Area Forecast Discussion
Issued by NWS Twin Cities, MN

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311
FXUS63 KMPX 160538
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1138 PM CST Sun Jan 15 2017

.UPDATE...
Issued at 1113 PM CST Sun Jan 15 2017

Updated to include 06z aviation discussion below.

&&

.SHORT TERM...(This evening through Monday)
Issued at 315 PM CST Sun Jan 15 2017

The concern in the short term, as well as the early part of the
long term, is the storm system approaching from the Southern
High Plains. Plenty has happened in the past 24 hours. The
deterministic models have resolved the phasing issue between the
northern and southern streams which has plagued us for many days
now. They are now unanimous with a separation being maintained.
This allowed the precipitation with the incoming system to slide a
little more east and south, along with the vertical profile being
a little colder and more supportive of snow.

Then the 12z solutions started coming in today and the
precipitation shield pushed even more to the south and east.
This was really evident on the CAMS. Investigation into why the
significant shift seems tied to more convection developing to our
southeast (MO/IL) on Monday then previous solutions were thinking.
This release in latent heat makes a big difference in the
pressure fields with the system stronger and more compact to our
southeast. This is quite evident with our local WRF solutions that
we run here, one with latent heat and the other without. The
results from 12z today are striking and show how important
convection is in the whole process with this particular system.

Hence, we have cancelled the Winter Storm Watch and issued a
Winter Weather Advisory for just the southern two rows of our
counties in MN from 12z Monday until 12z Tuesday. This is the area
where we have the best potential for up to a tenth of an inch of
ice Monday morning and afternoon followed by an inch or two of
snow Monday night. Precipitation amounts really dwindle to the
north with the latest 18z NAM only bringing the 0.01 inch line of
QPF to northern Rice and Goodhue counties Monday night. This
results in no precipitation across the Twin Cities, period. This
may be too conservative but is pretty realistic with the 12z GFS
and ECMWF which only had the 0.01 inch line touching the Twin
Cities Monday night for a brief period.

Otherwise, the January thaw got started a little early, with highs
at MSP cracking the 32 degree barrier this afternoon. There will be
plenty more of that coming later in the week. With skies clear for
much of the night, lows will likely drop into the single digits
across central MN and west central WI with guidance lows trimmed a
bit. Highs on Monday will again be around the freezing mark,
especially from I-35 on east with little adjustment made.

.LONG TERM...(Monday night through Sunday)
Issued at 315 PM CST Sun Jan 15 2017

The main issue in the long term is what remains of the weather
system into Tuesday. Then the warming trend through the week with
the timing and development of the next Western CONUS trough as it
moves into the middle of the CONUS be the end of the week.

Model trends continue to indicate the initial upper trough lifting
to the southeast of much of the cwa into early Tuesday. Temperatures
aloft have responded with slightly cooler with the less freezing
rain. It appears the precipitation shield may work as far north as
the southern metro into Monday night and then shift east...
affecting a portion of west central Wisconsin. The 12z NAM_wrf and
ECMWF were farthest north with QPF...with most other deterministic
and HIRES models coming in with a more southeast solution. The cause
of this trend was described in the short term discussion. With this
in mind...we will trim pops some to the northwest and keep the
categorical pops more to the southeast. Forecast QPF generates
maybe an inch or two of snow to the south as the system works east
Monday night. Some marginal ice/less than one tenth inch/ is
forecast mainly along I90 northeast to I94 into west central
Wisconsin. The expansion of any headline into Monday night depends
on further resolution of the models in the longer term in regards to
movement upper trough.

After Tuesday morning...warmer and dry conditions should ensue
across the area as upper ridging develops.  This should bring a nice
thawing period...through at least the lower and mid 40s into the
weekend. This is expected ahead of the next western CONUS trough
which is progged to move ashore around Thursday. Deterministic
models drive an initial short wave toward the region sometime Friday
and could linger through the weekend.  It does appear at least
initially it will remain as liquid...with the possibility of rain
and snow developing later in the period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1113 PM CST Sun Jan 15 2017

Tricky aviation forecast with respect to hours 18-30 as the models
continue to shift the amounts of moisture and where the p-type
change begins. Latest models indicate greater moisture further
north along with the wintry precipitation so have adjusted the
TAFs for KMSP-KRNH-KEAU to indicate a greater likelihood of FZRA
in addition to SN. That said, there looks to be a tighter gradient
of where the precipitation shield ends, so have maintained the
remaining three TAFs dry. Have also reduced the flight condition
during and after the precipitation as MVFR for a longer duration.
Confidence is still shaky in these scenarios with such frequent
model changes so additional adjustments to p-type and timing in
later TAFs are certainly possible.

KMSP...Have added in FZRA starting tomorrow evening to reflect
latest thinking in the models and have also dropped flight
category deeper into MVFR. The best timing for precipitation looks
to come just at the tail end of the evening push but the
possibility is still there that precipitation may start during the
evening push tomorrow and would start more as FZRA than SN.
Ceilings may also be troublesome after the precipitation ends as
IFR ceilings are possible which could extend into the morning push
Tuesday.

/OUTLOOK FOR KMSP/
Tue...MVFR possible early then clearing. Winds NW bcmg W 5-10 kts.
Wed...VFR. Winds SW 5-10 kts.
Thu...VFR. Winds S 5-10 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Winter Weather Advisory from 6 AM Monday to 6 AM CST Tuesday for
     MNZ082>085-091>093.

&&

$$

UPDATE...JPC
SHORT TERM...RAH
LONG TERM...DWE
AVIATION...JPC



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