Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
623 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 12z tafs through 12z Thursday morning)
issued at 610 am CDT Wednesday Jun 19 2013
VFR cirrus and isolated middle level deck over western half of
taf sites shortly after 12z. Look for this layer to overspread
remainder of region by about 15z. Proximity of warm frontal
boundary should be catalyst for widely scattered convection over most
Airport sites by middle to late afternoon. Light southeast flow becomes MDT
with mixing by 15z across southern Minnesota/western WI. Much better
chance for convection kicks off kaxn and krwf after 07z...and
over remainder of taf area by 10z...as low level forcing and
jet stream support increases markedly. VFR ceilings and visibilities
anticipated prior to overnight convective activity...with
occasional MVFR ceilings/visibilities as activity within vicinity or overhead.
Kmsp...
/outlook for kmsp/
VFR ceilings and visibilities through most of taf period...with light
occasional moderate southeast flow expected. Slight chance for strong
T-storms anticipated after 10z tonight...in tandem with low level
southerly jet stream. Possibility of short term low level wind shear 20/06z-20/12z
time frame. MVFR ceilings and visibilities will be very possible associated
with convection late. Could be vcsh at kmsp until 20/20z...until
forcing diminishes.
Thursday...VFR. Chance of MVFR. Thunderstorms and rain likely. South-southeast winds 10 kts.
Friday...VFR. Chance of MVFR. Thunderstorms and rain likely Friday night. S winds 10-15 kts.
Sat...VFR. Chance of MVFR thunderstorms and rain. S winds 5-12 kts.
Sun...VFR. Chance of MVFR thunderstorms and rain. S-SW winds 5-12kt.
&&
Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&
$$
Short term...ajz
long term...jpc
aviation...ajz
