Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 271156
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
656 AM CDT FRI MAY 27 2016

.SHORT TERM...(Today through Memorial Day)
Issued at 342 AM CDT Fri May 27 2016

Another day in a string of challenging convective forecasts, with
the focus primarily on an approaching convectively-enhanced
shortwave this morning followed by what if any additional
redevelopment we can muster for the afternoon. As mentioned by the
previous forecaster on this shift last night, the overall pattern
through much of the Memorial Day holiday weekend remains one muddled
by lots of uncertainty with regard to timing and coverage of various
precipitation/convective chances as we maintain broad southwest flow
aloft across the Plains/Miss Valley with a variety of shortwaves
traversing said flow. With such inherent uncertainty, by far the
best effort and most "bang for the buck" will be come in timing
precip over the next 24 hours, with a more broad brush approach
thereafter simply given uncertainty.

As for current trends, precip off to our south into Iowa has hit a
brick wall through much of the night, courtesy of a notably drier
airmass up this way and all the better warm ascent/theta-e advection
off to the south, tied to a convectively-enhanced shortwave working
through eastern Kansas at 07Z. In addition, reinvigorated
convection working through central Kansas effectively cut off any
northward progress of moisture transport earlier, though that is
changing recently with waning upstream convection and
redevelopment of a few showers/storms over the southern and
western CWA. Heading through the morning, do expect the upper
wave to work north with a band of showers and likely embedded
thunder as elevated CAPE values peak around 500 J/KG through mid
morning.

Behind the departing wave, the afternoon forecast remains lower
confidence, but there are hints of a secondary weak wave lifting
through southern Kansas which should cross the area toward mid or
late afternoon. Have some issues with guidance really trying to
lift a warm front this far north through the day with limited
upper support (especially if ongoing convection to our south
continues through part of the morning), but in spite of that,
deepening low level southerly flow should at the very least help
modulate dew points back up toward the 60-62 degree range (much
lower than current NAM/GFS depiction by the way). Pending cloud
trends and the degree of heating, that may prove sufficient to
raise MLCAPE values to around 1,000 J/KG but with limited forcing
mechanisms and weak low/mid level shear really arguing for not
much more than maybe some scattered afternoon showers and storms,
increasingly focusing toward the lower Great Lakes where moisture
transport becomes most focused through the evening.

After that, again the details remain murky, but the overall gist is
for the main upper trough axis to lift across the region later
tonight into Saturday, with a more focused axis of moisture
transport directed into the region. Given a better push of upward
forcing from that wave, suspect our better rain chances will reside
during that period, but once again, instability with northward
extent remains severely limited, such that we may see no more than a
few rumbles north of the IA/MN border. With that said, will need to
watch parts of western Wisconsin later Saturday afternoon where a
window of clearing is possible in the northward-lifting warm sector.
Should be manage any decent instability, decent 0-1km and deeper
layer shear could support a limited severe weather threat.

Thereafter for the remainder of the holiday weekend, focus for
additional rain chances appears limited as our flow really flattens
out with the passage of Saturday`s wave. In fact, there are
increasing hints for building shortwave ridging into Memorial Day
itself, and once again we see the typical NAM/GFS high dew point
bias showing up, with those respective models` boundary layer dew
point fields looking much more reasonable as we bleed in drier air
through the latter half of the weekend. As such, honestly not sure
there is much of an overall precip threat both Sunday and Monday,
save for perhaps late Monday with hints that our next upper wave may
makes its approach. For now will maintain some smaller rain chances
until we can refine the details.

.LONG TERM...(Monday Night through Thursday)
Issued at 342 AM CDT Fri May 27 2016

Plenty of detail differences heading through the work week, but
pretty good agreement among medium range guidance for another
northern stream trough axis to slide through the Plains states and
impact our area toward midweek. Modest moisture return from the Gulf
progged during this period does given one hope for some additional
needed rainfall, but some timing differences remain. Suffice it to
say that additional precip chances are more than warranted Tuesday
into Thursday with temps quite seasonable (barring any all-day
rains) though with hints of a trend toward cooler conditions perhaps
by late week with more pronounced upper troughing dipping somewhere
close by.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 656 AM CDT Fri May 27 2016

A trough of low pressure will provide a band of showers along and
north of Interstate 90 this morning. Additional showers will form
late this morning and afternoon as diurnal heating occurs. There
should be a break from the precipitation this evening...and then
another short wave trough will bring a round of showers and
scattered storms for the early morning hours of Saturday.

&&

.ARX Watches/Warnings/Advisories...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Lawrence
LONG TERM...Lawrence
AVIATION...BOYNE



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