Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Twin Cities/Chanhassen Minnesota
1211 am CST sun Nov 23 2014
Short term...(this evening through sunday)
issued at 238 PM CST Sat Nov 22 2014
Main concern during the short term period is the trend of stratus
and the potential extent of fog tonight. A secondary concern is with
precipitation potential tonight into Sunday...though models continue to
show precipitation amounts being pretty underwhelming through Sunday across
the entire mpx area...with deeper moisture going across eastern WI and
Extensive stratus across all but the northwest portion of the mpx County Warning Area has
held temperatures in check all day. Looking to the south...there are
a couple of moisture surges heading our way. The first is quickly
moving into northern Iowa and will likely be to the I-90 corridor by 00z
this evening. It is characterized by dewps in the 40s and more
concerning for the cloud forecast tonight...clear skies. The second
moisture surge is just now getting to I-80 and it is associated with
dewps in the 50s...and a return to LIFR stratus and fog. The
European model (ecmwf)/Gem show this second moisture surge and its associated lower
50 dewps getting clear up to I-90 Sunday morning before getting
shunted off to the east. Certainly dewps in the 40s with snow on the
ground favors stratus continuing through the night and the current
forecast certainly reads that way...but we will have watch how that
For fog...one thing we are positive about is it will be hazy trough
the night given dewps above freezing with snow on the ground. There
was talk of a dense fog advisory...but not confident enough on where
to put one other than anyone under stratus now...which is just about
our entire County Warning Area and did not want to issue such a large advisory at this
point. On top of that...we will be maintaining 8-12 knots winds through
the night...so that will supply a certain degree of mixing as well.
Not to mention we have that clearing racing north out of Iowa. At this
point...highest confidence in dense fog is where our deepest snow
resides across the northern mpx County Warning Area. The hrrr would support this idea as
it does show visibilities improving through the night across southern Minnesota as that
slug of slightly drier air across Iowa works into Minnesota.
For temperatures...they may go nothing but up through the night.
First run of the hourly temperature tool with the local superblend
brought a temperature of 53 to Albert Lea by 7z tonight. Did not go
quite that aggressive...but do think much of the area east of a New
Ulm to Mora line will rise into the 40s overnight. Given the mild
start...also gave highs Sunday a bit of an upward nudge to about a
50/50 blend between the previous forecast and the 22.12 Gem/ECMWF.
The Gem/European model (ecmwf) show highs in the low 50s for southeast Minnesota/western WI tomorrow.
Given the extensive cloud cover...do not think we will get that
high...but do have highs into the middle/upper 40s for all but western and
For precipitation...that continues to look underwhelming. Our biggest
problem through tonight continues to be the fact that the atmo can
not take on much more moisture below 900 mb...but above that...its
Bone dry. Continued to run with highest probability of precipitation Sunday out in eastern areas
as they will be closer to the 850 mb moisture transport...but liking
the idea the GFS/sref/nmm/arw show of a narrow band of rain centered
on fgen in the 700 mb-h6 layer coming out of sodak tonight and working
across southern Minnesota through Sunday morning. The 22.18 hopwrf members also
show this band of precipitation by 9z /the end of those runs/ moving into
the western portion of the fsd forecast area...similar to what the
models mentioned above show. Did boost probability of precipitation in SW Minnesota into the high
chance category Sunday morning for now. This may very will end up
being the best chance at seeing measurable precipitation with this system
for much of our Minnesota forecast area.
Long term...(sunday night through saturday)
issued at 238 PM CST Sat Nov 22 2014
Sunday night through Monday will bring a period of strong winds
and light precipitation to the forecast area...in the wake of a
deepening middle latitude cyclone. The strongest winds are expected
across the western forecast area and the highest potential for
accumulating snow remains across far eastern Minnesota...but especially
in west central WI.
By 00z Monday...rapid cyclogenesis will be ongoing in the middle
Mississippi River valley in response to a deep trough digging in
across the central Continental U.S. And a large area of 120-150m 500mb 12-hour
heights falls moving across the area. The amount of deepening is
still quite variable depending on which 12z solution one chooses to
follow. The 22.12z GFS is by far and away the most aggressive in
strengthening the low over the southern half of Lake Michigan by
06z Monday to 975mb...969mb over northern Michigan by 12z...and
966mb as it moves north of the Great Lakes by 18z. The NAM and
European model (ecmwf) seem more reasonable with a bit more modest deepening.
Typically...the kind of deepening the GFS is showing only occurs
with very strong baroclinicity and/or a negatively tilted upper
trough. We really don't have either. There is strong cold
advection and a decent temperature gradient across the middle/upper
Mississippi Valley...but they seem more in line with the NAM/European model (ecmwf)
that are bit more progressive with the low and not as wound up.
Therefore...we did not jump on the GFS snowfall forecast that
would give 6-8" to portions of west central WI. We think the
heaviest precipitation should be east of the forecast area and the
dynamic cooling on the back side of the low will be weaker than
the GFS indicates. It is notable that the 22.15z sref and Gem also
show the potential for several inches of snow near or just east of
the forecast area. This is something to follow over the next 12-18
hours...but we simply didn't have enough confidence to issue a
Winter Storm Watch at this point. Furthermore...even with the
expected strong winds...the warm today has likely limited the
amount of snow available for blowing and drifting. There were a
lot of highs in the upper 30s and lower 40s in western Minnesota today.
The next system to watch arrives on Wednesday and there is again
significant differences between the GFS and European model (ecmwf). The European model (ecmwf) has a
potent clipper system with 1-4" of snow...impressive cold
advection and a tight pressure gradient on the back side of the
system. The 22.12z European model (ecmwf) has sustained 25-30kts near the ND/SD/MN
border early Wednesday morning - quite impressive given its
coarser resolution. The GFS has a weak surface trough and much
less lift. This middle week system pretty much locks in our chance
for a well below normal Thanksgiving. It looks very cold.
Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1202 am CST sun Nov 23 2014
Impressive warm front has marched well into southern Minnesota
late this evening with conditions improving to the south of
it...in some cases to MVFR or VFR. Think all the taf sites will
improve some through the night if the warm front continues to push
north...but caution is advised as conditions are deteiorating
slowly again across northern Iowa. This moisture could keep ceilings
in longer across eastern Minnesota and western WI. Rwf and axn appear to be in
the best locations for greatest improvments with upstream observation VFR.
Rain will push into western WI syunday afternoon...with snow on the
western periphery...possibly as far west as msp.
Kmsp...conditions have improved quite a bit in the last couple
hours...but that trend may have stalled for the rest of the night.
Could see visible and ceilings fluctuate up and down for the next several
hours as surrounding observation indicate. Conds should largely be
/Outlook for kmsp/
Monday...MVFR/IFR ceilings chance -sn. Winds northwest 20g30 knots.
Tuesday...VFR. Winds west 5-10 knots.
Wednesday...MVFR/IFR chance -sn. Winds northwest 10kts.
Minnesota...dense fog advisory until 8 am CST this morning for mnz041>045-
WI...dense fog advisory until 8 am CST this morning for wiz014>016-