Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 210937

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
437 AM CDT Tue Mar 21 2017

.SHORT TERM...(Today and tonight)
Issued at 329 AM CDT Tue Mar 21 2017

Surface analysis early this morning shows a dry cold front sagging
west southwest over northern WI into southern MN, extending from
an area of low pressure near the southern portion of the
Ontario/Quebec border. Arctic high pressure is currently centered
on the central portion of the Saskatchewan/Manitoba border. Aloft,
upper level flow is generally northwesterly across much of the
north-central CONUS as a ridge axis builds over the Rockies and a
longwave trough shifts off the Atlantic seaboard. The Canadian
high pressure airmass will be the main feature through tonight as
it rides into the Upper Mississippi River Valley region on the
northwest flow, bringing colder and drier air into the region
through tonight. The cold front will exit to the southeast,
pushing any impetus for precipitation well away from this area.
Though there will be some passing clouds from time to time, the
cold air advection will most certainly overcome any sunshine over
the area today. Whereas highs yesterday hit the mid 50s virtually
everywhere within the WFO MPX coverage area, highs today will halt
in the 35-40 degree range area-wide. While the high pressure area
as a whole will shift off to the southeast, its center will remain
to the northeast of the area, moving into Lake Superior by
daybreak Wednesday. This will keep winds up overnight and not
allow for ideal radiational cooling conditions. Despite this, the
colder air will be felt overnight with lows expected to range from
10 to 20 degrees tonight which will be roughly 15 degrees below
normal. The ridge axis out west will attempt to shift east
overnight into tomorrow morning but a weak shortwave buckle trough
will develop within it and pass into the Dakotas. The timing of it
looks to hold off until after daybreak tomorrow so have been able
to maintain a dry forecast throughout the entire coverage area
this period.

.LONG TERM...(Wednesday through Monday)
Issued at 329 AM CDT Tue Mar 21 2017

The change in the weather pattern for a wetter scenario is on
track for the Upper Midwest starting Wednesday, and lasting
through the extended period.

Initially, a very dry air mass will keep most of the precipitation
south and west of our region. Some mixture of sleet/snow or rain
is possible on the initial surge of mid level warm air advection
and associated moisture. This will happen sometime Wednesday
morning before most of the precipitation dissipates as it moves
further eastward into the drier air mass by Wednesday afternoon.

The main onset of rain, possibly mixed with snow, sleet initially,
moves northward into the Upper Midwest Thursday afternoon/evening.
This has been advertised fairly well with the models over the past
several days in terms of timing. Placement of the warm front
remains south of Minnesota, but close enough to keep things
interesting in turns of convection. However, with the added
elevated instability expected late Thursday, and into Friday
morning, a few rumbles of thunder is probable. The elevated
instability is noted by both the EC/GFS, and the MPAS. Dew points
in the 50s are as close as the Iowa border Friday morning leading
to an increase of surface convection, especially along the Iowa
border. In terms of rainfall, and the increase of PWAT values
nearly 3 standard deviations above normal, the potential of
heavier rainfall is likely. Models are still too conservative on
QPF amounts, especially late Thursday night/Friday morning as the
added low level jet interacts with the elevated instability and
frontal zone. Even the CIPS has a low probability of 2+ inches in
southern Minnesota by Saturday.

As mentioned in earlier discussions, a change in the weather
pattern is difficult for weather models, and this is the case
again for this system. A few days ago, most of the precipitation
would have ended by Friday, but with the potential of a stronger
ridge holding this system further west, the precipitation could
linger into Saturday. Once this system moves out, it will be
followed by another system in the wake of this progressive
pattern. Due to the persistent chance of precipitation Thursday,
Friday and early Saturday, little diurnal temperature range is
likely. Lows and highs will likely be within 5 to 10 degrees
during this period.

It is also evident that most of the precipitation will be in the
form of rain as most of the cold air will hold in Canada,
especially considering the upper flow pattern from the


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1056 PM CDT Mon Mar 20 2017

VFR through the period with only few-sct high clouds. North-
northwest winds generally at 5-10kts with gusts in the mid/upper
teens on Tuesday late morning & afternoon. Shift to northeast
occurs Tuesday eve.

KMSP...No concerns with high confidence in the TAF.

Wed...VFR. Chance MVFR with -RA/-SN late. Wind SE 5-10 kt.
Thu...MVFR with -RA likely in afternoon & night. Wind SSE 10-15
FRI...MVFR with -RA likely. Wind NE 10 kt.




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