Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
941 PM CDT Sat Oct 25 2014
Update...00z NAM and earlier model runs continue to support
showers and scattered thunderstorms late Sunday evening through the
overnight. As southwesterly flow aloft moves into the western Great Lakes...the
nose of a 40-50 knots low level jet and associated warm...moist advection will
focus over southern and central WI. Precipitable waters will rise to 1.1 inches with
elevated cape as high as 1000 j/kg. The southwestern County Warning Area will see less
precipitation coverage as the focus of lift is to the north and east.
Stratus clouds to then prevail on Monday with additional showers and
perhaps thunderstorms Monday nt when the upper trough approaches from the
west and a wave of low pressure develops along the slow moving
Aviation/06z tafs/...MO clear skies and good visibilities to prevail sun
into sun evening. Scattered to numerous showers and thunderstorms to then
develop late sun evening into the overnight. Ceilings and visibilities will
eventually fall to MVFR late.
Previous discussion... /issued 339 PM CDT Sat Oct 25 2014/
Tonight - confidence...medium
the push of dry air has been aggressive with surface dew points down
into the low 30s and in some cases middle/upper 20s in the northwest County Warning Area. So
with surface ridge axis drawing closer to the western County Warning Area later
tonight...potential exists for temperatures to drop into the 30s. Still expect
some mixing into the evening until gradient eases enough to allow better
radiational conditions to set in. So some areas may need further temperature
reduction that decouple the earliest.
Sunday - confidence...high
surface ridge will start off across the County Warning Area at the outset and make a slow
translation into lower Michigan. So much lighter wind regime. Temperatures still
on the mild side but mixing not as deep and onshore component evolving....
so expect temperatures a smidge cooler....but still many lower 60s. Low level jet
takes aim into areas west of the County Warning Area during the afternoon as 850 ridge axis
shifts a bit east. Will keep southern WI dry for the day portion...but some
increase in middle/high clouds expected as the warm air advection gets underway.
Short term...Sunday night through Tuesday.
Sunday night...forecast confidence high.
Best forcing with focused warm air advection moves into northwestern County Warning Area
between 00z and 03z...then spreads south and east through the night
with low-level jet. Kept likely probability of precipitation in the northern County Warning Area with the
strongest isentropic adiabatic Omega and lowest condensation
pressure deficits. Backed off to showers and a mention of
thunderstorms for collaboration but with elevated cape values
topping out between 500 and 700 j/kg and 0-6km bulk shear of 35-
40kts...thunder a good bet with the potential for small hail.
Early lows then slowly rising temperatures after midnight with warm
Monday and Monday night...forecast confidence medium.
Precipitation tapers off for a time Monday with passage of short wave and
associated surface wave...though slight chance for showers along
surface warm front/baroclinic zone that lingers over region...then
precipitation redevelops and intensifies with forcing with approaching 500 mb
trough. In spite of model differences in the details of structure
and timing of surface/mid-level features... best chance for showers
and possibly a few storms...will be Monday night.
Not quite as warm as earlier expected with track of initial surface
wave keeping 925 mb temperatures slightly lower than previous runs and
mostly cloudy skies reducing the impact of the already limited
contribution of the late October sun. Cold air advection delayed
until passage of surface trough to the east between 06z and 12z so
an east to west gradient of low temperatures.
Tuesday...forecast confidence medium.
Chance for showers lingers in the southeast with slight chances to
the west Tuesday morning until cooler...drier air works in. Could
see some afternoon sprinkles/very light showers with instability and
middle-upper q-vector convergence as 500 mb trough moves through.
Coldest 925 mb temperatures hold off tot he west through the day...so
highs should reach the middle-upper 50s.
Long term...Tuesday night through Saturday. Forecast confidence
Dry Tuesday night and Wednesday with surface ridge then precipitation chances
return with warm air advection Wednesday night ahead of short wave trough in near-
zonal flow...with chances continuing Thursday into Thursday night
with the passage of the trough. Cold air streams in behind this
wave...with below normal temperatures and a good potential for lake-effect
showers...which models keep with best convergence over the lake with
expected offshore turn to winds due to isallobaric gradient with
density discontinuity between air masses over cooler land and warmer
Aviation/00z tafs/...VFR sky clear tonight into Sunday morning. Gusty west-northwest
winds will ease this evening as pressure gradient slackens and
decent mixing is reduced due to loss of heating. High pressure ridge
axis nudges into western WI by 12z Sunday and shifts into lower Michigan by 00z
Monday. Precipitation associated with low level jet/moist advection still looks to be
holding off until Sunday night.
Marine...gusty west winds will ease with reduced mixing and relaxed
gradient so will leave small craft going until expiration at 22z.
tonight/Sunday and aviation/marine...collar
Sunday night through Saturday...rem