Area forecast discussion
National Weather Service La Crosse WI
613 PM CDT Wednesday Jun 19 2013
Short term...(tonight through saturday)
issued at 303 PM CDT Wednesday Jun 19 2013
Main forecast concerns are precipitation chances and potential
severe with thunderstorms through period.
Latest water vapor satellite imagery indicates shortwave ridging over
eastern half of Minnesota and western Wisconsin and upper level
trough digging over the western United States. Latest 19z surface
analysis show surface ridge over northern Michigan and allowing for
partly sunny skies across much of the forecast area...per latest
visible satellite imagery.
The 19.12z GFS/NAM are in good agreement digging upper level trough
over western United States and developing southwesterly flow aloft
over the central United States. Big concern will be timing of the
series of shortwave troughs ejecting out into the upper Midwest
tonight into Saturday. The 19.12z GFS/NAM handle the first couple of
shortwaves through 00z Friday okay...then after 00z Friday flow
becomes muddled with mesoscale complex vorticies and confidence in
timing of shortwave troughs becomes very low.
Tonight into Thursday...first impulse to push over the area
after 06z Thursday. The 19.12z GFS/NAM show weak moisture transport
in association with the shortwave trough and the latest 19.12z
arw/19.17z hrrr produce convection over parts of Minnesota after 06z
Thursday. This convection moves east over parts of the forecast
area. Expect some scattered showers and thunderstorms across the
by 12z Thursday and continue during the daytime hours.
The latest 19.12z GFS/NAM indicate several impulses to eject out
into the upper Midwest Thursday night into Saturday and to affect
portions of the forecast area. The concern will be timing and
placement of each individual impulse into the region during this
timeframe. The 19.12z deterministic models show decent surge of
moisture transport and lift in association with each shortwave
troughs. Confidence is increasing the forecast area will receive
showers and thunderstorms...hence have increased precipitation
chances especially Thursday night.
The latest 19.12z GFS/NAM continue to show lack of deep shear with
up to 30 knots of 0-6km wind shear from Thursday into Saturday.
The deterministic models indicate around 30 knots of 0-3km shear...
with increasing low level moisture...instability will increase over
the area. This will allow for the potential of some of the complex
of thunderstorms to become severe with damaging winds the main
threat. Precipitable water values will increase to 1.5 to 2 inches
across the forecast area Thursday into Saturday. If any of the
thunderstorms move over the same area...flash flooding will be a
concern.
Long term...(saturday night through wednesday)
issued at 303 PM CDT Wednesday Jun 19 2013
Main forecast concerns are precipitation chances and temperatures
through the period. The 19.12z GFS/ECMWF/Gem are in good agreement in
carving out upper level trough over the western United States and
continue southwesterly flow aloft over the central United States
through 00z Tuesday. Then...the deterministic models begin to build
upper level ridge over the western United States for Tuesday and
Wednesday. Biggest difference between the models is timing the
embedded shortwave troughs in the southwesterly flow aloft into the
region through the period. This will have impacts on the strength of
the upper level ridge...as the deterministic models suggest ridge
flattening out over the northern tier states Tuesday and Wednesday.
With the uncertainty on timing of shortwave troughs into the
forecast area...will continue with chances of precipitation
through the period. Next concern are temperatures through period...
the 19.12z deterministic models show 925mb plus 20 to plus 25 degrees
celsius over forecast area through much of the period...with the
warmest air filtering into the forecast area Tuesday...where the
19.12z European model (ecmwf) indicates plus 26 degrees celsius over forecast area at
00z Wednesday. This would suggest around 90 degree high temperatures
across forecast area Tuesday.
&&
Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 613 PM CDT Wednesday Jun 19 2013
The main concern is whether any convection is going to impact the
taf sites during the period. Isolated convection is developing
over eastern South Dakota and Nebraska ahead of an approaching
short wave trough. As the low level jet intensifies this
evening...this convection is expected to become more widespread
and begin moving east. The best low level moisture transport is
not shown by the models to move east with the short wave trough
which makes it rather unclear how much of the convection will
survive once it moves out of the moisture feed and cape axis. For
this reason...have continued to show only some vcsh for late
tonight into Thursday morning. Similar concerns for Thursday
afternoon as the next short wave trough starts to approach the
area. By late afternoon...the 19.18z NAM suggests there should be
between 500 and 1000 j/kg of ml cape over the area with an
increase in moisture transport. The main area of moisture
transport will be off to the west...but the eastern and convergent
edge of this may be over the area. Varied ideas as to whether the
convection will initiate to the west of the area...or near the
area on a boundary left behind by the morning activity as
suggested by the 19.12z hi-res nmm. For now...have opted to
included a thunderstorms in the vicinity for the late afternoon to show the possibility of
some storms developing.
&&
Arx watches/warnings/advisories...
WI...none.
Minnesota...none.
Iowa...none.
&&
$$
Short term...dtj
long term....dtj
aviation...04
