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Area forecast discussion
National Weather Service La Crosse WI
1100 PM CDT Wednesday Apr 23 2014
Short term...(this evening through thursday)
issued at 345 PM CDT Wednesday Apr 23 2014
For late this afternoon and evening...the 23.12z models are in
very good agreement that the short wave trough currently over
southeast Minnesota will move northeast into northeast Wisconsin.
Meanwhile another north wave trough over north central Iowa
currently will move east across the southern third of Wisconsin
and northern Illinois. The hrrr...rap...and arw show that the
rain currently over southeast Minnesota and west central Wisconsin
will move east northeast across central and north central
Wisconsin. Meanwhile the rain along and east of Interstate 35
associated with the southern short wave trough will March east
across the remainder of the forecast area.
For late tonight and Thursday...the models are in good agreement
that strong 850 mb moisture transport will move into the area
ahead of an approaching short wave trough from the northern
plains. As this occurs...the rain will once again become
widespread across the area after a brief break in the evening.
With precipitable water values climbing into the 1 to 1.25 inch
range expect enhanced the rain rates across the area. A total of
1 to 1.5 inches of rain looks likely along and north of Interstate
90 and around an inch south of this Interstate. With most unstable
convective available potential energy up to 250 j/kg along and south of Interstate 94...kept a
mention of isolated elevated thunderstorms /above 2 km/ in the
forecast. While the 2-6 km shear is greater than 60 knots...this
is just too great considering the instability for any of these
thunderstorms to become severe.
Long term...(thursday night through wednesday)
issued at 345 PM CDT Wednesday Apr 23 2014
On Thursday night...the 23.12z models are just a bit slower at
moving the strong 700 to 500 mb frontogenesis and the 500 mb
short wave through western Wisconsin. Due to this...slowed down
the exit of the precipitation through the area. While temperatures
will cool into the middle 30s north of Interstate 94...soundings show
no ice seeding from aloft...thus kept the precipitation in the
form of rain.
From Friday night into Saturday...the models continue to show that
a back door Canadian cold front will push south and southwest
through the forecast area. Moderate to strong 900 to 600 mb
frontogenesis develops along this front over southern Wisconsin on
Friday night. This saturates this column in BUFKIT soundings. Due
to this...added a small chance of rain to the forecast.
From Monday night through Wednesday...the models continue to
struggle of their track of an upper level low through the middle and
upper Mississippi River valley. After days where the GFS and European model (ecmwf)
were at odds with each other...they came to a consensus in the
23.00z runs that the low would track more over the upper
Mississippi River valley. This would produce another 1 to 1.5
inches of rain across the area. However the 23.12z models are now
showing that the Hudson Bay high winds out and that the upper
level low will move east across the middle Mississippi River valley.
This would leave this time period dry. With the models continuing
to struggle with the track of the upper level low...confidence is
not that high...thus stayed with the model consensus.
Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1100 PM CDT Wednesday Apr 23 2014
The first band of precipitation has shifted east of klse late this
evening...while another band is moving northeast across IA/neb. This
next batch will be showery in nature at the onset...becoming more
widespread toward 09z per latest hrrr/ruc13/nam12. Ceilings will fall
into the IFR/MVFR categories overnight...and likely hold there
through Thursday night. The rain won't exit until close to 00z Friday.
Mostly forecasting MVFR visibilities with the rain...but a period of 1-2sm
Tight pressure gradient will keep winds fairly breezy from the
east/southeast through most of Thursday...with a swing to the
west/northwest as the low passes to the east toward 00z Friday. BUFKIT
soundings also suggesting about a 3 hour window where low level wind shear could be
a concern...roughly in the 10-13z time frame. Its borderline right
now...so will leave out of the forecast. Would be ws020/17048kt.