Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1129 PM CDT Sat may 25 2013
Short term...(this evening through sunday)
issued at 315 PM CDT Sat may 25 2013
Large area of surface low pressure over eastern portion of
northern rockies continues to slowly become better organized
into tonight. Warm frontal boundary associated with same
will again be the catalyst for any organized shower and
thunderstorm activity tonight into Sunday. Area of convection
already firing up along northern edge of this boundary as seen
on infrared satellite imagery. Conditions should remain dry over
much of the forecast area this evening...with possible development of
showers and isolated thunder after midnight mainly southwest
of a line from Morris to Olivia to Owatonna. Surface forcing
for this activity is minimal...per weak Theta-E advection.
Similarly...upper air support per gfs40 250mb divergence
is also quite lacking...save strong divergence couplet above
far southwest Minnesota near 26/12z. So at this juncture looks like
main threat for any organized overnight into middle morning
convective activity will emanate from mesoscale convective system generated tonight
over central sodak...and progression of same southeast into
SW Minnesota...and portions of south central Minnesota and much of northern
half of Iowa. Much of the rest of the daylight hours should be
dry...minus far west central Minnesota...where late Sunday afternoon
convection could easily fire near the warm frontal boundary...and
where best moisture transport vectors are observed. Gradient will
tighten a tad further by late Sunday morning over the
region...guaranteeing another day of moderate southeast flow. High
temperatures on Sunday will be similar to today's...as thick
strato-cumulus continues to blanket much of the forecast area.
Long term...(sunday night through saturday)
issued at 315 PM CDT Sat may 25 2013
A wet long term forecast period is shaping up for next week...as
the forecast area remains downstream of a deepening western
Continental U.S. Middle/upper trough. While there will be dry windows of time
here and there...the majority of model solutions indicate the
potential for widespread total rainfall amounts of two to four
inches between Sunday night and next Saturday.
The Sunday night into Monday morning time frame is looking like it
should be one of those windows where most of the forecast area
should remain dry...in between detectable shortwaves and in the
absence of a notable forcing mechanism. That all changes on Monday
however...as shown by the GFS and European model (ecmwf)...which continue to bring
a decent middle level shortwave across the area for the Memorial Day
Holiday. The NAM features it as well...but is a tad slower...and
is shifted slightly to later Monday into Tuesday. Models continue
to portray an impressively diffluent upper level thickness pattern
during this time frame. With plenty of moisture funneling north
from the Gulf /as shown by forecast precipitable water values 200
percent of normal on Monday night/ the potential for a good
soaking rainfall on Monday and Monday night with widespread 1 to 2
inch amounts is certainly quite possible.
The next time frame for notable precipitation is expected to arrive on
late Tuesday into Wednesday...as a warm front lifts north into the
forecast area...and is again supported by a broad upper level
diffluent pattern. In addition to the potential for heavy
rainfall...a threat for organized severe weather will enter the
picture...especially on Thursday and Friday as the surface low
nears the area and deep layer shear increases. In fact...the cips
analogs for severe weather indicate there are several matches to
historical outbreak events...including June 17th of 2010.
&&
Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1105 PM CDT Sat may 25 2013
While krwf-kaxn-kstc have all gone down to MVFR...eastern sites
have yet to drop down. Was thinking kmsp would have dropped down
to MVFR by this point...what with sites just west and S having gone
that low...but it should be within the first few hours of the
26/06z taf that conds drop to MVFR. Ceilings then remain at MVFR through
most of the day...then a few breaks in the lower /2000-3000 feet/
deck scatter out to allow for VFR conds before MVFR ceilings fill back
into the area. Only site to be hit hard with precipitation in this
issuance is krwf...which is in closest proximity to the lingering
surface fnt and its associated convection this morning. Showers/thunderstorms will
gradually spread from southwestern Minnesota into the rest of central-southern Minnesota through
the day today...then slowly into western WI tonight into early Monday. Conds
to gradually deteriorate as precipitation moves in...but timing issues
among the short-term models do not give a lot of confidence at this time.
Winds to remain between 120-140 with speeds at or above 10 knots...including
frequent gusts above 20 knots during the day tmrw.
Kmsp...VFR conds to start will eventually drop below MVFR levels
around 09z...then stay there through much of the day. Am not
expecting ceilings to drop below 2 kft. Ceilings may even rise above 3
kft earlier than advertised...but confidence is high that MVFR
ceilings return by late evening. Precipitation looks to hold off to the SW of
the terminal through the day...then precipitation slowly moves into the area
during the evening hours. Will start off the precipitation light then bring in
heavier precipitation tmrw night...which lines up with model forecasts of
having heavier and more widespread tmrw night rather than during the
day. Could easily have thunderstorms...but have started things more
optimistically and will allow later taf issuances see how
conditions develop.
/Outlook for kmsp/
Monday...chance MVFR or lower ceilings. Rain showers/thunderstorms and rain likely. Winds southeast 10-15 kts.
Tuesday...chance MVFR or lower ceilings. Chance shra/tsra. Winds south-southeast 5-10 kts.
Wednesday...chance MVFR or lower ceilings. Chance shra/tsra. Winds S 5-10 kts.
&&
Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&
$$
Short term...ajz
long term...ls
aviation...jpc
