Area forecast discussion
National Weather Service La Crosse WI
1209 PM CDT Sat may 25 2013
Short term...(today and tonight)
issued at 230 am CDT Sat may 25 2013
Low/middle level frontogenetic forcing...coupled with some low level
moisture transport and a bit of upper level energy...were helping
continue an area of east/southeast moving showers. Trends in the
latest hrrr/nam12 is to diminish this activity through the pre dawn
hours...while firing convection over the Southern Plains/western Iowa.
Satellite imagery and radar returns already show this
happening...where the nose of the low level jet/moisture transport
was located. This complex should move east through the rest of the
morning into the afternoon...riding along and north of a warm front.
This region should serve as the focus for more shower/storm
development tonight...with the low level jet reasserting itself and
some upper level energy moving out of a West Coast trough. Eastward
movement would again be favored...keeping the bulk of the precipitation south
of the forecast area.
Long term...(sunday through saturday)
issued at 230 am CDT Sat may 25 2013
High confidence its going to rain across parts of the region through
the upcoming work week. Timing and placement is more shaky.
The forecast Keys on a few areas...a surface warm front...low level
jet/moisture transport...and various mcvs. Where these elements all
come together will be where the greater threat for rain will lie.
Clarity for the mesoscale vorticies/spawning grounds and movement
is the main sticking point for increasing confidence.
The upper level pattern is slow to progress east as there is little
impetus via 250/300mb jet interaction - relatively quiet a loft.
So...the 500 mb ridge will remain across the upper Mississippi River
valley/Great Lakes into at least the middle part of the new work
week...with a broad trough over the West Coast. Bits of energy will
spin out of the trough...and then enhance via convection spawned by
it and the low level jet/moisture transport. With the ridge overhead
the next few days...and the surface warm front holding to the
south...these upper air inflections are prognosticated to ride along and
north of the warm front...keeping the best rain chances just south
-but not completely out- of the forecast area.
The warm front will start to lift north on Tuesday...a fairly consistent
signal in the NAM/GFS/ECMWF. How far north is not though...with the
GFS appearing the more aggressive in how far north and how fast.
Rain chances look to become more widespread for the forecast area
Monday-Tuesday as a result.
Depending on how quickly and how far north the warm front makes
it...the area could get into the warm sector...which would help cap
off the atmosphere to convection - outside of a kicker moving in.
Model differences start to become bigger as we move toward next
weekend...with the ec suggesting a closed low will develop in the
West Coast trough...slowly pushing east across the upper Mississippi
River valley next weekend. This could lay up a surface trough across the
region for several days. The GFS is more progressive...moving the
upper level energy northeast...but still has a couple surface boundaries
that could act as shower/storm producers. Will likely stay with the
consensus solution for the details in this part of the forecast.
As for storm chances...instability is limited the next couple
days...and so should be the thunderstorms. The chance for boomers
will increase with the encroachment of the warm front...and
subsequent increase in convective available potential energy. Don/T see a significant threat for
organized severe weather through next week.
&&
Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1208 PM CDT Sat may 25 2013
Area of MVFR ceilings over southern into western Minnesota has
slipped into krst. The 25.15z rap indicates these should remain
through about the middle of the afternoon before they rise to a
low VFR level from the heating of the day. The concern for the
overnight hours is whether the next convective complex will impact
the taf sites. The 25.12z NAM along with the 25.06z hi-res arw
both suggest the warm front will remain south of the area. The
next complex is expected to develop over South Dakota and then
ride southeast along the front moving across Iowa into Illinois
staying south of both airports. At this point...will not even
include a vcsh but will lower the ceilings expecting the northern
edge of the lower clouds from the convective complex to impact
both airports. The NAM BUFKIT soundings shows krst going down to
MVFR with klse staying VFR.
&&
Arx watches/warnings/advisories...
WI...none.
Minnesota...none.
Iowa...none.
&&
$$
Short term...rieck
long term....rieck
aviation...04
