Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
1145 PM CDT Sat may 25 2013
Update...
Watching developing convective complex over southeast S Dakota/northwest Iowa.
18z NAM had earlier looked to bring this complex into southern WI
Sunday morning...but 00z run has backed off with the GFS similarly
keeping precipitation just west of the County Warning Area as complexes follow instability
gradient/moisture convergence that will take them southeast...
possibly brushing the far SW County Warning Area Sunday morning. East winds off
the lake will keep temperatures around where they are now...close
to forecast lows...with the rest of the County Warning Area trending as expected.
&&
Aviation/06z tafs/...
Will keep VFR conditions going through the period and pull the
vicinity showers from kmsn at 12z as precipitation looks to remain SW of
there through at least 18z Sunday. 00z models are pushing the precipitation
slowly into the County Warning Area...but only expect it to reach kmsn by 06z
Monday. Could reach kmke by 12z Monday...but will leave out for now.
&&
Marine...
00z GFS and NAM increase east to southeast winds 10 to 20 knots
Monday into Tuesday that could build 4 foot or better waves
depending on fetch and persistence. Later shifts will have to
continue to monitor for possible Small Craft Advisory if trend holds.
&&
Previous discussion... /issued 318 PM CDT Sat may 25 2013/
Tonight and Sunday...forecast confidence is medium to high.
Northern edge of decaying mesoscale convective system rain shield sliding across far
southern Lafayette County...and should move out of that area in the
next hour or so...as 500mb shortwave trough slides to the south of
the area.
Main issue will be if showers and isolated storms from possible
mesoscale convective system would move into the southwestern
portions of the forecast area later tonight into Sunday morning.
Short term models develop this feature over central Iowa later this
evening and shift it east southeast later tonight into Sunday
morning.
The NAM/ECMWF/Canadian all show the northern edge of the quantitative precipitation forecast shield
clipping the southwestern counties in the forecast area...mainly
southwest of Madison. The 850mb baroclinic zone does shift a bit
further northward than last night/early this morning...into the far
southwestern counties. 850mb low level jet nose points into this
area by 12z Sunday as well. The GFS keeps the entire area dry during
this time...with the 850mb features further to the southwest.
Enough confidence with the NAM/ECMWF/Canadian trends to bring in
increasing probability of precipitation in the southwest counties later tonight into Sunday
morning...lingering lower probability of precipitation in the afternoon. Added isolated
thunder with weak instability in this area.
Middle level clouds will linger tonight into Sunday...and should keep
lows in the 40s tonight and highs Sunday in the upper 50s to lower
60s.
Monday and Monday night...forecast confidence is medium.
The transition to a warmer pattern begins during this period.
Monday will still feature the chilly easterly flow across the
area as the warm front remains south. The threat for any rain or
isolated thunderstorms will be mainly west and south of Madison.
The Canadian high pressure system that has brought our recent cool
regime will drift off to the east by Monday night...allowing the
warm front to move north into the area. The models differ on how
fast it gets up here. By 12z Tuesday...the GFS suggests it
pushes through at least the southern half of the forecast
area...while the NAM/European model (ecmwf) hang it up at the WI/Illinois border by this
time. Climatologically...I prefer holding it at the border at 12z.
Either way...the low level jet will be increasing Monday night...
impinging on that front. This should lead to a round of elevated
showers and thunderstorms across southern Wisconsin.
Tuesday through Wednesday night...forecast confidence is medium.
The warm front should advance through the forecast area on
Tuesday. We then remain in the warm sector out ahead of the main
low pressure system over the Central Plains. Look for the showers
and storms to diminish from south to north through Tuesday...then
rather low chances for rain through Wednesday night. The warm
sector will allow temperatures to climb back into the 70s and 80s. What
may go wrong with this scenario is that the convection with the
warm front will suppress that front from moving too far
north...possibly hanging it up over the forecast area...rather
than moving in north in a progressive fashion. This would allow
for a longer duration of showers and storms Tuesday into Tuesday
night.
Thursday and Friday...forecast confidence is medium.
We will be in a persistent...moist southwest low level flow with
some risk for an mesoscale convective system to roll in late Thursday night into Friday.
The GFS/ECMWF/Gem are all showing a nice short wave trough riding
northeast through the area...out ahead of the main upper low. This
is a dubious forecast a week out...but the cips analogs are
showing potential for severe weather late next week. It is
entirely possible for the low to stall out west and we remain in
the quiet warm sector as we head into next weekend. Lots of
possibilities. Stay tuned.
Aviation/00z tafs/...VFR conditions expected across taf sites
tonight and Sunday. Main issue is whether any showers or isolated
storms from the west will clip Madison later tonight into Sunday
morning. It appears that the best chances will remain southwest of
Madison during this period...so will leave mention out of tafs for
now.
Modest east southeast winds are expected at Madison during this
period. Modest east northeast winds at the eastern sites are
expected through tonight...becoming east southeast on Sunday. VFR
clouds will linger during this period as well.
Marine...
East southeast winds increasing into the 10 to 20 knot range Monday
afternoon and evening...may bring waves near 4 feet across the
southern nearshore marine zones. Will have to monitor wave
heights for this period in later forecasts.
&&
Mkx watches/warnings/advisories...
WI...none.
Lm...none.
&&
$$
Update...rem
tonight/Sunday and aviation/marine...wood
Sunday night through Saturday...Davis
