Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 190933

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
333 AM CST Mon Feb 19 2018

.SHORT TERM...(Today through Tuesday)
Issued at 330 AM CST Mon Feb 19 2018

Complicated forecast over the next 36 hours with a wintry mix precip
event commencing across the area, already underway in parts of the
WFO MPX coverage area.

Surface analysis shows a main area of low pressure over SE
Colorado/SW Nebraska with a cold front turning northeast through
central Iowa, southeastern Minnesota and northwestern Wisconsin. One
weak low pressure center per 3mb pressure analysis is found along
the front in southeastern MN. To the north of this front, surface
high pressure is nudging southward from Alberta/Saskatchewan
provinces into the Northern Plains. South of the front, deep
southerly flow on the western periphery of broad Eastern CONUS high
pressure is bringing above-normal moisture amounts from the Deep
South into the Great Lakes. In addition, southwesterly flow in
advance of a Pacific Northwest upper trough is bringing Pacific
moisture into the region. The position of the front is key to the
precipitation type as model soundings indicate a shallow subfreezing
layer near the surface, indicated by temperatures in the teens well
north of the front and in the 20s near and just south of the front.
However, the pronounced southerly/southwesterly flow is allowing for
a sufficiently deep warm layer aloft to keep liquid aloft rather
than ice for much of the southern and eastern portions of the area
for much of the day today through tonight. While the prevailing p-
type for much of the coverage area looks to be -SN, the portions
that do see -FZRA (mainly southeast of a line from Redwood Falls-St.
Michael-Rice Lake) may well see around a tenth of an inch of ice,
and potentially near a quarter inch (from Albert Lea thru Red Wing
thru Eau Claire). These increased QPF and hence ice amounts line up
well with the 00z progs of the HopWRF, HRRR, RAP and NAMNest along
with collab with other offices. So while warning criteria is not
expected, a larger swath of ice is expected so have nudged up ice
amounts. Going back further west, which actually is where -SN is
already occurring, the current wave of -SN will continue for much of
the day and diminish slightly late this afternoon into this evening
before picking up again overnight through daybreak Tuesday. In fact,
in general, the main waves of precipitation look to come this
morning through mid-afternoon, then become less widespread/intense
late this afternoon through this evening before picking up across
much of the coverage area during the early morning hours Tuesday. It
is in this second batch that the greater snow amounts will come for
western and northern parts of the coverage area (3-4" tonight-
tomorrow compared to 1-2" today). However, the greater ice amounts
look to come today with slightly lesser amounts tonight-tomorrow.

With the front having little movement until tomorrow, the transition
to all -SN for the entire coverage area will not occur until mid-to-
late day tomorrow. As such, have maintained the mention of -FZRA for
much of the southern and eastern portions of the coverage area,
including throughout the Twin Cities metro, through tonight then
shifting further east tomorrow. As such, have maintained the winter
weather advisory throughout the coverage area. Main change was to
move up the start time of the advisory in western/central MN due to
that part of the storm total snow accumulation is already being
realized this morning. The precipitation will gradually wind down
from west to east tomorrow as the surface front shifts further away
into the Great Lakes and mid-Mississippi River Valley while high
pressure slides south and east from the Northern Plains.

Highs today and tomorrow will run quite similar to one another, with
mid-upper teens in western MN to lower-middle teens in eastern MN
into western WI. Lows tonight will also run quite similar to lows
this morning, ranging from around 10 in western MN to the lower 20s
in eastern MN and western WI.

.LONG TERM...(Tuesday through Sunday)
Issued at 310 AM CST Mon Feb 19 2018

Long term concerns remain timing of any trough energy ejecting from
the southwest during the period. Also, some warming expected.

The Tuesday system will exit the area leaving decreasing clouds
Tuesday night along with diminishing winds as high pressure builds
over the area. Then we expect cool and dry conditions to continue
through at least the first half of Thursday.

The next snow threat arrives later Thursday afternoon into the
southern cwa. The short wave ejects northeast across the area
through at least early Friday. The ECMWF is faster with this system
and drives a more northern stream trough extension through then. The
slower GFS holds back the trough and the upper flow isnt as split.
It lifts a weak short waves northeast with a continuing threat of
small chance PoPs into Friday night. We will continue the blended
guidance trend at this time with the likely PoPs spreading through
Thursday night and trail them off through Friday night. Snow amounts
dont appears significant at this time, perhaps another 1 to 3 inch
type event.

The deterministic models diverge then into the weekend. Both models
drive more short wave energy northeast over the central CONUS with
cyclogenesis over the mid Mississippi River valley region Saturday.
It appears the anomalous Bermuda Ridge will flatten some as this
energy moves east and the western CONUS trough reloads. This will
mean at least a chance of precipitation moving through the area
Saturday/Saturday night.

Temperatures will remain below normal through much of the week but
should trend closer to normal again by late in the week and into
next weekend.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1045 PM CST Sun Feb 18 2018

Light snow is expected to develop across central MN overnight
(primarily affecting KAXN and possibly KSTC prior to daybreak),
and become more widespread across the area on Monday morning. The
freezing drizzle/rain threat still looks to be south of the TAF
sites, with KMKT and KEAU on the edge. Expect ceilings to continue
degrading to MVFR overnight, with prevalent MVFR on Monday. There
looks to be a brief break in the precip at most sites Monday
evening, another round developing early in the next period (06z
Tuesday). Will need to re-evaluate the freezing precip again with
this round, as some models are indicating a slight northward shift
of the threat, possibly as far north as KMSP. Northerly winds
tonight become more northeasterly for Monday, with gusts to
between 20 and 25 knots.

15Z still looks to be the most likely time for snow onset at KMSP.
Still expect the freezing rain to stay south and east of the site
this period. Northerly winds shift to the northeast and become
gusty tomorrow during the daytime hours.

Tue...MVFR/-SN. Winds N15 kts.
Wed...VFR. Winds NW becoming SW 5 kts.
Thu...VFR. Winds S 5 kts.


WI...Winter Weather Advisory until 6 PM CST Tuesday for WIZ014>016-

MN...Winter Weather Advisory until 6 PM CST Tuesday for MNZ041>045-



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