Scientific Forecaster Discussion
Area forecast discussion
National Weather Service La Crosse WI
1237 PM CDT sun Oct 4 2015
Short term...(today and tonight)
issued at 347 am CDT sun Oct 4 2015
Challenge today will be cloud cover and its impacts to temperatures.
Will follow the rap 0.5 to 1.0 km relative humidity output...which
seems to be handling current observational trends better than most
In short...today will be much cloudier than most of last week.
Surface high pressure is still in control of the regional weather
pattern. However...an expansive strato-cumulus deck from the Ohio
River valley has lifted north and west overnight and is expected
to maintain itself in some form at least across the eastern half
of the forecast area today. To the west...cirrus are streaming
northward associated with a short-wave trough moving into southern
Canada. Rather high confidence that low clouds will stay across
much of southern WI into portions of northeast Iowa through the
day...but less certain on its northwestward extent. Despite warmer
925 hpa temperatures today...these clouds will no doubt put a Dent
in the potential warm-up...not to mention mixing within the
boundary layer is weak. Will need to monitor cloud trends through
the day...but think highs will struggle to break the 60 degree
mark...especially for areas east of the river.
Low clouds will expand overnight...with the main impact being
keeping temperatures elevated. Lows tonight will be mainly in the
40s with no frost issues.
Long term...(monday through saturday)
issued at 347 am CDT sun Oct 4 2015
Surface ridge axis drifts overhead on Monday resulting in very
weak flow in the lowest 2-3 kft. This will keep low clouds in
place through the day and again limit the temperature rise.
Despite 925 hpa temperatures from +10 to +12 celsius...will cap
Monday highs in the low to middle 60s...but this may still be too
Surface winds shift to the west on Tuesday and increase to around
10 kts within the boundary layer. This...combined with slowly
increasing sunshine and 925 hpa temperatures soaring into the middle
teens above zero celsius should allow afternoon highs to break the
70 degree mark most places. Wednesday now appears mostly dry as a
Pacific short-wave moves through the High Plains. Should be
another warm day with highs similar to Tuesday.
Rainfall chances increase Wednesday night and especially Thursday
as a Pacific trough and associated cold front move across the
upper Midwest. Will keep likely probability of precipitation west of the river Wednesday
night...then overspreading the entire forecast area for Thursday
as modest forcing interacts with increased middle-level moisture
transport to create an area of showers along and ahead of the
advancing cold front. Isolated thunder on Thursday still looks
good with most unstable cape between 400 to 800 j/kg. Much of
Thursday will still be ahead of the front within the warm sector
of the system...so highs still expected to reach the lower 70s.
Slightly cooler and drier weather will be the rule Friday into
next weekend as 500 hpa ridge builds across the intermountain west
and slowly drifts into the nation/S middle-section by Sunday.
Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 1237 PM CDT sun Oct 4 2015
MVFR conditions are expected through the taf period. An overcast-broken
stratus deck will remain over the region through the taf period
with cloud bases ranging from 1500-2500 feet. Forecast guidance is
suggestions we could see some fog tonight and possibly IFR
conditions. Given the cloud cover in place not expecting fog
development. However...if cloud were to clear tonight we could see
some areas of fog. Will have to keep a close eye on cloud trends