Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 261937
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
237 PM CDT Mon Jun 26 2017

.SHORT TERM...(Tonight thru Tuesday night)
Issued at 237 PM CDT Mon Jun 26 2017

Main fcst concerns this period are lingering early evening SHRA,
cool lows tonight then returning SHRA/TSRA chances Tue night.

Data analysis at 18z had low pressure over the eastern great lakes
and high pressure centered near the MN/ND/SD border. NW flow at the
sfc and aloft remained over the region, helping keep temps on the
seasonably cool side. Early afternoon temps again some 10 to 20F
below the late June normals under this flow. One shortwave rippling
thru the troughing over the great lakes producing sct mainly SHRA
over eastern WI. Another dropping south thru western Ont producing
sct SHRA/few TSRA over NE MN into far NW WI.

No issues noted with 16.12z model initializations. Solutions quite
similar as the last couple of pieces of shortwave energy pass this
evening, then hgts rise later tonight thru Tue evening. Improving
consensus for hgts to already start falling late Tue night as the
shortwave energy from a northern plains trough quickly pushes into
the Upper Midwest. Overall short-term fcst confidence is good this
cycle.

In the short term, last of the shortwaves over SW Ont will ripple S-
SE across WI this evening. Plenty of SHRA with it up/around KDLH
early this afternoon, to at least accompany it into the area late
this afternoon. Hi-res/CAMs models linger a few of these SHRA across
areas NE of I-94 into the early evening hours. Increased SHRA in the
23-01z time-frame to account for some lingering SHRA to near sunset.
With passage of the last shortwave, hgts/temps aloft start to rise,
but at the lower levels the sfc-850mb ridge axis slides over the
area tonight. Signal among models for drying of the low levels
tonight for what should be clear/mostly clear skies after sunset.
This with lighter winds under the low level ridge axis, tonight may
well be the coolest of the last several. favored cooler of guidance
lows and trimmed these a few degrees in the normally colder, low
laying areas along/NE of I-94. With the light winds and potential
for BL decoupling, short-term/aviation forecaster added some patchy
fog in the river valleys for a couple hours either side of sunrise
Tue morning.

Quiet, warmer day advertised for Tue still on track as the low level
ridge axis slips east of the area and the low level flow becomes
SW/warm advective. With what should be plenty of late June sunshine,
consensus highs for Tue some 5F to 10F warmer than those of today
look good.

Hgts aloft already start to fall later Tue night with the approach
of shortwave energy from the west. Moisture/instability/lift
increase into the west end of the fcst area after midnight. Model
soundings over at least the west 1/3 of the fcst area showing
saturated 850mb parcels can be lifted/convected with minimal
CIN/capping late Tue night, with as much as 500-1500 j/kg CAPE.
Continued a dry fcst Tue evening, then favored higher 40-70%
SHRA/TSRA chances over the west 1/3 to 1/2 of the fcst area by
late Tue night/toward Wed morning. Will have to watch for a few
strong TSRA late Tue night. However appears bulk of the shear will
be in the 0-1km layer under an inversion with the 1-7km shear
progged generally less than 25kts.

.LONG TERM...(Wednesday through Monday)
Issued at 237 PM CDT Mon Jun 26 2017

For Wednesday thru Thursday night: main fcst concerns this period
are SHRA/TSRA chances Wed/Wed night, heavy rain and any possible
severe risk with them.

16.12z model runs offering a tightening consensus on the shortwave
to move across the region Wed/Wed night. Consensus then remains good
for shortwave ridging to quickly cross the region Thu, following by
falling hgts Thu night ahead of the next trough digging across the
northern plains. Fcst confidence for Wed-Thu night is average to
good.

Model consensus has falling hgts aloft, a 1.5 to 1.75 inch PW
airmass, instability and rather deep layered forcing/lift ahead of
the sfc low/cold front thru mid level trough spreading across the
area Wed into Wed evening. Model soundings (those that are not
already convecting) showing lifting parcels around 850mb results in
minimal CIN and as much as 1500 j/kg CAPE. Given the saturation,
forcing and lift, numerous SHRA/TSRA should be ongoing/spread across
the fcst area Wed morning. Due to the Wed morning convection, model
sounding generally showing the sfc-900mb layer capped with 150 to as
much as 300 j/kg CIN thru the afternoon into the evening. Models
progging sfc dew points of as much as 70-75F over the area around
00z Thu. This seems overdone and skewing the instability on the high
side. SREF/GEFS/ECMWF dew points more in the 65-70F range Wed
afternoon/evening appear more reasonable, with MUCAPE in the 1500-
2500 j/kg range. Models progging rather impressive 0-1km shear over
the area Wed, but this may well end up stuck under a stout cap. For
now, any severe risk per SWODY3 appears conditional that there is a
break in convection Wed that would allow for some clearing/BL
warming ahead of the sfc trough/cold front. There may be break in
the convection during the day Wed, but models progging a `dirty`
warm sector over the area with plenty of moisture in the 925-850mb
layer in what would be the warm sector over the area, limiting
diurnal warming. With the high PW values and a deep warm cloud layer
of 3500-4000 meters, appears greater threat may be locally heavy
rains Wed into Wed evening. See hydrology section below.

Trend is for the Wed wave to be progressive and stronger trend for
weak shortwave ridging/sfc high pressure to slide across the region
Thu. After SHRA/TSRA chances around 80% or higher Wed, trend toward
a dry day on Thu looks good. Highs Wed tricky, depending on cloud
cover and timing/coverage of SHRA/TSRA across the area. Thu does
trend drier, but progs keep plenty of 925-850mb moisture/RH over the
area for ample cumulus development. For now, consensus highs in the
70s Wed then more mid 70s to lower 80s Thu appear reasonable. SW low
level flow with some moisture increase and lower level thermo-
dynamic forcing already spreads back into the area Thu night. Small
SHRA/TSRA chances across mainly the SW half of the fcst area later
Thu night reasonable at this time.

For Friday thru Monday (days 4-7): main fcst concerns this period
are SHRA/TSRA chances much of the period and continued below normal
temps.

Medium range model runs of 26.00z/26.12z in general agreement for
some form of mid level troughing to persist over the Upper
Midwest/north-central Conus Fri-Sun. Plenty of detail differences on
progression and stronger shortwaves thru the flow though. Fcst
confidence for this period is average.

General troughing over the region Fri=Mon to keep this period
unsettled. Actual SHRA/TSRA chances will depend on timing/strength
of various shortwaves thru the flow, which is subject to change
several times between now and Fri-Mon. Given uncertainties with
shortwaves in the day 4-7 time=frame, little improvement to be made
on the model consensus SHRA/TSRA chances for Fri-Mon. With broad mid
level troughing over the region, higher confidence that temps temps
thru the period are going to remain below normal. May sneak in a day
with near normal highs, but the actual highs from day to day will
depend on the passing shortwaves, cloud cover and how much
convection may be around the area during any one afternoon. For now,
consensus highs mostly in the 70s for Fri-Mon appear well trended.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1235 PM CDT Mon Jun 26 2017

Mid-level trough of low pressure will continue to produce VFR
cumulus build-up through this afternoon but then expected to rapidly
scatter toward sunset with loss of surface heating. High pressure
builds in overnight for mostly clear skies and light winds. There is
some concern for river valley fog/stratus that could impact KLSE
early Tuesday morning. A few mitigating factors for fog/stratus
development will be short nighttime this time of year and a slight
gradient for westerly winds at blufftop level which would keep
valley stirred up enough to prevent widespread fog. For now,
included FEW005 stratus at KLSE in the 11-14Z timeframe. Will
continue to monitor.

&&

.HYDROLOGY...Wednesday and Wednesday Evening
Issued at 237 PM CDT Mon Jun 26 2017

For Wed/Wed evening, PW values progged into the 1.5 to 1.8 inch
range and warm cloud depths climb into the 3.5 to 4 km range.
SHRA/TSRA in this environment could be very efficient rain
producers. There remains a potential for 1 to locally 3 inches of
rain falling during this time period. Much of the fcst area has seen
2 to 4+ inches of rain in the past 2 weeks, with many soils wet and
many rivers and streams with higher than normal flows. If any
heavier rain would fall in a short period of time or on one of the
wetter parts of the fcst area, some flooding or flash flooding could
occur.

&&

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

$$

SHORT TERM...RRS
LONG TERM...RRS
AVIATION...DAS
HYDROLOGY...RRS


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