Scientific Forecaster Discussion
fxus63 kmkx 261148
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
648 am CDT Wed Apr 26 2017
Aviation(12z tafs)...an area of showers and tstorms over nrn Illinois
will move newd across srn WI this am. Cigs and vsbys may fall to
MVFR at times. The next area of widespread rain will start by
early evening. Cigs will fall to 1-3 kft but then fall below
1 kft by late evening. Vsbys will fall to MVFR but possibly to
2sm over far ern WI.
Previous discussion... (issued 351 am CDT Wed Apr 26 2017)
Today and tonight...forecast confidence is medium.
Areas of showers will move across srn WI this morning with the
passage of a shortwave trough. The cold front will then slowly
begin to move from W-E across srn WI thus more areas of showers
and possibly a tstorm will occur. Another mild and humid day is
For tnt, the strong upper trough currently over the srn rockies
will track to Texas then swing newd to Illinois by 12z Wed. This will
induce cyclogenesis from S-N along the front. The low will track
from srn Illinois to nrn Lake Michigan. Well organized low to mid level
frontogenesis and q-vector convergence will bring widespread
moderate to briefly heavy rainfall rates tonight. Total forecasted
amounts range from one half inch west of Madison to near 1.5
inches in se WI. Rivers will rise again with several rivers likely
reaching bankfull stage and perhaps a few reaching minor flood
Thursday - confidence...medium
primary 500 millibar low vcnty nrn Minnesota will lift north. A
negatively tilted shortwave will move northeast across WI. The
upstream surface low will be lifting northeast from NE WI. Def
zone precip shield lingers for the morning hours with 850 cold
advection wrapping in on NW winds. Some of the 850 temps in the
west drop below zero celsius so some concern for a mix in these
areas especially from the NAM, however other models suggest the
precip may out race the colder profile supportive of a mix. For
now leaned more towards the GFS low level profile and consmos
temps which keep things in liquid form. Precip becomes more
scattered during the afternoon.
Friday - confidence...low to medium
pattern looks to stay active on the Gem/GFS/NAM front while the
European model (ecmwf) keeps the precip to our south. All the models including the
European model (ecmwf) show shortwave energy shifting northward into srn WI with
time. However the European model (ecmwf) is showing much less of an isentropic
component to the forcing than the wetter solutions. Will steer
towards the blended approach and gradually lift pops north as the
day wears on going the with the consensus of a wetter look.
Saturday - confidence...medium
a high pressure ridge is proggd to be sprawled across the upper
Midwest with a cool easterly flow. The GFS keeps the next surge of
rain to our south while the Gem and European model (ecmwf) bring some light rain
northward especially during the afternoon. So again , we have a
northward push of the probability of precipitation into at least the southern County Warning Area as the
day wears on.
Saturday night through Monday - confidence...medium to high
little if any model disparity with next 500 millibar low moving
from the Southern Plains up through the western Great Lakes this
period. This will keep things quite wet and unsettled. A southerly
850 jet takes hold Saturday night then better upper dynamics
later Sunday into Sunday night, so likely to see two distinct
precip maxes within the overall wet period. Some elevated cape
noted at times so some thunder potential. System occludes as low
shifts across WI. Better convective potential appears to be
setting up in the warm sector ahead of the cold front to our
southeast Sunday into Sunday evening. Bulk of heavier precip wraps
up later Sunday night with cold advection wrapping in from the
southwest. A chilly Monday in the works with brisk west/northwest
winds and lingering cyclonic flow with low level thermal trough
Tuesday - confidence...low to medium
the European model (ecmwf) lingers the low level cyclonic flow with lingering shra
chances while the GFS builds in 850 ridging and a dry look. Will
go the blended approach on pops/temps.
Aviation(06z tafs)...look for VFR conditions through the night.
Moisture streaming north ahead of an approaching trough of low
pressure will bring increasing chances of showers. Ceilings will
gradually lower to MVFR levels Wednesday with showers and a few
thunderstorms, especially southeast. IFR cigs expected behind a
cold front Wednesday night.
Marine...a Small Craft Advisory is in effect until 11 PM tonight
due to breezy sly winds and high waves. Low pressure will then
track north along Lake Michigan with wly winds in its wake. Thus another
Small Craft Advisory may be needed on Thu for brisk wly winds.
Lm...Small Craft Advisory until 11 PM CDT this evening for lmz643>646.