Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
353 am CDT Tuesday Oct 21 2014
Short term...(today and tonight)
issued at 319 am CDT Tuesday Oct 21 2014
Today-tonight...very quiet period in the forecast. Surface analysis
shows an elongated north-S oriented area of high pressure atop the area
which will shift off to the east during the day today...then stall out
over the Great Lakes tonight. Aloft...a ridge of high pressure
straddling the border of Minnesota and western Dakotas this morning will
slowly slide east across Minnesota and WI during the day today...also
expected to stall out tonight over the western Great Lakes
southward through the middle Mississippi River valley. This deep
ridging combination will keep skies mostly clear for the period
through tonight...aside from some wraparound moisture from a
departing upper level low pressure center over the eastern Great
Lakes...bringing stratocu down over mainly eastern and northern
WI...possibly as far west as Barron/Rusk/Chippewa counties in western
WI. This cloud cover may linger for much of the day in the far
eastern portion of the mpx County warning forecast area while fair weather cumulus clouds
develop over eastern into central Minnesota. Cold air advection in
advance of the incoming ridge will keep highs in the low-middle 50s
for western WI. In contrast to this...modest warm air advection
will occur for central-western Minnesota on the backside of the upper
ridge where highs will range through the 60s...and possibly to
near 70 along the South Dakota border. For tonight...the best radiational
cooling conditions will be over western WI where lows will drop to
near the freezing mark. The spread in lows to central-western Minnesota
will be quite large as warmer return flow will have much more
influence out west. Lows tonight in western Minnesota will only drop to
the middle-upper 40s.
Long term...(wednesday through monday)
issued at 319 am CDT Tuesday Oct 21 2014
Early morning water vapor imagery showed a prominent circulation
moving east across northern California into Nevada. This
circulation is in association with an upper level shortwave that
is the main concern for the long term forecast period. This wave
is expected to move east-northeast across the western Continental U.S. And produce rain
across the forecast area from Wednesday through Thursday that will move west
to east across the area. There remain model differences in timing
and amounts expected that still need to be sorted out. The GFS
moves the energy through the fastest...while the NAM is several
hours slower with the expansion of isentropic ascent and
saturation across the forecast area. Rainfall amounts generally look to be
less than 0.5". Overall...forecaster confidence is below average
at this time due to these differences.
Once this system passes...upper level ridging will ensue across
the upper Midwest. Little change was made to the forecast beyond
Friday...as warm and dry conditions still look like a good bet.
Went warmer than blended guidance on Friday and Sunday as
temperatures warm under the ridge. European model (ecmwf) and GFS still indicate
cyclogenesis on the Lee of The Rockies toward the end of the
weekend with spatial and temporal differences in the evolution of
the system. This system gives US our next opportunity at
precipitation...most likely at the very end of the weekend into early
Aviation...(for the 06z tafs through 06z Monday night)
issued at 1049 PM CDT Monday Oct 20 2014
Surface ridging across Minnesota will work east to the western Great
Lakes during the taf period. A tightening pressure gradient on
the western side of the ridge will lead to southeast winds at 15g25kts
for kaxn and krwf from late Tuesday morning and afternoon. The
eastern taf sites will see southeast winds on Tuesday from 8-12 knots.
A concern remains on whether or not the western edge of the VFR
ceilings near Keau will become MVFR overnight as the light
northeast winds become east southeast. Confidence is not high on
the MVFR as each subsequent update to the lamp probabilities
continue to back away on the ceilings in the 12z-15z time frame.
Kmsp...VFR through the period. Light NE winds becoming easterly by
morning and southeast 10 kts during the morning.
/Outlook for kmsp/
Wednesday...VFR. Winds south-southeast at 15g20kts.
Wednesday night...VFR with MVFR/rain showers possible. Winds S at 10kts.
Thursday...VFR with MVFR/rain showers possible. Winds south-southwest at 8kts.
Friday...VFR. Winds south-southwest 5kts.