Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 192137

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
337 PM CST Thu Jan 19 2017

.SHORT TERM...(This evening through Friday)
Issued at 330 PM CST Thu Jan 19 2017

Earlier fog that moved slowly northward across eastern Minnesota,
and western Wisconsin, dissipated by the early afternoon.
However, deeper moisture that was evident on regional satellite
imagery, and local observations that had ceilings of 5-6k, was
spreading northward. Where skies were sunny for most of today,
temperatures climbed into the upper 30s to lower 40s. Elsewhere,
where clouds and fog were more prevalent, temperatures struggled to
reach the mid 30s. A few areas in south central/southeast Minnesota
where the dense fog held throughout the day, temperatures only rose
slightly above freezing.

Regional satellite and radar does show an expanding area of light
rain/showers moving into far southeast Minnesota as of 3 pm. This is
the main forecast concern as how far westward the deeper moisture
expands and whether freezing rain occurs in the colder areas of west
central Minnesota, and west central Wisconsin overnight.

Weather models have been very inconsistent with the shallower
moisture which led to temperatures and overall sky conditions
forecast problems today. However, the synoptic scale details have
been consistent on the evolution of the deeper moisture, and
associated upper level energy moving across the eastern forecast
area tonight. This is where both the moisture and lift will
generate an expanding area of light rain/drizzle across southeast
Minnesota before sunset, and northward into east central Minnesota,
and west central Wisconsin this evening. The best lift and moisture
depth remains in western Wisconsin where the best potential of
steadier rainfall is expected.

Although temperatures should remain above freezing, some of the
local terrain could drop to near freezing in west central Wisconsin.
But, the potential of widespread freezing rain is not expected,
therefore, an advisory has not been issued. Cooler temperatures are
expected further to the east into central Wisconsin which has led to
a freezing rain advisory tonight. Otherwise, the area of light rain
will slow lift across east central Minnesota, and west central
Wisconsin northward into central Minnesota and northwest Wisconsin
Friday morning. This is also where the higher chances of
precipitation will occur.

.LONG TERM...(Friday night through Thursday)
Issued at 330 PM CST Thu Jan 19 2017

The longer term continues to show a couple of precipitation
events possible if current model trends hold.

The first event develops as an upper trough lifts northeast into
the cwa. Thermal structure of the boundary layer suggests rain.
Surface temperatures will be critical and there could be a small
threat of freezing rain or possibly some sleet over the far west
into Saturday morning. The GEFS plumes and overall probabilities
show mainly rain Friday night into Saturday with perhaps the
change over to wet snow over the west later Saturday night into
Sunday. The main brunt of qpf appears to roll over the eastern cwa
into Saturday night as the trough/forcing moves through...with
amounts mainly on the light side...generally less than two tenths
of an inch.

The next weather system to affect the region appears to move in
next Tuesday and lingers into Wednesday. It appears to be moving
in a little faster than previous runs. The latest long term CIPS
extended analogue guidance shows a good probability of a snow band
affecting much of the cwa during this period. Models show a
deepening surface low traveling across Iowa into southern
Wisconsin which is a decent path for snow across our area. The 12z
GEFS probabilities are showing a greater than 40% chance of snow
accumulation of greater than 4 inches. There does remain some
small probabilities (generally less than 30%) of a rain/snow mix
in the far southeast cwa early in the period. We will continue to
monitor model trends but models so far have been fairly
consistent with this system.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1140 AM CST Thu Jan 19 2017

Areas of fog/low clouds and low visibility that expanded northward
across Iowa and into southern Minnesota this morning had started
to erode on the northern edge as of 1130 am. Typically dense
fog/low clouds would have nearly dissipated if we had a higher sun
angle. However, this is winter and the low clouds (although
shallow) moved northward in different areas and not affecting the
major airports in MPX forecast area this morning. However, this
should not be the case this afternoon as both shallow moisture and
deeper moisture across Iowa will eventually spread northward
across the state during the afternoon. Therefore, it was mainly a
timing issue not so much as if IFR conditions would develop. Once
IFR cigs/vsby develop, these conditions will continue through the
taf period with some fluctuation in the cigs/vsby from the
afternoon through the overnight hours. Drizzle/Light rain,
possibly mixed with freezing drizzle/rain in west central
Wisconsin overnight as a storm system moves northward across Iowa.
Kept cigs/vsby simple after this evening as changes will likely
take place.


Complicated aviation forecast this afternoon as the northern edge
of the IFR/LIFR cigs/vsby are nearly at the airport grounds.
However, there could be a few hours this afternoon where cigs
could scattered out so I introduced a tempo period from 18-21z
for this scenario. Otherwise, IFR cigs will develop this evening
and continue through the forecast period with high confidence.
Lower confidence on the amount of drizzle/light rain developing
overnight, but it should be all liquid as temperatures should hold
above freezing.


FRI...IFR/MVFR. -DZ/-RA in morning. Winds E 5-10 kts.
SAT...IFR/MVFR. Chc -RA. Winds E 5-10 kts.
SUN...IFR/MVFR. Winds bcmg W 5 kts.




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