through the Great Lakes.
today/tonight and aviation/marine...Davis
Sunday through Friday...wood