Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 302040

Area Forecast Discussion
National Weather Service La Crosse WI
340 PM CDT MON MAY 30 2016

.SHORT TERM...(This evening through Tuesday)
Issued at 340 PM CDT Mon May 30 2016

Primary concerns through Tuesday include timing, coverage, and
strength of thunderstorms as a slow moving Pacific trough moves
across the Northern Plains and into the Upper MS River Valley.
30.20Z analysis shows the mid-upper level low across north-central
MT with a broad surface trough from northeast ND into western NE.
The warm front is well defined by developing cumulus this
afternoon and stretches across southwest MN into central IA. This
front will lift northward this evening and overnight, bringing a
chance for showers and storms for most of the forecast area.
Increasing moisture transport behind the front will allow elevated
instability to increase up to 1000 J/kg, but with weak overall
shear, not expecting any severe convection overnight.

Attention then turns to Tuesday as the low and surface cold front
march slowly eastward across MN. Trends in the 30.12Z models show
a much slower frontal progression, such that it doesn`t reach the
far western forecast area until near 00Z Wednesday. With the front
serving as the primary focus for additional thunderstorm
development, there could be a several hour break in convective
activity Tuesday morning into the early afternoon, especially
east of the MS River. By Tuesday afternoon however, MLCAPE
increases to between 1000 and 2000 J/kg. Deep layer shear is
rather weak, but there is upwards of 30 kts below 3 km. Because of
this, primary convective mode should be multi-cellular with some
strong to severe storms possible. Primary threats with the
strongest storms will be damaging wind, large hail, and heavy
downpours. For now, forecast area is highlighted by a marginal
risk, but wouldn`t be surprised if a small area is eventually
upgraded to a slight risk if higher instability/shear values can
be realized.

Will also want to watch for areas of heavy rain given PWATS
increasing to near 1.5 inches and upper level flow parallel to the
surface front. Not expecting flooding at this time with much of
the area still below normal precipitation for the month of May,
but heavy rain may result in rises on area rivers and some issues
in urban areas. All said, slowed the eastward progression of
higher POPs Tuesday afternoon and evening, exiting the easternmost
forecast area by 12Z Wednesday.

.LONG TERM...(Tuesday night through Monday)
Issued at 340 PM CDT Mon May 30 2016

Wednesday will be mostly dry, but could see some lingering showers
and isolated thunderstorms in post frontal air mass. It will be a
cooler and breezy day with highs in the 70s and westerly wind gusts
up to 25 mph. Thursday will be cool and dry with surface high
pressure dominating the regional weather pattern.

Synoptic pattern still on track for a major shift Friday into
early next week with an amplifying ridge across the intermountain
west, putting the eastern half of the CONUS in a broad trough
with northwest flow aloft across the forecast area. This increases
the chance for showers and thunderstorms with short-waves dropping
south from Canada. The strongest of these is forecast to move
through the area Friday night into Saturday, but chance POPs still
seem reasonable at this time. Higher confidence in temperatures
with daily highs generally in the 70s and lows in the 50s.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 340 PM CDT Mon May 30 2016

A warm front will move northeast into the area this evening/
overnight. Moisture feeding into/over this frontal boundary will
produce scattered shra/ts this evening...mainly west of the
Mississippi River. Will go with vcts at KRST aft 02Z...through
tomorrow morning as it is hard to pinpoint exactly where these
storms will set up/move. Fairly confident this activity will
remain northwest of KLSE taf site until late Tuesday
kept any mention out for now. Otherwise...ceilings/visibilities
expected to remain vfr through the period.

A cold front will then push into the area Tuesday afternoon. Models
produce a broken line of thunderstorms along this front as it pushes
through. A few of these storms could be on the strong side with some
hail and gusty winds. The 31/00z taf issuance will detail this
a bit more.


.ARX Watches/Warnings/Advisories...


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