Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
249 PM CDT Thursday Jul 24 2014
Short term...(this evening through friday)
issued at 233 PM CDT Thursday Jul 24 2014
Short term concerns remain coverage of thunder overnight into
Friday. Also...chance of large hail mainly later tonight into south
central Minnesota with some severe potential lingering into Friday ahead of
Upper ridge is beginning to move east with one impulse dropping
southeast over western Minnesota and the next wave lifting into
northwest nodak and southern Manitoba. It appears the initial wave
will drop southeast this evening along the eastern periphery of the
instability gradient to the west and the edge of low level warm air advection/steep
middle level lapse rates. Models diverge on development thereafter...
with several hires models indicating Canadian system takes over and
drops southeast overnight. Still some potential of low level jet driving
convection into mainly south central Minnesota late. Will carry higher
probability of precipitation to the south once again...in spirit with the previous
forecast. Should see some quantitative precipitation forecast move through the most of area.
Friday still see some potential of isolated/widely scattered
convection developing along the front as it moves across the eastern
portion of the area into the afternoon. Will hold onto some low end
probability of precipitation for this potential. Instability along the front does increase
during the day but low level convergence remains weak. Much of the
high end forcing is driven east during the morning as well.
Temperatures should warm into the middle 80s to the southwest with mix
with the weak front and upper 70s/lower 80s elsewhere.
Long term...(friday night through thursday)
issued at 233 PM CDT Thursday Jul 24 2014
Main concern in the extended period is whether rain showers/thunderstorms and rain develop
further southward across Minnesota than expected for late Sat afternoon/early
Sunday as a strong...and unusual upper low for this time of year
moves east-southeast across the northern plains...and into the western
Great Lakes by Sunday. Will follow previous forecast with the main
area of rain showers across central Minnesota/ec Minnesota and wc WI where both upper
level energy and higher relative humidity fields are evident. K-index and 850 mb
showalter index fields indicated mainly rain showers with some embedded
thunderstorms and rain for the typical diurnal time frame. Sunday morning/afternoon will
likely be breezy as the surface low deepens as it moves southeast across the
western Great Lakes in response to the upper jet.
No changes in the extended period beyond this weekend with both the
ec/GFS advertising a strong upper ridge building off the East
Coast of North America with a deepening long wave trough across
the eastern 1/3 of the Continental U.S.. this will keep our region cooler
than normal and mainly dry. Although cooler temperatures are
expected...Standard anomalies are not too impressive compared to
the deep southeast U.S. Where anomalies could drop to 2-3 blw normal.
For comparison...our region will be slightly cooler...but still
nice for late July/early August.
Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1143 am CDT Thursday Jul 24 2014
Radar trends suggest scattered activity to move into western Minnesota
this afternoon. Believe it will hold off at kstc and east through
most of the evening with the best chance moving in after 06z
across the southeast portion of the area. Will bring in some
thunder to krwf this evening with perhaps a rain showers this afternoon
before 23z. Will spread this east overnight...leaving activity out
of west central Wisconsin doe to uncertainty. Cape builds into
Friday and may see some threat of widely scattered activity along
and east of the front into the afternoon. Appears frontal passage will only
make it into western Minnesota during the afternoon...and exiting wc
Wisconsin after 06z Sat. Some threat of MVFR ceilings
developing late tonight...especially if a more widespread mesoscale convective system
develops. Still some uncertainty to coverage...so will leave VFR
will continue to mention prob30 thunderstorms and rain in the 08z-12z period...per
model discrepancy in overall development/placement during the
night. Trends should favor something developing farther east after
06z Friday...like we have it as low level jet and instability gradient shifts
east. Some threat of MVFR ceiling into Friday morning...but will leave
VFR for now due to low confidence. Still some threat of thunderstorms and rain into
Friday ahead of slow moving front into the afternoon...but
believe it will be rather isolated in nature and will leave this out
for now. Southeast to south winds ahead of front becoming west
into Friday evening.
/Outlook for kmsp/
Friday...chance MVFR ceilings/isolated thunderstorms and rain. Winds south-southeast at 5-10kts.
Sat...VFR. Winds west-southwest at 5-10kts.
Sun...VFR. Chance rain showers/MVFR ceilings. Winds northwest at 10-15 kts.