Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
452 am CDT sun Aug 30 2015

Updated for 12z aviation discussion...
issued at 443 am CDT sun Aug 30 2015


Short term...(today and tonight)
issued at 330 am CDT sun Aug 30 2015

A few areas of fog and low stratus had developed across the region
once again this morning...with some sites reporting visibility less
than a mile. This low level moisture will quickly mix out as
southerly winds increase this morning. Warm air advection will
overspread the region this afternoon which should allow temperature
to warm into the 80s at most locations in Minnesota...and upper 70s
in Wisconsin. The GFS/NAM/rap guidance shows potential for 90 degree
readings this afternoon in western Minnesota...and would buy that if the
boundary layer winds were closer to 220deg as opposed to
190deg...but more importantly the smoke should filter out the
intense sunshine and try to keep todays highs in check.

Continued with a dry forecast...and included patchy fog along I-90
and in west central Wisconsin. However not anticipating much dense
fog since dewpoint depressions will be a tad larger...and the
synoptic pressure gradient will be stronger which should keep up the
surface winds. Overnight lows will fall into the middle 60s across the

Long term...(monday through saturday)
issued at 330 am CDT sun Aug 30 2015

The large scale pattern won't change much through the period...
with southwest upper flow prevailing as the western trough and
eastern ridge Don/T appear to move much until the very end of the
forecast period. As a result... we/ll see mainly warm and dry
weather. There will be a few chances for some precipitation as shortwaves
eject from the western trough and shear out as the try to work
into the upper ridge. Eventually... over the weekend... it looks
like we should get enough eastward shift of the main upper trough
to push the surface low and associated frontal boundary into the
area for more widespread chances of precipitation. The guidance is in
general agreement on the overall large scale pattern... although
there are some differences in how quickly the ridge breaks
down/shifts east... which affects how quickly we see the better
chances of precipitation move into the area. The European model (ecmwf) appears to be
slowest in doing so... while the GFS... fim... and Gem are more
progressive. Pattern recognition for this time of year would
suggest a slower evolution may be the more likely outcome... but
there is a fair amount of spread in the European model (ecmwf) ensemble members...
so tough to be too confident in going with one particular
solution. As a result... will go with a consensus approach... with
perhaps slightly more weight on the European model (ecmwf).

A weak shortwave will move by mainly to our northwest Monday into
Monday night... with any precipitation primarily occurring to our north.
Included some low chance probability of precipitation over the far northwest and north
Monday night along the remnants of the washed out front associated
with that upper wave. Lingered some low chance probability of precipitation over the far
north on Tuesday in the vicinity of the baroclinic zone... but
anything that occurs would be isolated. There is a chance for some
rain showers/thunderstorms and rain over the south and east Tuesday night and Wednesday in
association with some enhanced warm advection and elevated
instability advertised by the medium range guidance... but once
again would not expect anything to wide spread given the lack of
significant/persistent large scale forcing. Similar conditions
persist across much of the area Wednesday night into Thursday...
so will need to continue some chance probability of precipitation. However... at this
point Wednesday night would appear to be the better time frame for
rain showers/thunderstorms and rain given the nocturnal enhancement of the low level jet.
With the exception of highly isolated activity Thursday night and
Friday should be dry as heights rise and the better low-middle level
warm advection look to refocus back to the west again. However...
as we head into Saturday we should see increasing chances start to
shift eastward into the area from the plains as the main western
trough starts to push east into the northern plains. However...
this is also when significant timing differences exist in the
guidance... so it/S still a bit early to pin down when/where the
best chances for rain showers/thunderstorms and rain will be over the weekend.


Aviation...(for the 12z tafs through 12z Monday morning)
issued at 443 am CDT sun Aug 30 2015

Low stratus/fog will linger for the first few hours of the
taf...but should quickly mix out this morning as the southerly
breeze increases. Once it does...expect VFR conditions through the
duration of the taf. A few afternoon gusts will approach
15-20kts...but these will subside after sunset. Some fog could
develop once again...but the stronger winds should keep chances
low so did not include mention in the taf at this time.

there is a thin sliver of VFR conditions just to the west of tried to time this and started out the taf VFR.
However...another area of clouds to the west should move in during
the morning and last through 15z. VFR conditions will follow for
the rest of the taf.

/Outlook for kmsp/
Monday...VFR. Wind S at 15g25kt
Tuesday...VFR. Wind S at 5-15kt
Wednesday...VFR. Wind S at 5-15kt.


Mpx watches/warnings/advisories...


Short term...jrb
long term...999

National Weather Service Glossary of Abbreviations