Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 270246
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
946 PM CDT Wed Jun 26 2019

.SHORT TERM...(Through tonight)
Issued at 303 PM CDT Wed Jun 26 2019

Water vapor imagery/RAP analysis indicated broad fairly zonal flow
over the region early this afternoon. Some mid/high clouds have
spread across the area in association with dissipating convection to
the west. However, a fairly stable airmass continues to reside over
the area this afternoon with warm temps and humidity levels still
comfortable.

Mid-level heights will continue to rise tonight as a trend towards
ridge building occurs. Modest warm advection/moisture transport
develops tonight as a warm front lifts north, but the low-level jet
will be focused to the west where convection is forecast initiate
across the high plains. As a result, other than an isolated shot at
convection in the warm advection, higher chances look to remain to
the west. Consensus among the high res models has a complex of
storms developing across the Dakota and progressing into MN/IA by
early morning on Thursday, likely remaining near or west of the area
through daybreak.

.LONG TERM...(Thursday through Wednesday)
Issued at 303 PM CDT Wed Jun 26 2019

For Thursday thru Sat night: main fcst concerns are expected
convective complex Thu, another one Thu night then very warm to hot
temps by Sat.

Model runs of 26.12z in good agreement for shortwave energy to be
lifting out of the west coast troughing tonight to be moving across
the central/northern plains and across the region Thu afternoon/
evening. Once that passes, hgts rise over the region Fri thru Sat
night as the next energy out of the west coast trough lifts into
western CAN. Overall fcst confidence in the Thu thru Sat night
period is average to good this cycle.

Plenty of meso-scale detail differences among CAMs/Hi-res and
synoptic scale models already by Thu, impacting the sensible
weather outcome. All have a strong signal for increasing moisture
spreading into the fcst area by/during Thu morning with PW values
into the 1.5 inch range by mid to late morning. This with 3.5-4K
meter warm cloud depths, elevated CAPEs climbing into the 2K-3K j/kg
range and increasing 925-850mb moisture transport. Question is when
and where does the convective complex develop and track. CAMs
consensus develop it in western/central MN late tonight/early Thu
morning then allow it to track SE following the Corfidi vectors into
the fcst area. This while synoptic models generally keep it north of
the fcst area. Then there is timing. Faster of CAMs bring it
in/across mainly 14z-19z, slower more 16z thru the afternoon. Will
follow the CAMs consensus for now with highest SHRA/TSRA chances
during the late morning/early aftn hours. Plenty of uncertainty with
severe threat, with the day 2 slight risk per SWODY2 somewhat
conditional on a break from convection sometime Thu aftn/evening or
a slower arrival of convection Thu morning. The high warm cloud
depths/PW values also spell the threat of locally heavy rains and
potential renewed flooding.

What happens later Thu/Thu night (round 2) will depend on timing and
convection come thru early Thu aftn. Based on CAMs consensus, first
complex should lay out and outflow boundary SW of the fcst area.
This to then be the focus for convection initiation late Thu
afternoon/evening as low level moisture transport lifts over this
boundary. PWs in this plume by Thu evening in the 1.5 to 2 inch
range, warm cloud depth around 4K meters and MUCAPE of at least 2500
j/kg in the inflow airmass. If storms can organize there is the
threat of strong winds along with hail. Favorable set-up for storms
to train as well for additional locally heavy rain threat. Exactly
where remains uncertain, so no flood watch headlines at this time.

Beyond Thu night, rising hgts/ridging/warming temps aloft working to
cap the column, even as lower level heat and humidity build. Not
much for forcing signals seen either with winds aloft to 500mb
becoming quite light by Fri night-Sat night. Some small consensus
SHRA/TSRA chances yet Fri/Fri night with warming/humidity the main
focus by Sat. Mixed 925mb temps on Sat supporting highs in the upper
80s/lower 90s. This with sfc dew points in the upper 60s/low 70s.
Sat looking to fell quite summery as we near the end of June.

For Sunday thru Wednesday (days 4-7): main fcst concerns this period
are SHRA/TSRA chances mainly Sun night-Wed and warm temps thru the
period.

Medium range model runs of 20.00z/26.12z in decent agreement for
ridging over the central CONUS Sun, to be flattened a bit by a
shortwave moving across southern CAN Sun night/Mon. More of a zonal
flow signal across the north-central CONUS for Tue/Wed, with hard to
define/track shortwaves coming out of western CONUS troughing and
rippling thru the flow. Of course, plenty of detail differences by
Mon-Wed in this kind of flow. Day 4-7 fcst confidence is generally
average this cycle.

Sun continues to trend as a very warm to hot day under the ridging
aloft and S-SW low level flow between high pressure in the mid MS
valley and low pressure in the plains. Cannot rule out a small
SHRA/TSRA chance Sun with a very moist/unstable , but main frontal
boundary and focus for any convection looks to be west/north of the
area. Mixed 925mb temps Sun afternoon supporting highs in the upper
80s to perhaps mid 90s, plus sfc dew points around 70F or higher,
the 2nd half of the weekend is also going to feel rather summery.
Shortwave tracking across southern CAN Sun night/Mon give the front
a nudge south, with SHRA/TSRA chances spreading into the area. With
potential for more more clouds Mon, trend of highs a few degrees
cooler than those of Sun looks good. With plenty of detail
differences on shortwaves thru the flow a boundary and a moist/
unstable airmass in the area, the consensus 20-40% SHRA/TSRA chances
for Tue/Wed are good for now. Trend of Tue/Wed high temps remaining
near to a bit above normal looks good as well.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 946 PM CDT Wed Jun 26 2019

Main aviation concerns remain on timing thunderstorms through the
TAF sites during the day on Thursday and possibly again Thursday
night. Latest mesoscale models, mainly the HRRR, indicate that a
line of strong to severe thunderstorms could impact both TAF sites
on Thursday in the 19 to 22 Z timeframe. Storm threats could
include damaging winds, heavy rain, frequent lightning, and
possibly some large hail. Expect IFR conditions near any
thunderstorms and gusty erratic winds. Additional storms could
develop after 02Z. These storms would mainly contain a heavy rain
threat in addition to frequent lightning.

&&

.HYDROLOGY...Thursday and Thursday night
Issued at 303 PM CDT Wed Jun 26 2019

Moisture and instability will be increasing over the area for
Thursday and Thursday night, with potential for TSRA to train and
repeat over some locations. Where this may occur is uncertain yet,
but storms will be capable of producing downpours and locally
heavy rains. These rains falling on generally moist soils could
produce excessive runoff and the threat of flooding or flash
flooding.

&&

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

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...Wetenkamp
HYDROLOGY....RRS


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