Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 080005

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
605 PM CST Thu Dec 7 2017

.SHORT TERM...(This evening through Friday evening)
Issued at 212 PM CST Thu Dec 7 2017

We could see a few flurries over the area tonight into early
Friday as a weak surface wave currently over Manitoba drops
southeast through the region. Otherwise, it will mainly serve to
just increase mid/high clouds as warm advection increases. A much
more potent shortwave trough will drop southeast into the region
Friday afternoon and evening, bringing fairly widespread light
snow to the area, particularly east of I-35 where an inch or two
of accumulation is expected by late Friday evening.

.LONG TERM...(Friday overnight through Thursday)
Issued at 212 PM CST Thu Dec 7 2017

Things don`t look to change much at all through the period, with
the western ridge and eastern trough looking to hold on through
next Thursday. There are some indications that the western ridge
will begin breaking down toward the end of the period, with the
upper flow becoming more zonal along the northern tier of the
CONUS after that, but we`ll need to wait and see if that model
trend persists. In any event, with the pattern remaining largely
the same through the current 7 day forecast period, we`ll see more
of the same in terms of our sensible weather. Northwest flow will
prevail, with reinforcing shots of cold air and chances for light
snow every every 1-2 days or so. The model guidance is in good
agreement on the overall pattern through the period, favoring
mostly below normal temperatures and periodic light snow chances.
However, as would be expected, there are differences in the
details as we move beyond the weekend with respect to timing,
placement, and amplitude of the individual shortwave troughs and
associated surface features. This leads to a lot of chance PoPs in
the forecast, which will be refined as things get closer in time
(leading to shorter time periods with what will undoubtedly be
somewhat higher PoPs). The next more potent shortwave trough with
reasonable agreement in the guidance looks to be on Monday, and at
this point it appears to favor the eastern half of the area much
like tomorrow evening`s system.


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 605 PM CST Thu Dec 7 2017

We have two waves to deal with this period, one tonight, with a
second one inbound about 24 hours from now. The one tonight at
the very least will result in increased clouds down to about 6k
ft. More uncertainty with how widespread MVFR cigs will be with
it. In addition, confidence on cigs between these two waves is low,
with it certainly possible we see mainly clear skies through
Friday morning before clouds thicken again ahead of the next wave
in the afternoon. The second wave is much stronger and confidence
is much higher that this one will bring with both MVFR cigs and a
quick hit of snow. That snow looks to last only 2-4 hours, with
the west end of the snow shield likely going juts east of STC,
west of MSP, and down through RST. In addition, behind the cold
front associated with the second wave, we look to have good cold
advection, with NAM soundings showing 40+ kt winds getting mixed
down at AXN by the end of this TAF period.

KMSP...Low confidence on cig forecast tonight through Friday
morning with how widespread MVFR cigs will be. Could be as good as
VFR with the occasional MVFR cigs until the snow gets closer late
in the afternoon, to as bad as MVFR cigs moving in a little
before 12z and remaining in place through the rest of the period.
Confidence is increasing on a quick hit of snow around 00z as
well. 22z-03z looks to be the bounds of the window where snow is
possible, with some vis down to 1sm possible. At this point, any
accumulation looks to amount to a half inch at best.

Sat...Chc MVFR in morning. Wind NW 10G15-20kts.
Sun...VFR. Wind WNW SW 10G15 kts.
Mon...MFVR with chc IFR/-SN. Wind NW 15G25 kts.




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