Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 210840

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
340 AM CDT Sun May 21 2017

.SHORT TERM...(Today and tonight)
Issued at 337 AM CDT Sun May 21 2017

The short term concerns are timing of drying trend today and
extent of clearing into tonight.

Water vapor imagery showing the upper low lifting over southern
Minnesota this morning. Attendant occluded surface low moving
across the metro area this morning and into Wisconsin this
afternoon. We did manage to develop some isolated convection out
ahead of the occluded front and moved across far eastern portion
of of the cwa/west central Wisconsin. This will move out before
12z. the upper low lifts northeast we expect some
wraparound light rain/showers over the area. Went with some likely
pops stretching over central cwa into about mid morning or
so...and then expect forcing to wane...with PoP trend lessening to
chance into the afternoon. QPF will be much lighter today with
most areas below one tenth of an inch. We expect clouds to remain
most areas...perhaps some breaks developing to the far west into
the afternoon. Temperatures will be held in the upper 40s to lower
50s most areas.

Clouds will gradually break some to the west overnight but should
hold firm as a weak extension of the upper trough swings slowly
southeast. This will also hold a small chance of showers over the
northeast cwa into tonight.

.LONG TERM...(Monday through Saturday)
Issued at 337 AM CDT Sun May 21 2017

Monday and Tuesday...A bit of an interesting pattern is expected
to develop for the start of next week, particularly in the upper
levels. The upper level low responsible for all the weekend rains
will shift to a spot north of the Great Lakes by daybreak Tuesday,
atop its related surface low pressure center. The upper low will
continue to rotate and even spin off a secondary upper low which
will track south from the Minnesota Arrowhead down the Mississippi
River during the day Tuesday. While a fairly nondescript surface
pattern will accompany the upper level feature, the deep moisture
column will remain over the region. The stronger influence of the
upper level features will be conducive to scattered showers but if
even modest instability is present, the steep lapse rates and
cold air aloft may be enough to produce some hail Monday afternoon
and again Tuesday afternoon. Temperatures will still run below
normal with highs in the 50s and 60s.

Wednesday and Thursday...The upper level low will pull off to the
east Tuesday night into Wednesday morning, being replaced by
surface high pressure and longwave ridging. This will allow for a
drying out period Wednesday through Thursday along with warmer
temperatures. Highs will approach normal values with max temps in
the mid-upper 60s on Wednesday followed by highs around 70 on

Friday and Saturday...The end of the week continues to evolve
during each model run but some consensus is developing in the
pattern of warm-sectoring on Friday followed by a cold frontal
passage Saturday morning. This means continued chance PoPs in the
forecast along with mention of thunderstorms this far out. The
overall pattern looks to have a large upper level low from the
Pacific deepen significantly over south-central Canada starting
Thursday. The system will enhance the southern stream with a large
trough axis extending into the southwestern CONUS. This trough
will then aid in cyclogenesis over the TX/OK panhandles Friday
night, pushing the low pressure center into the Great Lakes next
weekend. There are still some timing/placement issues with the
smaller features but there is some growing confidence in the
overall pattern to maintain PoPs/thunder. Highs will run near to
possibly slightly above normal by the end of the week.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1103 PM CDT Sat May 20 2017

Surface low near Fairmont will move across the Twin Cities
tonight. Have high confidence in conditions ahead of the low and
occluded front...drizzle with IFR/MVFR vis and LIFR/IFR cigs.
Behind the low and front though, conditions in Iowa are a mix of
MVFR/VFR. For now, kept the TAFs relatively unchanged outside of
EAU. EAU will be in line to get into the warmer air associated
with the VFR conditions over Iowa, so have them going VFR for a
bit late tonight/early Sunday morning, in line with CIG forecast
from the HRRR. Though a period of VFR will be possible at MSP and
RNH as well. Looking at forecast soundings, we have enough lift
(omega) in the cloud layer to keep -dz/-ra going through mid
morning, but after that expect mainly dry conditions, with
afternoon shower activity confined more to the eastern Dakotas
where some sun and destabilization will be possible.

KMSP...HRRR continues to indicate a period of VFR conditions being
possible as the surface low works through between 9z and 13z,
which isn`t unreasonable when looking at obs down in IA. Think CIG
forecast is pessimistic if anything on Sunday when looking at the
mainly MVFR/VFR obs to the south of the low across ern Neb/wrn IA.

Mon...VFR. Chc MVFR/-shra. Wind NW at 5-10 kts.
Tue...VFR. Chc MVFR/-shra. Wind N 10-15 kts.
Wed...VFR. Wind NE 5-10 kts.




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