Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Twin Cities/Chanhassen Minnesota
1145 PM CDT Sat Aug 1 2015
issued at 710 PM CDT Sat Aug 1 2015
Convective allowing models continue to insist in convection
peaking around this time over western Minnesota/eastern South Dakota...then gradually
diminishing through the evening as it heads east into increasing
cin. Since the storms have already died south of Aberdeen...with
nothing else on radar...it is doubtful any additional storms will
develop this evening. The chance is not zero...so will maintain
the Severe Thunderstorm Watch for now...but will need to
reevaluate that in an hour or so. Did reduce probability of precipitation to schc for the
remainder of the evening.
Short term...(this evening through sunday)
issued at 258 PM CDT Sat Aug 1 2015
Altocumulus castellanus continues to increase across central and southern Minnesota at middle
afternoon as strong low/middle level Theta-E advection increases.
Showers have begun to sprout across west central Minnesota...ahead of a
short wave and surface low pressure system located over the
central Dakotas. The short wave will move into central and
southern Minnesota this evening and reach western WI late in the night.
Forcing and instability ahead of this feature should yield scattered
convection spreading across the forecast area late this afternoon and
evening. Consensus on timing and location between the cams is
rather poor with some solutions not showing much at all occurring
tonight. Based on the timing of the short wave...allowed for scattered
thunderstorms to spread from west central into central Minnesota for the
remainder of the afternoon with the activity reaching into the
Twin Cities and south central Minnesota during the early evening and
across west central WI during the middle to late evening hours.
There is a threat for severe storms through the evening. The best
cape and Li indications over the next few hours are from west
central into south central Minnesota. This is also at the nose of the low
level moisture transport and better 0-1km shear. Dcape values
remain well above 1000 j/kg as well. The aforementioned area is
also were a few cams have an axis of best updraft helicity. As
the evening progresses...the low level jet will increase and
spread northeast. This would increases the shear for storms across
east central Minnesota and west central WI. This area is also ahead of
the surface warm front. All of the showers and thunderstorms push
east of the forecast area by Sunday morning with the warm front.
Another concern overnight is the potential for fog and stratus
from central Minnesota into west central WI in the wake of the expected
evening showers and thunderstorms. The boundary layer will be
quite moist in the wake of the warm front along with light winds
expected. Confidence was not high enough to include fog at this
time given the variability in the cam solutions on the showers and
thunderstorms through this evening.
On Sunday...a surface cold front will lie east-west across
central Minnesota in the morning...with a slow southeastward progression
during the day. Instability increases once again and scattered storms
are forecast for the afternoon from the Twin Cities on east. These
should be east and south of the area by evening. The threat for
severe weather with these storms are low at this time.
Long term...(sunday night through saturday)
issued at 258 PM CDT Sat Aug 1 2015
Long range guidance continues to struggle with deciding exactly how
the large scale pattern will evolve toward the end of the upcoming
week. However... through at least midweek things are in fairly good
agreement... and essentially keep US quiet/dry through Tuesday. Next
feature of interest looks to affect the region around Wednesday...
although the guidance differs substantially on the strength of the
upper wave and position of the surface low and warm frontal
boundary. GFS is more pronounced and farther north... while the
European model (ecmwf) and Gem are to the south. Given the uncertainty from Wednesday
Onward we wind up needing to include chance probability of precipitation for most of the
forecast period through Saturday... with the highest probability of precipitation on
Thursday when there is currently the best overlap in solutions.
Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1145 PM CDT Sat Aug 1 2015
A few showers have formed east of msp...near rnh and eau. These
will diminish during the next couple hours with dry weather expected
for the rest of the night. A few more storms could develop Sunday
afternoon across western WI. Main story Sunday will be stronger
northwest winds behind cold frontal passage when some gusts could exceed 25
Kmsp...a shower or two near msp will diminish by 06z taf
issuance...then dry weather expected for the rest of the period.
/Outlook for kmsp/
Monday...VFR. Wind northwest 10-15kts.
Tuesday...VFR. Wind north 5-10kts.
Wednesday...VFR. Wind southeast 5-10kts.