Area Forecast Discussion
Issued by NWS La Crosse, WI
FXUS63 KARX 191709
Area Forecast Discussion
National Weather Service La Crosse WI
1209 PM CDT THU MAY 19 2016
.SHORT TERM...(Today and tonight)
Issued at 419 AM CDT Thu May 19 2016
Main forecast concerns this period: temperatures and cloud
Data analysis at 06Z had broad high pressure centered over the
western great lakes with ridging southwest into MO/KS/OK. Tighter
pressure gradient on the west side of the high was over the Dakotas
into far western MN where south to southeast winds 5-15 mph were
keeping the boundary layer stirred and early morning temps in the
50s. Closer to the center of the high winds were light/calm with
little to no boundary layer stirring and temperatures cooling into
the mid 30s to mid 40s.
For the most part, 19.00Z models initialized well. The exception
being the GFS that initialized surface dew points some 10-15F too
high across WI/MN/much of IA. This appears to perhaps impact the
GFS QPF output across MN/IA/WI this afternoon and again Fri.
Otherwise, models in generally good agreement as shortwave energy
near lake Winnipeg slowly sinks southeast into the Upper Midwest
thru tonight. This and downstream ridge building ahead of strong
troughing digging down the west coast shunts the southwest U.S.
trough/shortwave more eastward across the plain into mid MS
valley, well south of the forecast area. Overall forecast
confidence for this period remains above average.
For the short term: surface-850MB ridge axis is pushed a bit east
today as lee troughing strengthens in WY/MT. Southerly flow on the
west side of this ridge axis look to pull the airmass with more
850MB moisture that was over IA/MO northward over the forecast area
today. Thus expecting more diurnal cumulus this afternoon vs. the
past couple days. This moisture along with diurnal mixing should
also help keep surface dew points a bit higher and minimum RHs
this afternoon more in the 25-35% range vs. the 15-25% range of
the past couple days. Model soundings showing a mdt inversion
above the mixed layer (around 750MB) this afternoon, limiting CAPE
and cloud depth. Suspect GFS with its surface dew points
initialized 10-15F too high across the region is the reason it
tries to produce some light precip in/around the area this
afternoon. Soundings/X-sections do not support the GFS light rain
chances. Discounted its solution and sided with the drier models.
850MB temps this afternoon progged to be similar to those of Wed.
Some south winds for mixing today looking to off-set the increase
of diurnal cumulus, with highs today similar to those of Wed. Some
south/southeast winds tonight to keep boundary layer stirred
tonight and most lows a category or warmer than those of this
morning. Finally a night without mention of frost somewhere in the
forecast area. Trended toward warmer of guidance highs today, then
stayed near a blend of the guidance lows for tonight.
.LONG TERM...(Friday through Wednesday)
Issued at 419 AM CDT Thu May 19 2016
For Friday thru saturday night: Main forecast concerns this
period are continues to be temperatures and cloud trends.
19.00Z model runs in good agreement for the shortwave energy over
ND/northern MN at the start of the period to slowly drop south
across the region Fri/Fri night as strong ridging aloft builds north
behind it. Trend is slower/stronger with this feature. Models remain
in good agreement Sat/Sat night as rather impressive troughing
progressing across the western CONUS pushes the mid level ridge axis
into the Upper Midwest. Forecast confidence this period is above
Even as the shortwave energy is progged to drop south across MN/IA/
WI Fri/Fri night, the surface-850MB ridging retrogrades into the
western great lakes/WI. Lower level anti-cyclonic flow with this
ridging does little to help with lower level thermo-dynamic
forcing under the shortwave. Model soundings Fri maintain the mdt
inversion on top the mixed layer (near 750MB), limiting
mixing/cloud depth and any precip chances. Again discounted GFS on
Fri and maintained a dry forecast across the area. With a
continued increase of moisture around 850MB over the area, Fri may
well end up more of a partly sunny vs. mostly sunny day with
diurnal clouds. 850MB temps Fri perhaps 1C warmer than those of
Thu but with more clouds, highs similar to those of Thu look good.
Lighter winds but more clouds should keep Fri night lows similar
to those of tonight. Strong ridging aloft/ hgt rises finally build
over the region Sat/Sat night. Surface-850MB ridge axis is over
the area Sat with the rising hgts/deep layered subsidence aloft.
850MB temps progged around 10C Sat afternoon and with a mostly
sunny day expected, most highs should be in the mid/ upper 70s.
Still a cooler night Sat night with the center of the high
near/overhead with light winds and mostly clear skies. Used a
blend of the guidance highs/lows for Fri/Fri night then sided with
warmer of guidance highs Sat and cooler of guidance lows Sat
For Sunday thru Wednesday (days 4 to 7): main forecast concerns
this period are SHRA/TSRA chances from late Sun night thru Wed.
Medium range model runs of 19.00Z trend progressive with the western
CONUS trough Sunday. Mid level ridge axis is already pushed east of
the region late Sun/Sun night with the area coming under deep
layered south/southwest flow. Models remain consistent lifting a
lead piece of energy out of the western trough northeast across the
northern plains Mon then into Ont Tue. Reasonable model consistency
for weak shortwave ridging to build across the upper MS valley Wed,
but region remains under general southwest flow aloft ahead of
troughing/shortwave energy lifting into the central plains.
Forecastconfidence this period is average this cycle.
Surface high is pushed east Sun as the flow/ridging progresses
but maintains its influence on the area. Sunday trending to be one
of the warmer days with plenty of sunshine, an increase of south
winds for mixing and 850MB temps of +12C to +14C. Consensus has
highs mid/upper 70s Sun but would not be at all surprised to see a
few lower 80s pop up. tighter gradient spreads over the area Sun
night/Mon as the surface trough/front approach. Deeper moisture
plume/ higher PW airmass now progged to arrive late Sun night then
move across the forecast area Mon into Mon night. Arrival of small
consensus SHRA/TSRA chances into the west end of the forecast area
later Sun night reasonable, with 30-50% chances Mon/Mon night as
the moisture plume and thermo-dynamic forcing would move across
the forecast look good as well. Given the detail differences by
Tue/Wed and potential for more lower level moisture/lingering
troughing to remain over the region under southwest flow aloft,
small SHRA/TSRA chances these days okay for now. One or more of
the day 6/7 periods may well end up dry as details become clearer.
Other than Sunday highs looking a bit cool, model/ensemble
consensus highs/lows for days 4-7 appear well trended at this
.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1206 PM CDT Thu May 19 2016
VFR conditions are expected through the period and through the
weekend. just some returning moisture will allow a bit more VFR
cloud in the airspace.