Area forecast discussion
National Weather Service La Crosse WI
336 PM CDT Friday may 24 2013
Short term...(this evening through saturday)
issued at 334 PM CDT Friday may 24 2013
At 3 PM...a 1003 mb high pressure system...centered over Lake
Michigan...kept skies partly sunny across the upper Mississippi
River valley. Meanwhile further west...a short wave was producing
showers and thunderstorms across the eastern quarter of the
Dakotas and western Minnesota. The mesoscale and deterministic models are
continuing to struggle with the eastward progress of this
precipitation tonight. The European model (ecmwf) and hrrr move this precipitation
across most of forecast area by 25.06z. Meanwhile the
nmm...arw...GFS...Gem...rap... and NAM mainly confine the
precipitation west of the Mississippi River this evening...and
then moves it across the remainder of the area overnight. Since
the convection across the Dakotas will be moving into an area with
less frontogenetic forcing...moisture transport...weak isentropic
lift...and drier air...decided to trend the forecast toward the
latter model set. In addition...the radar echos across western
Minnesota are showing a decreasing trend. Even by doing
this...there is some variations amongst them...so tried to go with
an ensemble approach when assigning the hourly precipitation
chances. The highest precipitation chance and amounts /up to a
half inch/ will be found across across southeast Minnesota and
northeast Iowa.
On Saturday...the short wave will move east southeast across Iowa.
As this occurs...the 850 mb moisture transport and isentropic lift
will gradually weaken. As a result...went with a decreasing trend
in the precipitation trends from late morning into the afternoon.
Additional raifall amounts will be less than 2 tenths of an inch.
With the 24.12z and 24.18z models in good agreement that there
will be less than 100 j/kg convective available potential energy...just kept an isolated
thunderstorm chance mainly west and south if the Interstate 94
corridor.
Long term...(saturday night through friday)
issued at 334 PM CDT Friday may 24 2013
From Saturday night through Sunday night...the warm front will
remain well southwest of the forecast area. As a result...
southeast Minnesota...northeast Iowa...and southwest Wisconsin
will remain cloudy with periodic showers and maybe an isolated
thunderstorm. Over the past 3 days...the consall has continued
to trend toward cooler high temperatures for Sunday. It now has
high temperatures around 60. Meanwhile the European model (ecmwf) only has high
temperatures in the lower 50s for these areas. Since the European model (ecmwf)
typically verifies the best for this time period...went with a
blend of the consall...consallbc...and emcwf.
From Memorial Day into Tuesday...the models are continuing to show
that a warm front will move northward into the area. This will
allow ml convective available potential energy to climb into the 1k to 3k j/kg range. As a
result...expect the thunderstorm chances to increase during this
time period. The 0-3km shear would be favorable for the
possibility that a few thunderstorms may be capable of producing
large hail and damaging winds.
From Tuesday night into Friday...the models continue to struggle
on where the warm sector will be located. This greatly affects
the where the precipitation may be located. In addition...it will
also affect the shear and instability...thus...there is a lot of
uncertainty on whether there will be any severe weather.
&&
Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1214 PM CDT Friday may 24 2013
Focus of the forecast is on the potential for showers late tonight
into Saturday morning. Short wave trough in the Lee of The Rockies
over Wyoming is expected to top the mean ridge and slide across
the region late tonight and Saturday morning. An axis of moisture
transport is expected to develop this afternoon ahead of this wave
then Bend to the northeast and be focused into the area late
tonight. However...this will be weakening through the night and
will not be very strong by the time it becomes focused on the
local area. The forcing from the wave and the weak moisture
transport should be enough to generate some showers. Expect these
will move into both taf sites between 09z and 12z. The showers
should be light enough to not produce any visibility restriction
but could produce some MVFR ceilings as the rain saturates the low
levels of the column enough to allow the ceilings to lower. The
24.09z sref shows the better probabilities of this occurring are
west of the Mississippi River so have included this at krst. The
isentropic upglide on the 300k surface begins to weaken after 15z
Saturday but does continue for the remainder of the morning and
should be enough to keep some showers or sprinkles going through
the end of the forecast period.
&&
Arx watches/warnings/advisories...
WI...none.
Minnesota...none.
Iowa...none.
&&
$$
Short term...boyne
long term...boyne
aviation...04
