Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Milwaukee/Sullivan WI
506 am CDT Tuesday Jul 22 2014
Today and tonight...forecast confidence is medium.
Radar returns over west central and SW Wisconsin on leading edge of
850 mb warm advection...in region of decent convergence. However no
ground truth as precipitation is developing above dry...warm layer between
750mb and 650 mb resulting in virga only making it down to around 5k
feet above the ground.
This capping inversion will be problematic during the day as warm
advection continues to strengthen the cap ahead of the cold front.
Consensus surface-based cape increases to between 2500 and 3000 j/kg but
cin remains in the 150 to 200 j/kg range. NAM does show an eroding
cap towards the 22z-00z time frame...but it has dew points
approaching 80f and sb-cape approaching 5000 j/kg. Following lower
consensus temperatures/dew points trends toward the more capped solution.
Bulk shear of 25 to 30 kts accompanies meager 500 mb height
falls/mid-level cooling as southern edge of short wave trough passes
through leads to the potential for some isolated/scattered severe
storms if cap is broken as front passes through. Will limit probability of precipitation to
middle-high chance category late this afternoon and evening.
Forecast temperatures in the upper 80s to low 90s with low-middle 70s
dew points keep apparent temperatures below heat advisory headlines
except for a small portion of the western County Warning Area around Lone Rock. Not
confident in highs reaching the forecast if clouds remain thicker
than expected and too small an area for a headline. Will continue
issuance of Special Weather Statement highlighting the near-advisory warmth.
Precipitation chances exit with front late this evening with cooler and
drier air moving in. Temperatures down into the lower 60s and dew
points in the middle to upper 50s by Wednesday morning.
Wednesday and Thursday...forecast confidence...high
High pressure is expected to bring dry weather and ample sunshine
Wednesday and Thursday. It should be a couple of very pleasant
days with highs in the 70s most places. Threw in some low probability of precipitation
southwest Thursday night...as the high heads east and warm
advection may kick off a few storms.
Friday through Monday...forecast confidence...medium
A series of shortwaves are expected to bring shower/storm chances
to southern Wisconsin at times Friday through the weekend. Models
still have some details to work out...so left chance probability of precipitation through
the weekend. Looks like temperatures will be near normal through Sunday.
It looks like there will be less available moisture early next
week...but still went with some low probability of precipitation Monday as models are
advertising a weak wave. Temperatures should be a couple degrees cooler
Expect VFR conditions through the forecast. Current band of high-
based precipitation on radar over southern Wisconsin struggling
to reach the ground...though a few spots have reported very light
rain/sprinkles with only trace amounts. Best chance for showers
and storms will be along cold front...but will have to break
through warm middle-level cap. Will keep vicinity thunderstorms in
tafs for late afternoon/evening...which will bring MVFR ceilings/visibilities
if/when they develop. Gusty south to southwest winds ahead of
front will lower and turn north to northeast behind front tonight.
Marine...have left Small Craft Advisory hours from previous
forecast. Expect south to southwest wind gusts to reach criteria
middle-morning and continue into late this afternoon before lowering
as cold front/surface trough moves through. Waves will be slower
to lower...so 9 PM end time is looking good. Winds and waves will
rise on Wednesday as high pressure builds in
Beaches...south to southwest winds will gust to between 20 and 25
knots today. While southern zones will only see waves build to 1
to 3 feet at most along the beaches...the northern 2 zones may see
3 to 5 foot waves...especially at south-facing beaches. This
places Sheboygan and Ozaukee County beaches in a moderate risk of
Lm...Small Craft Advisory from 10 am this morning to 9 PM CDT this
evening for lmz643>646.
Today/tonight and aviation/marine...rem
Wednesday through Monday...ddv