Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 karx 291150 
afdarx

Area forecast discussion
National Weather Service La Crosse WI
650 am CDT Thu Jun 29 2017

Short term...today and tonight
issued at 330 am CDT Thu Jun 29 2017

At 3 am, a cold front was located from western tip of Upper
Michigan through La Crosse WI and then southeast to Omaha
Nebraska. The 29.00z models are in general agreement that this
front will shift south into northeast Iowa and southwest
Wisconsin this morning. Meanwhile, the western portion of this
front over western Iowa will surge northward as a short wave
trough over western Nebraska moves east. This short wave trough
will then move east northeast across Iowa this afternoon. As this
occurs, the instability will increase south of Interstate 90.
This is most dramatic in the rap which has the 0-1 km mean layer
convective available potential energy climbing into the 1 to 3k j/kg range. Meanwhile the NAM
keeps it boundary further south. As a result it only has convective available potential energy of
1 to 2k j/kg across Fayette and Clayton counties in northeast Iowa
and Grant County in southwest Wisconsin. The GFS is between these
2 solutions.

With the arw, nmm, and hrrr close with their solutions, trended
the forecast toward them for this afternoon and evening. Showers
and storms will move into northeast Iowa between 29.20z and
29.22z. This precipitation will then move out of southwest
Wisconsin between 30.01z and 30.03z. While there is good agreement
across southwest Wisconsin and northeast Iowa, there is still
some uncertainty on how far north these showers and storms will
get. Storm Prediction Center has south of I-90 in a marginal risk for wind and hail.
This seems reasonable since the 0-3 km and 0-6 km shear are weak.

In addition to the hail and wind threat this afternoon and evening,
the precipitable water values climb into the 1.5 to 2 inch range
and warm cloud layer climb depths rise into the 3.5 to 4.5 km
range across northeast Iowa and southwest Wisconsin. This would
make the showers and storms very efficient rain producers.
Fortunately, the cams are in good agreement that this convective
system will be progressive, so it should not aggravate the
flooding situation taking place along the Turkey River.

For tonight, the models are agreement that a short wave trough
will move east through the upper Mississippi River valley. This
will keep a chance of showers and storms in the forecast.

Long term...Friday through Wednesday
issued at 330 am CDT Thu Jun 29 2017

From Friday into Saturday night, a series of short wave troughs
will move east through the region. While the 0-1 km convective available potential energy climb
into the 750 to 1500 j/kg range, both the 0-3 km and 0-6 km shear
remain weak. As a result, not anticipating any severe weather.

From Sunday afternoon into Monday, a cold front will move slowly
south across the region. With a 40 to 45 knot mid-level jet
moving through the region on Sunday afternoon and evening, there
will be an increase in the 0-3 km and 0-6 km shear along and
north of Interstate 90. In addition, the 0-1 km convective available potential energy will be in
the 1 to 2k j/km range. This may result in some strong to severe
storms.

From Monday night into Wednesday, the models differ on the
location of the cold front. The GFS is further north, so it has
showers and storms south of Interstate 90 as a low pressure system
moves along this front from the afternoon of Independence day
into Tuesday night. Meanwhile the Gem and European model (ecmwf) are much further
south with this front and we remain dry.

&&

Aviation...(for the 12z tafs through 12z Friday morning)
issued at 650 am CDT Thu Jun 29 2017

VFR conditions with cirrus this morning and then some afternoon
thermal cumulus in the 3000 to 4000 ft agl layer will be the rule
at krst/klse today. Some thunderstorms are expected to develop
late this afternoon into this evening, but should remain south of
taf airfields across portions of northeast Iowa and southwest WI.
Otherwise, light west-northwest wind today will become variable
late this evening and overnight.

&&

Hydrology...through Friday night
issued at 330 am CDT Thu Jun 29 2017

Heavy rain fell across parts of southwest Wisconsin and northeast
Iowa on Wednesday and Wednesday evening. The legacy storm total
precipitation (stp) estimated anywhere from 2 to 5 inches across
much of Fayette, southern Clayton, and southern Grant counties.
This is in agreement with the storm total amounts from the dual
pol. This has resulted in flooding along the Turkey River in
northeast Iowa. Both Elkader and Garber have already rose above
flood stage. With the rapid rise taking place at Garber, this site
will have the potential of making moderate flood stage. Meanwhile
Elkader is beginning to slow its increase, so it looks like it
will stay with minor flooding.

We issued a Flood Warning for Whitewater park too. However, this
river has already crested and it is on its way down. We might be
able to cancel this warning sometime this morning.

For this afternoon and early evening, the precipitable water
values climb into the 1.5 to 2 inch range and warm cloud layer
rise into the 3.5 to 4.5 km range south of Interstate 90. This
would make the showers and storms very efficient rain producers.
Fortunately, the cams are in good agreement that this convective
system will be progressive, so it should not aggravate the
flooding situation taking place along the Turkey River.

&&

Arx watches/warnings/advisories...
WI...none.
Minnesota...none.
Iowa...none.
&&

$$

National Weather Service Glossary of Abbreviations