Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 210447
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1047 PM CST Fri Jan 20 2017

.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
accumulation.

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 06Z TAFS through 06Z Saturday night)
Issued at 1046 PM CST Fri Jan 20 2017

Very moist low level conditions due to snow melt along with
southerly flow ahead of an incoming low pressure system will
combine to keep ceilings AOB 005 through the period. Visibilities
overnight will likely fluctuate between a 1/2sm and 2 1/2sm. KEAU
is the last holdout, but will be deteriorating soon. A steady
light rain will push northward across the area Saturday morning.
This should help to increase visibilities into the 1-3sm range.
However, visibilities will likely drop Saturday evening with
little wind over the area along with an abundance of low level
saturation. Widespread visibilities of a 1/4 to 1/2sm possible.

KMSP...Confidence is high on ceilings staying AOB 005 overnight
and Saturday. However, visibilities are going to meander around
with anything from 1/2sm to 2 1/2sm. Visibilities should stabilize
in the 2-3sm range Saturday morning as rain moves through with
even some 3-4sm in the afternoon. However, Saturday night will
likely see a return of visibilities below 2sm.

/OUTLOOK FOR KMSP/
SUN...MVFR likely. Slight chance -RA/-SN. Winds NW 5 kts.
MON...MVFR likely. Winds NW 5 kts.
TUE...MVFR likely. IFR with SN aftn/night. Winds NE 5 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Dense Fog Advisory until 9 AM CST Saturday for MNZ041>044-
     048>051-054>059-064>070-073>078-082>085-091>093.

&&

$$

SHORT TERM...JPC
LONG TERM...27
AVIATION...RAH


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