Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 210002

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
602 PM CST Fri Jan 20 2017

Issued at 602 CST Fri Jan 20 2017

Updated to expand the dense fog advisory northward through much of
central MN as well as for a few counties in the western and
southern Twin Cities metropolitan area.


.SHORT TERM...(This evening through Saturday)
Issued at 414 PM CST Fri Jan 20 2017

Surface analysis this afternoon shows a weak
meridional pattern across the area between a high pressure area
centered over PA and a trough of low pressure along the lee side of
the Rockies with a pair of low pressure centers over northeast WY
and the TX panhandle. Aloft, a wobbling trough of low pressure is
holding fort over the northern-central Plains with an upper level
low developing within the trough over central NE. The upper level
trough overall combined with the weak surface pattern will maintain
low stratus over much of the area overnight. In addition, fog will
be prevalent across the area due to the plentiful low level moisture
in place and nothing available to scour it out. Where winds diminish
closer to 5 mph, mainly over western and southern MN, some of the
fog will be dense so have opted to go with a Dense Fog Advy for
those portions through Saturday morning. Going through the overnight
hours, the upper low will help drag the TX low pressure center
northward into western IA by daybreak Saturday morning. A strong
increase in isentropic lift in advance of the surface low and north
of its associated warm front will help more sustained rain showers
to develop in the pre-dawn hours, lasting through much of the day
tomorrow. Not much in the way of QPF is expected since upper level
support is not overly impressive despite the deep moisture; roughly
0.05" to 0.15" of rain can be expected. What the rain may accomplish
is to alleviate visibility issues in southern MN and hence the fog
concerns earlier than expected. The rest of tomorrow will remain
cloudy with occasional rain showers. Temperatures will remain rather
constant, with lows just below freezing and highs reaching the mid-
upper 30s. There may be some concern with deposition icing on roads
and bridges in central MN right around daybreak as temperatures drop
to freezing, particularly if fog remains overnight. Confidence is
not high in this to the point that supplemental products need to be
issued but will monitor through the overnight period.

.LONG TERM...(Saturday night through Friday)
Issued at 414 PM CST Fri Jan 20 2017

Rain lifting north Saturday night into Sunday, with more fog
expected Saturday night.  Snow is likely Tuesday night-Wednesday,
especially across southern Minnesota.

The warm and moist airmass will remain in place Saturday night
through Monday, with occasional drizzle, and patchy fog at a
minimum.  But in terms of precipitation amounts, do not expect much

The guidance is still suggesting a deep upper trough pivoting over
the Rockies and generate a surface cyclone that looks to track from
Colorado through Iowa and toward Michigan.  Little has changed so
given the consistency from last night, felt comfortable raising pops
for Tuesday-Wednesday.  Given the potency of this system and the
past analogs, this storm will likely be capable of producing 6+" of
snowfall.  Forcing still looks strong with this event, but it does
look like a rather warm atmosphere for this time of year.  Snow
ratios could be a bit lower than we typically see in January.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 540 PM CST Fri Jan 20 2017

Weak pressure gradient across the TAF sites tonight coupled with
above freezing temperatures and melting snow will result in
LIFR/VLIFR ceilings/visibilities through Saturday morning.
Improvement expected to IFR during the late afternoon and evening
as a low pressure system moves by. Light rain will precede the
low, especially across eastern MN and western WI Saturday morning.
Light SE to E winds tonight becoming light ENE Saturday

KMSP...Expect ceilings AOB 005 for the next 24 hours with
visibilities overnight and Saturday morning a mile or less.
Improvement to MVFR visibilities for Saturday afternoon and
evening. Light rain as well for much of the day tomorrow.

SUN...MVFR likely. Slight chance -RA/-SN. Winds NW 5 kts.
MON...MVFR likely. Winds NW 5 kts.
TUE...MVFR likely. IFR possible late with chance -RA/-SN. Winds NE
5 kts.


MN...Dense Fog Advisory until 9 AM CST Saturday for MNZ041>044-



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