Area Forecast Discussion
Issued by NWS Twin Cities, MN
FXUS63 KMPX 280923
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
323 AM CST Tue Feb 28 2017
.SHORT TERM...(Today and tonight)
Issued at 320 AM CST Tue Feb 28 2017
Complex short term as we will see multiple pieces of energy
emanating from a mean trough over the Rockies. The models have shown
little run-to-run consistency during what is now the today/tonight
period and there`s only decent agreement on what`s going to happen
today, with significant differences already showing up tonight.
At the surface this morning, there are two frontal features of
interest. There is what is left of the warm front that lifted across
the area yesterday that can still be found in the wind field from
west central into northeast MN. However, this front is becoming less
and less defined as a surface low over southeast Nebraska
strengthens, with its associated warm front near the I-80 corridor
taking over as the predominate frontal feature in the area. These
two features will drive the two primary areas of precip expected
through the day. The remnant boundary over central MN will drive a
snow chance up there through the day. However, this frontal band has
struggled to produce snow overnight thanks to dry low levels it is
encountering we have seen a downward trend in its potential in
guidance. Still the HRRR and HopWRF show light snow working across
west central/central MN through the day, so continued high
chance/likely pops in these areas, with maybe an inch of snow
possible from Alexandria over to Little Falls. Strong isentropic
lift ahead of the warm front will drive multiple rounds of showers
and thunderstorms into the afternoon from southern Iowa toward
central MN. However, this forcing looks to remain largely southeast
of the MPX, so significantly reduced pops southeast of the remnant
boundary, with a primarily dry day expected from southwest MN back
across the Twin Cities into western WI as these areas remain between
the two areas of forcing. Not expecting any drizzle either, as one
look at the 00z sounding from MPX last night shows we are just
starting off too far on the dry end of things in the low levels with
For tonight, things are beginning to look a bit more intriguing,
with the ECMWF/NAM/NSSLwrf showing snow expanding across southern
MN. This is in response to the wave currently near Seattle that is
beginning to dig into the Rockies trough. ECMWF/NAM show this wave
taking on a negative tilt and strengthening as a TROWAL develops
from central IA northeast into central WI tonight. The enhancement
of baroclinic forcing on the poleward side of the TROWAL results in
these models expanding the snow across southern MN through the
night. These models are pretty aggressive with the snow that
develops in this region, with a couple of inches of snow possible by
the end of Tuesday night. However, the GFS and Canadian are more
progressive with this wave and show just light precip moving across
southeast MN overnight. SREF members show a pretty even split
between these two solutions. The ECMWF solution would represent a
pretty significant change in continuity in terms of our forecast, so
trended that way, but held pops at 50% and QPF under a tenth of an
inch, though both of these may need to be doubled if what we are
seeing from the ECMWF/NAM/NSSLwrf is correct.
.LONG TERM...(Wednesday through Monday)
Issued at 320 AM CST Tue Feb 28 2017
The longer term concern remains the snow potential Wednesday and
again Thursday. After this will be timing and strength of warming
into the weekend ahead of the next trough.
Models have continue to have problems handling the western CONUS
trough and timing of impulses/short waves ahead of the main wave.
It now has slowed overall movement of the upper trough some 6 to
12 hours. This lingers the precipitation chance well into
Wednesday. The deterministic ECMWF and the 03z SREF continue to
produce around 0.10 to 0.15 inches of QPF with the passage of the
trough. Lift becomes more enhanced as the surface low lifts off
toward the Great Lakes wednesday morning. The ECMWF is slower with
the main upper trough and leaves southeast Minnesota in more of
trowal at least through midday. We will follow this model a
little closer...but not so robust with QPF amounts at this time.
It does look like it will be cold enough just snow Wednesday so
this will leave an inch or two of snow across about the southern
third of the cwa through Wednesday evening.
The models diverge on the potential strength of the northwest
flow clipper-type storm moving in for Thursday following this
initial wave. The GFS is a little stronger with the wave and drops
southeast affecting the southern CWA late Wednesday night and
Thursday. The ECMWF...because it was slower with the initial
wave...is not as strong with this second wave. This has been the
trend of this model while the GFS has continued to show a
potential for a band of snow along the path of the wave. We will
continue the chance pop trend for this system for now. If the GFS
trend verifies...we will need to increase pops and possible snow
accumulations over about the southwest half of the cwa. Taking a
looks at the 00z GEFS probability plots > 1 inch in 24 hours...
the potential snow band aligns along a 70 mile wide swath from
KAXN-KMSP...a little northeast of the current forecast.
Following this system...cooler temperatures are expected through
about Friday. A more zonal flow pattern develops with ridging
aloft in response to a strong trough forecast to move ashore over
the Pacific northwest later in the weekend. This should lift
warmer air into the area for the weekend. Sunday and perhaps next
Monday have the potential of being some 15 to 20 degrees above
normal...if the model trend continues. We raised temepratures
about 2 to 3 degrees above superblend guidance which did yield
lower and mid 50s Saturday and especially Sunday for the area.
Both deterministic runs indicate the strong northwest CONUS
trough to move east and drag a cold front through the region
Monday/Monday night time frame...with cooler temperatures
following for a day or two early next week.
.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1058 PM CST Mon Feb 27 2017
Confidence is beginning to wane on the MVFR or lower ceilings
overnight and Tuesday morning as well as on the coverage of the
precipitation. The TAF sites look to be stuck between a new warm
front developing over IA and the old front north of central MN.
Evidence for the ceilings not developing at all are seen in the
NAM and RAP 0.5km CPD`s. The HRRR ceiling forecast shies away as
well. Not totally sold on the idea as the LAMP guidance has hardly
changed this evening on the timing. Therefore, compromised a
little and slowed down the downward trend with the ceilings.
Still feel there will be some light snow Tuesday morning for KAXN.
Better chances for precipitation and MVFR or lower ceilings
develop Tuesday afternoon as the surface winds shift to the north.
In fact, some light snow is now likely for much of the area late
Tuesday night and early Wednesday morning.
KMSP...As alluded to above, confidence is low on the TAF forecast
overnight and early Tuesday morning. Still believe once the wind
begins to shift to the northeast Tuesday morning, MVFR or lower
ceilings will develop along with some drizzle. Also inserted snow
late Tuesday night as an upper trough moves through.
/OUTLOOK FOR KMSP/
WED...MVFR ceilings/-SN likely. Winds NW 5-10 kts.
THU...Chc MVFR/-SN. Winds NW 5-10 kts.
FRI...Mainly VFR. Chc MVFR ceilings. Winds S 5-10 kts.