Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
301 am CDT Thursday Sep 18 2014
Today and tonight...forecast confidence is high.
A cold front is sweeping south across the forecast area early this
morning and will be south of Wisconsin by the time most folks head
to work this morning. There is some low level moisture and clouds in
the wake of the front...but it/S not looking as solid as expected
and may result in more of a mix of clouds and sunshine before
scattering out completely this afternoon. Will therefore bump temperatures
up a notch. The clouds will most likely hang on the longest across
Mostly clear and cool tonight as high pressure settles in...but it
does slide east by morning with the return flow setting up by
sunrise on Friday.
Friday - confidence...medium
high pressure will be well to the east and a cold front slowly
approaching from the Dakotas. Decent pressure gradient sets up
with southerly windflow ramping up. Decent 850 warm air and moist
advection. Core of 850 low level jet aims more to our north and middle level
negative vorticity advection is fairly pronounced into southern WI so shortwave activity will
also focus further north. Models continue to show just a bit of
quantitative precipitation forecast clipping our far northern County Warning Area so will retain the small pop
there though much of County Warning Area will remain dry...warmer and breezy.
Friday night - confidence...medium
airmass will be moist as dew points climb into the 60s. 850 low level jet
has greatest impact on Friday night. Upper ridge does flatten
though any vorticity maxes are north or northwest. However surface
trough approaches. 00z European model (ecmwf) has the most southern placement of
precipitation into southern WI while the GFS and NAM keep precipitation more into
northern/central WI. The southern translation of the 850 low level jet may
supportthe quantitative precipitation forecast pattern played out by the European model (ecmwf). Will have a north
to south gradient in probability of precipitation. The 00z NAM sounding shows elevated
cape values of over 3000 j/kg. The GFS sounding much less but
still shows convective potential rooted aloft.
Saturday - confidence...medium
while primary vorts stay north all models suggest an axis will
swing through along with the surface feature...so expect
shra/tsra. Degree of clearing and buildup of instability will
drive degree of severity. However models have been trending
towards the stronger storms setting up across to areas south.
Spcday3 has US marginal and this makes sense given the cloud
cover uncertainties at this time. The NAM is the slower solution
and lingers precipitation into the evening hours while the GFS and European model (ecmwf)
suggest dry after 00z. Cloud cover will make for a tricky temperature
forecast though 925 temperatures into the lower 20s celsius would support
sneaking in some low 80s with some sun...but trended a bit cooler
Sunday - confidence...medium
upper flow proggd to be strongly cyclonic though surface high
pressure gradually building in. Appears GFS overdoing areal extent
of light precipitation but even the European model (ecmwf) is suggesting potential for
spotty light precipitation. Will keep a small pop in the far NE County Warning Area.
Cooler with 925 temperatures down to 12-15c.
Sunday night through Wednesday - confidence...medium
high pressure and dry weather expected to dominate this period.
Benign north-northwest broadly anticyclonic flow Monday and Tuesday gives way
to upper ridge building across for Wednesday. This will further
support the dry forecast. 925 temperatures in the 12-16c range support
highs in the upper 60s to low 70s.
Aviation/12z tafs/...look for a period of low clouds in the area this
morning in the wake of a cold front that will move south of Wisconsin
by 12z this morning. These clouds will be a mix of IFR and MVFR...but
it isn/T a solid deck and there will be variability. These clouds
are expected to linger the longest across the southeast...but scatter
out this afternoon. Then look for VFR conditions through the remainder
of the taf period.
Marine...high pressure retreating to the east and a low pressure/cold
front approaching from the west will likely bring Small Craft Advisory
conditions Friday afternoon through Saturday due to breezy southerly
winds. The highest waves would be located north of Milwaukee.
Today/tonight and aviation/marine...Davis
Friday through Wednesday...collar