Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service La Crosse WI
647 PM CDT Sat Mar 28 2015

Short term...(this evening through sunday)
issued at 345 PM CDT Sat Mar 28 2015

At 3 PM...a 1028 mb surface high was centered over Southern Lake
Michigan. This high was producing sunny skies across the upper
Mississippi River valley. The snow from earlier in the week
continues to show up on the visible and infrared satellite
imagery across southeast Minnesota...and parts of northeast Iowa
and southwest Wisconsin. The combination of this snow and 925 mb
temperatures ranging from -1 to -6c has kept temperatures 10 to 15
degrees below normal /ranging from the middle 30s to lower 40s/. Dew
points across the region range from 5 to 20f.

Further to the west...a warm front was located across the central
Dakotas. Temperatures west of this front ranged from the lower 60s
through lower 80s. The 28.12z models are in very good agreement
that this warm front will move quickly across the eastern
Dakotas...western Minnesota...and western Iowa this evening...
eastern Minnesota and eastern Iowa tonight...and through Wisconsin
on Sunday morning. Soundings continue to show that a 200 mb warm
layer between 700 and 900 mb will nose into the area during the
overnight. The warmest nose of this warm layer will be south of
Interstate 94 where temperatures warm into the 2 to 8c range. As
the warm front moves into the dry air across the region...there
will be strong evaporative cooling this will provide a brief
opportunity of sleet and snow...and then as the air mass moistens
the warm nose will re-establish itself and there will be a lost of
ice aloft. This will result...the precipitation being mainly
liquid. The main question at this time will be how cold the
surface temperatures will be. At this looks like the
areas along and west of the Mississippi River will be mainly above thinking that it will be mainly rain. However cannot
rule out a brief period of freezing rain completely. Meanwhile in
central and north central Wisconsin...there looks to be a slightly
better chance of freezing rain. Even here icing looks to be
minimal. Many of the mesoscale models show that the precipitation will
be a narrow band and this makes sense considering the narrow band
of frontogenesis along the warm front. The soundings show that
there may be some elevated instability above 700 mb. In
addition...there will also be a potential for slantwise
convection. Storm Prediction Center has the area under general thunder. Considered
putting thunder in the forecast...but with the threat being
minimal opted to not include it at this time.

On Sunday afternoon...a cold front will move quickly southeast
across the area. In the wake of this front...the combination of
strong subsidence and steep 900 to 850 mb lapse rates will mix
the stronger winds from aloft to the surface. At this
looks like the winds will gust up to 40 miles per hour. The strongest wind
gusts will be found across northeast Iowa and southeast Minnesota.

Long term...(sunday night through saturday)
issued at 345 PM CDT Sat Mar 28 2015

On Monday afternoon and night...both the Gem and European model (ecmwf) have
shifted their precipitation further north. They now show that much
of their precipitation will be found along and north of Interstate
94. Meanwhile both the NAM and GFS only clip Taylor and northern
Clark County in north central Wisconsin. With still a bit of
uncertainty...took a blend of these models and kept the
precipitation chances below 30 percent.

On Wednesday afternoon and night...the models have now speed up
the timing of the cold front movement across the region. As a
result...this allows less time for both surface based and most
unstable convective available potential energy to build up ahead of this front. Due to
this...opted to keep the mention of thunderstorms out of the

From Thursday night into Friday...the models differ on the
northern extent of a short trough ejecting out of the Southern
Plains. The European model (ecmwf) is much further north and brings rain too much
of the area. Meanwhile...the GFS is further south and the area
remains dry.


Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 647 PM CDT Sat Mar 28 2015

Sunny/clear skies with southerly wind in the 10 to 16 knots range to
persist through the midnight hour at krst/klse. For the overnight
period...expect increasing high clouds from the west. Bigger
concern will be very strong south-southwest winds aloft from 45 to
60 kts in the 1500 to 2000 feet above ground level layer. Nocturnal cooling should
limit gusts at the surface...but sustained winds will increase up
to 20 kts. Will continue low-level wind shear mention.

Precipitation quickly moves through Sunday morning ahead of a
strong cold front. Should be a quick shot and narrowed
precipitation timing to between 29.10z to 29.13z at krst and
29.11z to 29.14z at klse. Phase will be highly dependent on
surface temperatures...but appears most if not all precipitation
should fall as rain. As rain moves in...ceilings expected to
rapidly drop into the MVFR/possible IFR range. Once rain pushes
east...lower ceilings to continue at least through Sunday morning
with some improvement expected by 29.18z. Southwest winds will
increase through Sunday morning with frequent gusts from 26 to 34
kts. Cold front moves through Sunday afternoon...after which
winds will shift to the northwest and gust as high as 38 kts at
krst and 30 kts at klse.


Arx watches/warnings/advisories...


Short term...boyne
long term...boyne

National Weather Service Glossary of Abbreviations