Scientific Forecaster Discussion
fxus63 kmpx 190920
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
420 am CDT Sat Oct 19 2019
Short term...(today through sunday)
issued at 408 am CDT Sat Oct 19 2019
Surface analysis early this morning shows a north-south oriented
cold front bisecting Minnesota, continuing to progress to the
east. Behind it, high pressure encompasses The Rockies and
intermountain west. A potent low pressure center is moving onshore
over the Pacific northwest. Aloft, a longwave ridge axis is
aligned from eastern Ontario province southward through the Ohio
River valley, with generally zonal flow behind it to the West
Coast. A weak shortwave disturbance is traversing the North Dakota
This shortwave is aiding the cold front eastward and is also
helping produce a few rain showers in the vicinity of the front.
Much of the activity on kmpx radar this morning is virga due to a
fairly deep low level dry layer. However, enough moisture recovery
is expected such that accumulated rainfall can and will be
realized mainly over eastern Minnesota through western WI through this
afternoon. The front will push across WI by this evening, allowing
high pressure to settle over Minnesota/WI tonight.
Attention then turns to the system which moves onshore the West
Coast today. This system will shift across The Rockies through
tonight, being drawn eastward by a longwave trough digging sharply
over The Rockies. This system will strengthen as it comes off The
Rockies tomorrow over South Dakota/NE and steadily shifts eastward during
the day Sunday. This will result in an increase in clouds plus
more widespread and steadier rainfall developing in western
Minnesota late day Sunday.
As for temperatures, with the passage of the cold front today,
modest cold air advection plus zonal flow through tomorrow will
result in little day-to-day difference between high temperatures
today and tomorrow. Will look for highs to range from the upper
50s to the mid 60s.
Long term...(sunday night through friday)
issued at 408 am CDT Sat Oct 19 2019
Main weather concern in the long term continues to be the
widespread rainfall and gusty winds expected from a potent
extratropical cyclone impacting the area Monday through Tuesday.
Guidance is in good agreement with a trough digging through the
Central Plains and Great Lakes, with a surface low tracking from
the High Plains through central Minnesota and into the western
Great Lakes. The GFS continues to be the quickest member and the
European model (ecmwf) the strongest with the low, but both have trended closer to
the general guidance consensus tonight. Expect widespread rainfall
to overspread the area from west to east Sunday night as the
surface low approaches, with the low passing directly over the County Warning Area
sometime during the day on Monday. Could see a brief break in the
rain Monday afternoon as the dry slot of the cyclone noses into
southern Minnesota, but think the support for areas of light rain
or drizzle is high enough to keep pops at least chance area-wide.
At least a few hundred j/kg of MUCAPE also looks to be present
with this initial shield of precipitation, so will continue to
include at least isolated chances of thunder. The wrap-around
region of the cyclone moves overhead Monday evening through
Tuesday, with rain expected to continue overnight before wrapping
up from west to east through the day on Tuesday. The strongest
winds with this system are expected in this wrap-around region of
this cyclone as well, as the pressure gradient tightens behind the
cold front and steep low-level lapse rates allows for wind gusts
of 40-50 mph to mix down to the surface across western and
southern Minnesota. The current timing of this system would have
these strongest wind gusts occurring late Monday night into
Tuesday morning which would mitigate the impacts somewhat, but
there is still a chance this timing shifts by a few hours and
places the strongest winds more during the daylight hours. By the
time rainfall exits the system exits the area on Tuesday, expect
widespread rain totals of around 1 inch, with locally higher
amounts of 1.5-2 inches possible.
A weaker trough comes right on the heels of the Monday-Tuesday
system, but there is still quite a bit of spread on timing and
precip chances for our area. One noted trend is that guidance is
weaker and drier, with only a swath of light precipitation
expected in the Wednesday-Thursday timeframe with the members that
bring the surface reflection far enough north to impact the County Warning Area.
Will continue to mention low-end chance pops for now, but
potential quantitative precipitation forecast amounts look to remain on the order of a quarter to
a tenth of an inch or less. Temperatures profiles still look cold
enough to support some light snow should precipitation occur
across northern portions of the cwa, but there's a decent chance
any precip stays across southern portions of the County Warning Area and safely
falls as rain.
After the Wednesday-Thursday trough, drier conditions look
possible through the weekend with high confidence in
temperatures falling well-below normal. Daytime highs look to
remain in the 40s and overnight lows well into the 30s across the
area, which would be around 10 degrees below normal.
Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1002 PM CDT Fri Oct 18 2019
VFR conditions with rain expected to be a bit more widespread.
From a passing cold front. This front will bring mid level clouds
and a wind shift from southerly to westerly, as well as some
showers. Skies will clear from west to east on Sunday.
Kmsp...VFR conditions with rain expected to be a bit more
widespread. From a passing cold front that should bring showers to
msp around or shortly after 12z. This front will bring a wind
shift from southerly to westerly. Skies will clear from west to
east on Sunday.
/Outlook for kmsp/
sun...VFR with MVFR/IFR/-shra late. -Tsra possible. Winds southeast at
Mon...IFR/-shra with -tsra possible early, then MVFR. Wind northwest at
Tue...VFR/MVFR ceilings. Wind northwest at 25g30 kts.