Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 100544

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1144 PM CST Sat Dec 9 2017

.Updated for 06Z Aviation Discussion...
Issued at 1135 PM CST Sat Dec 9 2017


.SHORT TERM...(This evening through Sunday)
Issued at 230 PM CST Sat Dec 9 2017

The forecast concern near term is cloud trends during the period.

Pesky lower clouds continue to plague parts of the southern cwa
this afternoon. Does appear to be clearing/eroding from the north
and the near the edges. HRRR trend does break this out but high
clouds move in rapidly behind the cloud area into the night.
Meanwhile, models drop a weakening short wave in the northwest
flow affecting mainly eastern areas later tonight. Will drag a
cold front south over the area into Sunday morning and should
bring a return to some lower clouds after 06z. Depending on
thickness of clouds this evening, temperatures may drop off a few
degrees to the est, but nearly steady to slowly rising
temepratures are expected over the west. CLouds may linger at
least the first half of the day and may limit warming, especially
to the east.

.LONG TERM...(Sunday night through Saturday)
Issued at 230 PM CST Sat Dec 9 2017

The long term trends continue the northwest flow pattern over the
cwa with timing and strength of short waves riding the western
CONUS ridge to the eastern CONUS trough.

The first wave arrives Sunday night affecting mainly the eastern
half of the area. Snow, mainly light, appears to be the main
concern with the passage of this wave. The GEFS probability has
100% chance for snow over the eastern cwa with perhaps some
freezing drizzle across the west if ice is not present aloft when
the overall lift moves through mainly Sunday night. The ECMWF is
a little slower with the trough and this may result in a longer
precipitation threat to the east into Monday morning. At the
moment, we have a general 1 to 2 inches accumulation mainly along
and east of the I94. Timing will be critical but the Monday
morning commute could be cumbersome.

This system exits to the southeast Monday with windy and colder
air filtering in behind through at least midweek. The next short
wave rides southeast over the area Wednesday into Thursday. It
looks cold enough for just snow with this feature, and
accumulation should remain light. The deterministic models trend
some flattening of the western ridge as a stronger trough moves
ashore over the Pacific Northwest later in the week. This may
allow somewhat warmer Pacific air to make some headway into at
least the southwest part of the state early next weekend. This
appears to be only a brief interruption in the overall mean flow
with the west coast ridge rebuilding and the eastern CONUS trough
amplifying once again after that.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1135 PM CST Sat Dec 9 2017

A frontal boundary will move through and bring northwest winds
today. Could see some MVFR ceilings, but most locations should be
VFR. Later Sunday night another quick moving system will bring
southwesterly winds back across the region and some light snow
will develop.

Did include a brief period of MVFR clouds Sunday afternoon based
on the persistent trend in the forecast soundings that show a
broken layer around 1500 to 2000 ft. There is a chance for snow
showers Sunday night into Monday morning which could bring a brief
period of MVFR or even IFR conditions.

Mon...MFVR with chc IFR/-SN early. Wind NW 15G25 kts.
Tue...VFR. Wind NW 10 kts.
Wed...MVFR with -SN. Wind SE at 10 kts.




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