Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
345 am CDT Friday Jul 25 2014
Today and tonight...forecast confidence is medium.
Pockets of convection extending from northeast South Dakota and
SW Minnesota into eastern Nebraska developing along leading edge of surface to
850 mb moisture plume in region of deep moisture convergence and
Theta-E advection ahead of 850 mb low/surface low with most unstable
cape of 1000 j/kg or higher.
These pockets of convection are setting up to the SW and west of
strong 850 mb frontogenetic response to the low level jet
impinging on 850 mb baroclinic zone stretching across west central to
south central Minnesota into NE Iowa.
Hi res/rapid update models catching on to lack of moisture and
instability over WI and keeping precipitation out of County Warning Area until after
12z...with a few altocumulus castellanus sprinkles possible before then.
Models agree that areal coverage and amount of precipitation will
diminish as weakening forcing and Omega pushes across state with
diurnally weakening low level jet this morning/early afternoon. Will keep
probability of precipitation in chance/scattered category and mainly showers with only a
slight chance of thunder due to capping and marginal middle level
Looking for a break in the precipitation middle afternoon...then redeveloping
as low level jet begins to strengthen late this afternoon and
evening. Cap at 700 mb erodes early to middle evening...but still
some question to amount of surface based cape. However decent
elevated cape for thunderstorms. 0 to 6km shear sufficient for
sustained updrafts...and with steepening middle-level lapse
rates...some hail not out of the question though probability for
severe hail is low. Precipitable water/S reach near 2 inches by 06z so heavy
downpours possible... especially in the far south and southeast.
Short term...Saturday through Sunday night...forecast confidence
Models showing quantitative precipitation forecast associated with main push of warm air advection
moving off to the east on Saturday. Area forecast soundings
showing capped airmass over southern Wisconsin...with not much
forcing for upward vertical motion seen. Thus...kept Saturday dry
across the area. Warm and humid conditions will prevail...with
highs reaching the middle 80s in most areas per 925 mb temperature
Kept low probability of precipitation in the western counties Saturday night...with
approach of 500 mb shortwave trough. However...this will still
have to contend with fairly strong cap over the area. So...most of
the night may remain dry in this area.
Models then bring cold front southeastward through the area Sunday
morning into early afternoon...with trailing 500 mb shortwave
trough moving through during the afternoon and early evening. Area
forecast soundings do mix out cap during the day...though it may
be after the frontal passage in northern portions of the area.
Kept likely probability of precipitation for thunderstorms most of Sunday...though best
chances will be in the morning before frontal passage. Some
question as to how much mean layer cape will exist before front
moves through. This will determine if there will be a hail
risk...given the strong deep layer shear.
Cold air advection Sunday night should bring in cooler and less
humid air...and end the probability of precipitation during the evening hours.
Long term...Monday through Thursday...forecast confidence is
GFS/European model (ecmwf) showing high pressure slide southeast from the northern
plains into the middle Mississippi River valley region Monday into
Wednesday. 500 mb trough remains anchored over the northeast and
Middle Atlantic States...with north northwest flow over the
western Great Lakes region.
Various 500 mb vorticity maxima move through the area during this
time. Enough moisture lingers to carry lower end probability of precipitation for most of
this period. Continued probability of precipitation through Thursday using consensus
probability of precipitation...as overall pattern lingers. Temperatures should be pleasant
for this time of year.
Aviation/12z tafs/...coming shortly...
Today/tonight and aviation/marine...rem
Saturday through Thursday...wood