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Area forecast discussion 
National Weather Service La Crosse WI
1144 PM CDT Friday Jul 11 2014

Short term...(this evening through saturday)
issued at 332 PM CDT Friday Jul 11 2014

Main forecast concerns are on severe thunderstorm potential on
Saturday into Saturday evening. Focus then turns to unseasonably
cold temperatures early next week.

Surface observations showed a cold front extending from northwest
Minnesota into extreme northeast South Dakota...edging southeast.
A broad warm air advection regime was in place over the upper
Mississippi River valley with a shortwave moving through and
exiting the area late this afternoon . This wave brought showers
and isolated thunderstorms to parts of the region today. A warm
front is expected to lift into central Iowa/northern Illinois
tonight and will be the focus for more showers and thunderstorms.
Across the local area it should be pretty quiet tonight outside
of seeing mostly cloudy skies and possibly some patchy fog. The
cloud cover and south winds should help hold temperatures in the
middle to upper 60s.

A shortwave rough then races east across South Dakota early Saturday
morning and pushes through the forecast area late Saturday morning
through Saturday afternoon. This wave will interact with the cold
front edging into the forecast area from the northwest and the warm
front over portions of northern Iowa into far southwest Wisconsin.
While this feature will generate widespread showers and
thunderstorms over the region there is some uncertainty regarding
severe weather potential. The main concern looks to be heavy rain
through midday on Saturday then...if the instability can lift
north into locations along and south of Interstate 90...we could
see the threat for damaging winds and large hail. While 0-1 km
shear isn/T could possibly be enhanced over
portions of northeast Iowa and extreme southwest Wisconsin closer
to warm front. This would lead to the possibility of an isolated
tornado over these areas. There is excellent upper level support
for showers and thunderstorms tomorrow thanks to the right
entrance region of an upper jet streak positioned over the
region so have increased precipitation chances significantly. 0-6
km bulk shear is weak Saturday morning but then ramps up Saturday
afternoon when values increase to 40 to 50 kts. Most of the shear
is located in the 1 to 7 km even elevated storms could
possibly become severe. Precipitable water values increase to 1.5
to 2.0 inches tonight over much of the forecast area and remain in
this range through tomorrow afternoon for locations along and
south of Interstate 90. These precipitable water values combined with warm cloud
depth of 3.5 to 4 km will increase the potential for heavy
rainfall. Will have to keep a close eye on heavy rain potential
over northeast Iowa into southwest Wisconsin. The front.

Long term...(saturday night through friday)
issued at 332 PM CDT Friday Jul 11 2014

The front then pushes southeast of the forecast area Saturday
evening with showers and thunderstorm ending. A secondary cold front
then drops south across the area on Sunday and may generate a
couple of showers and thunderstorms but instability is rather
lacking with this feature. A potent upper trough will drop south
out of Canada and into the upper Mississippi River valley Sunday
night into Monday bringing unseasonably cold air into the region
along with chances for rain showers. 850 mb temperatures fall to
around 4 c Monday night into Tuesday with standardized anomalies
of -2.0 to -2.5 placing US in record cold
temperatures...especially for high temperatures on Monday into
Tuesday. Tuesday looks to be the coldest day when highs will
struggle to get out of the lower to middle 60s. The trough exit the
region Tuesday night into Wednesday . Temperatures then start to
moderate Wednesday through the end of the work week with highs
climbing back into the 70s.


Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1143 PM CDT Friday Jul 11 2014

The area of MVFR clouds has dissipated or lifted up to VFR
ceilings with the back edge working steadily east and by 06z the
clouds should be past klse. This increases the probabilities that
some fog can form overnight but at the same time...high clouds are
beginning to spread in from the west...which would decrease the
fog probabilities. The high clouds appear to be dissipating some
as they come into the area and if this trend continues...some fog
could form so have held onto this in both forecasts. A warm front
sits across southern Iowa and as the moisture transport increases
into this overnight some convection is expected to form along this
boundary. This combined with the ongoing activity over Nebraska
and South Dakota could drift northward into the area early
Saturday morning. This is the trend that has been shown by the
last few runs of the hrrr and have introduced a vcsh for this by
middle morning with a VFR ceiling. The better chances for convection
will be tied to the short wave trough coming across Wyoming and
Montana. The 12.00z NAM shows convection developing around middle day
over South Dakota and Nebraska and then moving east into the area
late in the afternoon into the evening. Based on this
timing...have pushed the timing of the thunderstorms in the vicinity back a little at both
sites but did introduce a MVFR ceiling at krst.


issued at 332 PM CDT Friday Jul 11 2014

Record cool high temperatures are possible on Tuesday as an
unseasonably cold airmass settles over the upper Mississippi
River valley. Forecast high temperatures for Tuesday are 65 at
Rochester and 66 at La Crosse. These temperatures would break the
record lowest high temperatures for July 15th. The old records are
68 at La Crosse set back in 1962 and 67 at Rochester also set
back in 1962.


Arx watches/warnings/advisories...


Short term...wetenkamp
long term...wetenkamp

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