Scientific Forecaster Discussion
fxus63 kmpx 181148
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
548 am CST Sat Nov 18 2017
Update...for 12z aviation discussion below
Short term...(today and tonight)
issued at 358 am CST Sat Nov 18 2017
Northwest flow in the wake of the cold front will yield a
relatively cold day with below normal temperatures and brisk
winds. Highs will be around 5 degrees below normal, ranging from
the upper 20s to mid 30s. Low clouds generally along and east of
the i35 corridor will gradually shift east by early afternoon.
Expect some scattered-broken cumulus cloud development this
afternoon, and then we clear out tonight with subsiding winds.
Lows tonight will be in the teens area-wide.
Long term...(sunday through friday)
issued at 358 am CST Sat Nov 18 2017
No significant changes in the long term with dry weather expected
to prevail through Friday, while temperatures hop on the roller
coaster with a mild day expected Monday, cool days
Tuesday/Wednesday, back to mild air Thanksgiving day/Friday,
followed by a cold finish to the Holiday weekend. Only changes
made to the initialized forecast blend were to increase wind
speeds Monday night/Tuesday and boost highs around 5 degrees for
First system of significance comes Monday as 988mb low tracks across
southern Canada. This will draw mild air back into the region
beginning Sunday afternoon, though we won't really notice it until
Monday. Unlike the last two surges of warm air we saw Tuesday and
again Friday, the low levels are expected to remain dry this time
around, with dewpoints remaining in the 20s. So no stratus this time
around, instead, we should see a good deal of sunshine until
mid/upper clouds begin to increase from the northwest. We currently
have highs into the low 50s forecast up to the Minnesota river, though a
high hitting or exceeding the 50 mark is still in the realm of
possibilities for the Twin Cities.
Monday night, the bottom looks to fall out with temperatures as
strong cold air advection kicks in behind a cold front. Isallobaric high with this
front is quite impressive and winds gusting to between 40 and 50 mph
are possible Monday night into Tuesday morning. For winds Monday
night/Tuesday, nudged speed forecast toward the consmos, which
verifies better than the superblend in situations like this. 925-580
temps Tuesday are also forecast to bottom out around -12c, so
temperatures Tuesday will remain pretty steady from what we see for
morning lows. We will have a ridge axis over US Wednesday morning
with mainly clear skies expected, so it will be a chilly start to
Wednesday, with lows in the single digits and teens expected. Though
we will see warm air advection kicking in by the afternoon as west-southwest winds develop,
the chilly start will keep highs Wednesday around 10 degrees below
Thursday and Friday, upper ridging building in from the west, will
bring another push of mild air with. Still discrepancies on how
quickly the warm air returns Thursday, but by Friday, we look to
have very warm air over the area. Mixing down from just 950mb on the
GFS yielded highs ranging from the upper 40s near Ladysmith to the
low 60s in the upper Minnesota River Valley. This is about 10-15 degrees
warmer than what superblend had, which is being held down by MOS
guidance. Given 925-850 temps, mainly sunny skies, and favorable
southwest winds, 18.00 models definitely support near record highs
for black Friday. However, this is still a weak out and a lot could
still change with the timing of this thermal ridge, so went a bit
more conservative with highs for Friday, but did get them closer to
the consraw values. The roughly 5 degree increase in highs for
Friday brought our forecast up to near the Mid Point of the model
spread, as opposed to being down in the lower quarter of guidance.
Behind this system, much colder air comes back to finish the Holiday
weekend. Along this baroclinic zone Friday night is also where you
will find the only precip generated in the models over the next 10
days with the GFS, though the European model (ecmwf)/Canadian have nothing.
Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 547 am CST Sat Nov 18 2017
Main taf concern is when we will shake the IFR deck from
east/south central Minnesota across west central WI. With kmsp on the
western fringes, think VFR will prevail by 13-14z, 15z at krnh and
closer to 18z at Keau. The only other impact this taf period is
the gusty northwest winds. Expect sustained speeds around 15-20
knots with gusts to between 25 and 30 knots this afternoon. Gusts
gradually diminish this evening, decreasing below 10 knots
overnight and backing to the southwest.
expect to see the stratus deck push east of the site during the
first couple hours of the taf period. After that, no concerns
other than gusty northwest winds.
/Outlook for kmsp/
sun...VFR. Winds SW 5-10 kts.
Monday...VFR. Winds SW 5-10 kts.
Tuesday...chc MVFR. Winds northwest 15-20g30-35 kts.