Scientific Forecaster Discussion
fxus63 kmpx 181135 aaa
Area forecast discussion...updated
National Weather Service Twin Cities/Chanhassen Minnesota
635 am CDT Wed Oct 18 2017
Short term...(today and tonight)
issued at 413 am CDT Wed Oct 18 2017
Very little was changed from the last forecast for today and
tonight. A cold front will be dropping in today which will be the
main focus in the short term for a couple reasons despite it
passing through dry.
1. High temperatures ahead of the front should reach levels
similar to yesterday, maybe a degree or two warmer given the
head start we have this morning in the 50s. The exception to this
will be over west central Minnesota where the front will reach late this
2. Already dry dew points will become even drier following its
passage which will lead to elevated fire weather concerns. Even
behind the front temperatures will be quite mild in the 60s. This
will allow min relative humidity values to reach the low to mid 20s as dew points
drop into the 20s and 30s. Gusty winds will also contribute to a
heightened fire weather risk with gusts to 30 mph becoming common
this afternoon across central and western Minnesota.
The brief trough will swing through this evening and warm air advection will
already be redeveloping overnight. Diminishing winds and clear
skies will allow temps to drop to chilly levels, but the wind is
not expected to fully decouple on a widespread basis, which
should keep lows in the mid 30s to lower 40s.
Long term...(thursday through tuesday)
issued at 413 am CDT Wed Oct 18 2017
Confidence is high that the abnormally warm weather will continue
through the first part of the weekend.
The strong zonal flow that has dominated most of North America over
the past week will become more amplified this weekend, and into next
week. The change in this amplified pattern will stop the abnormally
warm conditions, to more seasonable next week. There is even a
chance of light snow or flurries next Tuesday as several short waves
rotate southward along the back edge of a long wave trough forming
across eastern North America.
One of the major changes to this pattern is possibly a blocking
ridge developing between Greenland and eastern North America. This
is a -nao type of pattern which is conducive to cold waves moving
southward across Canadian, and into the eastern half of the United
States. In addition to the -nao, a +pna is developing. These two
type of upper level flow patterns is again conducive to a colder
pattern for the upper Midwest, which the current deterministic
models have been advertising over the past few runs.
First, the abnormally warm weather, and possibly record breaking
temperatures this Friday, is on track as a strong southwest flow
develops at the surface and aloft. Models have been consistently too
cool and hold down temperatures in the extended period. The best
method is to extrapolate the height of the mixing layer to the
surface. Over the past few days, during the heat of the day, the
mixing level has been around 875/850h. Friday is a good example of
strong mixing, and if we mix to around 850h, surface temperatures
could rise to around 80 degrees. The record high for the Twin Cities
is 83 degrees which occurred in 1953. 83 degrees is also the record
high in Eau Claire, and 81 degrees in St. Cloud. All of these record
occurred in 1953. 850 mb are similar to this pattern in 1953 with
strong anomalous temperatures in the northern plains.
As the pattern begins to change late in the week, and into the
weekend, a very strong and amplified short wave will move across the
upper Midwest Saturday. There could be some timing differences, but
consensus remains that our dry weather will end this weekend. In
addition, once a secondary short wave moves across southern Canada
Sunday, it will bring down the coldest air of the season early next
week. Again, these temperatures are not too extreme, but with the
recent warm spell, it will be an abrupt change.
Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 635 am CDT Wed Oct 18 2017
Only concern for the period will be a wind shift with the cold
front. Expect gusty south winds ahead of it and west winds behind
Kmsp...front should push through around midday.
/Outlook for kmsp/
Thu...VFR. Winds S 5-10 kts.
Fri...VFR. Winds S 10-15g25 kts.
Sat...VFR. Chc thunderstorms and rain. Winds south-southwest bcmg west 10-15 kts.