Scientific Forecaster Discussion
fxus63 karx 240750
Area forecast discussion
National Weather Service La Crosse WI
250 am CDT Sat Jun 24 2017
Short term...(today and tonight)
issued at 250 am CDT Sat Jun 24 2017
24.07z water vapor loop shows a potent short-wave along the
ND/Manitoba border which will drop southeastward and across the
forecast area today. A 500 hpa 60 kt speed Max on the southern
periphery of this wave will interact with roughly 500-1000 j/kg of
MUCAPE, producing showers and thunderstorms this afternoon and
evening. Although instability is on the weaker side, strong
dynamic forcing may be enough to produce some small hail. In
addition, inverted-v forecast soundings suggest some gusty winds
are also possible. Convective activity should diminish with loss
of heating and deep layer subsidence in the wake of the departing
wave later this evening.
Otherwise, today will be another cool one with highs only in the
60s. It will also be breezy with around 30 kts in the well mixed
boundary layer, resulting in some northwesterly surface gusts up
to 25 mph. Expect a cool night with partly cloudy skies. Winds
will light from the west with temperatures dropping into the mid
40s to around 50 degrees.
Long term...(sunday through friday)
issued at 250 am CDT Sat Jun 24 2017
Another short-wave will move across northern Minnesota/WI on Sunday. This
wave is much weaker than today's and with limited instability,
only a few afternoon thunderstorms are possible. Otherwise, there
is a chance for accumulating rains across most of the forecast
area, but the highest threat will be across north-central WI
closest to the wave aloft. Temperatures again will be cool Sunday
with highs staying in the 60s. Mixed boundary layer winds won't be
as strong as today, but still around 20 to 25 kts, which should
result in some surface gusts to around 20 mph.
One more weak short-wave moves through the region on Monday for
another chance for showers/isolated afternoon storms, but most
activity should be confined to areas east of the MS river.
Temperatures warm a degree or two, but generally remain under the
70 degree mark. Winds will also be much lighter, but remain from
Tuesday still looks dry with ridging aloft and surface high
pressure passing to the south and east of the forecast area. As a
result, expect mostly sunny skies with increasing southerly winds.
This warming pattern will allow temperatures to climb back into
the mid 70s.
Wednesday and Thursday are shaping up to be more interesting.
Convective environment still fuzzy given model differences, but
general idea is for increasing mid-level moisture transport to
interact with instability plume and increasing westerly flow aloft
to produce shower and thunderstorm chances ahead of an eastward
advancing cold front. This front could stall somewhere in the
vicinity of the forecast on Thursday into Friday before finally
moving out by next weekend. Too early to provide meaningful
detail, but ingredients may come together enough to produce some
stronger (possibly severe) thunderstorms. Temperatures for the
latter half of next week will warm, topping out in the mid 70s to
lower 80s each day.
Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1115 PM CDT Fri Jun 23 2017
Cigs/wx/vsby: areas off mid level VFR clouds hanging out over
northern parts of Minnesota/WI at late evening, and should continue their
slow shift east overnight, dissipating a bit in areal coverage as
Sat and sun look much like today, as a couple shortwave troughs,
good low level lapse rates, and afternoon instability work to
produce bkn cu fields along with scattered shra and possible ts.
Shower/storm activity will be more widespread compared to today,
with greater forcing to work on the environment. Could be a short
lived vsby restriction with any thunderstorm. On the whole,
expecting VFR conditions.
Winds: should stay northwest through Sat. Look for gustiness to
return by late morning Saturday, and some enhanced gusts around any
heavier shower or thunderstorm - upwards of 30 kts possible.