Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
414 am CDT Wednesday Jun 19 2013
Short term...(today and tonight)
issued at 410 am CDT Wednesday Jun 19 2013
Cirrus shield noted on infrared satellite entering far western Minnesota.
Shield is just ahead of deepening surface cyclone above eastern
Montana. This feature will be ejected out of 500 mb trough over Pacific
northwest during the next 24 hours into western nodak and southern
Saskatchewan. Warm frontal boundary attached to surface cyclone
will be catalyst for scattered showers and isolate thunderstorms
late this morning over far western County Warning Area. Used gfs40 Theta-E
advection and hrrr guidance for placement and timing of daytime
convection over forecast area. Could be a few strong to near severe
thunderstorms this afternoon over central and portions of SW Minnesota
to...as joules increase into the 1500 to 2500 range. Moderate
250mb divergence Couplets also noted over these areas along with
lifted indice's plunging into the negative 4 to negative 8 category. Only
limiting factor would be thicker cloud deck then current cirrus
shield prognosticated for much of the daytime hours.
Presence and progression of warm frontal boundary deeper into
southern half of Minnesota tonight should portend slightly enhanced
chances for convection...with quantitative precipitation forecast values also rising noticeably.
Could be a quick quarter inch to one half inch of moisture
generate from continue scattered activity during the overnight. 850mb
lapse rates and lifted indice's will also rise slightly overnight. Moderate
southerly low level jet will also form by late tonight over much
of Minnesota forecast area ... 25 to 30kt magnitudes common south of a line from
Alexandria to Owatonna. Could be additional isolated strong to
near severe T-storms over western half of forecast area during the
evening...switching to far east central Minnesota/west central WI after
midnight.
Long term...(thursday through tuesday)
issued at 410 am CDT Wednesday Jun 19 2013
Warm and moisture-rich pattern will remain in place for the end of
this week into the start of next week...including periods of
strong thunderstorms and heavy rain. An upper level ridge building
over the Dakotas and Minnesota/WI through today will shift to the east through Thursday
while a longwave trough develops over the northwest. Several
shortwave disturbances riding not only over top the ridge but also
around the base of the trough Thursday into Friday will work with an
incoming surface frontal system developing over the central-northern
plains. Solid SW flow will bring not only warmer air /which will
raise 500 mb heights to enhance capping but also stronger jetting/ but
also moisture-rich air /helping raise precipitable waters above 1.50 inches and
enhance instability/...and the surface frontal waves combined with
upper level disturbances will allow for periods of convection.
Thursday continues to be highlighted by Storm Prediction Center in vicinity of the approaching cold front
for the western half of Minnesota. Once the capping inversion is lost over
western Minnesota...strong middle- and upper-level jetting with steep lapse
rates within a highly unstable environ /including dewpoints near-
over 70 degrees/ will promote strong to severe thunderstorms capable of
producing large hail and damaging winds. The regime then transitions
to one of heavy rain over the weekend as the surface low pressure system
opens up and becomes caught up in the prolific southwesterly flow while the
northwest upper level trough opens to more of a trough than cutoff low.
Long plume of southerly surface flow will aid in bringing moisture well north
into the upper miss River Valley region. Model quantitative precipitation forecast continues to
advertise between 3 and 6 inches of rain for the area through the
weekend...but with much of it convective...trying to pinpoint
where such rainfall events may occur is highly problematic.
Still...have kept high-end chance probability of precipitation going in the forecast. Probability of precipitation
diminish for the start of next week as a more zonal upper level
pattern develops...keeping any organized low pressure systems away
from the area. That said...several middle- and upper-level shortwave
disturbances will still be capable of producing isolated to scattered
convection as the warm/moist air will remain in place through
early next week.
&&
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1137 PM CDT Tuesday Jun 18 2013
VFR conditions tonight and for most of the area Wednesday.
Potential for fog tonight has diminished such that it has been
removed from the tafs. A few thunderstorms may develop Wednesday
afternoon across Minnesota...but they should remain fairly isolated and
short-lived so was not confident enough to include mention in any
tafs. If it does hit a taf site...brief MVFR conditions would be
likely. Winds will veer southerly and strengthen
Wednesday...before diminishing and backing southeasterly during
the evening.
Kmsp...VFR expected through the period. Little weather impact expected
through most of Wednesday...but there is an outside chance of a late day
storm. Wind will increase southerly and could gust to nearly 20 knots
Wednesday.
/Outlook for kmsp/
Thursday...VFR. Chance of MVFR. Thunderstorms and rain likely. South-southeast winds 10 kts.
Friday...VFR. Chance of MVFR thunderstorms and rain. S winds 10-15 kts.
Sat...VFR. Chance of MVFR thunderstorms and rain. S winds 5-10 kts.
&&
Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&
$$
Short term...ajz
long term...jpc
aviation...borghoff
