Scientific Forecaster Discussion
Area forecast discussion
National Weather Service La Crosse WI
1147 PM CDT Sat Apr 18 2015
Short term...(this evening through sunday)
issued at 348 PM CDT Sat Apr 18 2015
At 3 PM...a backdoor cold front was located from Mankato Minnesota
to Dubuque Iowa. East winds in the wake of this front has brought
dry dew points into the area. These dew points range from the middle
20s to lower 40s. The dew points are slowing the northeast
progress of the lower clouds and precipitation into southeast
Minnesota and northeast Iowa this afternoon.
For tonight...the 18.12z models show that the inverted trough
extending from western Iowa northeast into the Dakotas will move
slowly northeast tonight. As this occurs...the low level moisture
will slowly climb into 50s across northeast Iowa and southeast
Minnesota. In addition...the 700 to 500 mb frontogenesis
will gradually increase across the area. As this occurs...a band
of showers and isolated thunderstorms will move into these areas.
Meanwhile the dry air will keep western Wisconsin mainly dry...so
lowered or took out the precipitation chances for this area.
On Sunday...the 700 to 500 mb frontogenesis will move slowly east
across southeast Minnesota and northeast Iowa. This will continue
to be the main focus for the precipitation across the area.
Meanwhile there is continual concern that the dry flow and
subsidence ahead of this system will keep western Wisconsin dry
during the morning. Due to this concern...lowered the
precipitation chances some. If the arw and nmm is correct...these
areas may remain dry until middle afternoon. The precipitation
chances across the entire area will increase on Sunday afternoon
as the deformation precipitation associated with a short wave
trough moves northeast from Illinois into lower Michigan and the
700 and 500 mb frontogenesis continues to move east into western
Long term...(sunday night through saturday)
issued at 348 PM CDT Sat Apr 18 2015
On Sunday night...many of the deterministic models continue to show
that a strong 900 to 500 mb frontogenetic band will move east
through Wisconsin. There continues to be steep lapse rates between
850 and 800 mb layer in the wake of the system. However the
soundings are suggesting that the depth of the moisture may become
a concern...so we may be holding on to the 20 to 40 percent
precipitation chances too long.
On Monday and Monday night...very steep lapse rates develop from
900 to 700 mb. This will likely result in the development of
showers. The wind gusts may even gust up to 30 miles per hour during the
afternoon and evening. As temperatures cool on Monday night...
there may be even some snow mixing in at times mainly north of
Interstate 94. If it does...not expecting any accumulation.
For the remainder of the week...the upper level low will remain in
place across the Great Lakes and eastern Canada. This is due to
strong ridging across the eastern Atlantic and Greenland. The
cyclonic flow will continue to reinforce the cool Canadian air
across the region. As a result...highs will remain mainly in the
40s and 50s. Low temperatures will range from the upper 20s to
Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 1147 PM CDT Sat Apr 18 2015
Warm advection and moisture transport ahead of the approaching
weather disturbance continues to generate showers and a few
embedded rumbles of thunder. The initial forcing is about to push
north of the region from the first piece of short wave energy...so
anticipate a wane in precipitation for the krst area. But overall
weak lift does continue through the night so light sprinkles
remain possible from time to time. Rain is still fighting the dry
boundary layer further east. There have been some returns but
precious little ground truth. The second piece of energy will be
coming through the region on Sunday...so do anticipate that there
will be another round of rainfall. Ceilings will gradually lower
as saturation of the boundary layer continues. Overall conditions
will remain VFR for the most part...but there will be pockets and
periods of MVFR conditions. More widespread limited visibility and
lowered ceiling will be seen by Sunday and Sunday night...
especially as a cold front moves through late in the day.
issued at 700 PM CDT Sat Apr 18 2015
With the loss of daytime heating...the deeper mixing has ended and
therefore winds are diminishing. Humidity is also climbing...and
thus the risk for fire starts is waning. Have allowed the red flag
warning expire on schedule at 7 PM. With rain anticipated
overnight...through Sunday...and into early next week...the
critical fire concerns are all but gone for a time.