Area Forecast Discussion
Issued by NWS La Crosse, WI
FXUS63 KARX 202049
Area Forecast Discussion
National Weather Service La Crosse WI
349 PM CDT FRI MAY 20 2016
.SHORT TERM...(This evening through Saturday)
Issued at 345 PM CDT Fri May 20 2016
At 3 PM, a short wave trough was located over northern Missouri.
This system was bringing some mid and high clouds areas south of
Interstate 94. Meanwhile a 1024 mb surface high located over
southern Ontario kept the low levels dry. Dew points this
afternoon ranged from the upper 20s to upper 30s. Finally, another
short wave trough was located over central Minnesota. This system
was bringing clouds to areas north of Interstate 94.
For tonight and Saturday, the short wave to our south will move
east into the Ohio River Valley and the short wave over central
Minnesota will move southeast through the Upper Mississippi River
Valley. With the Canadian high continuing to bring very dry air
into the region, not anticipating any precipitation from either
of these systems. With skies becoming mostly sunny on Saturday
afternoon, temperatures will warm into the mid and upper 70s.
There may be even a few lower 80s in the river valleys. Like the
past couple of days, the model dew points look too high, so
lowered them by 5F.
.LONG TERM...(Saturday night through Friday)
Issued at 256 PM CDT Fri May 20 2016
On Sunday afternoon, the combination of mostly to partly sunny
skies and 850 mb temperatures in the 10 to 13C will allow
temperatures to warm to around 80F. In addition, soundings
continue to show that there will be plenty of dry aloft to mix to
the surface. This will likely lower the dew points into the lower
to mid 40s which is about 5F below MOS. This will cause the
afternoon relative humidity values to fall into 25 to 35 percent
From late Sunday night through Tuesday morning, the models
continue to show that a long wave trough will move slowly east
through the Upper Mississippi. The best chance of rain will be on
Monday afternoon and night. Like the past 3 days, the ECMWF
continue to suggest that the best synoptic forcing and 850 mb
moisture transport will be north and south of the forecast area.
As a result, still a bit concerned that the precipitation chances
may be a bit too high along the front in the Upper Mississippi
River Valley. In addition to this, the models continue to differ
on the potential instability ahead of this system. The GFS
continues to have the highest mixed layer CAPES with values around
1500 J/kg. Meanwhile the ECMWF only has mixed layer CAPES up to
200 J/kg. With both the 0-3 km and 0-6 km shear less than 25
knots, still not anticipating any severe weather with this front.
Beyond this time period, the models have been less consistent. As
a result just stayed with the model consensus.
.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1236 PM CDT Fri May 20 2016
VFR conditions continue through the TAF period as high pressure
just to the west slowly works overhead into midday Saturday.
Diurnally driven cumulus deck (briefly some brief broken ceilings
around KRST) should mostly dissipate with sunset, leaving just
some higher cirrus at times floating through the area overnight.
Winds from the southeast up to 10 knots will become light and
variable tonight into Saturday morning with the ridge axis
centered squarely overhead.