Scientific Forecaster Discussion
Area forecast discussion
National Weather Service La Crosse WI
1216 PM CDT Monday Mar 17 2014
issued at 723 am CDT Monday Mar 17 2014
Precipitation is becoming more widespread across south central
Minnesota as low level warm air advection increases across the
region. The low level warm layer is pushing a bit further to the
east per the 17.11z rap which takes a +1c to +3c warm nose around
800mb into southeast Minnesota and northeast Iowa through this
morning. So far...there have not been many observations showing
snow in SC Minnesota...rather sleet/up where this warm layer is in place.
Further east across north central Wisconsin...the dry low level
air...as noted on the 17.12z mpx radiosonde observation...between 850-700mb has kept
any of the snow from reaching the ground despite copious amounts
of radar returns picking up on the middle level precipitation. Short term
guidance suggests that this layer should start to saturate out
later this morning as the more potent wave moves in from the west.
The warm nose does not look like it will make it east of the
Mississippi until middle afternoon when most of the precipitation
should be done. Will maintain the current snow forecast and also
add in some sleet to portions of southeast Minnesota/northeast
Iowa the morning/early afternoon.
Short term...(today through tuesday)
issued at 348 am CDT Monday Mar 17 2014
Immediate concern will be accumulating snow mainly north of I-94
today...then focus turns to rain chances Tuesday.
Surface map early this morning has low pressure moving into the
northern plains with a warm front extending southeastward into the
Central Plains. Infrared satellite showing a good stream of warm air
advection middle-cloud pushing into the region ahead of the low and
warm front. Radar mosaic was showing some echoes out of this cloud
across northern WI...but nothing falling at ground level due to
drier lower levels. Also...farther upstream...radar mosaic was
showing an increasing band of precipitation moving southeast across
ND in stronger warm air advection/isentropic lift. This band is expected to
translate southeast into areas northeast of I-94 this morning. More
on this later. Otherwise...clouds and increasing south winds have
pretty much shut down the temperature slide overnight with readings
early this morning in the teens to around 20 degrees.
For today...looking for the wave of low pressure to slide east along
the Canadian/U.S border...pushing a warm front to into the region
today. Increasing isentropic lift and fairly strong 850-700mb
frontogenesis associated with the wave and warm front depicted by
the rap/NAM...moves into areas along/north of I-94 this morning.
This forcing is expected to set up a band of light to moderate
snowfall along/northeast of I-94 this morning...lasting through this
afternoon. Right now...fairly confident 1 to 3 inches of snow will
fall in this area with the higher-end amounts focused across
Clark/Taylor counties. Will have to monitor this forcing closely for
snowburst potential which could lay down locally heavier amounts
which may warrant headlines. Otherwise...temperatures moderate some
today with highs ranging from around 30 across north central
WI...to the upper 30s across northeast Iowa/far southwest WI.
For tonight...will be monitoring strong surface cyclogenesis over
the Central Plains which will push another warm front through the
region. Lift ahead of the front could produce a light dusting of
snow across north central WI before pushing through by midnight.
Fairly breezy southeast winds ahead of the surface low over the
Central Plains expected to keep temperatures up overnight in the 20s
to around 30 degrees.
On Tuesday...the deep surface low will move into southern Iowa with
main deformation precipitation setting up across Nebraska into northern
Minnesota. Models showing lighter precipitation developing over our region
in isentropic lift within the warm sector of the low mainly during
the afternoon hours. Temperatures warming into the upper 30s to
middle 40s would support mainly rain with generally less than a
tenth of an inch expected.
Long term...(tuesday night through sunday)
issued at 348 am CDT Monday Mar 17 2014
Main concern is on the potent storm system affecting the area
Tuesday night into Wednesday with rain changing to snow and strong
Model consensus takes the deep surface low through the region
Tuesday night and then into Upper Michigan during the day Wednesday. This
would keep warmer air wrapped into our area for a slower transition
from rain to snow Tuesday night and thus limiting snowfall amounts
into Wednesday in the 1-2 inch range. Right now...more confident on
heavier snow band setting up farther northwest across
Central/Northeast Minnesota...but will of course have to keep a close eye
on the model trend for the exact track. Any shift with the track
farther southeast could easily shift the heavier snow into our area.
Other facet of this storm will be strong northwest winds on the
backside of the low in the 20-30 miles per hour range with gusts approaching 40
miles per hour in the more wind-prone areas of southeast Minnesota/northeast Iowa. This
may warrant the potential for wind headlines...or could be winter
headlines if heavier snowfall materializes with the winds.
Looks like a quiet break Wednesday night through Thursday as high
pressure moves into the region. Highs on Thursday expected to be a
few degrees below normal...topping off in the middle 30s to lower 40s.
Models showing a middle-level trough coming across the plains into the
upper Mississippi River valley Thursday night through Friday night
with frontogenetically-forced precipitation possibly setting up across
the area. Could be a rain/snow mix initially Thursday night...going
over to snow late in the night...and back to rain with warming on
Friday into the middle 30s/lower 40s.
Models then showing a cold signal for next weekend as a large area
of Canadian high pressure slides southeast into the region. Looks
like well below normal temperatures with highs Saturday and Sunday
looking to top off in the 20s and 30s.
Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 1216 PM CDT Monday Mar 17 2014
Radar trends indicate the band of precipitation has already moved
past krst and will be past klse by 18z...thus plan to start both
tafs without any precipitation. Middle level VFR ceilings behind the
precipitation and looking at visible satellite and observations
back to the west...expect to see these middle level clouds move out
during the late afternoon with either a high VFR ceiling or high
scattered clouds for much of the night. The winds will settle down
early this evening as the low level inversion develops and cuts
off the mixing. As the next system starts to approach from the
west Tuesday...it appears the area should remain in the warm
sector. This will keep the winds out of the south to southeast and
also keep the deeper moisture off to the northwest through 18z
Tuesday. Appears that the forcing will become strong enough for
precipitation to develop from this system...but current timing
would place this between 18z Tuesday and 00z Wednesday.