Area Forecast Discussion
Issued by NWS La Crosse, WI

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766
FXUS63 KARX 190451
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1151 PM CDT MON JUL 18 2016

.SHORT TERM...(Tonight through Wednesday)
Issued at 345 PM CDT Mon Jul 18 2016

Fairly messy weather pattern the next couple days will result in
showers and thunderstorms for parts of the region...the where/when
the best chances will lie is harder to narrow down.

Sfc front hanging out to the south will gradually make its way north
Tue/Wed. Piece of upper level shortwave energy progged to shift from
the southern plains and across the boundary by Tue
afternoon/evening. Swath of low level warming and a branch of the
low level jet will help this area become a focus for shower/storm
develop. Most models favoring eastern IA.

Threat would increase late tue night into wed as another piece of
energy is expected to move from the northern plains to across the
region. Low level jet intensifies into northern MN/WI over this
period. Model trends here favor the higher pcpn chances from far
eastern MN eastward through WI.

Atmosphere is juicing up...sbcapes +3000 J/KG along and south of the
sfc front. Some wind shear to play with...mostly 0-3km at around 30
kts...but some deeper 0-6km layer also suggested for Wed. Some
strong-severe storm threat as a result. There will be a heavy rain
threat too - with more on that in the HYDROLOGY section below.

.LONG TERM...(Thursday through Monday)
Issued at 345 PM CDT Mon Jul 18 2016

Significant heat moving in for Thu/Fri...dangerously so.

Upper level ridge builds across the region for the later 1/2 of the
work week...with a strong southerly fetch pulling hot/humid air
northward into the region. 925 mb temps expected to climb to around
30 C over these 2 days...while NAEFS 850 mb temp anomalies near +3.
Dewpoints making a jump too...low to mid 70s are likely...but a few
locations flirting with 80 is not out of the question. Highs in the
low to mid 90s are expected...with little relief thu night as lows
will only dip into the low to mid 70s. Resulting afternoon heat
indices from the temp/td combination for thu climb into the low to
mid 100s...a just a bit less for fri.

Will go with a Extreme Heat Watch for the forecast area to account
for the heat relate threats Thu afternoon-Friday mid evening.

A cold front sweeps in from the west Friday night, bringing some
relief from the extreme heat. Highs by Sunday should drop back to
more seasonable norms.

Some suggestions in the models of bits of upper level energy trying
to work through the top of the ridge for the later half of the
week...bringing some small rain chances (mostly north). With so much
warm air in place...cap will be rather sturdy and work against any
pcpn chance. Will continue to let consensus models paint the rain
chances for now...but setup favors dry.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1151 PM CDT Mon Jul 18 2016

Forecast sounding from the 19.00Z NAM continue to suggest the
possibility of some fog late tonight for KLSE. The trend in the
RAP has been toward saturation occurring as well. Of concern
though is the possibility of some high level clouds coming in off
the convection over South Dakota and Nebraska. Will include a BCFG
to cover the possibility of some fog forming. The latest runs of
the HRRR and CR-HRRR bring the convection from the west through
the upper level ridge axis and into both airports by mid to late
Tuesday morning. Have doubts that this will survive a trip through
the upper level ridge axis and the Corfidi vectors from the RAP
would suggest it should turn to the southeast about the time it
reaches the Missouri River. More convection should develop over
the Missouri River Valley Tuesday afternoon ahead of the
approaching short wave trough. The hi-res models are really
struggling with this development with the 19.00Z CRNAMNest
bringing in some activity for the late afternoon while the 19.00Z
CR-HRRR takes it south of the area. For now, will introduce some
scattered clouds in the 3 to 4 thousand foot range and let later
shifts refine this aspect of the forecast.

&&

.HYDROLOGY...
Issued at 200 PM CDT Mon Jul 18 2016

Tue-Wed posing a high risk for heavy rain. Warm cloud depths
climbing above 4 km by Wed while pws reach or exceed 2 inches. The
storms will be efficient rain producers. With many river systems
running high and grounds saturated across much of the local
area...any heavy rainfall (especially high rainfall rates) could
cause problems. Rises on river systems should be expected...along
with a threat for flash flooding.

Confidence on where the higher threat for heavy rain is not overly
high...but moving in an upward direction. Smaller/weaker nature of
some of the weather forcers make pinpointing timing-location
problematic. At this time, consensus favoring a higher threat for
eastern IA on Tue...then eastern MN/WI on Wed.

&&

.ARX Watches/Warnings/Advisories...
WI...Excessive Heat Watch from Thursday morning through Friday
     evening for WIZ017-029-032>034-041>044-053>055-061.

MN...Excessive Heat Watch from Thursday morning through Friday
     evening for MNZ079-086>088-094>096.

IA...Excessive Heat Watch from Thursday morning through Friday
     evening for IAZ008>011-018-019-029-030.

&&

$$

SHORT TERM...RIECK
LONG TERM....RIECK
AVIATION...04
HYDROLOGY....RIECK



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