NWS Twin Cities, MN wrote its last area forecast discussion before the first event at Feb 21, 12:48 PM CST, 1 hour 12 minutes earlier.
Area forecast discussion, Feb 21, 12:48 PM CST, 1 hour 12 minutes before
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1248 PM CST Tue Feb 21 2023
.UPDATE...
Issued at 1245 PM CST Tue Feb 21 2023
Update to include the 18z aviation discussion.
&&
.DISCUSSION...(Today through Monday)
Issued at 401 AM CST Tue Feb 21 2023
KEY MESSAGES:
- Historic winter storm composed of two rounds of snow totaling 1 to
2 feet of snow will begin this afternoon. Round one will put out 4
to 7 inches and round two will add 10 to 15 more in addition to
gusty winds.
- A blip of cold air will strike Friday morning on the back end of
the system. Temperatures will moderate to normal over the weekend.
- Keeping our eyes on another potential system late Sunday into
Monday.
As you are reading this, keep in mind our greatest certainties and
uncertainties at this time. Highest confidence exists with respect
to:
1) A frontogenetically driven band of heavy snow Tuesday night
with non-significant winds.
2) A larger and more widespread shield of all snow Wednesday through
Thursday with increasingly gusty winds creating life-threatening
travel impacts.
Lower confidence exists with respect to:
1) Snow ratios. We know they will be slightly above climatology
around 15-20:1, but even a slight shift upwards or downwards can
drastically affect snow totals. If the event leans closer
climatology (13:1), expect 3 to 5 inches less from the event.
2) The timing and extent of blizzard conditions with round two. We
know it will be gusty and that the freshly fallen and ongoing snow
will be primed to blow, but areal and temporal extent of the
impacts from this are hard to pinpoint.
Today... All will be quiet until snow begins around the lunch hour
in western Minnesota. These PoPs will progress eastward throughout
the afternoon, reaching Eau Claire between 2 and 4PM. This batch
will be most productive in a band between Mankato and St.Cloud and
anywhere between 5 to 7 inches can be expected. Some areas hit with
the heaviest banding could see upwards of 8 to 9 inches. On the
contrary, locations south of a line extending from St.James to
Owatonna will only be grazed by this round, and will likely see less
than 2 inches (hence the lack of headline on Tuesday). Winds will
behave themselves today, generally remaining under 10 to 15 MPH from
the east/southeast.
Tonight... Snow will be falling across the entirety of our CWA by
this evening as the fgen band expands before contracting early
Wednesday morning. Once the contraction occurs, the snowfall
gradient will sharpen, especially along the southern edge, and the
band will narrow. Where this narrow band sets up is where the
highest event total snowfall amounts will lie come Friday. As Hi-Res
models filter in, confidence is increasing in this location being in
a line near and just south of the Metro into west central WI. The
GFS continues to show the narrow band setting up further south,
nearer Mankato, than other Hi-Res guidance. While this southerly
track cannot be ruled out entirely, it isn't likely.
Wednesday Morning... Early Wednesday will likely be precipitation
free along and south of I-90 as the aforementioned band sets up near
the Metro. Locations within this band may experience a lull of
lighter snow and not a true break from the precipitation.
Regardless, most all locations will see less than an inch of snow
between 6AM and 12PM on Wednesday.
Putting the content from the above three paragraphs together is the
justification for a Winter Storm Warning for the middle chunk of our
CWA, an advisory on the northern edge where snow will linger but not
be in the band, and no headline along I-90.
Wednesday Afternoon through Thursday... As the frontogenesis wanes,
the upper level dynamics take charge and the main show begins.
Between noon and 6PM Wednesday, things will still be ramping up.
During this six hour block, 4 inches are forecast along I-90 with 2
inches or less in areas northeastward of a line from Redwood Falls
to Mankato. By 6PM, the phasing and vertical continuity of the upper
levels is evident, creating a phenomenal scene at the surface.
As the surface low moves up from the southwest, winds will approach
25 to 35 MPH areawide, with gusts approaching 45 to 50 MPH in
western and central MN. These winds in conjunction with actively
falling snow and freshly fallen snow are the reason we opted to
upgrade the Winter Storm Warning to a Blizzard Warning mid-afternoon
Wednesday. At present time, the Blizzard Warning only extends as far
east as I-35, but this could very well change and expand to include
the Twin Cities Metro. This would be similar to what occurred April
2018, when the Twin Cities received 15.8 inches of snow. Due to
obstructions, it is hard to get blizzard conditions in major
metropolitan areas such as the Twin Cities, but with the actively
falling snow and strong winds, this would be an event that could do
so.
Speaking historically, this event could very well break top five
snowfalls in the Twin Cities dating back to 1884. The top event, a
memorable one that seems to come up every year, was the Halloween
Blizzard of 1991 with 28.4 inches of snow. Number two was a storm
over Thanksgiving weekend in 1985 that amounted to 21.1 inches.
Numbers three and four were in January of 1982, with totals of 20
and 17.4 inches respectively. To round out the top five and provide
a more recent example, the Domebuster of 2010 with 17.1 inches.
Reigning it back to history in the making, travel will be
treacherous Wednesday night through Thursday. As can be inferred
from the above historical perspective, this is not a once-a-year
event. These systems tend to linger, so it may not be until Thursday
evening when the snow stops in a west to east manner. As for how
long impacts are felt with respect to the clearing of roads, that
will depend on the longevity and severity of strong winds and
potential blizzard conditions.
When all is said and done, we're looking at a solid inch or more of
QPF across the southern two thirds of the area. North of St.Cloud,
0.75 inches of QPF is more reasonable. Going back to snow ratios,
this will lead to snow in the order of feet, not inches. The
northern and southern extent of the CWA will see the least, around
12 to 15 inches. Everywhere else will see more, if not double, than
that. One last thing to consider is the settling and blowing of the
snow, making measuring hard.
Friday through Monday...Cold settles in on Friday morning, but we
should avoid any advisories from that. It won't linger as zonal flow
takes hold. There is decent model agreement in another system
striking the Upper Mississippi Valley by Sunday night, but we won't
hone in on that until we say good riddance to this system.
&&
.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1245 PM CST Tue Feb 21 2023
Flight categories are expected to gradually worsen over the next few
hours as a winter storm begins entering our region from west to
east. By late this afternoon all sites will see -SHSN/+SN through
the overnight hours tonight into tomorrow morning. A brief reprieve
in snowfall intensity is expected tomorrow during sunrise to around
noon before the second heavier round of snow resumes during the next
TAF period. Given current snowfall ratios, blowing snow will likely
become a factor tomorrow morning across all sites as winds become
gusty 25-35kt range through the end of this TAF period.
KMSP...VFR category through the first half of this afternoon. A
narrow band of -SHSN is expected to reach MSP over the next hour or
so before coming more persistent after 20z. Cigs/Vsby will downgrade
to IFR/LIFR overnight with increasing northerly winds with gusts
nearing 30-40kts. Increasing winds will also create chances of blowing
snow through the overnight hours tonight into tomorrow morning.
/OUTLOOK FOR KMSP/
Wed...IFR/-SN early, then LIFR/VLIFR/+SN late afternoon and night
with BLSN. Wind NE 15-20G30kts increasing to 20-25G35-40kts.
Thu...LIFR/VLIFR/+SN early, then MVFR/IFR/-SN likely. BLSN. Wind NE
20-25G35kts becoming NNW 15-20G30kts.
Fri...Chc MVFR. Wind WNW 5 kts becoming S.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Winter Weather Advisory until 6 PM CST Wednesday for Benton-Douglas-
Morrison-Todd.
Winter Storm Warning from 6 PM Wednesday to 6 PM CST Thursday for
Benton-Chisago-Douglas-Isanti-Kanabec-Mille Lacs-Morrison-Todd.
Winter Weather Advisory until 6 PM CST Wednesday for Chisago-Isanti-
Kanabec-Mille Lacs.
Winter Storm Warning until 3 PM CST Wednesday for Brown-Chippewa-
Kandiyohi-Lac Qui Parle-Meeker-Pope-Redwood-Renville-Stearns-
Stevens-Swift-Watonwan-Yellow Medicine.
Blizzard Warning from 3 PM Wednesday to noon CST Thursday for Brown-
Chippewa-Kandiyohi-Lac Qui Parle-Meeker-Pope-Redwood-Renville-
Stearns-Stevens-Swift-Watonwan-Yellow Medicine.
Winter Storm Warning until 6 PM CST Thursday for Anoka-Carver-
Dakota-Goodhue-Hennepin-Ramsey-Scott-Sherburne-Steele-
Washington-Wright.
Winter Storm Warning until 3 PM CST Wednesday for Blue Earth-Le
Sueur-McLeod-Nicollet-Rice-Sibley-Waseca.
Blizzard Warning from 3 PM Wednesday to 6 PM CST Thursday for Blue
Earth-Le Sueur-McLeod-Nicollet-Rice-Sibley-Waseca.
Winter Storm Warning from 6 AM Wednesday to noon CST Thursday for
Faribault-Freeborn-Martin.
WI...Winter Storm Warning from 6 PM Wednesday to 6 PM CST Thursday for
Barron-Polk-Rusk.
Winter Weather Advisory until 6 PM CST Wednesday for Barron-Polk-
Rusk.
Winter Storm Warning until 6 PM CST Thursday for Chippewa-Dunn-Eau
Claire-Pepin-Pierce-St. Croix.
&&
DISCUSSION...PEM
AVIATION...RMD