Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 230852
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
352 AM CDT Thu Mar 23 2017

.SHORT TERM...(Today and tonight)
Issued at 352 AM CDT Thu Mar 23 2017

Shortly after midnight, an area of light snow, mixed with rain
developed between the Twin Cities and St. Cloud. This area of
precipitation expanded in areal coverage as it moved into west
central Wisconsin. A few locations dropped to 1SM in -SN. near Rush
City and Forest Lake as this band of higher reflectivity moved
across the area. This area will quickly move eastward into northern
and eastern Wisconsin during the pre dawn hours.

The forecast remains the same with precipitation developing during
the day, and expanding north and east across the western Great Lakes
overnight. CAMS and short term models continue to support an area of
light rain developing across southwest, south central Minnesota by
noon, and moving this area north-northeast across the rest of
Minnesota and western Wisconsin during the afternoon. The best
isentropic lift in the 295-305K gradient is along and north of I-90
this afternoon, and then is moves further northward by the evening.
This will lead to most of southern Minnesota having the
precipitation early today, and then more isolated activity this
evening before coverage increases once again late tonight as a
secondary frontal boundary moves slowly southward. This seems
reasonable due to the strength of the low level jet and drier mid
levels moving northward into southern Minnesota this evening. Even
if the precipitation tapers off across southern Minnesota this
evening, low clouds, fog and drizzle are likely to continue.

Another aspect to this system is the elevated instability expected
to increase this afternoon across southern Minnesota. The latest
CAMS support isolated thunderstorms in the area with some stronger
storms possible if this storms become more organized. Several of the
severe weather parameters do support Mucape of 500-1000 j/kg moving
across Minnesota this afternoon and 200-400 j/kg late tonight.
Updraft helicity of 25-50 m2/s2 in the 2-5KM level are also noted
across far southern Minnesota late tonight as the low level jet
interacts with the strengthening frontal boundary.  SPC also has a
marginal risk of severe thunderstorms in southwest Minnesota tonight
due to these parameters. The morning HWO will highlight the marginal
risk with isolated severe hail the main threat.

.LONG TERM...(Friday through Wednesday)
Issued at 352 AM CDT Thu Mar 23 2017

Long term concerns remain the series of short waves that will push
into the western U.S. over the next seven days and how they will
eventually impact our area.

The first wave has pushed into the far west early this morning.
This feature will quickly reach the central and southern Plains by
Friday morning with a slower movement to the lower Great Lakes by
Monday morning. Overall, confidence has increased on the handling
of this wave by the various deterministic models with the
consensus on the main precipitation axis being across far
southern MN. This was the idea shown by the GFS 24 hours ago with
the ECMWF and Canadian now coming in line with that idea.

The concern on excessive rainfall is waning a bit even though PW
values are progged over an inch across the southern FA from late
today through Friday. These values are at the top of the MPX
sounding climatology for late March. Fortunately, by Friday
morning the low level jet has sagged into northern IA along with
the flow becoming orientated from west to east. Elevated
instability is south of us as well. Checking the GEFS/GFS IVT
shows the river coming northward into IA and then abruptly turning
eastward across far southern WI and then heading on across the
lower Great Lakes. As for precipitation amounts from Friday
through Saturday, they range from zero in the northwest FA to
around a half inch from Redwood Falls through the Twin Cites to
Ladysmith with three quarters to one inch along the I-90 corridor.

In the wake of the first wave, a second one will be quickly on
its heels. However, the second wave has been well advertised to
stay a bit further to the south of us Sunday and Monday. However,
there will be northern stream short wave passing across the Upper
MS Valley and a few showers can`t be ruled out.

A period of dry weather is then expected from late Monday into
Wednesday as a ridge of high pressure from central Canada on
southward through the Plains works slowly eastward.

Although technically outside the discussion window, but now in our
gridded data set is Thursday. This is where the models have the
biggest disagreement tonight. This centers around short wave
number three, which moves into the west on Monday. This is a
strong one, which ends up causing differences between the GFS and
ECMWF. The latter model is farther north with the upper low and
when yet another short pushes into the west around mid week, it
acts as a kicker, which drives wave three smack dab into our area
while the GFS is way to the south. It`s interesting to note that
three of the GEFS plumes do show some significant precipitation
occurring for MSP while the remainder of the members are
essentially flat. Hence, there are some members that see what the
ECMWF is showing. Right now the grids have some high chance pops
across southern MN for Thursday.

Temperatures during the long term will be above normal. Highs in
the middle to upper 40s late this week will rise into the lower to
middle 50s for next week with lows pretty much in the lower to
middle 30s. Normals right now for STC/MSP/EAU are 43/23 45/27 and
45/24 respectively.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1111 PM CDT Wed Mar 22 2017

Two concerns this TAF period are timing arrival of low cigs and
shower/thunderstorm potential Thursday afternoon. Downstream obs
lead to some hesitation with bringing in lower cigs too fast
Thursday, as MVFR cigs (015-020) are still way down in central OK.
Models have been way to fast in moistening the low levels
recently, so continued to go a bit slower than guidance with
bringing in low cigs. Lower cig chances look to increase
significantly Thursday night as a warm front pushes up to the
MN/IA border. We could certainly be lower with cigs than we
currently have at the end of the period, but at 20+ hours out,
was more conservative with how low to take things than what the
LAMP guidance has. As for precip potential, the NAM shows
1000-1500 j/kg of MUCAPE coming up Thursday, but ridging aloft
looks to create dry mid-levels and a capping inversion to keep
TSRA activity in check. Looks like light rain should expand
across the area Thursday afternoon as the LLJ noses into southern
MN. Again, we may be too bullish with precip mention at this point
this taf period given the dry mid-level air.

KMSP...Very dry low level air remains in place and will be tough
to displace, so continue to run later/higher with cigs than LAMP
guidance. Also concerned we won`t see much in the way of rain
until Friday morning when deep moisture finally arrives.

/OUTLOOK FOR KMSP/
Fri...MVFR/IFR with -RA likely. Wind NNE 5-10 kts.
Sat...Chc MVFR -RA. Wind ENE 10 kts.
Sun...Chc MVFR. Wind ENE 5 kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

SHORT TERM...JLT
LONG TERM...RAH
AVIATION...MPG



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