Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
700 PM CDT Monday Sep 1 2014
Short term...(this evening through tuesday)
issued at 256 PM CDT Monday Sep 1 2014
Isolated instability rain showers/thunderstorms and rain will occur through sunset across wc/SW Minnesota
as a weak shortwave moves across the area. Later tonight a stronger
shortwave moving across southern South Dakota may generate a few more rain showers
across mainly SC/SW Minnesota during the pre dawn hours. However...moisture
is limited so will continue with mostly cloudy skies and let the
evening shift handle any adjustments based on coverage in South Dakota this
evening. No other changes on Tuesday as skies clear behind this
aforementioned shortwave later tonight.
Long term...(tuesday night through monday)
issued at 256 PM CDT Monday Sep 1 2014
Tuesday night-Thursday...high pressure will be centered over the
Appalachians at the start of the period with pronounced surface return
southerly flow and zonal flow aloft. Surging moisture and warmer air
behind the high but ahead of an incoming low pressure system will aid
increases in humidity and instability for the middle of the week.
Clouds will be on the increase but precipitation coverage will be
somewhat sparse for Wednesday due to lack of support aloft and no
influential surface features...leaving pure convection as the Mode for
precipitation generation. Will carry chance probability of precipitation for mainly afternoon
development. Chances increases for increased coverage and strength of
storms Wednesday night as several shortwave buckles in the zonal flow
aloft cross over the region...but the larger culprit will be a
digging longwave trough over eastern Montana into the Dakotas. This trough
will shove a development low pressure center from The Rockies into the
eastern Dakotas Wednesday evening then into northern Minnesota early Thursday morning. This system
will drag a cold front along with it...while low level jet develops over NE/Iowa
and shifts into southern Minnesota. There is some disagreement as to
potentially where the best convergence is for the development of
thunderstorms...specifically severe weather...whether over northern or southern Minnesota and
western WI...but enough ingredients are in place to at least think
about the potential for severe weather in portions of the weather forecast office mpx County warning forecast area
Wednesday night into Thursday. The parent low pressure center shifts off into
lower Ontario province along with the upper level trough during the day
Thursday...while the surface cold front slowly pushes into the Great Lakes. Some
lingering showers and thunderstorms are possible Thursday into Thursday night but
the vast majority of the precipitation looks to be out of the County warning forecast area by
then. Temperatures will go on a noticeable warming trend for Wednesday-Thursday
ahead of the aforementioned cold front. Highs will climb to the low-middle
80s...along with dewpoints rising to the lower 70s...spelling a pair
of early September warm and muggy days.
Friday-Monday...cooler drier Canadian high pressure will slowly slide
east-southeast across the northern plains and upper miss River Valley Fri-sun. This
will result in mainly clear skies...or at least a mix of sun and
clouds during the daytime periods...and noticeably cooler
temperatures that will make it feel like early September. Highs
will be bumped back down to around 70 with lows to around 50.
However...more unsettled weather looks to be the story for the start of
the full work week next week as high pressure shifts off to the east
and another Gulf of Alaska longwave trough drops into the Pacific northwest
over the weekend...digging into the western Continental U.S. Early next week.
Return flow on the backside of the high pressure area on Monday combined
with a developing low pressure system over the northern plains in advance
of the longwave trough will make for a setup of scattered
showers/thunderstorms on Monday.
Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 700 PM CDT Monday Sep 1 2014
Subtle impulses aloft will aid in widely scattered showers and
thunderstorms tonight and Tuesday morning. The activity in
progress between krwf...kaxn and kstc is expected to dissipate
before reaching kmsp. However...more widely scattered showers and
thunderstorms are expected into krwf after 08z and pass across
southern areas of Minnesota and west central WI...including the Twin
Cities...early Tuesday morning. VFR conditions outside of the
rain showers/thunderstorms and rain are still expected. Light west winds tonight increasing
to around 10 knots on Tuesday.
Kmsp... some light showers are possible late tonight and Tuesday
morning (08z-14z) with VFR conditions prevailing.
/Outlook for kmsp/
Tuesday evening...VFR. Winds SW 5 kts.
Wednesday...VFR. Chance MVFR/thunderstorms and rain late. Winds S to southeast 10-15 kts.
Thursday...VFR. Chance MVFR/tsra. Winds S becoming west 10-15 kts.