Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 260018
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
618 PM CST Fri Nov 25 2016

.UPDATE...
Issued at 610 PM CST Fri Nov 25 2016

Updated to include 00z aviation discussion below.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 356 PM CST Fri Nov 25 2016

Main issue during the short term is what happens with stratus
tonight. On the 12z MPX sounding, the stratus went up to about 800
mb, or 5600 ft AGL, hence why it has been so slow to move across
southern MN and has even stalled across central MN. Given current
dewpoints in the low and even mid 30s, chief concern tonight will
turn to fog potential. We should achieve our cross over
temperatures within 3 hours of sunset and spend the next 9ish
hours with temperatures below the cross over temperature, which
means dense fog could become a significant issue on the west edge
of the stratus field. Right now, followed a blend of hi-res model
visibility forecasts to get fog into the weather grids. This
resulted in the strongest fog mention extending from central MN
into southeast MN, or near where the west edge of the stratus
field will likely setup. Other change to the forecast for tonight
was to increase lows 3-5 degrees thanks to the current dewpoints
and expected cloud cover/fog tonight helping keep temperatures
warmer than what most of the guidance has depicted. Our diurnal
temperature ranges the last 3 days have been minimal (less than 5
degrees) and don`t anticipate temperature drops as large as what
the majority of guidance would have to achieve the lows they have
for tonight. What we have going right now most closely resembles
lows forecast from the RAP.

For Saturday, we are currently expecting the stratus to finally
clear the area, but would not be at all surprised if the stratus
hung tight in western WI. Though we may lose the stratus, dense
cirrus/cirrostratus moving across the Dakotas today will be over
us tomorrow, so we will just be replacing the low clouds with high
clouds. For highs, we will see 925mb temps increase to between
+2C and +6C. This is what we are seeing today in eastern SD, where
temperatures easily climbed into the mid 40s and this is what we
basically have south of I-94 Saturday, a good 10 degrees above
normal.

.LONG TERM...(Saturday night through Friday)
Issued at 356 PM CST Fri Nov 25 2016

The big story for the long term continues to be a potent Plains
storm system this weekend that eventually closes off over
Minnesota early next week with lingering rain/snow showers and
extensive cloud cover for the rest of the week.

Rain will rapidly develop over the central Plains Sunday morning
in response to strong moisture advection and 1 to 1.25 inch pwats.
That maturing rain shield will be lifting into Minnesota late
Sunday afternoon and across the rest of the region Sunday evening,
before exiting to the north late Sunday night or early Monday. A
few embedded thunderstorms are also possible given neutral
stability. Rainfall amounts of 1/2 to 3/4 inch are likely.

Temperatures will rise steadily Sunday night as moisture
increases. The dry slot will reach southern half of Minnesota
Monday morning which could dry the column enough for some sun.
Good mixing with gusty winds should bring a pretty mild day with
highs in the 50s along and east of I-35 unless the dry slot
doesn`t progress as far north and east as the ECMWF indicates.

The rest of the forecast will depend on where the system closes
off. If this occurs northwest of the area, the dry slot will
linger longer across south central MN to west central WI. If it
closes off overhead or to the east, almost continuous light
rain/snow showers are likely for much of the week. Continued the
low chances for much of the area, with the highest PoPs (40-50
percent) across western and central MN.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 610 PM CST Fri Nov 25 2016

Back edge of low stratus continue to trudge eastward but where it
clears out in western MN, fog is filling in. The problem is having
the elevated dewpoints remain in place, even in places where some
partial clearing has allowed temperatures to temporarily drop into
the upper 20s. Slow snowmelt is feeding the low level moisture
while no dry air advection is available to scour it out overnight.
In fact, am expecting most areas to have winds drop to calm late
this evening through the overnight hours. This combination will
then is fairly susceptible to more widespread fog formation. Thus,
have continued the theme of IFR-or-lower conditions for the 26/00z
TAFs, which is what was inherited from the 25/18z TAFs. May need
fairly frequent amendments as around the back edge of the stratus
but will continue to monitor. Conditions will gradually improve
during the day tomorrow as ceilings lift then decks scatter out.

KMSP...Will be a rather tricky overnight period as the ragged
western edge of low stratus will be nearly atop KMSP. This will
play with the low stratus versus fog setup overnight. Either way,
am fairly confident that IFR conditions will be experienced
overnight through daybreak Saturday morning but it is a matter of
how it is realized. Mild temperatures are still prevalent at
initialization time but am expecting the dewpoint depression to
diminish which will allow fog to develop later this evening.

/OUTLOOK FOR KMSP/
Sun...Mainly VFR. MVFR/IFR with -SHRA late. Wind SE 10-15 kts.
Mon...MVFR early with -RA. Wind S 10-15 kts.
Tue...MVFR/IFR. Chc -RA/-SN. Wind SW 5-10 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

UPDATE...JPC
SHORT TERM...MPG
LONG TERM...BORGHOFF
AVIATION...JPC



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