Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 251147
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
647 AM CDT THU AUG 25 2016

.SHORT TERM...(Today and tonight)
Issued at 404 AM CDT Thu Aug 25 2016

Fair weather is expected during the short term, with low pressure
sliding across southern Canada with high pressure moving across the
Dakotas today and over southern MN tonight. This pressure center
configuration will result in breezy WNW winds today, with NAM bufr
soundings showing mix down winds to 25 mph for eastern MN and
western WI this afternoon. Moisture deep enough to generate showers
will remain closer to the low center, so any precip will remain up
in northern MN, but there is an overcast deck of stratocu working
across NoDak tonight that will spread into central MN this
afternoon. This extra cloud cover is why we continue to only
advertise highs in the upper 60s for central MN. For southern and
eastern MN into western WI more sun and mixing to between 875-850mb
on the NAM and GFS would yield highs in the upper 70s, which is
similar to what is seen with the MAV/MET, so did up highs a couple
of degrees in these areas from the previous forecast.

For tonight, with high pressure coming in, we will see both winds
and diurnally driven cu fields drop off quickly after sunset. Really
only sensible weather concern will be whether or not we get
radiational fog. Drier air will limit extent of any fog, but with
lows falling back to the upper 40s to mid 50s, we will likely see
fog develop in the larger river valleys. In addition, for western
WI, they will remain east of the ridge much of the night, with
resultant winds likely keeping any fog formation at bay until close
to sunrise Friday morning.

.LONG TERM...(Friday through Wednesday)
Issued at 404 AM CDT Thu Aug 25 2016

The main concern in the long remains precipitation chances from Friday
night through Saturday night as a large scale upper trough moves
through.

High pressure will be over the FA on Friday with one more pleasant
fair weather day. Overnight model solutions remain in good
agreement on pushing an area of showers and some thunderstorms
across much of the FA Friday night and early Saturday. One thing
noted is that the incoming precipitation is a little faster Friday
night with rain spreading quickly northeast across the area in the
06z-12z time frame. What makes this precipitation event a little
tricky is the nature of the upper trough approaching from the
west. It is really two troughs, a northern stream and southern
stream. The southern stream is the trouble maker with a fairly
strong area of vorticity still seen making its way from the four
corners of the southwestern United States on Friday to MN/IA/WI by
Saturday morning. This is also where the best 925-850mb moisture
transport exists along with PWAT values climbing to around 1.5
inches. The southern stream wave is very well pronounced on the
00z NAM at 700 mb. Hence, an area of showers and thunderstorms
will likely spread across southern MN and adjoining areas of west
central WI Friday night and continue through Saturday morning then
diminish rather significantly in the afternoon. Precipitation
chances can not be completely eliminated on Saturday due to the
northern stream portion of the wave moving through Saturday
afternoon and night. The main precipitation axis with this wave is
across northern MN. So, with two waves there will be two axises of
precipitation, one across IA, far southern MN/WI with the other
across northern MN. This places the Twin Cities and areas to the
west in the middle with lesser amounts of rain. This shows up well
with the GEFS plumes with the deterministic run showing almost
three-quarters of an inch for MSP while the GEFS mean barely has a
quarter inch which is also quite close to the EC total. Go
southeast to LSE and the deterministic and GEFS mean area nearly
the same. At this point is looks as though any significant heavy
rain will stay just south and east of the FA.

Dry weather is anticipated for Sunday and Monday as high pressure
passes by. Things become unsettled for Tuesday and Wednesday as
we get on the backside of the high pressure system, allowing low
level southerly flow to return. In addition, a frontal boundary
will drop south into central MN/northern WI providing a focus for
some small pops.

Friday and Saturday will be the coolest days in the long term with
highs in the lower to middle 70s. Highs next week will return to
the upper 70s early in the week with lower 80s by mid week. This
is actually a few degrees above normal for late August.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 647 AM CDT Thu Aug 25 2016

Fairly straight forward TAFs here with high pressure moving across
the Dakotas today that will settle over southern MN tonight. a BKN-
OVC stratocu field has worked into the Red River Valley this
morning, with the HRRR/RAP still indicating we could see MVFR
cigs down into AXN this morning, but deeper moisture for MVFR
cigs looks to remain just north of MPX terminals, so maintained
VFR TAFs. NAM soundings for central and eastern MN and western WI
show gust potential up to 25kts this afternoon, so did go a bit
above LAMP guidance for wind speeds in these regions. With high
pressure moving in tonight, we will see skies clear out and winds
quickly diminish with the setting sun. Main concern for fog
tonight is at STC and EAU. STC because they look to fall into the
upper 40s tonight, well below their cross-over temperature and EAU
due to the likelihood of seeing fog along the Chippewa River.

KMSP...Went with wind speeds a bit above LAMP guidance based on
forecast soundings from the NAM and RAP. Otherwise, this is a
high confidence forecast with VFR conditions prevailing.

/OUTLOOK FOR KMSP/
Fri...VFR. Wind SSW 5 kts.
Sat...MVFR psbl. TSRA likely. Wind SE 5-10 kts.
Sun...MVFR psbl early. SHRA early. Wind SW 5 kts.

&&

.MPX Watches/Warnings/Advisories...
WI...None.
MN...None.
&&

$$

SHORT TERM...MPG
LONG TERM...RAH
AVIATION...MPG



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