Round #1: Metro mostly rain today; Historic “Top 10” April snowfall event by Thursday PM?

Looking For An Escape Hatch

The optimist in me is still in "snowfall denial."

Somehow, some way this cruel hoax of an extended April fool's joke will not happen. Some divine intervention will prevent us from getting widespread 6"+ snowfall totals by Thursday.

The realist in me...the analytical weather forecast guy says keep dreaming. The maps are what they are...and they all point toward several rounds of increasingly wintery precip that end as heavy wet snow Wednesday night and Thursday.

The overnight and early Tuesday model runs didn't do much to feed the optimistic weather guy side.

All indications still point to a blockbuster, possibly an historic "Top 10" April snowfall event this week.

I'll keep looking.

"Incredibly complex" Twin Cities NWS description of incoming storm system

-Latest Twin Cities radar loop with precip type

Winter Storm Warnings in effect starting tonight including the Twin Cities

INCLUDING THE CITIES OF...ELK RIVER...CAMBRIDGE...CENTER CITY...

MONTICELLO...MINNEAPOLIS...BLAINE...ST. PAUL...STILLWATER...

HUTCHINSON...GAYLORD...CHASKA...SHAKOPEE...BURNSVILLE

452 AM CDT TUE APR 9 2013

...WINTER STORM WARNING IN EFFECT FROM 7 PM THIS EVENING TO 1 PM CDT THURSDAY...

THE NATIONAL WEATHER SERVICE IN TWIN CITIES/CHANHASSEN HAS ISSUED A WINTER STORM WARNING FOR A MIX SLEET...FREEZING RAIN...AND HEAVY SNOW...WHICH IS IN EFFECT FROM 7 PM THIS EVENING TO 1 PM CDT THURSDAY. THE WINTER STORM WATCH IS NO LONGER IN EFFECT.

* TIMING: RAIN WILL TRANSITION TO A WINTRY MIX OF PRECIPITATION THIS EVENING AND CHANGE OVER TO SNOW LATE WEDNESDAY. SNOW WILL SLOWLY TAPER OFF THURSDAY MORNING.

* MAIN IMPACT: SNOW ACCUMULATIONS OF 6 INCHES OR GREATER...MAINLY BETWEEN WEDNESDAY EVENING AND MID DAY THURSDAY.

* OTHER IMPACTS: ICE ACCUMULATIONS UP TO A TENTH OF AN INCH DUE TO SLEET AND LIGHT FREEZING RAIN TONIGHT INTO WEDNESDAY.

April Snows: Not that unusual

April snow is not unusual. Bigger April snows over 6" are more rare. Here's a look at the "Top 10" April snowfalls in the Twin Cities and some perspective on April snow courtesy of the MN Climate Working Group.

Could this week's storm earn a spot in the top 10? It's possible.

Blizzard in St. Paul: April, 1923

Courtesy the Minnesota Historical Society

Top ten largest April Snowstorms in the Twin Cities 1891-2007

Rank Date Year Amount (in)

----------------------------------------------------------------------

#1 April 14, 1983 13.6

#2 April 27-28 1907 13.0

#3 April 19-21 1893 10.0

#4 April 29-30 1984 9.7

#5 April 6-9 1923 9.6

#6 April 13-14 1928 9.5

#7 April 13-14 1949 9.3

#8 April 27 1967 8.5

#9 April 1-2 2002 7.6

#10 April 8-9 1980 7.6 (tie)

Historic April Snowstorms

Heavy snows in April are fairly common in Minnesota's past. The transition from winter to spring can spawn some rather strong storms and given the right conditions, can also tap into leftover cool air from the winter. Looking through historical anecdotes, the greatest chance of having a large snowstorm appears to be in the first half of the month. One of the greatest April snowstorms (besides the April 5-7, 2008 event.) was the storm that began on April 5, 1933. The old Pigeon River Bridge crossing in Cook County saw 28 inches in one day from that storm. This still stands as the 24 hour state record for snowfall in April. Two Harbors in Lake County saw 17 inches of snow from the 1933 storm.

Another historical snowstorm is the event that unfolded beginning on the morning of April 19th and ending on April 21, 1893. When it was all over 30 inches buried St. Cloud, with 24 inches in a single day. The 1893 Minnesota Weather Service bulletin describes this storm. "The (Low) caused the most disagreeable weather of the month, heavy snow fell varying in depth from six to thirty-six inches throughout the state: railroad lines were blocked, and traffic of all kinds was almost entirely suspended." The Twin Cities saw 10 inches from this event and this is the third largest April snowstorm in the Twin Cities.

Wave #1: Mostly metro rain today

The lead wave with our unusual April storm is working north today. Temps are above freezing in the lowest mile of the atmosphere over the metro, but sub-freezing not too far west where snow, ice and sleet will mix in. There is even some sleet mixing in in the west and north metro today.

[image]

Redwood Falls and Tracy and other locations in southwest Minnesota are already reporting moderate to heavy snow.

CITY SKY/WX TMP DP RH WIND PRES REMARKS

MONTEVIDEO LGT SNOW 25 23 93 NE16G23 30.16R VSB 1 WCI 12

GRANITE FALLS SNOW 26 23 89 NW18G26 30.14R VSB 1/2 WCI 13

CANBY SNOW 20 19 93 N16G24 30.17R VSB 1/2 WCI 6

MARSHALL CLOUDY 25 19 80 N22G32 30.09R VSB 1/2 WCI 10

REDWOOD FALLS HVY SNOW 29 26 89 N14G24 30.08R VSB 1/4 WCI 18

OLIVIA LGT SNOW 30 27 86 N20G26 30.08R WCI 18

PIPESTONE LGT SNOW 23 21 93 NE12 29.88F WCI 12

WINDOM MIX PCPN 32 30 93 N15 29.98R WCI 22

WORTHINGTON CLOUDY 30 27 86 N15G24 29.96S WCI 19

JACKSON MIX PCPN 32 32 100 VRB22G33 29.89F WCI 19

TRACY SNOW 25 24 94 N16G23 30.07R VSB 1/4 WCI 13

SLAYTON LGT SNOW 26 26 99 N9 29.99F VSB 3/4 WCI 17

The combination of a slow moving, long duration precip event and a good fetch of moisture from the Gulf of Mexico will produce some impressive "liquid" QPF (Quantitative Precipitation Forecast) totals for this storm.

The metro looks in line to pick up as much as 2" of liquid this week...rain today trending toward snow by later Wednesday.

Rain & Flood Concerns:

To the south, as much as 2" to 3" rainfall totals has forecaster in La Crosse rightfully concerned about some rapid river rises... and the potential for flooding this week.

Big Snow West:

This storm will produce mostly snow...and some prolific snowfall totals of up to 20" in central South Dakota.

418 AM CDT TUE APR 9 2013 /318 AM MDT TUE APR 9 2013/

...WINTER STORM WARNING NOW IN EFFECT UNTIL 7 PM CDT /6 PM MDT/

WEDNESDAY...

* TIMING...HEAVY SNOW WILL CONTINUE TO DEVELOP ACROSS THE AREA.THERE MAY BE A LULL IN ACCUMULATION TONIGHT...WITH ANOTHER SHOT FOR HEAVY SNOW WEDNESDAY.

* WINDS/VISIBILITY...NORTH WINDS FROM 25 TO 40 MPH WITH HIGHER GUSTS TODAY. THE POTENTIAL EXISTS FOR LOW VISIBILITY WITHIN ANY AREAS OF HEAVY SNOW AND STRONG WINDS. WINDS WILL DIMINISH TONIGHT.

* SNOW/SLEET ACCUMULATIONS...THERE WILL BE A STEEP GRADIENT IN SNOW AMOUNTS...FROM NEAR 6 INCHES IN NORTH CENTRAL SOUTH DAKOTA...TO UPWARDS OF 20 INCHES IN CENTRAL DAKOTA.

Remarkable Temperature Contrasts:

Temperature contrasts in the atmosphere drive big storms. Late Monday temps ranged from the balmy 70s in Iowa to near 0F in eastern North Dakota. That tight "temperature gradient" helps spin up storms in the Midwest.

Transition:

The transition from rain to snow will be a gradual...halting, sometimes reversable process in the next 36 hours in the metro.

A wintery mix of ice may develop as soon as tonight...and it looks like precip could change phase several times Wednesday between ice, sleet, rain and snow.

By Wednesday night it's all snow...and most of the snowfall accumulation should occur Wednesday night into Thursday.

Main Event:

The main snowfall event should be Wednesday night & Thursday. 12 to 18 hours of heavy wet April snow still looks likely.

All indications are snowfall rates could reach 1"...and maybe 2" per hour at times.

The heaviest snowfall band still appears to lay out in a west to east swath across southern Minnesota including Wheaton through Morris-Willmar-Alex-St. Cloud-Mille Lacs-Twin Cities-Eau Claire & Rice Lake.

I can't find a model that delivers less than 6" of snowfall in the metro with this system. And some... like the GFS are cranking out ridiculuous totals...from 12" to as much as 20"+.

I would easily dismiss the notion of a 20" snowfall total in Minnesota in April...but I recall the days before the Halloween Mega Storm in the WCCO Weather Center as we stood in disbelief at the model output of 20"+ snowfall totals... in October.

It's extremely rare to get that much snow...but it has happened, and the transitional seasons of fall and spring can add additional moisture and energy to storm systems.

Bottom Line?

I think a forecast at this point of a general band of 6" to 12"+ across central and southern Minnesota including the metro is reasonable. I'll watch the model and storm trends through tomorrow....but I won't be shocked if we see some totals (well?) in excess of 12" in Minnesota by Thursday evening.

Stay tuned...and be ready for rapidly changing forecast and weather conditions this week.

PH