Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 karx 300838 

Area forecast discussion
National Weather Service La Crosse WI
338 am CDT Tue may 30 2017

Short term...(today and tonight)
issued at 338 am CDT Tue may 30 2017

30.08z water vapor loop shows at least three distinct short-waves
rotating around the parent low over central Ontario. The second
two waves, currently across northern Minnesota and along the Manitoba/ND
border respectively, will drop south across the forecast area
today. As a result, expect periods of scattered showers, with the
best chances being mid-late afternoon for areas south of I-90
where a developing surface trough will provide a boundary for
additional low-level lift/convergence. Kept isolated thunder
mention for the southeast half of the forecast area where MUCAPE
increases up to 500 j/kg. Otherwise, expect increasing cloud cover
through the day, which will help keep temperatures in check with
afternoon highs from the mid 50s across the north to mid 60s
across the south. Westerly winds will be breezy at times with some
gusts to around 20 mph.

Showers will dissipate this evening after sunset with gradually
decreasing cloud cover overnight from southwest to northeast.
Temperatures will be dependent on clouds, but should drop into the
mid 40s for most areas.

Long term...(wednesday through monday)
issued at 338 am CDT Tue may 30 2017

Wednesday/Thursday now look dry as surface high pressure builds
across much of the upper Midwest. A short-wave aloft Wednesday
night/Thursday morning will interact with a warm front across the
Central Plains, keeping showers/storms south across NE into
northern MO/southern IA, so main impact farther north will be
increasing cloud cover on Thursday. Temperatures Wednesday in the
mid-upper 60s will warm 5 to 10 degrees for Thursday with most
areas reaching the mid 70s.

Aforementioned warm front then lifts northward Thursday night into
Friday, increasing chances for showers and thunderstorms, especially
across the southern forecast area. Friday through Sunday, shower/
storm chances will depend on position of the warm front with some
rather Stark differences between the GFS/ECMWF. The European model (ecmwf) stalls
the front in the vicinity of the forecast area, allowing for multiple
rounds of showers/storms and thus increasing the heavy rain threat
with precipitable waters around 1.5 inches and warm cloud depths to 3.5 km. The
GFS, however, pushes the front well south Friday night, resulting
in a mostly dry Saturday with additional rain chances on Sunday
due to another Pacific short-wave that's not depicted by the
European model (ecmwf). With a more northern frontal position, instability/shear
profiles support potential for severe thunderstorms in addition to
heavy rain. Too many differences within current model suite, so
overall forecast confidence is low. However, something to watch
closely over the next several days.


Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1145 PM CDT Mon may 29 2017

The afternoon/evening showers have finally dissipated, but there
are still more clouds upstream of both airports as another short
wave trough moves south across Minnesota. All the short range
models indicate this wave will not produce any showers overnight
and that most of the clouds should dissipate before getting too
far south. Even if they do move over either Airport, it would be a
VFR ceiling anyway. Another short wave trough will move across the
region Friday. This should produce another round of
afternoon/early evening showers and will continue to mention a
vcsh for both airports with a lower ceiling, but still VFR. For
the showers that do form, expecting these to dissipate by early
evening with the VFR ceiling continuing for a few hours before the
clouds scatter out.


issued at 338 am CDT Tue may 30 2017

Flood warnings continue along the Mississippi River at both
McGregor and Guttenberg dam 10 through at least the latter half of
the week. Meanwhile, elevated water levels continue along the
Mississippi River farther north.

Heavy rainfall is possible at times Thursday night through Sunday,
but the threat is highly dependent on the position of an expected
warm front. Large differences in forecast guidance at this time
result in low confidence, but something to watch over the next
several days.


Arx watches/warnings/advisories...


National Weather Service Glossary of Abbreviations