Scientific Forecaster Discussion
fxus63 kmpx 052347 aaa
Area forecast discussion...updated
National Weather Service Twin Cities/Chanhassen Minnesota
547 PM CST Thu Dec 5 2019
Short term...(this evening through Friday night)
issued at 410 PM CST Thu Dec 5 2019
A passing cold front will result in a wind shift to the
north/northwest and usher in much colder air tonight. Depending
upon the amount of cloud cover remaining behind the cold front
this evening, will impact the temperatures Friday morning. If more
clouds hold on, temperatures will be warmer. However, if the
clouds move out faster, the low temps will likely need adjusted
Several high res models attempt to develop a low cloud layer
through 06z Friday while others clear out. Confidence is low, but
temperature and sky cover trends will have to be monitored in case
the temperatures need to be decreased for tonight. High pressure
will cause cooler temps on Friday, but return flow develops by the
afternoon with temperatures recovering into the teens and 20s.
Friday night lows will remain in the teens with light winds from
Long term...(saturday through thursday)
issued at 410 PM CST Thu Dec 5 2019
The long term forecast was focused mostly on the shot of snow
Sunday night-Monday and then the Arctic cold for next week.
Southerly flow will continue Saturday before a cold front comes
through Saturday night. Models have been painting light quantitative precipitation forecast in the
warm sector, particularly the NAM, implying freezing drizzle. The
NAM is notorious for an overly saturated boundary layer which is
likely the cause. There may be some low clouds, but the saturated
layer is too thin to support any precip.
The first front will pass through Saturday night, but the second
coming through Sunday night will be much more influential. At the
same time, a clipper system will be tracking southeast along the
same cold front across the Canadian rockies and into the northern
plains. Snow is expected to spread east, along and behind the cold
front Sunday night and Monday morning. The temperature profile
suggests there may be two dendritic growth zones, one between
10-15kft and possibly another around 2kft depending on the degree
of low level cold air advection. Isentropic lift isn't the best
with the system positively tilted, but the system will be tapping
into deeper moisture as it tracks east across the mid Mississippi
Valley. Quantitative precipitation forecast has increased on the deterministic models to between
0.25-0.4 inches along a stripe across the County Warning Area. The ensembles
aren't quite this wet, aside from the highest members. So, still
some uncertainty with this snow forecast. Snow ratios should be
high as temperatures fall into the teens, thinking at least 15:1.
This is bolstered by light winds along the cold front that only
begin to strengthen toward the end of the snow. Deterministic
models would suggest 4-8 inches, while the ensemble mean would be
more like 2-4.
Behind that system, very cold air will bleed south for the rest of
the period. Temperatures will drop below zero Monday night and may
not rise back above zero until Thursday. GFS appears a bit too cold
with lows in the mid -20s Tuesday night and highs in the negative
teens Wednesday. The European model (ecmwf) is a bit more reasonable. The official
forecast took roughly the 50th percentile for temps, which was a few
degrees below the nbm. MOS is probably having a negative influence
keeping temps milder given near record temps, fresh snowpack and
light winds Tuesday night. Cloud cover is always a concern, but at
the moment models indicate mostly clear conditions. A few records
could be tied or broken. Msp records are -3 for a high and -14 for a
low on Wednesday, pretty close to the current ndfd forecast.
Aviation...(for the 00z tafs through 00z Friday evening)
issued at 547 PM CST Thu Dec 5 2019
MVFR cigs across western and northern Minnesota are heading south and
should impact all taf sites this evening. Models are having issues
with this stratus and seems to clear it out too early tonight. The
taf may need to extend the timing of these cigs well into the
night in future amendments.
Kmsp...appears the MVFR cigs will arrive between 01-0130z and
stick around for several hours tonight. It is possible these cigs
will persist into Friday morning.
/Outlook for kmsp/
Sat...VFR. Wind SW 10kts.
Sun...VFR/MVFR. IFR/-sn Sun night. Wind SW 10kts bcmg north late.
Mon...IFR/sn likely, mainly in the morning. Several inches
possible. Wind north-northwest 10-15 kts.