Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 191022

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
522 AM CDT Sat Aug 19 2017

.updated for 12z aviation discussion below...

.SHORT TERM...(Today and tonight)
Issued at 351 CDT Sat Aug 19 2017

The short term concerns are fog early and then shower/thunder
chances developing late tonight.

Patchy/areas of dense fog but seems to be pretty spotty and limited
to the low lying areas. Nothing locally...yet. The boundary layer
has decoupled with weak ridging moving across the area. Still have a
little wind over the far southeast where earlier short wave trough
exited. This too is expected to see some form of fog the rest of the
morning. Thought about an advisory, but overall lower visibility
isnt that widespread. Expect it it burn off fairly quickly...through
14z. We should see plenty of sunshine and temepratures warming
through the upper 70s to lower 80s.

Late tonight...a fairly weak LLJ develops to the southwest ahead of
the next frontal boundary over the Dakotas. Models suggest some
sort of weak short wave/convection developing to the southwest
mainly after 08z as the LLJ increase 25-30kts and some weak WWA
takes hold. Most models increase mid level RH to the southwest as
well. We will mention some lower end chance pops into SC MN later
tonight. Will hold onto the slight chance PoP to the northwest as
well...ahead of the frontal boundary.

.LONG TERM...(Sunday through Friday)
Issued at |351 AM CDT Sat Aug 19 2017

The long term forecast period starts off on an active note, with a
cold front passing across the area on Sunday. This looks about 6-9
hours faster than progged 24 hours ago, and is now forecast to be
bisecting the forecast area from roughly the Twin Cities metro to
Redwood Falls at 00z Monday. However, there has been a considerable
amount of variance in timing from run to run, so confidence isn`t
high and have kept the precip mention to high chance on Sunday eve
(vs. likely). Depending on where the boundary sets up during peak
heating, there could be a threat for severe weather for a fairly
large portion of the forecast area. The boundary sags slowly
across the area Sunday night and Monday, continuing the
possibility of showers and thunderstorms, and adding the threat
for heavy rainfall into the mix with precipitable water values
around 2 inches. The nocturnal periods (Sunday night and Monday
night) will feature the highest POPS given the extra support
provided by the low level jet, and Monday night will also have
better support upstairs with mid-level energy, so likely pops have
been included.

Temperatures Sunday will be a bit tricky given uncertainty with the
boundary placement/convection. Generally expect low/mid 80s.

The evolution of the northwest Ontario trough features a farther
east solution, which places the Northern Plains in more of a
ridging aloft regime. This gives a bit better confidence in a dry
forecast for mid to late next week. Highs in the 70s still look
to be common for Wednesday into the weekend under northwest flow


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 530 AM CDT Sat Aug 19 2017

LIFR/IFR CIG/FG should burn off around 14z or so. May see a few
cumulus around 4k ft or so mainly to the east during the day.
Otherwise VFR trend with mid/high level clouds building into the
western areas after 06z. Surface winds sw-s generally less than

Fog should burn off around 14z with VFR trend thereafter. SW-S
wind less than 10kts.

Sun night...VFR. Chance MVFR/TSRA overnight. Wind SW 5 kts.
Mon...Chc MVFR/-TSRA. Wind SE 5 kts.
TUE...Chc MVFR/-TSRA early, bcmg VFR. Wind N 5-10 kts.




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