Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
334 am CDT Sat Mar 15 2014
Short term...(today and tonight)
issued at 251 am CDT Sat Mar 15 2014
Incoming light snow event for about the southern third of the County Warning Area is
the main concern for the short term.
The right front entrance region of the exiting upper jet is forecast
to generate a narrow band of snow across the south during the day.
Both the NAM and GFS show an area of light snow dropping
south...mainly along and south of the Minnesota river. We will
continue the highest probability of precipitation far south with this...as best isentropic
lift/Omega and frontogenesis moves through here into early
afternoon. Expect any snow accumulation to be less than an inch.
Temperatures should be held mainly in the middle 20s to lower 30s over
most of the are today...as a cool north/northeast flow continues.
Any remaining light snow will have exited the far south through
about 00z sun. High pressure will move across the state during the
night. Expect clouds to thin over the region during the night. We
also expect temperatures to drop back to around zero in the
northeast County Warning Area...to some lower teens in the areas to the southwest
where little or no snow cover remains.
Long term...(sunday through friday)
issued at 251 am CDT Sat Mar 15 2014
The long term will begin fairly benign as high pressure builds
southeastward into the Great Lakes Sunday. After a rather cold
start and a polar airmass remaining in place...temperatures will
struggle to get much above the middle 20s...aside from western
Minnesota where warm air advection should begin by afternoon. With the
approaching warm front will come a band of light precipitation...
confined to mainly central Minnesota/northwestern WI Sunday night and Monday.
Enough cold air will remain for mainly snow Sunday night...but
warmer middle level temperatures will surge northward Monday and there is a
chance of more mixed precipitation especially over Minnesota. Amounts
will be light.
There is still quite a bit of uncertainty of how the middle level
trough traversing The Rockies and plains will evolve early next
week. The NAM/GFS remain the northernmost guidance with surface
lows over southern Minnesota. The ec/Gem/UKMET are all further south with
the UKMET the furthest south. Prefer the ec and Gem for surface
low evolution although a bit slower similar to a compromise
between the ec and GFS. The Gem appears too progressive...stemming
from a shallower trough over the Central Plains. Building heights
in advance of this system will bring milder air northward...especially
in the middle levels. Thus...mixed precipitation will be a problem at least
initially...which is something all models agree on. Fortunately...
they also pretty much agree there will be little precipitation to
the south and to the east of the low so not anticipating too many
issues with the mixed precipitation aspect of the system. The model
differences come when as the low passes across Iowa and how the
deformation snows materialize. Intensity has certainly decreased
on the quantitative precipitation forecast fields from last night...but am not willing to throw
in the towel with MDT-heavy accumulating snow potential yet. The setup
remains rather good with the system becoming negatively tilted over
the upper Midwest and the low track is climatologically favorable
for heavy snow. Kept probability of precipitation in the high chance range for now until
model solutions stabilize and converge which should hopefully
Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 1024 PM CDT Friday Mar 14 2014
Cyclonic flow will allow some pesky near-MVFR level clouds to
scrape the west central WI portion of the taf area overnight.
Primarily expect Keau to be affected...and possibly krnh as well
but to a lesser extent. Have included a mention of 3500ft ceilings at
both Keau and krnh...but models do indicate an eastward drift with
time. Otherwise...will be waiting for middle level clouds to arrive
from the Dakotas overnight as previously planned. 00z models did
continue the trend of a southward shift...so may not even see -sn
at krwf. Have downgraded to just a tempo group there tomorrow
morning...with the other sites remaining dry. Northwest winds
gradually veer to northeast in direction overnight. Prevalent
speeds should be 5-10 kts...with the exception of western sites /krwf
and kaxn/ where gusts in the middle/upper teens appear possible on
middle/high clouds will thicken overnight and Saturday morning. Bases
lower to around 4kft by around 16z Saturday...with scattering
around/after 00z Sunday. -Sn is expected to remain to the south of
msp. Northwest winds become northeasterly by daybreak...and
prevail through Saturday with speeds between 08 and 12kts.
/Outlook for kmsp/
sun...VFR. Winds east-southeast 5-10 knots.
Monday...VFR. Chance MVFR/-sn or -rasn. Winds S 10-15 knots.
Tuesday...MVFR with IFR possible in light-moderate snow. Winds NE 10-20 knots.