Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 171122
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
622 AM CDT Sat Jun 17 2017

.SHORT TERM...(Today through Monday)
Issued at 317 AM CDT Sat Jun 17 2017

High Impact Weather Potential: Thunderstorm chances continue this
afternoon and early evening, especially across far southern portions
of the area. Any storms that develop could become severe, though
thankfully the main axis for widespread severe weather looks to be
south and east of the local area.

After another bout of active weather yesterday evening, things have
really quieted down out there at this early hour, with dry
conditions overtaking the local area the past few hours. On the
weather front, a flat flow regime remains in place at the moment but
with hints of incoming change to our west with a stronger shortwave
noted working across Montana currently. That feature is expected to
amplify through the northern Plains into early evening, dropping
over our area into tonight. Earlier frontal boundary draped near the
I-90 corridor has been convectively shoved well into central and
southern Iowa as of 06Z, and unlike yesterday, it appears that
feature will struggle to mix/advance back northward today with
weak low level ridging building in from the west in advance of a
cold front dropping south out of North Dakota and northern
Minnesota.

That`s potentially very good news for us locally from a severe
weather standpoint, as there are increasing signals that convection
will fire along that boundary as the stronger upper forcing arrives
late this afternoon. Current trends suggest those storms may just
clip our far southern areas (Grant over toward Fayette?) before
really expanding in coverage and organization into portions of Iowa
and Illinois and perhaps southeast Wisconsin into this evening.
Plenty of deep layer shear for storm organization, so we`ll have to
closely watch where storms form for some small initial severe
threat, but it looks like we may dodge this one by just a bit.
Instead, as the upper wave approaches, can envision a smattering of
showers and perhaps a few embedded thunderstorms working across the
area into tonight, with waning thunder chances after sunset and
probably the best coverage well north of I-90 within the axis of
better deformation forcing with the upper wave.

Sunday still looking notably cooler with pronounced upper troughing
overhead, with another flare-up of diurnal showers and maybe a
rumble of thunder through the afternoon and early evening hours
(MUCAPE up to 500 J/kg 18-00Z), with a similar setup on Monday,
though with the best shower chances likely near and east of the
Mississippi River. Bigger story through here remains temperatures
with highs back below normal and overnight lows very comfortable for
a change over recent days.

.LONG TERM...(Tuesday through Friday)
Issued at 317 AM CDT Sat Jun 17 2017

Another period of transition may be on the way through much of next
week, with increasing confidence that our upper troughing in place
through Tuesday will be replaced by building heights and warmth
through midweek, before some semblance of upper troughing makes a
return into late week or just beyond. Lots of details for any one
given period still to be determined in such a changeable weather
regime, though the idea for continued cooler temps and some chance
for mainly diurnal showers on Tuesday looks good at the moment,
before high pressure drops directly overhead Tuesday night with the
possibility for some quite cool overnight lows in spots. In fact,
already seeing MOS numbers for the "usual" cold spots showing lower
40s, and can`t argue with that idea given the setup.

Return flow looks to kick into gear a little earlier than this time
yesterday, with increasing chances for showers and storms by as
early as midday Wednesday through Thursday as a few weaker waves zip
through the flow and interact with another frontal boundary
somewhere nearby (exact location to be determined). Beyond Thursday,
there have been consistent signals for another bout of upper
troughing and cooler weather toward Friday or next weekend, though
of course plenty of time to sort out those details the next few
forecast cycles.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 622 AM CDT Sat Jun 17 2017

VFR conditions are expected through the day after any early
morning low clouds/fog mix out. At least isolated/scattered
showers/storms are expected later today into tonight, but
confidence on timing and coverage remains low. Will not introduce
thunder at this time, but a brief period of IFR/MVFR conditions
may occur with any storms. Some guidance suggests ceilings may
dip into the MVFR range towards the end of this TAF period, but
will not mention yet. Winds will remain generally under 10 kts
through the period.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Lawrence
LONG TERM...Lawrence
AVIATION...JM



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