Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 311650
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1150 AM CDT WED AUG 31 2016

.UPDATE...
Issued at 1143 AM CDT Wed Aug 31 2016

Updated for 18Z aviation discussion below.

&&

.SHORT TERM...(Today and tonight)
Issued at 427 AM CDT Wed Aug 31 2016

Surface analysis shows a ridge of high pressure over Lake Winnipeg
and an area of low pressure over James Bay. High pressure will
dominate the weather pattern through Thursday with a light north to
northeast wind, clear skies, very seasonable temperatures and low
humidity readings during the day. Some patchy fog will be noted
Wednesday night in the more fog prone areas. A few cumulus clouds
will develop Thursday afternoon as high pressure sends a
reinforcement of cooler air aloft.

.LONG TERM...(Thursday through Tuesday)
Issued at 427 AM CDT Wed Aug 31 2016

Not much has changed with thinking in the extended outside of the
arrival of precip continues to slow down. At this point, dry weather
looks to remain in place through Saturday, with the only sensible
weather of significance being an uptick in winds for Friday and
Saturday. A very active pattern then looks to set in Saturday
night that will last through the first half of next week.

Models continue to be in good agreement on the large scale pattern
evolution with the developing h5 ridge over the high Plains this
evening slowly working to the east, eventually setting up over
eastern NOAM over the weekend. As it moves over to eastern NOAM, a
broad trough will become established from the Rockies out into the
Plains, placing us within southwest flow that will be sending
numerous shortwaves our direction. Though there is general agreement
on the large scale, there remain significant differences in the
details from this weekend on in terms of timing and strength of
individual waves that will be riding the southwest flow through.

Again, the main change we continue to see in the extended guidance
is a general slowing in precip arrival this weekend, with it now
looking like precip arrives Saturday night in MN and Sunday in WI.
As a result, we continued to reduce pops Saturday and Saturday
night, but go full steam ahead Sunday/Sunday night with likely pops
now in place for much of the area these two periods. Once we get
beyond Sunday night, we are seeing considerable spread in the models
with timing some of the finer scale waves through, though we look to
see at least two more rounds of precipitation between Monday and
Wednesday, but there is enough spread in when those waves come that
we have chance pops from Monday on in the forecast. Between 12z
Saturday and 12z Wednesday, WPC fronts forecast shows a frontal
boundary going from NW MN/south central SD Saturday morning to south
central MN/northern WI Wednesday morning.

Though there are detail issues, one area where there is high
confidence is that we will be seeing another anomalously moist
environment move in with this front, with PW values expected to
increase to above 1.75" which will put us right up around max
observed values for early September. Both the GFS and ECMWF show
widespread 1-3" of QPF across the area, though given the degree of
moisture and slow progression of the frontal system, amounts as
much as double that will likely be seen in parts of the region as the
wet pattern we saw in August continues right into September.

Beside the heavy rain threat, we will likely see a severe weather
threat or two emerge as we get closer to the weekend, especially
considering that as this boundary is working across the area over a
four day period, we will likely see at least two surface lows work
up across the area along the boundary. So it certainly looks like we
may have our work cut out for us this holiday weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1143 AM CDT Wed Aug 31 2016

High pressure continues descending from Canada toward the great
lakes. Continued mostly sunny skies expected. The winds will start
northerly and slowly become easterly tonight as the high advances
south. Some patchy fog still looks possible as hydrolapses
indicate that potential especially at KEAU and KRNH. Some cu will
pop tomorrow but looks scattered based on the cu rule in eastern
MN and western WI.

KMSP...No change from the main discussion, quiet VFR period ahead.

/OUTLOOK FOR KMSP/
FRI...VFR. Wind SSE 5-10 kts.
SAT...VFR. Wind s 10-15G20 late afternoon.
SUN...VFR. TSRA possible. Wind S 10-15G20 kts.

&&

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

$$

SHORT TERM...DRL
LONG TERM...MPG
AVIATION...SPD


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