Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
117 PM CDT Thursday Aug 27 2015
Short term...(today and tonight)
issued at 355 am CDT Thursday Aug 27 2015
Short term concerns are shower threat riding east this morning.
Then development of closed circulation and heavy rain threat over
the southern County Warning Area overnight.
Storm Prediction Center mesoanalysis has a narrow band of middle level frontogenesis over
southern North Dakota this morning. Area of middle clouds/showers and
thunder the farther south in South Dakota. Mesoscale convective system over South Dakota
should continue to ride east/southeast this morning and gradually
decay. There will be a lot of clouds associated with this feature
along with the front band that moves across. Jet streak riding
north of the South Dakota complex should drive this middle cloud
layer /forcing east during the morning. The trend of the hrrr and
hrrr-CR bring this area east to the metropolitan by early afternoon. Had
to include some chance probability of precipitation for this threat. Neighborhood probability of precipitation
from the hires cams are just now beginning pick up on this. Dont
anticipate any significant thunder threat until late this
afternoon to the southwest where better instability if forecast.
That all depends on how much heating will occur however. High
temperature forecast also tricky...with the thicker cloud cover
possible at least through the morning. Middle/upper 70s look likely.
The deterministic models are in fair agreement with placement of
heavier rain across southern quarter of the state overnight into
Friday. The European model (ecmwf) is slower with movement of the trough however.
At the moment have about 0.80 to 1.25 inches quantitative precipitation forecast forecast for the
overnight over south central Minnesota. The hires cam solutions
were moving the heavier quantitative precipitation forecast south into Iowa. The 03z sref was
still was focusing heavier rain across south central Minnesota so we will
continue the higher quantitative precipitation forecast this region for now.
Long term...(friday through wednesday)
issued at 355 am CDT Thursday Aug 27 2015
The long term period starts out on an active note...and then
features overall dry weather with moderating temperatures next
The northern extent of /heavy/ rainfall continues to be the
primary concern for Friday...given models have fluctuated north
and south with the track of the surface low and associated
precipitation for several days. The European model (ecmwf) has been the farthest
north and most persistent with rain spreading into central
Minnesota on Friday morning...and the other models have trended
that way. Have therefore maintained categorical probability of precipitation as far north
as the Interstate 94 corridor /including the Twin Cities metropolitan and
Eau Claire/. The Interstate 90 corridor still looks to bear the
brunt of the heavy rainfall...where one to three inch amounts
appear possible as precipitable waters increase to climatological maximums /1.75
inches/ and combine with a healthy low level jet of 45kts.
The European model (ecmwf) solution also lingers precipitation well into Friday
afternoon along and east of the Interstate 35 corridor...given it
is much stronger and slower with the low. Leaned toward a slightly more
optimistic scenario closer to what the 27.00z GFS
indicates...but it still looks like a soggy day from south/east
central Minnesota into central WI. Friday high temperatures will be
impacted notably with the anticipated clouds/precip...with middle 60s
/southeast/ to middle 70s /northwest/ expected.
Regardless of what model is selected...we should clear out for
Saturday...with light winds and mild temperatures in the middle 70s to lower
The remainder of the long term forecast is marked by moderating
temperatures as low level temperatures gradually rise. Should see middle/upper
80s for most of the upcoming week. A washed out front will hang
out near the area middle to late next week...but temperatures aloft are
likely too warm for convective development given the lack of
forcing. Have therefore kept the forecast mostly dry for next
Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1250 PM CDT Thursday Aug 27 2015
The first 12 hours of the forecast look mainly VFR...with the most
interesting time period from midnight and beyond. For the
remainder of today...expecting high level cloudiness to continue
streaming in...with middle level cloudiness and showers pushing into
southwestern Minnesota. Rwf will be the most vulnerable to precipitation this
afternoon. The surface low is expected to remain south of the Minnesota
border...but guidance still indicates widespread MVFR possible.
Pushed back the onset slightly...mainly very late tonight through
the morning on Friday. In fact...at this point it looks like the
ceilings may be lowest tomorrow after daybreak and we may carry MVFR
until at least 18z...potentially all day. Some guidance indicates
IFR ceilings possible...but not ready to bite on that at this time
with the low being so far south.
Kmsp...most of the precipitation will stay south of msp...but still
expect the possibility of some light rain at msp early tomorrow.
/Outlook for kmsp/
Sat...VFR. Winds southeast 5-10 kts.
Sun...VFR. Winds S 5-10 kts.
Monday...VFR. Winds S 5-15 kts.